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IR ANID SEDIMENTS. ;]'"

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GOVERNMENT OF THE VIRGIN ISLANDS
DEPARTMENT OF HEALTH, DIVISION OF ENVIRONMENTAL HEALTH
WATER POLLUTION REPORT NO. 16
CONTRACTED BY
CARIBBEAN RESEARCH INSTITUTE
COLLEGE OF THE VIRGIN ISLANDS

ENVIRONMENT, WATER AND SEDIMENTS
OF
CHRISTIANSTED HARBOR, ST. CROIX

Maynard Nichols
David Grigg
Asbury Sallenger
Robert

Robert vanEepoel
'Robert Brody
Janet Olmon
Crean

February, 1972

,kTHE RALPH M. PAIEWONSKY LIBRARy
UNIVERSITY OF THE VIRGIN ISLANDS

L.

0

CONTENTS

TABLE OF CONTENTS i
LIST OF FIGURES ii
LIST OF TABLES v
PROLOGUE
P-I Conclusions P-1
P-II Recommendations P-7
P-III Future Research Needs and Studies for Students P-12
1. INTRODUCTION
Statement of the Problem 1-1
Organizations and Objectives 1-3
Scope and Previous Studies 1-4
Acknowledgements 1-6
2. SUMMARY OF PROCEDURES
Field Methods 2-1
Station Locations 2-1
Sample Collection and Measurement 2-4
Laboratory Procedures 2-7
3. DESCRIPTION OF THE HARBOR
Bathymetry 3-3
Aerial Photographic Studies 3-7
Shoreline Features 3-15
4. HYDROGRAPHY
Tides 4-1
Tide Character 4-3
Seasonal Variations 4-4
Tidal Exchange 4-6
Circulati on 4-6
Dye Dispersal and Photography 4-10
Longshore 4-13
Discussion 4-16
Inflow from Land 4-17

5. WATER QUALITY DATA
Temperature 5-1
Suspended Solids 5-1
Secchi Disk Depth 5-3
Bacteriology 5-3
Dissolved Oxygen 5-3
Summary of Water Quality 5-5

6. ECOLOGY OF REEF COMMUNITIES
Introduction 6-1
Prospective Stresses 6-2
Procedures 6-4
Observations 6-7
Status of the Reefs 6-11

7. NOTES ON FISHERIES 7-1
8. BOTTOM GRASS AND ALGAE 8-1

9. BOTTOM SEDIMENTS
General Lithology 9-1
Grain Size Distribution 9-3
Cumulative Curves 9-5
Sand Composition 9-9
Cores 9-18
10. SEDIMENTARY ENVIRONMENTS
Sedimentation and Depth Changes 10-6
11. UTILIZATION OF THE HARBOR AND ITS ENVIRONMENTAL
IMPACT 11-1
12. REFERENCES CITED 12-1

APPENDIX I, ANCHOR STATION HYDROGRAPHIC DATA
Explanation of Data A-i
Hydrographic Data A-3
APPENDIX II, FIELD SEDIMENT DATA
Explanation A-23
APPENDIX III, PARTICLES SIZE PARAMETERS A-33
APPENDIX IV, CHARACTERISTICS OF SAND COMPONENTS A-34
APPENDIX V, PERCENTAGE COMPOSITION OF SAND COMPONENTS A-38
APPENDIX VI, WATER QUALITY DATA FROM CHRISTIANSTED
HARBOR A-48

I

LIST OF FIGURES

Figure Page
1. Location of hydrographic stations. 2-2
2. Location of bottom sediment collecting stations. 2-3
3. Bathymetry of Christiansted Harbor. 3-4
4. Aerial Photograph of Christiansted Harbor, 1954. 3-9
5. Aerial Photograph of Christiansted Harbor, 1971. 3-13
6. Photographs of shoreline conditions, A,B,C,D. 3-17
7. Variations in the character of the tide displayed in time-height
curves. 4-2
8. Monthly change in mean sea level at Havanna for an annual
cycle. 4-5
9. Vertical distribution of mean current speed in meters per
second at selected anchor stations. 4-5
10. Mean surface current, speed and direction, for harbor
currents and for littoral currents, August, 1971. 4-8
11. Circulation from dye patch dispersal at different release
points and various dates. 4-12
12. Suspended solids mean concentrations in surface water. 5-2
13. Secchi Disk depth. Mean values, May through August,
1971. 5-4
14. Index to coral reef observations. 6-6
15. Mounds built-up by burrowing shrimp or polychaete worms. 8-2
16. Distribution of turtle grass beds in 1954 and 1971. 8-4
17. Gross lithology of principal sediment types on the harbor
floor. 9-2
18. Distribution of median grain size. 9-4
19. Size distribution diagram relating to different sediment
groups. 9-6
20. Representative cumulative curves of grain size. 9-7
21. Relation of percent coral sand to Halimeda sand in differ-
environments of the harbor. 9-11
22. Distribution of sand components in percent by number. 9-12

Figure Page

23. Distribution of grey and black colored carbonate sand grains
in percent by number in samples throughout Christiansted
Harbor. 9-15
24. Core sections showing sediment variations with depth for
stations 64 (left), 18 and 78 (right). 9-19
25. View northeast from west Christiansted to Protestant Cay
showing sandy dredge spoil in foreground a source of tur-
bidity when acted on by waves. 9-19
26. Major sedimentary environments of deposition; Reef, Central
Harbor, Inner Harbor, Lagoon, and Gallows Bay, an embay-
ment of the inner harbor. 10-2

27. Photomicrographs of sand components from different sedi-
mentary environments in Christiansted Harbor. 10-5
28. Distribution of depth changes and landfill between 1924
and 1971. 10-7
29. Graphical Summary of the status of harbor activities and
shoreline use, 1971. 11-2
30A. View of eastern harbor from Protestant Cay to the Buccaneer
Beach. 11-5
30B.Eastern harbor shoreline viewed toward Fort Louise Augusta
from Chandlers Marine. 11-5
31A.Air view of shoreline use and harbor conditions at the
cement plant. 11-7
3 IB.Air view of crowded waterfront at downtown Christiansted. 11-7
32. Areas of environmental sensitivity and problems, Christ-
iansted Harbor, 1971. 11-14

r

LIST OF TABLES

Page
1. Anchor station observations and corresponding instruments
used. 2-5
2. Summary of geographic and hydrographic data. 3-2
3. Distribution of area in depth intervals. 3-2
4. List of available charts. 3-6
5. Sources of aerial photo coverage. 3-7
6. Longshore transport data. 4-14
7. Coverage of grass beds between 1954 and 1971. 8-6
8. Summary of sand fraction composition in different environ-
ments of the harbor. 9-17
9. List of dredging permits. 11-4
10. Intercompatibility of multiple uses, Christiansted Harbor. 11-11

PROLOGUE

V-I CONCLUSION

1. The harbor floor is shaped into broad shoals cut by a

deep winding channel in the eastern sector. The shoals are built

mainly of coral sand supplied from the barrier reef. The chan-

nel initially was cut during a period of lower sea level and its

course partly follows the local geologic structure. Presently,

erosion is deepening the channel floor near Barracuda Ground

whereas sedimentation is filling the western channel shoulder,

particularly near Sorensen Ground. Elsewhere the floor is rela-

tively stable.

2. Most harbor shores are stable. Attractiveness of beaches

is reduced by accumulations of marine grasses, by ledges of beach-

rock, abandoned boats, and by rubble washed from dredge fill.

Erosion is locally active at Turquoise Beach and on shores of

unstabilized landfill.

3. Water quality varies from excellent in the western harbor

and seaward reaches to poor in the eastern and inner parts. Poor

water quality is indicated by high turbidity and locally high fecal

coliforms. Suspended solids increase with distance toward the

shoreline source; from less then 2 mg/l near Long Reef to more than

10 mg/l near Christiansted and Gallows Bay. Greatest change occurs

in a "gradient" zone trending eastward from the Cement Plant to

Protestant Cay and Round Reef. High turbidity is traced to high

content of suspended material partly introduced by occasional

sewage and sediment discharge, but mainly generated by wave ero-

sion of unstabilized dredge spoil.

P-i

4. Spatially, water temperature, salinity and dissolved

oxygen vary within narrow limits. Spasmotic runoff from the

land and occasional "northerners" may alter the hydrographic

regime at times, but relatively uniform conditions prevail

most of the time. The salinity of harbor water is close to

ocean water and its uniform distribution at depth indicates

the water is well-mixed by wind and currents.

5. Harbor circulation is driven by the mass transport of )

ocean waves breaking on Long Reef. Water enters the harbor

through shallow channels in the reef. It flows eastward

through the harbor proper in an anti-clockwise direction with

an average speed of 0.07 m/sec (0.14 knots) and leaves the

harbor through the main entrance channel. The circulation is

regulated by the reef elevation, height of ocean waves and

height of the tide. The influence of offshore currents is

insignificant but local wind driven currents within the harbor

are important at times.

6. Although tidal exchange is insignificant, waters are

rapidly flushed and mixed by the over-reef flow supplemented

by wave motion. Mixing is greater in the western harbor, es-

pecially in seaward reaches and over shoals, than in inner

reaches and deeper parts. Thus, transport and dispersal of

materials, wastes and sediment is better in near-ocean areas

than near-shore or on the channel floors.

7. Bottom sediments are predominately coral sand with

admixtures of mud and Halimeda sand occurring in eastern and

inner reaches. The coral sand is derived from the barrier

reef whereas Halimeda was formerly produced on the inner

P-2

harbor floor. Supply of detrital sand from the land is rela-

tively low.

8. Five sedimentary environments are recognized, each charac-

terized by distinct grain size characteristics, sand composition

and physical properties indicative of environmental quality.

These environments are: (1) reef, (2) central harbor, (3) inner

harbor, (4) lagoon, (5) Gallows Bay, an emerging new environment

of the inner harbor. Sediments are mainly transported landward

over the barrier reef by mass transport of breaking waves. Addi-

tionally, they are carried eastward toward the main harbor chan-

nel and westward of Scotch Bank by the predominate flow.

9. Several biological zones can be identified, the most

important of which are:

.. the fore reef, dominated by Acropora palmata, lush and

productive to the west but diminishing toward the east.

.. The shallow back reef area composed primarily of Thalassia,

Syringodium, and associated algae.

.. The inner reaches of the bay proper dominated now by

filamentous Enteromorpha, an indicator of eutrophic con-

ditions, with Thalassia only in shallower water where it

can receive sufficient light.

.. The nearshore, with plant cover varying with localized

conditions from Thalassia in the west to Enteromorpha and

Ulva in the center and east.

.. Large bare sand areas of the bay bottom produced by dred-

ging and natural sand shifting which prevents colonization

but supports large numbers of tube-building worms.

10. Reef communities of Long Reef are dominated by Acropora

palmata on the front-reef between 0-10 m depth, and by Porites

P-3

porites and small Acropora colonies on the back reef. The octo-

coral population has fewer species and lower density than in many

other Virgin Islands reefs. Long Reef is in relatively good

"health" except for the immediate sewage outfall environs and

Barracuda Ground which is under the direct stress of wave attack

and indirect stress of harbor dredging and pollution.

11. The area around the Long Reef sewer outfall displays

high concentrations of fecal material and paper wastes in addi-

tion to numerous dead corals and reduced species diversity. The

bulk of the sewage discharge is dispersed outside of the reef and

transported away from the harbor in the prevailing currents.

During the several months of observations only a very small frac-

tion was transported over the reef into the harbor. However, with

certain combinations of wind and sea directions, this general

situation is temporarily changed so that a much larger fraction

may be swept back into the harbor.

12. An estimated 46 percent of the harbor floor has been

directly or indirectly disturbed by dredging.

13. The environment shows signs of faltering under the com-

bined stress of pollution and utilization. The chief changes

since 1954 are:

.. A lowering of the harbor floor by dredging with a conco-

mitant increase of harbor volume by 14 percent, restric-

ted circulation of bottom water and locally increased sedi-

mentation. The stagnation effected is a stronger degrading

influence on quality of the deeper waters than the benefi-

cial effect of increased dilution which results from the

greater water volume.

P-4

.. A 34 percent loss of natural shoreline by conversion to

land, artificial beaches, or waterfront resulting in a 5

percent reduction of harbor area, restricted flushing of

Altona Lagoon and loss of natural habitats.

.. A 65 percent loss of the productive Thalassia-Syringodium

grass beds and invasion of the alga Enteromorpha.

.. Destruction of reef communities on Round Reef, Barracuda

Ground, north of Protestant Cay and about the Long Reef

outfall.

.. Loss of sand by erosion along 20 percent of the shoreline.

.Loss of seasonal shellfish beds in the central and eastern

harbor.

14. Pollution and disturbance of the inner and eastern harbor is by

.. Low water transparency with secchi disk depths reduced to 1 m

and high turbidity with suspended solids reaching 25 mg/l.

.. Almost complete extirpation of coral on Round Reef and the

death of reefs north and east of Protestant Cay.

.. Thick growths of benthic alga Enteromorpha which cover 41 per-

cent of the harbor floor.

.. Lush growths of Enteromorpha and Ulva at many places along

the shoreline in shallow water areas of Gallows Bay and the

central harbor. Growth is promoted by "pirate" waste/sewage

discharges and from the occasional discharge from the sewage

system bypass system.

.. Widespread contaminants in bottom sediments including small

percentages of poisonous copper paint chips, plastic and

paper packing fibers, vermiculite, coal and cinder particles,

P-5

glass fragments and metal shavings.

.. Accumulations of soft, poorly sorted organic-rich mud (Type

E) containing organic material in deeper areas of the harbor.

.. An abundance of grey-black carbonate sand grains, a product

of dredging older sediment.

.. Oil and asphalt spills and leechings along the western shore-

line of Gallows Bay.

15. Coastal shipping places the greatest demand on the harbor

environment. Its impact has produced a sequence of stresses:

dredging-filling- ecological destruction-shoreline erosion-

turbidity-sedimentation. Although each stress is relatively small,

successive stresses carry with them a potential for cumulative

effects with time, and for extending their effects throughout the

harbor via the active circulation.

16. Problems in the harbor are mainly produced by intense demands

concentrated in small areas and by disturbance of ecologically

sensitive areas. The prospects are that conflicting demands and

incompatible use will intensify in the future.

17. The harbor could be improved by holding pollution and

disturbance to a low level locally, by intelligent planning for

conservation areas in an effort to achieve an optimal balance of

environmental quality and utilization in a context of multiple use.

P-6

P-II. RECOMMENDATIONS

1. Waste discharges and bottom and shoreline alterations,

mainly dredging, must be held to a minimum within small areas

taking into account the circulation pattern and rates of mixing

that extend their effects. To minimize further deterioration of

water quality and ecological regression, correct and effective

regulations must be formulated for the various users of the har-

bor. A form of marine zoning is required in which areas are

designated for multiple use according to their intrinsic natural

values.

A. For the central and western harbor, in the area

bounded by Long Reef, a north-south line from Barracuda Ground

to Protestant Cay to the Christiansted shoreline, and along the

shoreline westerly and north-westerly to Pelican Cove at the

junction with Round Reef, we recommend

... No further sand mining or bottom or shoreline alter-

ations be allowed for at least ten years after which

time a reassessment can be made.

... Industrial and commercial shipping traffic be cur-

tailed. Location of the cement plant/utility plant

complex at this site has proven to be extensively

damaging to the harbor and attempts at restoration

are needed.

... Gradual phasing out over the next 2-3 years of opera-

tions at the cement plants so that eventually the

only shipping or industrial utilization of this sector

of the harbor will be that required for fuel transport

to the utility plant.

P-7

... Elimination of waste discharges on to Long Reef over

the next 2-5 years.

... If the existing outfall is to be kept as an emergency

bypass in the event of lift station failure, the out-

fall should be lengthened at least 200 meters.

... Limitation of the electric power generating and water

production capacities at this site to those already

installed or under contract. Continued expansion of

the utility capacities will negate the beneficial

effects to be derived from elimination of the cement

plants.

... Elimination of "pirate" waste discharges from water-

front businesses, hotels and restaurants, and better

control of operation of pumping stations so that

frequency of sewage bypass discharges is reduced.

... Revision of section 186-9, Legal Limits of the Water

Quality Standards for Coastal Waters of the Virgin

Islands to transfer central sector (Protestant Cay

to Golden Rock) from class "C" (Harbors) classifica-

tion to class "B" (Propogation of Marine Life and

Water Contact Recreation).

... Further reduction of the harbor area by landfill not

be allowed.

B. For the eastern harbor, including Gallows Bay and the

entrance channel, we recommend

... Very close supervision and control be exercised over

all bottom and shoreline alterations including sand

mining. These should be allowed only after adequate

P-8

expert review and study specifies that project con-

figuration and the control procedures which insure

minimum lasting degradation beyond the present con-

dition of the area.

... Any expansion of waterfront industrial, commercial,

or shipping activity in the Christiansted area be

allowed only in this eastern harbor sector.

... Cleanup of the eastern shoreline of Protestant Cay

and close supervision of the effluent discharges

from the Cay. Equipment and waste lines design,

including stand-by power, should be specified so that

effluents are not ever discharged into the harbor.

... Continuing development and future utilization of

Altona Lagoon be carefully controlled to the end

that there is no restriction of water flow through

the entrance.

... The present entrance to Altona Lagoon be reopened,

either by addition of 8-10 large culverts or by low

level bridging, which could allow skiff and outboard

motor boat passage into the Lagoon.

... No reduction of the harbor area be allowed. Addi-

tional small boat services, bulkheading and dockage,

should be made by cutting into the harbor shoreline

more than filling out from the existing shoreline.

2. Areas of unique value and high environmental sensitivity

should be designated as marine preserve or conservation areas.

They can alternatively support recreation or serve as open space

for residents and visitors because of esthetic appeal. Long Reef

P-9

acts as a baffle to ocean waves; it is a potential nursery ground

or spawning area and it supplies sand to the harbor.

A. For Long Reef from Barracuda Ground to Pelican Cove

we recommend

... Designation of Long Reef as territorial marine preserve

and park.

... Section 186.9, Legal Limits of the Water Quality Standards

of the Virgin Islands be revised to add Long Reef to Class A

(Natural Phenomena).

B. An opportunity exists for expanded recreational use in the

central and western harbor areas, after upgrading of the water quality

classification of the central harbor to Class B (Propogation of

Marine Life and Water Contact Recreation). We recommend promotion

of shoreline resorts, public beaches and water sports uses, outside

of the seadrome and channel to the dock at the cement plants/utility

plant site.

C. For Altona Lagoon, after widening of the access water way,

we recommend full development of the recreational potential of the

area boating, fishing, picnicking, minor sports.

3. In the central harbor, much damage to the benthic ecology

and degradation of water quality has occurred. Investigation must

be made into possible restorative action. We recommend specifically

stabilization of actively eroding shorelines and submarine slopes

by planting with both terrestrial and marine grasses. The restoration

costs should be charged to users of the channels and waterways as

a necessary return payment to the harbor for the special use extracted.

P-10

I

4. To provide for the many diverse and conflicting future

demands on the harbor, both public and private, and still obtain

maximum long-term socio-economic benefits we recommend that a

comprehensive plan of development be formulated and implemented

through an appropriate agency of the Government of the Virgin

Islands. A set of planning objectives should be established,

data obtained regarding past and present utilization of the har-

bor, ecological values, etc., and these evaluated in alternative

multiple use plans.

5. Our limit of detection in estimating transport of sewage

effluent discharged from the outfall seaward of Long Reef was

grossly insensitive. To properly measure the effluent fractions

transported back over Long Reef into the harbor, we recommend

that a series of dye studies be conducted, under different con-

ditions of wind and sea, using a sensitive flourimeter to detect

the dispersal of the flourescein dye.

P-11

P-III FUTURE RESEARCH NEEDS AND STUDIES FOR STUDENTS

Results of this study have raised many questions, exposed

gaps in our knowledge that require further research. The harbor

environment must be further understood to achieve optimal quality

for future human use. The needs are:*

1. Monitoring of basic physical and chemical parameters

of the environment.!tide, salinity, temperature, dissolved oxygen

content, wind and stream discharge at several stations situated

in environmentally sensitive areas. These data should provide a

record of daily and seasonal changes that indicate the effects

of ecological disturbance and extreme events, stream flooding

and "northerners".

2. An inventory of the harbor, its water and ecology,

during the winter season. Attention needs to be given to dissolved

oxygen content, plankton and pollutants in near-bottom water. The

mean circulation pattern and rate of flushing which predict the

fate of pollutants and sediment, needs to be defined especially

during extremes of flooding and northerners. Detailed field

studies are required to determine the character and rate of

over-reef flow as it relates to the reef elevation and tidal

heights as well as the harbor circulation and its capacity for

waste receival. Hydraulic model studies should be of use in

predicting effects of future engineering works, channel deepening

or alignment on circulation, salinity and sedimentation, as well

as on the ecology which depends on these factors. Because tides

are weak, an analysis of the effects of wind on harbor circulation

and mixing is of interest.

*The numerical order given does not imply priority.

P-12

3. An analysis of wave energy dissipation as it affects

(1) destruction of reefs and (2) sheltered anchorages in the re-

sponse of boats moored at anchor and at loading docks, including

the conditions of high swell during tropical storms and harbor

oscillations induced by mass transport of wave groups breaking

on the barrier reef.

4. An understanding of energy flow through the harbor and

effects of prospective changes that tie, or separate, the system

such as restricted circulation of bottom water and lagoon water.

Productivity measurements are needed in different environments of

the harbor and through a range of sun energy levels to prepare

an annual budget of organic matter and to integrate effects of

different processes throughout the harbor.

5. A knowledge of the distribution and ecology of fishes.

It is of special interest to know if the reef, lagoon or harbor

floor are spawning areas or nursery grounds important to the life

cycle of certain species.

6. A detailed knowledge of the composition and distribution

of the bottom fauna, flora and reef communities. There is a cri-

tical need for quantitative data concerning specific levels and

specific kinds of disturbance and pollution effects on the communi-

ties. We need to know the extent and degree of impact, its "side"

effects and "after" effects. How fast are communities eliminated

around outfalls or reestablished on dredged slopes and excavations?

And what is their capacity to tolerate stress? The long history

of dredging in the harbor provides an excellent opportunity for a

comparative study of populations in various stages of recovery.

P-13

Any quantitative information on adaptations and species sub-

stitutions also are of special interest, in addition to the

variety and mass of organisms that are supported or eliminated.

7. Land-borne sediment and pollutant sources have been

identified but the fate of these materials in the bottom sediments

is poorly understood. The possible cleansing action of burrowing

shrimp or polychaete worms should be investigated. The chemical

sequences involving trace metals and "sub-lethal" compounds in

the sediments require study, particularly as they interact with

early diagenetic changes. The probably diagenetic formation of

grey-black carbonate grains with increasing age and depth of

burial in the sediments is of considerable interest.

8. Although the modern sedimentary environments and rates

of deposition are partly known, their relation to older deposits

needs to be established through coring or drilling. Little is

known of the recent geologic history of harbor deposits as in-

fluenced by changing conditions during the post-glacial rise in

sea level.

9. An understanding of how to achieve an optimal balance

of uses in the harbor. A basic inventory of harbor and shoreline

activities is urgently needed in addition to quantification of

esthetic (e.g. scenic) and ecological values. Possible archaeologic

and historic sites on the harbor floor and shoreline should be

identified. Intelligent management of the harbor will require at

least thorough evaluation of multiple socio-economic uses and

resource values to ensure optimum use and enhancement of the en-

vironment.

P-14

ENVIRONMENT, WATER AND SEDIMENTS OF CHRISTIANSTED HARBOR, ST. CROIX

1. INTRODUCTION

With t h e emerging demand for environmental quality, there is a

need to gain a new knowledge of the environment in which we work and play. Never

before has the public been so conscious of the necessity for protecting the quality

of water, for managing resources and for maintaining the balance for nature within

the limits of progress. The realization is growing that the environment is dynamic,

ever changing and interacting with forces imposed by man or nature. It is now recog-

nized for instance that pollution of coastal waters has a potential for extending its

effects over wide areas and for concentrating its products with time. Even engineering

works though small, often carry with them many side effects which permeate an entire

coastal environment and produce major, or at times catastrophic, changes in the natural

balance. Few more illustrative examples of such changes exist in a compact setting,

than in Christiansted Harbor.

Statement of the Problem

At Christiansted, where development has been historically linked to the

harbor, the shoreline and water have been put to a variety of different but inter-re-

lated uses. Renown as a sheltered anchorage, its waters serve as an airdrome for

amphibious planes and its channels as a transfer medium for coastal shipping and

recreational boating. The harbor floor is a local source of sand for landfill and

construction aggregate and its offshore reaches are a source of food. Additionally,

the harbor is a place in which to dump wastes and to disperse thermal effluents.

By contrast, its shores provide recreational beaches and sites for boat repair

and berthing. Not only does the harbor serve a variety of demands, but it pos-

sesses esthetic qualities and scenic values important both to tourists and to local

residents alike.

These diverse and often conflicting demands have exposed a multitude

of problems, some natural, others man-made or created by man interfacing

with nature. Beaches are reportedly eroding and parts of the coral reef destroyed

by violent winter storms. Sedimentation is smothering productive grass beds and

filling the shipping channel. Man has added to the complexity of these problems

through his efforts to excavate sand, to dredge shipping channels, and to bridge

contiguous waters like Altona Lagoon. All such activities have disrupted harbor

ecology and reduced the harbor's self-flushing capacity. Most striking is the

continual discharge of untreated sewage off the coral reef that protects the harbor.

As problems of development mount with growing industrial activity and an increasing

flow of tourists, new stresses are placed upon the harbor.

If we are to keep pace with the necessity to resolve the problems arising

from intensive use in addition to the emerging demand for environmental quality,

there is a need to gain new knowledge of the harbor environment. We need to learn

the nature of the place. What is the quality of the water and the character of the sedi-

mentary materials ? What processes are active in circulating materials and wastes ?

What is the "health" of the reef communities? Where are the ecologically sensitive

areas ? What changes have occurred in response to stresses of man and nature ? And

further, what problems require attention to improve the environment? Where are the

limitations to development --- the opportunities for use ?

Organization and Objectives

To address the questions posed by the harbor environment, and by custodians

concerned with its welfare, a study was brought to life through funds contracted from

the Division of Environmental Health, Department of Health, Government of the Virgin

Islands to the Caribbean Research Institute. A broad, but intensive research effort

was organized, objectives delineated and a team of scientists employed covering

different environmental disciplines. The team consisted of: R. vanEepoel, project

director; M. Nichols, principal investigator/oceanographer; R. Brody, reef ecologist;

D. Grigg, water chemist/marine ecologist; R. Crean and A. Sallenger, marine geo-

logists; and J. Olmon, marine biologist. Numerous summer students and laboratory

technicians were recruited for short-term assistance both in the field and in the labora-

tory. The team was directed to collect, chart and analyze all data on the harbor which

would aid in evaluation of the environment.

The broad objective of the study was to determine the status of environmental

conditions in the harbor. More specifically:

(1) To describe and inventory the "status" or distribution of the basic

environmental elements in the harbor, its bathymetry, sediments, water

and ecology.

(2) To evaluate these elements in an interacting system. Inasmuch as

the harbor environment is dynamic and ever-changing in response to waves,

currents, light, etc., an attempt was made to understand how the basic

elements respond to environmental processes operating on them.

(3) To interpret the environmental processes and responses in terms

of potential changes that may affect continued use of the harbor and main-

tenance of its environmental quality. Specific problems are delineated

and recommendations offered for their solution with priorities for future

research.

Scope and Previous Studies

The present study is part of a longer term investigation of the environmental

quality and pollution in bays, harbors and insular waters of the Virgin Islands. Com-

pared to previous studies of the Caribbean Research Institute, it is more comprehensive

and utilized more scientific and technical expertise and more sophisticated equipment

than here-to-fore available; yet, it was mobilized within a relatively short time.

The approach taken was to consider the harbor as an ecological unit. Spatially, it is

limited to the harbor proper, the entrance reaches, protecting coral reef and the shore-

line from Beauregard Bay on the east to Pelican Cove on the west. Upland sources of

water and contiguous waters offshore and in Altona Lagoona are included as appropriate.

Temporally, the study is limited to the period May through October 1971, essentially

the summer season. Time available did not permit observations during the winter

season, when certain environmental processes are more active than or different from

those of summer. Because environmental conditions in the harbor are so variable

with time and place, the investigation did not cover all local changes or permit an

examination of the full range of conditions, including extremes important to the life

of organisms. Observations necessarily were made at selected stations and along

a number of tracks; future studies utilizing a greater sampling density would un-

doubtedly show even greater variation than reported here. Also, as a status

report it is merely one "snapshot" out of the long history of changing environmental

conditions, and though we have attempted to document these conditions, they

will change with time as the harbor becomes more extensively utilized and altered.

Thus, this report does not provide final answers for all local development problems.

Rather, it is a baseline study of harborwide conditions within the scope outlined above.

Such basic studies are required because so little is known about the effects of pollu-

tion and ecological disturbance in tropical coastal waters.

A major difficulty confronting the formulation of the study was the lack of

previous quantitative data. Such background data are needed to assess trends in

the present conditions as well as to measure their rates of change, and to record

their history so that future trends can be predicted. No previous data on water

quality came to our attention except for the two week study by Jacobssen (1951) for

the Virgin Islands Department of Health and the reconnaissance sampling by the

Federal Water Pollution Administration (1967). The Division of Environmental

Health, Virgin Islands Department of Health collects water samples monthly for

enumeration of coliform and streptococci indicators, and records temperature

and chloride ion concentration of the surface water at selected stations. The

most recent bathymetric charts of the harbor are those of the U. S. Coast and

Geodetic Survey which date to 1924. Tides were recorded last in 1924 for a

limited period of 4 months. No inventory of fisheries or benthic ecology has

ever been attempted, except for the broad island-wide survey of Dammann (1970).

Despite the available aerial photographic coverage of federal agencies obtained

every 5 to 7 years no effort has been made to extract ecologically significant

information. Morever, there are no long-term stations in the harbor which

monitor basic environmental parameters like wind, stream discharge, salinity,

tide and temperature. These data are of use to provide a multiple "look" from

season to season, before and after changes are effected, and to evaluate extreme

events.

Acknowledgements

The authors are grateful to many individuals who gave freely of their time.

Students in training at the Fairleigh Dickinson West Indies Laboratory assisted with

long hours of anchor station measurements on the "Reef Sampler", skippered by

Don Neil, amid squalls, rolling and occasional sea-sickness: M. Dong, D. Malaspina,

D. Jenner, M. Perrone, S. Whipple, W. Marchion, E. Clark, N. Samuel, L. Firth,

D. Jenus, J. Duerbig and J. Mikulak. Additionally, Mr. John Yntema of the Virgin

Islands Department of Conservation assisted with many aspects of field work and data

analyses including compilation of dredging activities, fisheries notes and basic tidal

data. Mr. J. Larsen, of CRI, installed tide gages and obtained aerial photographs

of dye releases; C. Gellert of CRI processed photography and typed parts of the

original manuscript. R. Galiber assisted with field and laboratory activity, and

E. Shatrosky with the assistance of N. Carlson, Wayne Neal, and P. Lierhaus,

accomplished most of the laboratory water analyses. Kaye Stubblefield and June

Hogman drafted the figures. K. Fiederer and V. Hodges cheerfully accomplished

the tedious task of typing and retyping the draft and final text material.. Ideas

expressed in this paper were shaped in discussions with harbor masters Captains

Grey and Conway, and with Dr. Grey Multer, Dr. John Adams, and Dr. John

Zeigler.

2. SUMMARY OF PROCEDURES

Field Methods

Most of the field work was done from a runabout or skiff; but to measure

currents,12 "anchor" stations were occupied with the "Reef Sampler" an 11-meter

sportfishing vessel. The broad character of the study, and requirements of dif-

ferent investigations necessitated separate trips and different types of field sam-

pling. Altogether, a total of 94 sediment samples were collected, 12 anchor sta-

tions were occupied, 15 stations were repetitively occupied for water quality de-

termination, 7000 meters of "track" line observations run on coral reefs and

18, 000 meters of sounding lines run throughout the harbor. Field work was

accomplished between May and October, 1971, but was concentrated during tho

6-week period July 21 to September 3.

Station Locations

Stations were positioned in the field by ranging on buoys and landmarks

or by pelorus bearings. Positions were plotted on a hydrographic chart or

aerial photograph. The location of hydrographic stations, including water qua-

lity, anchor and littoral current stations is presented in Figure 1, and the

location of sediment sampling stations is given in Figure 2. Coordinates and

water depths are tabulated in the respective appendices. Water quality sta-

tions were located on a basic grid at 300 m intervals,. Anchor stations were

located primarily to delineate the harbor-wide circulation whereas sediment

stations were located to include a range of different sediment types, and dif-

ferent morphologic reaches of varying water depth and varying rates of fill,

scour and disturbance.

Figure 1.

Location of hydrographic stations for measurements of tide, water quality, and
current ("anchor stations"). Littoral current stations are identified by roman
numerals. Depth contour at 6 meters and dredged channel is dashed.
*_____*___

I

.53
52 *54
Scotch
B 5Bonk
*50
*55
*51
PELICAN 6m 6m
<,.CO VE

*82
6@0,98 68
6 l' ",-, ,' *84 *57
62" --. ---J e8L -.
*64 60 V-8a *86 5
6 64 277 LONG REEF 8659
63 +64a 6/ --8 87 R 85 58
65 70 93 92 .42 600 2 V
15 60 b*
72 *7 *76 020 470 48*
o69 91o0 41 40
24 11,022 37 35 I *80 AL:
75 86- 36
9 5 --" 23 90 4
960 3 t

BOTTOMM SEDII

SCALE 0m STATIONS
0 0.5mi 0 SURFACE SAMPLE
+ CORE

Figure 2. Location of bottom sediment collecting stations and location of cores. B G is
Barracuda Ground; P C is Protestant Cay; R R is Round Reef.

j

Sample Collection and Measurement

Most surface sediment samples were collected by forcing a 5 cm

diameter plastic coring tube into the bottom by hand. The top 2 cm of near-

surface sediment was removed from each core and the resulting equal-area

and equal volume sample retained for analyses. In water deeper than about

7 m, mainly in channels, a "Ponar" grab was used. Areas inaccessible by

boat were sampled by skin diving and "grabbing" the upper few centimeters

of sediment. Cores were obtained manually by driving a 2-3 m length of 3.5

cm diameter PVC pipe into the bottom. Cores were cut lengthwise on a table

saw and split with piano wire, photographed while fresh and sampled at 10 cm

depth intervals. An explanation of field data is given in Appendix II.

Observations of water characteristics and current measurements were

made at a number of fixed points or "anchor" stations, August 2-4 and August

10-17, 1971. As planned, the anchor station observations encompassed a period

of relatively stable weather, spring tide range and diurnal phase of the tide.

Observations were repeated every 1 to 2 hours for 1 tidal cycle of 25 hours

and 1 to 4 depth intervals throughout the water column. Stations in the eastern

and central harbor were occupied simultaneously two at a time, e.g. numbers

4 and 9, 5 and 10, 6 and 11. Table I summarizes the observations made and

corresponding instruments used. Further details are given in Appendix I.

_I _

TABLE 1. Anchor Station Observations and Corresponding Instruments Used.

Parameter

Current Speed

Current Direction

Salinity

Temperature

Transparency

Turbidity

Water Depth

Wind Speed

Tidal Height

Instrument

Oceanographic Engineering Corp. Savonius Rotor;
TSK Propeller Meter

Oceanographic Engineering Corp. Vane;TSK Recording
Meter

Beckman RS5-3 conductivity-temperature indicator;
Water samples pumped by a Western Brass "Blue
Cascade" plastic submersible pump and titrated in
the lab with silver nitrate

Beckman RS5-3 conductivity-temperature indicator

Secchi, white-black disk, 20 cm diameter

Water samples pumped by a Western Brass "Blue
Cascade" submersible pump and filtered in the lab

By sounding line, Ross model 300-100 and Rathyeon
DE 119 fathometers

Sims anenometer

Recording portable automatic tide gage of the USC & GS

Water quality measurements were made and samples collected from surface

waters at 15 stations (Figure 1) from May through September between the hours

of 1000 and 1400. Temperature and dissolved oxygen were measured either

with a Precision Scientific model 10 or a YSI model 54 galvanic oxygen meter

calibrated in water at each station. All D. O. values are corrected to ambient

water temperatures. Salinities were determined on water samples returned to

the laboratory by Mohr titration and suspended solids were analyzed gravimetri-

cally using membrane filters with a 0.45 u pore size. Fecal coliforms were

determined on undiluted water samples by the membrane filter technique (APHA,

1965).
2-5

For surveying the bathymetry several different methods were used

according to water depth and equipment available. In shallow water of the

western harbor (Turquoise Bay) and nearshore areas, water depths were

measured by lead line at horizontal intervals less than 10 meters and posi-

tioned by reference to features shown on aerial photographs. In water depths

greater than about one meter encompassing the greater part of the harbor floor,

portable fathometers were used from small boats and depths were sounded con-

tinuously along previously surveyed "tracks" or lines marked with range poles.

Positioning was done underway by repeated ranging on landmarks and bouys

and by pelorus cross bearings. Accuracy of the fixes is better than 3 meters.

A Ross model 300-100 was used in the eastern harbor, a Rathyeon DC-119 in

the central and eastern harbor and a Ross "Fineline" was used in deeper water

of the entrance. A depth change less than 0.3 meter could be detected most of

the time.

Track lines were plotted on USC and GS hydrographic chart (#935), and

depths transferred to the charts after correction for transducer draft and reduc-

tion to mean low water. The distribution of track lines is given in Figure 6.

Interpolation of contours around dredge holes and isolated reefs was facilitated

by use of a 1971 US-SCS air photo.

In addition to the forgoing sampling and observations special efforts were

made to obtain tide-controlled aerial photography of dye releases. Procedural

details of these related efforts are given in subsequent report sections where they

apply.

2-6

Laboratory Procedures

Grain size of selected sediment samples was determined by a com-

bination of sieving and pipette analysis following procedures of Folk (1961).

Approximately 15-25 gm of sample was washed with tap water through a 4

phi (0. 0625 mm) sieve. The mud fraction collected in a 1500 ml dish was

decanted after settling 24 hours, and subsequently poured into one liter

containers. It was further analysed by pipette according to Folk (1961)

at time intervals corresponding to 4, 5,6, 8 and 10 phi. The mud fraction

was processed wet without adding a dispersant whereas the sand fraction

was dried, sieved into Wentworth size fractions and weighted.

Results of the size analyses were plotted as cumulative curves on

probability paper using a logrithmic phi scale for diameter, where 0 is log2

of the diameter in millimeters. The particle diameters at the 16, 50 and 84

percentile values were obtained from the curves and used to derive size para-

meters based on the relations of Inman (1952):

Median diameter (Md 0) = 0 50

Standard deviation (d0)= 0 84 0 16
2

The composition of different constituents in the sand fraction were exa-

mined under a binocular microscope in two size classes: (1) greater than 250 u

and from 62 to 250 u. Several aliquots were spread out on a gridded petri dish

and at least 200 grains in each fraction were counted along the grid lines. Per-

centages of different constituents were calculated and their distributions plotted

on chartlets following Shepard and Moore (1954).

2-7

3. DESCRIPTION OF THE HARBOR

Along the north coast of St. Croix, the shoreline is indented by nu-

merous bays and fringed by submerged coral reefs that give a distinctive

character to this part of the island. Christiansted Harbor, the largest em-

bayment on the north coast, is broadly lunate-shaped in plan view. It lies

behind a practically continuous intertidal coral reef, Long Reef, and is backed

by hills alternating with stretches of alluvial lowland. A small alluvial delta

protrudes into the harbor near the cement plant (Golden Rock). This is in

contrast with the shoreline elsewhere along the southwest shore where erosion

over long periods of time appears to have smoothed the shore and created low

bluffs. On the east side, a rocky headland, Fort Louise Augusta, is tied to

the upland by broad sand beaches which in turn, separate Altona Lagoon from the

harbor and the ocean. A geologic map of the area by Whetten (1961) gives some

indication that faulting has been responsible for the morphology along the south

and east shore.

Christiansted Harbor is 3.30 km long and 0.70km wide, Table 2.
2
Its total surface area is 2.31 km (570 acres). The harbor receives drainage

from an area of 7.25 km2 in addition to 0.48 km2 from Altona Lagoon and

2.71 km2 surrounding the lagoon. Its maximum depth is 23 meters (75 feet),

but because its depths are very irregular and include many broad shoals, its

overall average depth is only 1.80 meters.

I

Summary of Geographic and Hydrographic Data

Parameter

Length

Av age width

Are

Volum

Mean depth overall

Shoreline length

Maximum depth

Drainage Basin

Mean tide range

Tidal pri m

Christiansted Harbor

3.30 km

0.70 km
2
2.31 km
3
4,150,000 m

1.80 m

5.70 km

23.0 m

7.25 km2

0.19 m

439,000 m3
439, 000 m

Altona Lagoon

1.70 km

0.28 km
2
0.48 km

624,000 m3

1.31 m

4.6 km

3.0 m

2.71 sq. km

Distribution of areas at various depth intervals in Christiansted
Harbor, 1971.

Area, sq. km

0.87

0.67

0.42

0.20

0.14

Percent of Total

37.8

29.2

18.7

8.6

5.4

TABLE

Depth, m

0-2

2-4

4-6

6-8

>8

3-2

TABLE 2.

TabUlation of the distribution of harbor area in different depth "zones",

Table 3, indicates the largest fraction of the harbor floor, 37.8 percent,

lies in the depth range of 0 to 2 m, whereas deeper portions, greater than

8 m are limited to less than 6 percent. Thus, the harbor is essentially

a shallow pan and its floor is susceptible to wave action as well as distur-

bance by boats and sea planes.

Bathymetry

Bathymetry of the harbor in its present state is presented in Figure 3.

The floor of the eastern harbor is molded into a deep winding channel that is

surrounded by submerged shoals and shallow reefs. The channel sides are

relatively steep; especially in deeper central parts whereas the shoals are

relatively flat and extend over a broad area of the western harbor. The main

channel has only a few short tributaries and these enter the main channel

nearly at right angles. This pattern, and the sharply winding entrance

course, a course that is notoriously difficult to navigate, suggests the initial

channel course was controlled by geologic structure, such as faults or large-

scale joints. However, only the north-south channel axes parallel known faults

on land as mapped by Whetten (1961) and no direct connections have been found.

The outer entrance channel is distinguished by a V-shaped profile incised in the

shelf edge below the 16 m depth. Erosion most likely occurred during a period

of lower sea level and sub-aerial exposure in the Pleistocene, at a time when

Figure 3. Bathymetry of Christiansted Harbor, August 1971. Based on sounding lines, inset.
Depths in feet.

streams probably emptied into the ocean at the platform edge. Farther

inward, the entrance channel is U-shaped due to sedimentary infilling,

but inward between Barracuda Ground and Round Reef the channel is V-

shaped. In this reach, the channel attains its greatest depth, 23 m (75

feet) and the depth is increasing with time indicating sediment is being

eroded by currents.

An historical examination of old charts shows bathymetry has

substantially changed in different parts of the harbor. Table 4 lists

the charts examined. Comparison of depths on charts dated 1794 1799

(by Oxholm), and 1856 (by the British Admiralty) show that the harbor

floor was extensively altered prior to intensive development. In 1794-99,

a natural channel averaging about 4 m (12 feet) deep, extended to Christian-

sted west of Protestant Cay and a channel 6 to 8 m (18 to 24 feet) deep ex-

tended east of Protestant Cay landward almost to the Old Fort. Additionally,

in Sloop Channel depths averaged about 3 meters (18 feet), When these depths

are compared with those of 1856, the U. S. Coast and Geodetic Survey chart

of 1924 and the present survey, they show the inner harbor shoaled by 1 to 2 m

between 1794-99 and 1856. From 1856 to 1924, shoaling was small in the inner

harbor but reached more than 1 m in Sloop Channel. Filling of the inner

harbor may have been caused by a supply of sediment released by soil erosion

following early agricultural development of the island. Today, depths of 5 m

(16 feet), formerly the natural depth, are attained only by frequent dredging.

3-5

I

List of harbor charts that provide a source of historical
data on bathymetry.

Source

P. L. Oxholm, Danish

J. Parsons, British Admiralty

U. S. Coast and Geodetic Survey

U. S. Army, Office of the District
Engineer

Date

1794 1799

1856

1924

1947

3-6

TABLE 4.

Aerial Photographic Studies

Aerial photography is a relatively new tool that is proving very useful

for analyzing coastal environments. From an aerial or birds'-eye view di-

rected vertically downward one can see at a glance, variations of tone repre-

senting distributional patterns of biota and sediment. Such patterns are diffi-

cult to recognize or chart from on or below the water surface. Besides

showing environmental detail and physiographic features not shown on charts,

a sequence of photos of the same area taken from time to time reveals changes

resulting from environmental processes that is, processes like sediment

transport, recession of bottom communities, and shoreline erosion. In

some photographs, the processes are portrayed directly.

Aerial photographic coverage of the harbor is listed in Table 5. All

photos are vertically oriented, black and white, 9x9" size, and they were re-

duced to a common scale of 1: 15, 000 for comparative examination. Most

information was derived from coverage dated 1954 (U. S. G. S.), 1964 (U. S. C.

& G. S.), and 1971 (U.S. S.C. S.).

TABLE 5, Aerial photo coverage for Christiansted Harbor

Source Date Scale

U. S. Geological Survey 1954 1:23,600

U. S. Coast and Geodetic Survey 1959 1:30, 000
1964 1:24,000
Mark Hurd Aerial Surveys (Minn.) 1962 1:24, 000

Aero Service (Phila. Pa.) 1962 1:12,000
1963 ----
U. S. Soil Conserv. Service 1971 1:20,000
National Ocean Survey (U. S. C. G. S.) 1971 1:30, 000

3-7

Most aerial mapping photography is flown with a 6" (0.5 ft.)

focal length camera; therefore, the flying altitude is close to

0.5 times the reciprocal of the scale; e.g., USGS 1954 photos were

flown at 0.5' x 23,600 or 11,800 ft.

Figure 4, a reproduction of an aerial photograph dated 1954,

shows the harbor more or less in its "natural" condition before

the intensive development and alterations which took place in the

1960's. Most conspicuous is the change between contrasting light-

dark tone areas of land which partly represent cultural features

such as streets and buildings in Christiansted (CH, in Figure 4)

or natural features such as grassland and trees between (CP) the

site of the present day cement plant and (LP) and Little Princess.

In the Harbor, dark-toned (almost black) and light-toned (almost

white) patches represent either areas of grass (dark) or sand

(light) on the floor.

Because of the high water transparency at the time of photography

in 1954, bottom features can be seen at a depth of about 5m in the

vicinity of Gallows Bay, and at about 15m near the entrance (E).

Wave crests are displayed by surface sun glint near bg, seaward

of Long Reef, and breaking surf is shown by overlapping and irre-

gular white bands.

Along the crest of Long Reef there is an inter-tidal ridge

which is recorded in the photography as a "diffuse line" landward

of the breaker zone, Figure 4. Composed of broken coral heads

and dead branches encrusted with calcareous algae, the ridge is

dis-continuously exposed 15 to 30 cm high.

3-8

FIGURE 4. Aerial photograph of Christiansted Harbor taken at 11, 800 foot altitude,
January 28, 1954. U.S.G.S. photo number GSYM 1-145 (AF 5577),
enlarged for reproduction 2 times.

This photograph shows the harbor in plain view prior to intense develop-
ment in the 1960's. Natural elements include Long Reef, an inter-tidal
and sub-tidal coral reef "ribbed" on its landward side with submerged
sand trains, st(white) interpersed with dark-toned coral
covered ridges, and "striated" on its submerged seaward side with
groove and buttress structures, bg. Wave crests displayed by sun
glint are seen approaching the reef at a slight angle and the breaking
surf line is represented by overlapping and irregular white bands.

The outer entrance E, is marked by dark landward extending tongues
showing the main channel with water depths greater than 12 meters.
An accumulation of coral sand flanks the entrance at s (light tone),
and extends landward in a tongue to the right side of the photo.
Farther landward, dense beds of turtle grass, t, cover the bottom
broken occasionally by lunate blow-outs, or sandy patches displayed
by light tones.

The dark-toned grass beds extend inward behind Round Reef (Rr), and
Fort Louise Augusta; a few irregular dark-toned grass patches are vi-
sible off the mouth of Altona Lagoon. Mangrove trees fringe the lagoon
shore and extend lagoonward at m. Near Barracuda Ground, coral sand
(white -toned) penetrates dense turtle grass beds in finger -like patterns
at t. Elsewhere, turtle grass is displayed in dense beds to the north of
Protestant Cay (t), as well as to the west in a broad zone (t2), and farther
westward-along the shore to Little Princess (LP).

The southwest shore between Little Princess and Christiansted is largely
undeveloped except for land fill at sites f and a shore facility with pier
extending seaward just southeast of the present-day cement plant (CP).
Most of the Christiansted waterfront is bulkheaded with wharves and
docks, just as today except in the Gallows Bay area (GB).

0

:'r.,~L' I c

.As

_ I

~ ~F '

'' iI~~aB

4ES: .~

U.
dLti,

iq~ ~
i :~

4

JIe~''

- ,
~c r'~~
... nd,

IE
rii;r
i-

at low water, but is largely submerged at high water. Seaward of the breaker

zone the reef is "striated" with living coral that forms a groove and buttress

system (bg on Figure 4 and in the vicinity of 0, Figure 5). Although sun

glint in the photograph of Figure 4 limits observable grooves and buttresses

to the eastern part of Long Reef, they are found more or less continuously

distributed along the entire reef length such as shown in Figure 5. Addi-

tionally, the grooves cross more than three "bands", or depth zones of

algae and coral paralleling the reef.

Landward parts of the reef, or backreef, are "ribbed" by a series

of light-toned submerged shallow channels (st, Figure 4) alternating with dark-toned

ridges of massive finger coral (Porites sp.). Locally, these channels or "trains"

which are floored by coral, rubble or sand, and ridges penetrate the harbor over 100

meters from the reef crest in the form of a lobe, as st, Figure 4. Their landward

margin is fringed by a relatively steep sand slope 100 200, 15 -20 m wide, (white

in Figure 4) and this passes into the flat harbor floor represented by the large light-

toned area between st and t2, Figure 4. The light-tone areas are bare sand churned up

by burrowing organisms, whereas, the slightly darker tones are produced by a very

sparse grass cover, areas of less intense sediment reworking.

In the outer entrance, E, dark trough-like tongues reveal the main channel

at depths greater than about 15 m. A sill, or shoal of sandy sediment across the

channel at a water depth of 9 m, is visible in the channel bend northeast of Round Reef

(Rr). Additionally, a large accumulation of coral sand (s, in Figure 4) extends

westward (channelward) at two points as well as landward to the photo edge.

3-10

Turtle grass beds appear on the photograph as dark patches with
irregular boundaries (t, Figure 4). East of the outer entrance channel the
grass beds are interrupted by light-toned and lunate-shaped sandy patches
called blowouts. The dark-toned grass beds (t) extend into the harbor
behind Round Reef (Rr) and to the entrance of Altona Lagoon. Near Barracuda
Ground two "fingers" of coral sand penetrate, and partly bury, the large
grass bed at (tl). Elsewhere, dense turtle grass beds are displayed by
dark somewhat mottled, patches north of Protestant Cay, and westward
in a broad zone (t2) as well as along the southwest shore to Little Princess
(LP).

South and east of Fort Louise Augusta, the shoreline is marked by
a narrow white band representing coral sand beaches more than 15m wide.
This is in contrast to the dark-toned (almost black) band of mangrove trees
bordering Altona Lagoon and occupying the Lagoon corner, m, Figure 4.
Between Little Princess (LP) and Christiansted (CH), beaches are generally
absent and the shoreline is undeveloped except for a rum distillery, at the
present-day cement and power plant side (CP), and landfill areas, f, Figure
4. Less than a dozen small vessels and boats occupy anchorages in
Gallows Bay (GB), and southwest of Protestant Cay.

3-11

By comparing the photograph dated 1954, Figure 4, with another

dated 1971, Figure 5, the environmental and cultural changes that have

taken place during a 17-year period are indicated. In tracing changes,

the slightly smaller scale of Figure 5 must be taken into account, as also

the sun glint over the surface of the eastern harbor, (a feature that prevents

complete examination of the bottom in this photo, but is absent in an adjoining

photo not reproduced here). The most striking change is displayed in the

blotchy dark-toned areas of the central harbor designated d in Figure 5.

These are excavations, 4-8 m deep, dredged for sand, either construction

aggregate or landfilL .Growths of algae, Enteromorpha, now covering the

bottom of these holes, contribute to the dark-tone of the photograph. Ad-

joining these areas to the south and east are elongate dark-toned areas marked

c that represent segments of a shipping channel, 5.5 m deep, leading to the

power plant and the Cement Plant (CP). Sandy spoil dredged from the channel

is deposited as landfill in areas designated f, Figure 5 (white tone) in an effort

'to reclaim shoreward portions of the harbor floor. Channel dredging resulted

i iextrpatf6n-of grass beds along the channel course and landfill eliminated

* beds north of Protestant Cay as well as east of the Cement Plant (CP). Another

change,though of smaller magnitude, is visible near Barracuda Ground where

grass beds are eliminated by natural progradation of a sand lobe, tl, directed

southtoward the main channel. Additionally, there is less turtle grass coverage

on Round Reef (.Rr) and inward of Fort Louise Augusta (FL)than in 1954. Bridging

the lagoon entrance at b, with attendant restriction of flow to a 190 cm diameter

3-12

FIGURE 5. Aerial photograph of Christiansted Harbor taken at 10, 000-foot altitude,
February 17, 1971. U.S. -S. C. S. photo number PCFD-241, enlarged for
reproduction 1.45 times.

Natural elements include FL, Fort Louise Augusta, a rocky headland which
protects the harbor on the northeast; RR, Round Reef, is an isolated coral
reef in the inner harbor entrance; E is the outer entrance, a deep opening
between coral reefs to the west and east; s is Scotch Bank, and i, near
Gallows Bay (GB), is the main site of stream inflow.

Among the cultural features are CS, Christiansted business area and
waterfront; GB, Gallows Bay, a embayment dredged for shipping, White
patches designated f, are sandy areas of landfill and the dark patches, d,
are excavations in the floor left by sand dredges; LP is the waterfront re-
sidential area of Little Princess; o indicates site of outfalls which discharges
wastes and thermal effluents into the harbor and vicinity; g indicates guts
that discharge local runoff into the harbor.

'~F T~?Jur~>*~~T 4LT~~
~ I ~

*li tn ay .
, ;;IL

; f

p .-:I

A '
l f A>- ,'

-?~ I~F

-~

f

h j'I,-
L' I;

'.,
3.I4

~tr '' g-
a f
i

~L~mi r

~?iri~~r..L

-a "

Zvi

culvert constitutes a relatively small physical change, but it has had a

large effect in reducing exchange, water quality and biota of the lagoon.

Similarly, exchange in Gallows Bay (GB) is probably reduced by harborward

extension of a major wharf and by landfill (f). Since 1954, the number of

small vessels and boats occupying anchorages has increased more than three-

fold.

Although sources of pollution and waste disposal are not directly

shown in the photographs of Figures 4 and 5, information presented by

Jacobsen (1951) indicates that four sewers discharged directly into the harbor

at Christiansted. Additionally, nightsoil and garbage were dumped into the

harbor along the shore between Christiansted and the present-day cement plant.

And a rum distillery, located at the present-day site of the cement plant, re-

portedly discharged a substantial quantity of waste products directly into the

harbor. A municipal abattoir contributed wastes to Gallows Bay lowering the

dissolved oxygen content below 5 ppm. Today by contrast, most sewerage is

discharged into the ocean off Long Reef, 0 in Figure 5. But thermal effluents

are released from the power plant, 0 near CP, Figure 5; sewage wastes and

oil are discharged from anchored vessels and surface runoff from streets,

gutters and backyards of Christiansted carry miscellaneous wastes through

guts directly into the harbor in times of heavy rainfall. Municipal sewerage

discharge into the harbor is limited to intermittent periods of emergency opera-

tions.

3-14

Shoreline Features

A variety of different shoreline types are recognized according to

their natural character and utilization:

1. Wharves and bulkheaded waterfront

2. Rocky shoreline backed by bluffs

3. Artificial beaches fronting landfill

4. Natural beaches

Man-made structures consisting of wharves, sea walls, ramps, docks

and bulkheads, occupy 41 percent of the shoreline today, whereas in 1954, they

occupied only 16 percent. Built mainly for berthing, shipping, off-loading and

dockage, these structures secondarily serve to protect the shoreline from ero-

sion. However, such structures often have a deleterious effect on the water

quality and bottom sediments. By interfering with flow of natural currents,

they locally reduce circulation promoting anaerobic conditions. Additionally,

sediment is trapped and shoreline equilibrium upset, When waves attack

these structures they are reflected and sand is stirred up from the nearshore

bottom. This increases erosion, possibly undermines'the atrm~cturp,- ad con-

tributes to turbidity of the water.

Stretches of rocky and cobble-strewn shore backed by rock cliffs or

bluffs of alluvium, make-up 26 percent of the harbor shoreline. Located

chiefly around Fort Louise Augusta, Mt. Welcome and the east side of Pro-

testant Cay, this shoreline type was formerly much more extensive. Since

1954, 34 percent of the harbor shoreline formerly of this type has been eli-

minated or transformed to artificial beaches by landfill.

3-15

I

Although of limited practical use, rocky shoreline of headlands afford

sheltered anchorage and adds a great deal to the varied wealth of landscape

that enhances the natural setting of Christiansted.

Beaches make up 33 percent of the shoreline, of which 12 percent

are natural and 21 percent are artificial. The longest and most attractive

beach faces the ocean east of Fort Louise Augusta. It is relatively straight,

more than 15 m wide and firm to walk on. The sand is mainly coral, rich

in yellow-colored grains of Acropora palmata. It is medium to coarse-grained.

With increasing steepness toward the east, grain size increases and cobbles

are common at the east end (Figure 6 C). Because of seasonal variations in

intensity and direction of waves marked by "northerners", the beach is fre-

quently changed in width and steepness. Such changes reduce its stability.

Long-term recession of the beach is indicated by exposed tree roots and by an

exposure of beach rock 30 to 40 meters offshore (fb, Figure 6 C). Like beach

rock common to many shores of the Caribbean, it consists of calcareous sand

and shell debris that is most likely cemented in the vicinity of the water table

of a former beach (Russelland McIntire, 1965). Although the beach rock dis-

sipates wave energy and thus protects the present beach to some degree, it is

treacherous to boating and undesirable for bathing, especially when covered by

moss and coral.

The natural beach bordering the western harbor near Little Princess,

is stable, firm to walk on, and narrow, mostly less than 3 m except on the

westernmost point where it is more than 15 m wide. Despite the potential

3-16

FIGURE 6.

Photographs of shoreline conditions at Christiansted Harbor, August, 1971.

A. Sandy beach on point of land at Little Princess, partly covered with
accumulations of dead grass ( t ) that is derived from shoals just
offshore and to the east. The beach is relatively wide (>20m), and
erosion is minimal. Easterly waves shown breaking at an angle re-
sult in a westward flowing littoral current and transport of sand.

B. Eroded bank (b) at Turquoise Beach fronted by rock debris (r), a fill
emplaced to arrest erosion. Note tree roots exposed by erosion.

C. Beach along Beauregard Bay, view southwest from the Bucaneer.
Beach rock (fb) marks a former beach seaward of the present beach
(pb). Exposed tree roots (t) indicate erosion is active at this poift.

D. Eroding beach along the eastern shore between Mt. Welcome (MW) and
Ft. Louise Augusta. Erosion has exposed several generations of landfill
consisting of white sandy sediment overlying dark clayey sediment. Tree
roots and stumps (t) indicate land extended farther seaward in the recant
past.

O

rr:
~3~:
~r ~-
-~ L

a
%r- ~L :jllC: ~ IJYC~L~
'.'' r,
~ ~
Rab c. LL~C~-~Pn

supply of sediment from eroding bluffs of alluvium, particularly on the

east end at Turquoise Beach (Figure 6 B), most of the sediment consists

of the fine to medium-grained coral sand. Beachrock is intermittently

exposed 5-15 cm above the shallow nearshore bottom. Between Little

Princess and Pelican Cove erosion has reduced the beach to less than

3 meters width, but wave attack is retarded by the broad shoals of living

coral offshore and by short groins and rock fill. Attractiveness of the

beach is limited by thick accumulations of rotting grass derived from beds

just offshore and farther to the east (t, Figure 6 A).

Artificial beaches consist of sandy dredge spoil emplaced as land-

fill. Most of the material is derived from nearby channels and is rich in

white coral sand mixed with small proportions of shell and calcareous

nodules. It is distinguished by: (1) a substantial percentage of grey and

black sand grains which locally give it an overall grey color, and by (2)

its poor sorting, i.e., a range of grain size from fine to coarse sand,

plus calcareous cobbles.

The quality of the artificial beaches depends on the character of

the spoil and effectiveness of wave action in "reducing" the spoil to a

beach. On the west side of Protestant Cay where wave action is mini-

mal, spoil forms a firm, steeply sloping and relatively smooth beach.

But on the more exposed north side, and along the extensive landfill

east of the cement plant, wave action has effectively cut a scarp 2 m-high,

in the spoil and redistributed erodable materials offshore where they are

3-18

spread out on shoals of the nearshore bottom (e.g., s, Figure 2I). Coarse

material, shell and rubble, too heavy to be transported, are left on the beach

as a lag deposit whereas fine-grained silt and clay released from the spoil,

produce intense turbidity that is dispersed over a wide area (e.g., t, Figure

25). Unless the exposed landfill is stabilized these processes will continue

to a greater or lesser degree until the beach profile and plan configuration

reach a new equilibrium with the local wave energy and until the rate of

sediment supply balances the rate of loss.

Erosion is active along all the artificial beaches except the west

shore of Protestant Cay, and at Mill Harbor. At the public beach fronting

Altona Lagoon (Figure 6, D) several generations of cut and fill are super-

imposed on long-term recession which is evidenced by a prominent off-

shore ledge of beach rock and by eroded stumps of trees. Although groins

have been constructed at different places to arrest erosion, they are largely

ineffective. At.Turquoise Beach a groin-like structure is partly responsible

for accelerating erosion. Failure of groins attests to the lack of knowledge

of wave and current processes that they are intended to resist.

4

3-19

4. HYDROGRAPHY

Tides

Rise and fall of the tide is relatively small being less than 35 cm

most of the time. The mean range in the harbor is 19 cm and the highest

extreme limit of tide is estimated at 60 cm, whereas the lowest tide is

-30 cm below mean low water. But what the tide lacks in magnitude is

made up in its variety and complex character.

Height of the tide was measured on continuously recording tide gages

installed at Chandlers Marina, Gallows Bay, June 29, 1971 and at the Cement

plant pier,, August 3, 1971. A tide gage installed by the U.S. Coast and

Geodetic Survey (NOS) at Gallows Bay for 4 months from April to July, 1924

provides data for secondary determination of mean low water as well as data

for predicting the approximate heights and times of the tide throughout the year.

These predictions are given in tide tables issued annually by the National

Ocean Survey (1971). Because the character of the tide at Christiansted is

like that at Galveston, Texas where the tide has been recorded since 1909,

predictions are made by reference to Galveston, Texas. For example, the

time of high water is 9 hours and 17 minutes earlier and heights are lower than

at Galveston by a factor of 0.57. Tides recorded in this study agree closely

with those of predicted tables as shown in Figure 7. Once reduced by com-

parison to the primary reference station, the new records will provide a new

preliminary tidal datum for the harbor.

LL

JUNE JULY

JULY

Variations in the character of the tide displayed in time-height curves, from
predicted tables and from observed tides in the harbor from June 29 July 19,
1971.

Figure 7

__

Tide Character

Character of the tide changes from day to day during a month. As

shown in figure 7,at neap range June 29 July 1 and July 12 13 the tide is

mixed; there are two high and two low waters daily, each of unequal height.

By contrast at spring range, July 5 7 and August 17 18, the tide is of the

daily type; there is one high and one low water each day. Intermediate

periods have low waters of different height indicating the mixed tide is mainly

due to a diurnal inequality in the low waters. At certain times however, the

differences between lower high water and higher low water are so small, the

mixed tides merge into a daily type with one high and one low water each day.

This transformation, which occurs about once a week is known as a vanishing tide;

and results in a near still stand of water in the harbor for about 12 hours. This

sequence of variations arises from changing positions of the moon in relation

to the earth and sun as demonstrated by Marmer (1954). It is these tidal

changes which promote an exchange of water and which alternately flood and

expose the shore;

Although the tide changes character from time to time throughout a

month, it is predominately of the mixed type like other areas in the Antilles,

according to the U. S. Navy Oceanographic Atlas (U. S. Navy, 1965). In con-

trast to the regular daily variations, irregular fluctuations were noted in the

tide records, especially at neap range of the tide. When the records are com-

pared with the periodic rise and fall of predicted time-height curves as shown

4-3

in Figure 7 departures occur which relate to short-term effects of wind and

weather.

From place to place within the harbor tidal differences are small.

Differences in the time of high and low water between Chandlers Pier and

the Cement Plant Pier, a distance of 1.6 km, are less than 20 minutes and

the range is essentially the same. Thus, the tide rises simultaneously

throughout the harbor. Because the harbor entrance is relatively large and

unrestricted, tide levels in the harbor most likely follow those in the ocean

within relatively narrow limits.

Seasonal Variations

Superimposed on the daily variations of range there are variations in

the average height of sea level or of mean low and high water from month to

month over an annual cycle. Although tide data at Christiansted are limited

to a few months of record, the magnitude of monthly variation over a year can

be inferred from data at Galveston, the reference station, as well as Havanna.

Figure 8 shows that mean sea level is more than 15 cm lower in winter than

in late summer. Likewise, monthly mean high water and mean low water may

be expected to follow a similar trend. Such variations have long been noted and

ascribed to the seasonal changes in wind and weather but quantitative data are

needed. Nonetheless, low levels of the tide are commonly observed by local

inhabitants during winter months, and the exposure of a large portion of Long

Reef must limit the transfer of ocean water across the reef.

24-

18-

cm-

12-

6-
t

0

- -

MEAN MONTHLY HEIGHT

L _____________________________________________________

I I I IM J
J F M A M J

I I1 I I
J A S 0 N D

MONTH

Figure 8.

Monthly change in mean sea level at Havanna
for an annual cycle, 1947-1950. Height in
centimeters above mean low water. Modified
from Marmer (1954).

SPEED,

m/sec.

Figure 9.

Vertical distribution of mean current speed in
meters per second at selected anchor stations
2, 7, 8, August 1971.

Y__

MSL
- MSL -

S -

CURRENT

.04

20

.I

Tidal Exchange

The periodic rise and fall of the tide is one of the important elements

of water exchange. Vertical range of the tide determines the extent of shore

that is alternately flooded and exposed, and the range determines the amount

of water entering and leaving the harbor each tidal cycle, i. e. the tidal prism

or volume of water between the mean low and high water planes. In Christian-

sted, the mean range, 19 cm times the harbor area, 2.31 sq. km. gives an

immediate estimate of the volume of tidal flow, or 4.4 x 105 m3, a figure which

indicates 10 percent of the harbor volume is exchanged each tide. This com-
53
pares with a figure of 3.78 x 10 m per hour determined by direct measurement

of volume transport through the entrance. Thus, tidal transport contributes

only a small part to the exchange of water, less than an estimated 10 percent

of the total water exchange. Wind drift and mass transport are much more

important.

Circulation

Special effort was applied to study of the circulation because movement

of water is of great significance in determining the character of the environment;

it is essential to problems of pollution and sediment transport. Additionally,

little is known about circulation in the harbor or in similar tropical environments

of the West Indies. Without a study of circulation, few logical conclusions could

be drawn from corollary geologic, ecologic and water quality data.

Because of the many current producing forces active in an harbor -- tide,

wind, waves and mass transport -- the measured current at any one place and

4-6

time is a resultant of components having several driving forces. These forces

vary in strength with time and interact with bottom geometry and shore con-

figuration from place to place to produce complicated patterns of convergence

and divergence. For this reason coastal circulations are studied by continuous

observations and analyzed statistically.

Circulation of water follows a broad counterclockwise pattern directed

eastward through the central and eastern harbor. The pattern is illustrated

in Figure 10 and is derived from current speed and direction measurements at

12 fixed "anchor" stations occupied over a 24-hour period. In areas where currents

were not metered, directions are inferred from the continuity of flow. The

measurements indicate currents are generally faster in central reaches and about

the entrance than elsewhere. Instanteous peak speeds reached more than 0.25 m/sec

in near-surface water of the entrance (Station 7) whereas in inner harbor reaches,

speeds are generally less than 0. 06 m/sec. In shallow water less than 3 m deep,

both surface and bottom water flow in a similar direction and at like speeds but in

deeper water of the channels speed is much reduced, and direction follows the channel

configuration. For example, the mean surface current exceeds bottom current more

than two-fold at Station 7, as shown in Figure 9. Only at Station 10, Sorensen Ground,

are bottom currents of greater strength than surface currents, a condition probably

controlled by channel configuration.

Figure 10.

Mean surface current, speed and direction for harbor currents and for littoral
currents, August 1971. Length and width of arrow indicates speed in meters per
second. Harbor currents based on anchor station measurements; littoral currents
on dye patch measurements. indicates two alternating predominate directions.

0 0

Although current measurements were made near spring range of the

tide, a time when tidal currents are most active, no tidal reversals are in-

dicated except at Station 9, Long Reef, offshore. At this station, there is

an indistinct reversal in the near-surface water, from flood to ebb every 10

to 12 hours. In near-bottom water, there is a weak and incomplete rotary

tidal current superimposed on an erratic coastal flow. It is possible that

during the period of current measurements wind-driven currents obscured

the tidal currents. During calm periods, however, there may be a flood

flow through the main entrance channel and an ebb flow through Sloop Chan-

nel.

The harbor-wide counterclockwise current is, undoubtedly, driven by

large-scale mass transport of waves breaking over Long Reef. Over-reef

transport is partly substantiated by drift of dye patches and by the distribu-

tional patterns of backreef sediments. Such a transport builds up a head of

water in the central and western harbor. Local accounts indicate that the

eastward harbor flow is speeded up during "northerners", when high surf

overtops the reef. Excess water driven into the harbor over the reef must

leave it through the main entrance to the east. The current measurements

leave no doubt that flow through the entrance is predominately seaward.

The stress of easterly trade winds on harbor water locally alters the

predominate easterly flow and may reinforce the set-up of mass transported

rIc wailer ;aloIg tliu southwest shore. Wind drift locally mn:sks the easterly

harbor flow at station 4, with speeds up to 0. 15 m/sec. And when the wind

gains strength during the day, it temporarily reversed the predominate flow

4-9

L

at Station II between 0900 and 1300. In exposed waters of Scotch Bank Channel,

wind drift is the chief current. Farther seaward in the outer entrance, this

wind drift merges with outflowing harbor water and the two currents flow seaward

with a mean velocity of 0.16 m/sec.

A westerly flowing oceanic current, part of the prevailing North Equatorial

Current, reportedly sweeps offshore areas. Established in the region by the U. S.

Navy Oceanography Office, and summarized in vanEepoel, et al. (1971), this current

has a mean speed of about 0.35 m/sec. It is generally assumed (Dammann, 1970)

this current flows shoreward and eastward as a large counterclockwise loop between

White Horse Shoal and the Scotch Bank Buck Island area. But the extent to which

this flow impinges on coastal water or influences its movement is unknown. The

easterly flow detected off Long Reef, Station 9, has a reciprocating and rotary tidal

character rather than a component of permanent flow. Moreover, measurements

at Station 8, Pelican Cove, offshore, indicate a westerly flow in both surface

and bottom waters, a direction opposite to the supposed easterly flowing loop.

Dye Dispersal and Photography

On three occasions, August 3, 5 and September 9, a series of dye releases

were made simultaneously with aerial photo coverage. The dye consisted of 1 to 2

pounds of fluorescein and it was released as a slug at mid-depth. The photographs

were taken single-handed by Jean Larsen flying at about 300 m altitude in a Cessna

150 equipped with a Hasselblad 500 EL camera having a 50 mm lens, in addition to,

35 mm Nikon and Contarex Super cameras. Different types of film were used: Ektacolor,

4-10

Kodacolor and Plus-X. Winds blew east to northeast on August 3-5th,

and east to southeast September 9th. The photographs show the path

and dispersal of dye under the combined action of current, wind stress

and wave action. Additionally, some of the photographs reveal gross di-

rectional trends of sewerage effluents and turbid plumes as well as a

number of short-term irregularities and variations in the local circulation.

Release points, and tracks of the dye which were determined from a

sequence of photographs at approximately 15-20 minute intervals, are plotted

in Figure II. Dye released off the Turquoise Beach on August 3rd drifted

northwestward, whereas on August 5th, dye released from the same point

drifted southeastward. Elongation of these patches, like others, is presumably

due to current-shear, being more or less along the wind. Northwesterly drift

from the Long Reef and Pelican Cove outfalls is consistent with offshore current

measurements. But, at station 5 near the site of dredging, the dye drifted slowly

west to southwest, a direction quite different from the northerly flow measured at

this site. Dispersal trends of dye, as well as of turbid plumes for August 3-5th

in the eastern harbor indicate a convergence of ocean water, driven harborward

through Sloop Channel,with harbor water flowing seaward east of Protestant Cay.

From the point where the flows meet in the vicinity of Station 5, the current passes

westward and thence seaward through the main channel. It cannot be presumed,

however, that these dye paths and turbid patterns represent the mean circulation.

Instead they show the variations that may be expected from time to time as a result

of changes in winds, waves and mass transport.

4-11

Figure 11. Circulation from dye patch dispersal at different release points and various dates.
+ values indicate time after release. Current direction derived from analysis of
turbid plumes shown in aerial photographs taken at the same time as dye studies
is also indicated by arrows.

0

Longshore currents and littoral drift

In a narrow zone dominated by swash and backwash of waves,

there is a local current that carries sand alongshore. Since waves

approach the harbor and its inner shores from an easterly direction,

they break on the shore at a slight angle as shown for the eastern harbor

in Figure 5, and at Little Princess, Figure 6 A. The forward motion

of the water keeps moving in the direction of wave approach with a com-

ponent parallel to shore. Sand trapped around beach structures and minor

irregularities in the shoreline give evidence that longshore currents are

active, but direct measurements are often difficult.

A series of dye experiments were conducted daily between August

31 September 3 to estimate the direction and rate of sand transport at

selected sites (Fig. 1). The significant wave height was measured from

trough to crest at the breaker line; the wave angle between approaching

wave crests and the shore (or reef) was measured by pelorus; the wave

period was determined by counting the number of waves arriving in one

minute; the beach slope was measured by clinometer; and water depth

at the breaker line was measured with a meter stick. Longshore current

velocity was determined from the travel of dye introduced at the breaker

line. Northeasterly winds blew 6-9 m/sec during the period. Appropriate

data are summarized in Table 6.

4-13

Longshore transport data for selected sites, August 31 September 3, 1971.

Date

Experiment
Number

I
II

IV

V

VII

VIII

IX

Wave
Angle
(o)

20

12

19

Wave
Height
(m)

.20

.20

i. 05

.93

.08

.08

.08

Longshore
Velocity
(m/sec)

.08

.08

.12

.09

.09

.05

* Q/F (A) is the relative littoral transport.function
along ocean shores, assuming Ho/ Lo is constant.

N. B. Winds were 7-10 m/sec from 450 550 T during
experiments.

Wave
Period
(sec)

2.9

6.0

Beach
Slope
(m)

5

10

6.0

1.5

1.8

1.5

Stillwater
Depth
(m)

.35

.30

.60

.60

Sand
Transport
Q/f(A) *

Sand
Transport
Q/f(B) **

.07

.-08

3.56

3.58

** Q/F (B) is the relative littoral,X tRapoport
,function along harbor shores, assuming
Ho/ Lo is constant.

0

560

0

TABLE 6.

The littoral drift of sand was estimated according to a relation of

LeMehaute and Brebner (1967):

Q 112I f(s,aL m, Ho / Lo)

wherr s is the beach slope, oi is the angle of wave approach, m is the material

characteristics, Ho and Lo are the deep water wave height and length, and Q is

the rate of littoral sand transport. Because Ho / Lo and m were not measured,

they are assumed constant, and for comparative purposes, the functions f(A) and

f(B) are substituted; F(A) is designated ocean shores and f(B) is designated for

inner harbor shores.

The measured velocities and inferred directions illustrated in

Figure 10 indicate relatively strong westerly currents, greater than 08 m/sec,

along the outer reef except near Fort Louise Augusta where a local easterly

flow was detected. Interestingly, at three sites on Long Reef the flow was

directed harborward across the reef. Currents along the inner harbor shores

are weak and variable. On the northwest side of Protestant Cay sand is partly

transported westward whereas eroding landfill just east of the Cement Plant

(site VIII) is carried eastward. At Mill Harbor, near Turquoise Beach

large quantities of beach fill are carried westward and trapped on the east

side of a groin-like structure. Farther to the west near Little Princess,

a westward current appears to converge with a slight east flow resulting in

a stable beach .

4-15

Discussion

There are many ways in which the current data of this study are

of practical use. Inasmuch as water is introduced into the harbor mainly

by mass transport over Long Reef, and flows easterly through the harbor

and out the main entrance, areas of the eastern harbor that lie "downstream"

are vulnerable to disturbance or loading from the west. For example, if

material were released by dredging off the Cement Plant, it would spread

eastward toward downtown Christiansted and Protestant Cay. By contrast,

if surface-borne wastes were discharged seaward off Fort Louise Augusta,

they would disperse away from shore in the northwesterly flow. In this

way, the basic pattern of circulation can serve to delineate areas vulnerable

to disturbance and to determine the effectiveness of waste dispersal.

The pattern of near-surface circulation predicts where sites of local

convergence or divergence may occur; such a feature may concentrate flota-

bles in surface water. Similarly, opposing flows that meet near station 5,

as indicated by dye dispersal produce a high horizontal gradient of turbidity

that should lead to an accumulation of suspended materials. Refraction of

waves on Barracuda Ground may result in building up a local head,of water

resulting in a diverging flow away from the Ground, partly channelward.

A predominate westerly current offshore off Pelican Cove, and at times, off

Long Reef predicts a weak upwelling. And local convergence of longshore

currents near Little Princess, favors accumulation of beach sand, whereas

4-16

farther east at Turquoise Beach erosion predominates.

The distribution of current speeds indicates water movement is

faster in entrance reaches and offshore than in inner reaches like Gallows

Bay. Additionally, near-surface water of the channel moves faster than

near-bottom water. Thus, mixing and diffusion which are active in seaward

areas and over shoals promote rapid dispersal of wastes and transport of

sediment. Whereas in inner reaches and deeper parts of channels, these

processes are so slow that waste is retained and sediment is trapped. Current

velocities also indicate that flushing of the harbor is relatively good. For

example, a waste introduced in surface water at the Cement plant would be

expected to pass out the entrance via the Protestant Cay-Christiansted passage

in less than 24 hours. Flow measurements of this study, indicate 8 percent

of the water in the harbor passes out the entrance every hour. But with long-

term enlargement of the harbor floor and deepening of the main channel, the

proportion of bottom water (by volume) actively mixed and exchanged becomes

less.

Inflow from Land

Direct measurements of stream inflow and surface runoff are not avail-

able. However, occasional flooding is observed following rain squalls and

showers especially during the months of August through November. Although

the mean annual rainfall is 104 cm, mean annual potential evapotranspiration is

149 cm and the loss consistently exceeds the monthly rainfall throughout the year,

except for perhaps one or two months. Inasmuch as the harbor lies outside the

main paths of most tropical storms and hurricanes, major storm runoff and

4-17

tidal flooding are infrequent. There are less than 3 hurricanes per 100 years

(Mills et al. 1970).

4-18

5. WATER QUALITY DATA

Temperature

Water temperature throughout the harbor on a given day reveals that

the surface waters are well mixed. Spatial variation in water temperature on

individual days was 1.0 to 1.30 C. Generally, the inner reaches of the harbor,

particularly, Gallows Bay, tend to be warmer than ocean water. Water tempera-

ture at individual stations varied 2.2 3.50 C during the study period and were

higher in August than in June or September.

Salinity

From May to September salinities ranged from 34.7 ppt. to 38.3 ppt.

throughout the harbor and from 2.4 to 3.4 ppt. at individual stations between

June and September. There was no significant gradient of salinity within

the harbor; the range of values among 15 stations on any given day was 0.4 to

2.3 ppt., most of which is likely due to local freshwater discharge.

Suspended Solids

The concentration of suspended matter in surface waters was higher in

the nearshore waters of the southern harbor (Figure 12). Here the concentrations

were 5.2 to 12.9 mg/L. Seaward to the northwest and northeast, suspended solids

decrease to intermediate levels (3.6 4.8 mg/L), and in the clear water just

behind and outside of the reef, mean concentration were 1.3 3.2 mg/L. This

distribution parallels the distribution of Secchi Disk depth (Figure 13).

L.D *5. .

.. . .. :.... :.

Figure 12. Suspended solids, mean concentrations in surface water,

May through August, 1971.
........
......... ...
.. ...
Att
...........
USPENDEV*
SOLIDS
. ..........

Fig re 2. Sus end d oli s, ea co cen raion in sufac wa er

May through August, 1971.:~:I:

Secchi Disk Depth

The water in Gallows Bay and the southeast area of the harbor are

always very turbid. Visibility is lowest in the south central section of the

harbor, especially east of the Cement Plant. Measurements at station numbers

12 and 16 were 1.5 to 2.5 meters. Water depth at these points is 2 to 6 meters.

North of Protestant Cay most of the bottom can be seen from a boat,

except over the deeper dredged channel. In the western half of the harbor, and

over the fore and back reef water is clear enough to allow visibility to the bottom

at depths up to 16 meters (Figure 13).

Bacteriology

Water from each of the fifteen stations was analyzed six times between

June and August for the presence of fecal coliform organisms. Most stations were

negative or had only very low counts. No fecal coliform were isolated from

Stations 4,5, and 9. Station 2, near the sewage outfall had the most consistently

high densities. There was only one positive test at the two stations inside the reef

closest to the outfall (5 and 6). High densities were encountered, once each, at

Stations 8 and 13. Relatively low fecal coliform densities (1-64 cells/100ml)

were regularly found at Stations 15 and 16 in Gallows Bay.

Dissolved Oxygen

The surface waters are adequately oxygenated throughout most of the harbor

during mid-day hours of measurement. Average concentrations less than 6. 0 mg/L

were found only at Stations 2, 13, and 15. The highest levels of dissolved oxygen,

6.0 8.0 mg/Ls, were measured at Station 5, an area of shallow, clear water

5-3

Figure 13.

Secchi Disk Depth in meters.
Mean values, May through August, 1971

overlying a lush Thalassia bed which must produce high oxygen. Generally,

distribution of oxygen varies within narrow limits throughout the harbor.

Summary of Water Quality

Turbidity increases more than 5 times with distance landward from the

ocean and barrier reef to the inner harbor. With this broad trend of turbidity

there is a corresponding inward decrease of disk depth or transparency. The

most striking gradient in water clarity was found in a band running from the

cement plant to the north end of Protestant Cay, and to Fort Louise Augusta.

Locally high turbidity east of the cement plant is mainly produced by carbonate

fines released by wave action from dredge spoil of the landfill, area. Added to

this, terrigenous fines are intermittently discharged from guts by land runoff

during times of storm. And growth of phytoplankton promoted by nutrients of

intermittent sewage discharge also contributes to the high turbidity level of inner

reaches.

During the course of this work it was noted that the color of the water

south of Protestant Cay often suggested large numbers of planktonic algae. The

lush growths of filamentous green algae along the bulkheads and piers in this

area support the inference that the waters are highly enriched. The occurrence

of fecal bacteria in these waters indicates the source of this enrichment, but

because of the transient nature of these organisms the present data probably

underestimate the degree of sewage contamination to which the area is subjected.

According to present Government designation, stated in Title 12 of

V. I. C., Subchapter 186, all of Christiansted Harbor from Fort Louise Augusta

to Golden Rock (Cement Plant) is Class C water "for harbor and docking faci-

lities". By exclusion, that part of the bay west of Golden Rock is Class B "for

propagation of marine life and for water contact recreation". Pertinent quality

criteria for these classes are:

Class B Class C

Dissolved Oxygen not less than not less than
5.5 mg/L 5. 0 mg/L

Fecal Coliform monthly mean not monthly mean not
to exceed 70/100 ml to exceed 1000/100 ml

For harbors criteria are relaxed "for areas immediately adjacent to outfalls

or drainage ditches" to allow for "admixture of waste effluent with harbor

waters". In this context, all of the waters of Christiansted Harbor meet the

local quality criteria for both classes. However, current trends in development

and use of the harbor will certainly lead to further degradation of water quality.

The territorial water quality standards include a non-degradation clause designed

to protect water quality existing at the time the standards were adopted (1969).

This report establishes several baseline descriptions which can be used in

assessing the quality of the harbor water in the future. To minimize further

destruction of water quality, different areas of the harbor should be designated

for particular uses and the uses should have priorities. Along with such a plitn,

strict enforcement of pollution practices is required. Christiansted Harbor

currently serves two distinctly different uses: commercial traffic in the eastern

two-thirds, and tourist oriented water contact recreation in the west. This

dichotomy of uses is recognized by explicit classification of the harbor for

these two uses in the Water Quality Standards, but planning is needed now to

ensure this separation in the future.

(6. ECOLOGY OF REEF COMMUNITIES

Introduction

A short survey of the reef communities of Christiansted, St. Croix w;is

made to determine the "state of health" of the reef populations, and to assess

damage which the reef reportedly sustained as a result of development-asso-

ciated projects in the Christiansted area. It must be understood that there are

no previous data as to the "healthiness" of reef communities in this area, and

that all judgements made about the Christiansted reefs stem from comparisons

with reef communities elsewhere in the Virgin Islands (e.g. Brody et al, 1969,

1970). This in itself is a somewhat specious line of reasoning because no two

biotic communities are precisely the same and the physical, chemical, and bio-

logical interactions of any one community are probably never equivalent to those

of any other community. In addition, there is a great paucity of experimental data

from which correct extrapolations can be made about either acute or chronic ill-

effects which reef organisms may suffer as a result of input of sewage, suspended

particulate matter, and marine traffic with their corollary changes in light pene-

tration, oxygen and nutrient concentrations, BOD, COD, pH, etc. Thus, this

section does not describe a biological study of the area which pin-points the

problems facing the reef communities, but rather presents an educated "impression"

of the most general types of problems easily noticed by the trained observer.

It was undertaken with several preconceptions as to the effects of human

development on coral reef communities. In Christiansted Harbor there are two

major types of environmental modifiers (indeed pollutants) which give cause for

concern.

Prospective Stresses

The area inside the reef has been the site of several dredging projects

for improving or maintaining navigable channels, for stockpiling of calcium

carbonate sediments for concrete production, and for development of re-

creational areas as beaches. Dredging produces a variety of pollution pro-

blems, some of which are obvious and others more subtle. The distinct,

short-term effects are the obvious ones: some benthic organisms are re-

moved outright, others are damaged and die as a result of abrasion or la-

ceration, still others are smothered by the fraction of sediments moved but

not retained within the dredge pipe. In addition, some of the organisms in

the immediate vicinity of the dredging work may be exposed to a radically

different chemical regime when newly exposed anaerobic sediments are

uncovered, perhaps causing their death or severely impaired metabolism.

There are several probable effects of large-scale dredging which are

more subtle and thus more likely to be overlooked. A portion of the sediments

disturbed in any dredged area will be too small in size (or too far away from

the suction of the dredge) to be effectively pumped up and will become suspended

in the water column. These small size particles can produce either or both of

two negative effects. Where wave energies or current velocities are sufficiently

high these particles will be carried out of the dredging area and into lower energy

areas where they may fall out of suspension and abrade the surface tissues,

olog Ith poues (or mouths, or gut cavities) or even smother the sessile organisms.

And while these particles are in suspension they are responsible for a very signi-

6-2

ficant increase in turbidity. This turbidity increase effects a decrease in

radiant energy which reaches the sessile primary producers, and may cause

a serious reduction in the carbon fixation and oxygen production associated

with the photosynthetic activity of the plant cells. This is particularly true

in a typical coral reef community where photosynthetic productivity is

the result of the combined activity of marine grasses and algae at the margins

of the reef and in the back-reef areas, calcareous algae on the reef and the

algal symbionts of the coral animals. The ultimate health of the coral colonies

and the calcareous algae is an especially important consideration near dredging

areas because these are often the very organisms which produce the sediments

being dredged. The observed consequences of dredging to the Christiansted reef

and calcareous alga communities are discussed later.

The population of Christiansted has grown rapidly in the past decades and

of course, so has the sewage output. The effects of the various chemical and bio-

logical qualities of human sewage on coral reef organisms are poorly known, but there

are at least a few statements which can be made. Excessive BOD and COD are dele-

terious to most natural'communities and it can probably be assumed that the reef

complex is no exception. If these oxygen demand levels are coupled with low oxygen

production as a result of turbidity, it is quite possible that community health may

suffer. The physical agitation of the water column as it crosses the reef with breaking

surf may not be sufficient to deter a serious problem with the reef community's oxygen

balance. It is important to note that it is the extremes (eg. low tide, low circulation,

high BOD) which cause the mortalities, not the average of daily variations.

I

We have very little data on the nutrient requirements of reef systems,

but there is certainly abundant evidence that the reef does not have an infinite

capacity for nutrient enrichment. The reef system can (and has) undergone

drastic changes in some areas where eutrophication occurs. In addition,

changes in the composition of the reef community's species structure are a

probable step in nutrient enrichment and these changes may have severe

long-range consequences.

The biological changes caused by dredging and sewage outfalls cannot

easily be separated from the consequences of several other forms of pollution.

Thus, turbidity produced by erosional runoff, storm drainage, and boat traffic,

the hydrocarbons from engine exhausts, and myriad lesser forms of pollution

are not considered separable from the highly visible forms within the context

of a brief ecological survey such as this one. Such work is important and should

be pursued as separate research projects in the future. Until the interactions

of specific levels of specific kinds of pollution has been quantified, we are forced

to speak only in generalizations.

Procedures

A series of observational dives were made with snorkel and SCUBA tech-

niques over the entire length of Long Reef and Round Reef, Christiansted, St.

Croix. The fore-reef and back-reef environments were studied with an eye

to distinct changes from the normal patterns of faunal association and organism

healthiness. Normal is defined in terms of characteristics of other similar

reef systems which have been observed rather than as a comparison to an ear-

lier, "pre-pollution" state of the ecosystem; healthiness is primarily based upon

variations in color pattern, polyp expansion, colony shape, and obvious new

growth in the scleractinian corals; the same characteristics apply in the octo-

coral groups with the added one of colonial mesoglial condition. The echinoderm,

crustacean, poriferan, and other macro-invertebrate groups were casually

examined when encountered. The fish populations were likewise noted, but

their mobility and desirability as food make fish a poor pollution indicator

without careful study. In the base-reef and back-reef environments, the abun-

dance, color, growth, and depth-light level patterns notable in the marine algae

(particularly the Siphonalean genera Caulerpa, Halimeda, Penecillus, and Udotea)

and the abundant marine spermatophytes (Thalassia and Syringodium) were used

as indicators of the normalcy of the benthic community.

The bulk of the area was observed during late October, 1971, by divers

towed slowly behind a small boat; where warranted, a more detailed reconnaissance

was made. Figure 14 shows the areas observed; place-names and compass bearings

were taken from USC & GS chart #935 and from local knowledge.

0

6-5

64 43' 64042'

1-7 e__

I u n L o n g R e e f
t- \t ; ----- -

Sorensen
S-s- -x-_--- Ground
\ ''' < ''~.-~--';''- TBT----

CORAL REEF

OBSERVATIO NS

,- C
--- TRANSECT SCALE 0.8K
Ci AREA 0,

lHRST/A NSTED
M.

_ _ _ --I

Figure 14. Index to coral reef observations. For details see text.

. U.V l l.

Observations

Area I is a front reef area composed almost exclusively of Acropora

palmata which forms substantial colonies (height up to three meters) in close

proximity to one another. Other prominent corals comprise only about 5% of

the population. This community extends seaward from the breaking reef off

Pelican Cove Beach to depths of seven-fifteen meters. Acropora in this area

were seemingly undisturbed with new growth evident in most colonies. The

octocoral population was minimal; presumably, high wave energy and the dense

areal coverage of Acropora limit colonization. The fish population seemed typi-

cal of many similar Virgin Islands reefs; the obvious piscivores were few and

coral feeders predominated. This population structure is perhaps encouraged

by high fishing pressure.

Area II is an adjacent front reef environment. Acropora palmata pre-

dominated with Diploria and Montastrea as genera of secondary prominence. As

one proceeded from west to east along the reef the variety of scleractinian corals

increased with Acropora accounting for approximately 70% of the sessile growth,

Montastrea and Diploria (in that order) about 15%, and other scleractinians and some

species of gorgonaceans (notably Plexauriids of the genera Eunicea, Pseudoplexaura

and scattered Gorgoniids, eg: Gorgonia, Pseudopterogorgia). The remaining bottom

cover, about 10%, was made up of Poriferans, colonial anemones, etc. There were

scattered clumps of coralline algae. The area tended to grade away from the closely

packed stands of Acropora to a more broken-up, cosmopolitan community with sandy

patches and "surge channels". There was no noticeable die-back or particularly un-

usual pattern of growth, but it was estimated that the sessile biomass decreased along

6-7

I

a west-east gradient.

The vicinity of the sewer outfall itself is an exception to the generalities

presented above. The area about 20 meters east and west of the pipe and about

100 meters north of the pipe's end was a distinctly barren one. The area is

generally uniform in depth with the open end of the pipe at a depth of about six meters.

The density of sessile organisms was markedly decreased although there was no

radical change in species diversity. There was a 200 to 300% increase in the

fish population (much greater in the case of the black durgon, Melichthys niger,

and surgeonfishes, Acanthurus coeruleus. These fishes had modified their

normal diet to include pieces of toilet paper and feces. Although one may decry

the sight of a gorgoniid axis festooned with pieces of all sorts of sewage waste

materials, it was not observed that a very large area had been severely affected by

discharge. On the day of the observational dive, the wind was blowing from the ESE

at a speed of 4-6 knots, and the sea was calm at State 1-2 on the Beaufort scale.

There was rapid dispersal of the effluent to the West outside of the reef, but the

observed dispersal pattern cannot be presumed to be a fixed one. Several residents

of the Christiansted area have reported distinctly seeing "slicks" emanating from

the outfall and spreading south across the reef into the harbor.

Area III includes a transitional zone from the eastern section of Area II,

and an obviously disturbed zone eastward. Visibility decreased markedly from west

to east from 15+ meters at Area II to less than five meters at the east end of Barracuda

Ground. Acropora palmata was noted to be far less dominant in this area, representing

less than 20% of the bottom cover off eastern Barracuda Ground; total coral growth

covered less than 50% of the bottom with uncolonized coarse sand over reef rubble

6-8

i

comprising the rest. There was a noticeable reduction in the active growth of

new polyps in Acropora when comparison is made to Area I. This reduction in

growth-rate was not detectable in the gorgonaceans in depths of five to ten meters

to the north of the reef. With increasing depth, Acropora disappeared at about

five meters and was replaced by scattered gorgonaceans (Pterogorgia in sand, then

Pseudopterogorgia and Eunicea). Also, the community increasingly was comprised

of mixed gorgonaceans (about 75%) and small scleractinians (Diploria, Montastrea)

with scattered small Acropora cervicornis visible; scleractinians represented about

5% of the sessile macro-invertebrate growth at ten meters.

Area IV, including Round Reef was investigated to complete the survey of

the fore-reef environment off Christiansted. The area between Barracuda Ground and

Round Reef (Great Middle Ground) was virtually devoid of coral growth to depths of about

six meters, the limit of visibility. The ship channel cut into the natural western slope

of Round Reef had not yet been re-colonized. The coral kill on Round Reef is about 90%;

the dead colonies of Acropora, Montastrea, Diploria, and Porites could still be

recognized. Visibility was reduced to about two meters with scattered colonies

of Porites porites, P. asteroides, and an occasional fragment of Acropora palmata

noticeable. These live corals were not laying down new skeletons at as rapid a

rate as elsewhere off Christiansted; several colonies were obviously being rapidly

buried by shifting sediment.

Area V is the most active area of the back-reef due to its proximity to the

channel and to current flow. A series of observations were made on tracks across

Sorensen Ground, Figure 15, south and west of Barracuda Ground and across the

back-reef of Long Reef as far west as the western boundary of Area III; The zone

6-9

immediately south of Barracuda Ground and adjacent to the ship channel was

obviously undergoing rapid change and had a very low sessile biomass. West of

this there were bands or patches of Porites porites (with occasional P. asteroids and

small Acropora palmata colonies) alternating with Thalassia or Syringodium mixed

with calcareous algae. Several patches of Sargassum ( as a sessile plant) were

also noted. This back-reef seems typical of similar reef areas throughout the

Virgin Islands; these organisms are among the hardiest and are adapted to occasional

high wave energy, high turbidity, and rapid sedimentary variations. Syringodium

was noted in water somewhat shallower than is perhaps typical; it was an unusually

long and luxuriant growth. This depth-distribution may be correlable with the higher

turbidity at the western margins of the recently dredged channel to the west of Protestant

Cay.

Area VI is a small area along the north shore of Protestant Cay. A short

track was run to assess possible damage to the patch reefs. The turbidity was

quite high throughout the area; visibility was less than water depth except shallower

than 1 meter. The Thalassia-algal assemblage at the edge of the dredge-cut was

obviously a new community but shows a typical speciation pattern. The coral

at the edge of the old reef was virtually all dead; there were scattered live Porites

colonies amongst dead ones. The dead reef was populated by scattered colonies

of brown algae (Dictyota, Ectocarpus). The sessile community changed abruptly

with the change in depth at the easternmost point of Protestant Cay; at two meters

there was a dead reef with patchy algae; at 20 meters depth ( only

6-10

i

a few meters away) the Thalassia-algae community was established. A

distinct increase in water clarity could also be noted.

Status of the Reefs

The front-reef areas of Long Reef, Christiansted, were in good con-

dition except (1) Barracuda Ground, Area III at the eastern end, and (2) the

section of Area II about the sewer outfall. The community is composed

primarily of Acropora palmata in the zone from ten meters to the surf, with

Montastrea annularis, Diplora, and Porites as other important scleractinians.

The octocoral population is somewhat reduced from the numbers of species and

densities normally found on similar Virgin Islands' reefs. The back-reef areas

of Long Reef with the exception of eastern segments of Sorensen Ground are

typical of most back-reef communities with Porites, Acropora, and Thalassia-

Syringodium algae assemblages present. This area is populated by organisms

best adapted to higher stress resulting from sedimentary changes.

Barracuda Ground is under stress from a combination of several factors

and it is difficult to assess the differences observed between the western and

eastern sections of Area III. Density of bottom cover was less than 50 percent

in the eastern section with large, open, coarse sand patches uncolonized by the

usual benthic biota; the scleractinian coral cover was less than 10 percent in

parts of the section. There were very few large dead coral colonies. The pattern

of growth and the absence of large dead coral colonies suggest that the eastern

end of Long Reef has historically been an area of relatively rapid sedimentary

6-11

change because of high incident wave energy, and the bottom environment

is somewhat hostile to potential colonization. If there had been large numbers

of dead colonies, a recent radical change resulting in extirpation of the com-

munities would have been suggested. -Other stress factors are (1) lowered

light penetration because of increased suspended particulate matter (turbidity).

One result of the higher turbidity nearshore is a turbidity increase above that

which formerly obtained in the waters over Barracuda Ground in the new gradient

now established to the still clear waters in the western section of Area III.

(2) Polluting substances, including those from the bypass sewage discharges

and hydrocarbon leaches and spills, etc., carried seaward in the prevailing

harbor current. Without baseline data, or long time series observations it

is not possible to establish if there had been in the recent past more abundant

growth.

The section of Area II around the sewage outfall is obviously under

severe stress. Numerous dead corals, reduced species diversity and concen-

trations of fecal matter, paper and other suspended wastes were observed. The

status suggests to the reef ecologist that increasing the volume of sewage dis-

charged much above the present level could oveistep a limit beyond which much

more widespread destruction would be effected;

Round Reef has been almost completely extirpated as a result of develop-

ment and use of the harbor. Only scattered colonies of Porites and occasional

Acropora were noted alive. Turbidity was high, and visibility was less than

6-12

two meters. It is impossible to assign a single cause for this particular reef kill.

All of the stress factors discussed above for Barracuda Ground are to be found here

and at much higher levels, except that the level of wave energy and the resultant

coarse sand transport rate are lower. It is probable that the most severe of recent

stresses was dredging alongside the reef with the resultant sediment fall out onto

the reef. It is unlikely that the area will repopulate unless there is drastic change

in the harbor use pattern. Uses now promote high turbidity, fine sediment erosion

into the waters and low light levels, all of which make the Barracuda Ground hostile

to re-colonization by corals and coraline algae.

6-13

7. NOTES ON FISHERIES

Inasmuch as lagoons, bays and shallow harbors support fisheries

and shell fisheries of major economic value and are among the most productive

environments in the world (Odum, 1971), a cursory inquiry was made into the

status of fisheries of Christiansted. A comprehensive study of fisheries

potential throughout the Virgin Islands is given by Dammann (1969).

Fishes dependent on the reefs and banks include parrot fishes, grunts,

groupers, butterfly fishes, sharpnose puffers, and moray eels. In areas of

grassy bottom there are halfbeak, porgies, rays, and probably small tarpon.

Lagoon areas of mud or grass have black and white mullet. Among the fishes

that inhabit offshore waters, and occasionally are found in the harbor either in

search of food or to spawn, are mackerel, barracuda, snappers and kingfish.

Besides fishes, certain shellfish like conchs are reported, as also shrimp,

lobsters and green turtles.

As a result of blasting rock in the cement plant channel near bouy 4

on Sept. 18, 1971, John Yntema of the Virgin Islands Department of Conservation

reports: "I was surprised there were so many fish in so barren a spot. There

was one mutton snapper (Lutjanus analis) one immature french angelfish

(Pomocanthus paru), 20 to 30 french grunts (Haemulon flavolineatum), 15 to 20

mojarras (probably Gerres cinereus) and 6 to 8 squirrel fish (Holocentridae).

..... we also spotted a green turtle of about 30 to 50 lbs."

Reports of local fishermen indicate a sport and commercial fishery

thrived in the harbor more than ten years ago. Degradation of the industry

was blamed on a distillery in the southwest corner of the harbor which

occasionally discharged effluents, causing massive fish kills. Although the

distillery was closed about 1965 the number of fish have not returned.

Similarily, Altona Lagoon, which formerly was very productive, has been

restricted at its entrance from a natural width of 15 m, to a 1. 9 m diameter

culvert, causing a near-stagnant environment unsuited to many fish. In a

report by F. J. Mvather (1957) it was noted:

"Some inshore fishing was done in Christiansted Harbor. In early

April, a 23 1/2 lb. tarpon was caught from the Comanche dock, and a 31 lb.

barracuda was taken by trolling in the harbor. A short casting trip was made

in Altona Lagoon. Although no fish were caught, many were seen jumping or

swimming close to the surface. It is reported that there are some large jacks

and many bonefish in this lagoon. It is recommended that the entrance to this

lagoon be kept open to provide a good fishing ground for inshore fishermen..."

These notes suggest the harbor had a fisheries potential but what remains

needs to be fully evaluated and compared to that of other coastal fisheries about

St. Croix. before its importance, future trends, and the impact of environmental

status can be assessed.

8. BOTTOM GRASS AND ALGAE

More than 60 percent of the harbor floor and contiguous reef is

covered with marine grass and algae. The chief rooted plants are broad-

bladed turtle grass, Thalassia testidinum and round bladed grass Syringodium

filiforme. Species of Chaetomorpha and Diplanthera and occasionally Sargassum

are often interdispersed in minor amounts. Blades of turtle grass reach heights

of 30-40 cm above the bottom and act as a "baffle" in trapping current-borne

suspended material (Multer, 1969). Near the bottom matted stems and roots

form a firm carpet with the sediments and stabilize the bottom. Animals of

great diversity and beauty live in the "meadows" including sea cucumbers, tube

worms, molluscs, fishes, urchins, and welks plus polychaete worms and the

burrowing shrimp that churn up the bottom into depressions and conical mounds

such as shown in Figure 15. In addition to these grass-consumers, filter feeders

keep the water clear by processing decomposed grass. As a result, organic

material buried beneath the meadows is scarce and plant detritus throughout

the harbor is remarkably low (Figure 22C) less than 2 percent except for one

station, despite the potentially high gross production of Thalassia beds (Odum

and Wilson, 1962).

The filamentous algae Enteromorpha sp, mixed occasionally with

Cladophora sp., forms a thin bright pistachio green carpet over turbid reaches

of the inner and eastern harbor. Additionally, it covers the floor of less turbid

Mounds built up 20-30 cm high by burrowing shrimp or polychaete
worms such as common to turtle grass beds of Christiansted Harbor.
Photo reproduced from Multer (1969).

0

Figure 15.