Title: Life history patterns of three estuarine brittlestars (ophiuroidea) at Cedar Key, Florida
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Permanent Link: http://ufdc.ufl.edu/UF00097558/00001
 Material Information
Title: Life history patterns of three estuarine brittlestars (ophiuroidea) at Cedar Key, Florida
Physical Description: vi, 78 leaves. : illus. ; 28 cm.
Language: English
Creator: Stancyk, Stephen E., 1946-
Publication Date: 1974
Copyright Date: 1974
Subject: Ophiuroidea   ( lcsh )
Echinodermata -- Florida -- Cedar Key   ( lcsh )
Zoology thesis Ph. D
Dissertations, Academic -- Zoology -- UF
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
Thesis: Thesis -- University of FLorida.
Bibliography: Vita.
Bibliography: Bibliography: leaves 73-77.
Additional Physical Form: Also available on World Wide Web
General Note: Typescript.
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Bibliographic ID: UF00097558
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: alephbibnum - 000580862
oclc - 14092471
notis - ADA8967


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I owe-a great deal to all the people who made the completion of

this dissertation possible. The members of my committee deserve special

tanks, particularly Drs. Frank Maturo and Thomas Emmel, who were always

ready with encouragement and advice. I thank Drs. John Brookbank and

Ariel Lugo for their careful reading of the manuscript, and

Dr. John Ewel for his timely services. Dr. John Anderson was generous

with both equipment and time.

Of the many fellow students and friends who assisted me,

William Ingram deserves special thanks for his indispensable aid in

fostering an agreeable relationship between myself and the computer.

Jbho Caldwell, John Paige, Christine Simon and Michael 0esterling were

of particular help in- the field, and I would like to thank Dave David,

Renee Lir:dsiy,.Kent-M'urphey, Dave Godman and Steve Salzman for their

assistance in thelaboratory.

Marine biologists are often in need of a safe haven in a storm,

and- L am therefore very grateful to Lee and Esta Belcher and their

wonderfu"F family for-their hospitality, and for making my work at

Ced6;rKey such a:pleasurable experience.

Ms.Libby. Cier tfcJd the final manuscript, and Mr. Paul Laessle

pmgvided.-materials and advice for completion of the figures. The

fadci'ities. of'the University of Florida Marine Laboratory at Seahorse

Key were :.,:1j -re,7:ively during this study. Part of this research was

supfported b Unlri.vEr it, of Florila Division of Spa3n.:,nr-e Pseircn Gr..r.

rNo. 2;71 :., .hrrough the Dii isiorj Si iolo ical Scien:es ::

. J. l.1.it ur'o. Computer fjnd ere ol itan. ed ir-,m trlt Nor thea'.t

Fqgional Dat. Cenrier at the Universict :o Floriida

ACKNOWLEDGMENTS ..................... .. .............. ........ ii

ABSTRACT .................................................... v

INTRODUCTION ................................................ 1

DESCRIPTION OF SPECIES ...................................... 3

DESCRIPTION OF AREA AND STATIONS ............................ 13

rATERIALS AND METHODS ...................... ................ 23

RESULTS .............................................. ...... 31

DISCUSSION AND CONCLUSIONS .................................. 58

SUMMARY .................................................... 70

LITERAI URE CITED ............................................ 73

BIOGRAPHICAL SKETCH ......................................... 78

Abstract of Dissertation Presented to the Graduate Council of the
University of Florida in Partial Fulfillment of the Requirements
for the Degree of Doctor of Philosophy



Stephen Edward Stancyk

August, 1974

Chairman: Frank J. S. Maturo, Jr.
Major Department: Zoology

The polyhaline estuary at Cedar Key, Florida, has a high diversity of

echinoderms, most of which possess reproductive modifications that appear

to adapt them to unpredictable environmental variability. To gain

clearer insight into this problem, populations of three opniuroids with

different modes of development were studied. Collection of monthly

population samples and analysis of growth, mortality, reproduction and

respiration showed that the three populations exhibit different life

history patterns, each providing them with high fitness in an

unpredictably variable environment. The disappearance of the

Ophiothrix angulata population at the end of the first year of study

(July, 1973) was correlated with a poor spring recruitment due to low

salinities and with high summer mortality of adults during periods of

warm water temperatures. 0. angulata has a short life and low

tolerance of environmental fluctuations. It has a short-lived

planktotrophic larva and spawns year-around. Individuals have only one

spawning season. It is a fugitive species selected for high dispersal

and the ability to colonize and recolonize disturbed habitats after

local extinction. Ophiophragmus filograneus is a short-lived species,

probably has direct development, and breeds year-round. Individuals

have but one spawning season. Its tolerance of environmental variability

is broad and it appears to be selected for low disperal and high

survival of both adults and young through most environmental fluctuations.

Ophioderna brevispinum is long-lived, has a short-lived vitellaria larva

and broad environmental tolerance range as an adult. The spawning

season is short, but individuals spawn each season for several years.

0. brevispinum seems to be selected for high adult survival, with adapta-

tions in the larval stage to help avoid environmental fluctuations while

retaining some dispersal abilities. The life history patterns of these

three ophiuroids provide empirical evidence which supports theoretical

predictions for life history and reproductive strategies in disturbed

or variable environments.

Sha i rman


Echinoderms are usually considered to be relatively stenohaline

organisms, although there are numerous examples of species which occur

in low or variable salinity regimes (Binyon, 1966). The occurrence of

at least 25 species of echinoderms in the euryhaline estuary at Cedar

Key, Florida, suggested that this might be an interesting area in

which to examine echinoderm adaptations to variable estuarine

conditions. Since the youngest stages or larvae of many benthic

populations are most sensitive to variable conditions (Kinne, 1964),

reproductive and larval biology were studied first. Stancyk (1973)

found that up to 75% of the echinoids and ophiuroids at Cedar Key had

some sort of developmental modification which helped to reduce larval

exposure to the capricious pelagic environment. These were of three

basic types: short-lived planktotrophic development, in which feeding

plutei remain in the plankton for a week to ten days; planktonic

lecithotrophic development, in which non-feeding motile vitellariae

metamorphose in three days; and direct development, in which a juvenile

emerges directly from the egg, with no intermediate larval stage.

Concerning older stages, Turner (1974) found distinct adaptations for

avoiding variable surface conditions in juvenile Ophiophragmus

filograneus, a common brittlestar of the area. He stated (p. 276) that "0.

filograneus has probably developed physiological, morphological, and

behavioral mechanisms at all stages of its life cycle for avoiding or

reducing contact with extreme conditions in the water column." The

idea that organisrr hate :uch adapter tion: i; in 3'r-eeTment with the v'iers

of num rcl: u: population bij-loigist Iuch a Gadil aInd EOs 7rt (1970, p. 21),

who wroLte that "the tremendous .arlation in life hi:tor, patterns of

organisms is best explained as adaptive."

Since Cole (1954) published his classic paper on life history

phenomena, a great deal has been written about life history patterns

and their adaptive nature (e.g., Murdoch, 1966; Holgate, 1967;

Murphy, 1968; Calow, 1973; Schaffer, 1974). Most of this work involved

models or was based on scant empirical evidence, and all of it dealing

with marine or unpredictably variable environments was theoretical.

However, there have been some excellent qualitative reviews of the

reproductive and larval strategies of marine invertebrates (Thorson,

1950, 1964, 1966; Mileikovsky, 1971), and these have helped to generate

some intriguing theoretical papers concerning the life history patterns

of marine benthic invertebrates (Strathmann, 1974; Vance, 1973, 1974).

The purpose of the research reported here was to study the biology

of three estuarine ophiuroids with different developmental patterns

(Ophioderma brevispinum (Say), Ophiothrix angulata (Say), Ophiophragmus

filograneus (Lyman)) in order to elucidate their adapations to an

unpredictably variable environment, and to see the effects of these

adaptations on their life history patterns. The information derived

from this study may lend support to certain of the theoretical

arguments in the.literature, and help to shed light on life history

strategies of benthic invertebrates in unpredictably variable environments.


Ophioderma brevispinum (Say) is a large (adult disk diameter about

15 mm) and motile green or brown brittlestar with a leathery disk

covered by fine granules (Figure la). It has four bursal openings in

each interbrachium (Figure Ib), a characteristic of the family

Ophiodermatidae. The arms are sturdy, of medium length (4-5 times

disk diameter), and have closely appressed short spines. It is a

common species, occurring in littoral areas from Massachusetts to

Florida, the Gulf of Mexico and the Caribbean (Ziesenhenne, 1955).

Stancyk (1970) found that 0. brevispinum was capable of feeding on

detritus, as well as being an active scavenger-predator, which

inhabits the substrate surface of the extensive grass flats of the

Cedar Key area of western Florida. The adults have a high tolerance

of salinity fluctuation, surviving prolonged exposures to 15 parts per

thousand (o/oo) with no apparent ill effects.

The embryology of 0. brevispinum was described by Grave (1899,

1916), who also made several observations on its ecology, parasitology

and physiology. The larva is a lecithotrophic, short-lived planktonic

form called a vitellaria which metamorphoses in 4-5 days. This type of

development has since been described in only four other species

(Mortenson, 1921, 1938; Fenaux, 1969; Stancyk, 1973) and its

adaptiveness to an unstable environment has been discussed by Stancyk


Figure la. Aboral view of Ophioderma brevispinum (Say, 1825).

Figure lb. Oral view of same.


If I I I I I lt

Ophiothrix angulata (Say) is a member of the widespread and

diverse family Ophiotrichidae. At Cedar Key it is most abundantly

found clinging to sponges in high-current areas, although it also

occurs less commonly on tunicates and in crevices of mollusk shells

of pilings. A typical adult has a disk diameter of about 9 mm,

possesses large radial shields and trifid spines aborally (Figure 2a),

and lacks oral papillae on the jaws (Figure 2b). The arms have long,

thorny, glassy spines and the tube feet are long and covered with

papillae. These are used in the process of feeding, which consists of

secretion of strands of mucus between the spines to capture suspended

detritus particles and subsequent wiping of the spines and forming

of a bolus to be passed to the mouth (Fontaine, 1965; Stancyk, 1970).

The color of 0. angulata is so variable that Clark (1933) named nine

varieties, of which only one is common at Cedar Key. This variety is

generally light blue, gray-green, or violet, with an orange arm-band

every fourth segment. While a completely orange form is found

occasionally, the more "typical" variety, which has a distinct, white

aboral arm stripe, is never taken at Cedar Key. Ophiothrix angulata is

widespread, from Cape Hatteras and Bermuda to Brazil, and from

littoral regions to 200 fathoms.

Ophiothrixangulata is thought to have a short-lived planktotrophic

larva. Mortenson (1921) raised the larvae to an early pluteus stage

in 4 1/2 days before they died, and they were of the typical

ophiotrichid pluteus form. However, they had reached the same develop-

mental stage that the boreal Ophiothrix fragilis reaches in 18 days

Figure 2a. Aboral view of Ophiothrix angulata (Say, 1825).

Figure 2b. Oral view of same.



(MacBride, 1907). Were this trend to continue. they would

metamorphose in much less than the month required by Ophiothri,

frajilis, and the possible significance of this abbre.iated develop-

ment was discussed b; Stanc)F (1973). No one has succeeded in raising

the larvae to metam-orpho;is.

Ophiophragmius fi lograneus (Lyman) is; remember of the family

Amphiuridae. It has e.,treTely long arms (up to 150 mr) and a small

disk (up to 9 mriT). There is a loh fence of papillae, characteristic of

the genu;. on the edge of the aboral side of the otherwi :. ssToothl,

scaled dis; (Figure 3a). The or3l side of the dist is co,,ered with low

spines or papillae (Figure I3 ). helping to distinguish thi- species fro.T

OphlophrajTimus wurdemani wi t which it is syipatric at Cedar 'e.,. The

aboral side is light gray-brown and the oral side is cream-colored. The

type locality of 0. fT lograneus is Cedar Key and it is imi ted in

distribution to Florida. occurring from All igator Harbor or the west

coast to Lape Kennedy on the east coast ('homas, 1962, Stanci'. 1970).

OphiophragmTis filoo.iraneus buries itS .dis in silty sand and extends

one to three anris to the surface through rmuc:us-l ined tubes. These arns

pick up detritus, which is passed down to the mouth. Like most

amphiurids, 0. filograneus autotomizes easily, and will readily throw

off the disk (consisting of gonads, stomach and disk cover) or parts of

the arms upon disturbance. Most adult animals show some regeneration of

the arms, and many individuals with newly regenerated disks are fund in

any collection. While regeneration has not been extensively studied in

this species, J. L. S'mon (personal communication) indicates that it

might be quite rapid, with individuals regenerating at least a rudimenta3r

disk cover within two weeks.

Figure 3a. Aboral view of Ophiophra.mus filograi;eus (Lyman, 1875).

Figure 3b. Oral view of same.



TliO':.; 0i' 1) four 'op'u .a iorns or f :, l hiophragmus filograneus in

Co) r in,1J 1:.1z.euter 1 -.:. F, i F' i '..rer' t,e bottom salinity was

recorded at 7.7 o/oo. This is the lowest recorded salinity within the

geographic range of any echinoderm (Binyon, 1966). It is probable that

the ability of this ophiuroid to withstand such low salinities is not

purely physiological. Stancyk (1970) found that adult 0. filograneus

probably could not withstand prolonged exposure to salinities lower than

about 15 o/oo, and Turner (1974) described differential postmetamoprhic

arm growth which would allow young brittlestars to burrow into the more

stable substrate and still reach the surface to feed wit the longer arms.

The embryological development of 0. filogcra:eRs han not been

described, but Stancyk (1973) argued that it is probably modified from

the planktotrophic type, and may be direct demersal development, such as

that described by Hendler (1973) for AmohiopDus abditus.


The area of Cedar Key, Levy County, Florida, consists of a group

of mangrove islands, sand hills, and shell mounds located in the Gulf

of Mexico (29 07' N, 830 04' W; Figure 4). It is situated about

11 miles southeast of the mouth of the Suwanee River and 14 miles west

of the mouth of the Wacassassa River, and is thus subject to large

amounts of freshwater runoff. The whole area can be characterized as

a broad, vertically homogenous estuary. The islands are surrounded by

extensive shallow, soft-bottomed flats whose dominant vegetation consists

of three species of marine angiosperms: Halodule wrightii (Ascherson);

"turtle grass", Thalassia testudinum Koenig and Sims; and "manatee grass,"

Syringodium filiforme Kutzing (Phillips, 1960, 1967). The extent of

these banks is shown by the six-foot depth contours in Figure 4.

Environmental conditions at Cedar Key are extremely variable, with a

relatively predictable seasonal pulse and frequent unpredictable changes,

particularly of salinity. The acidity fluctuates (pH 7.3-7.9) and is

below the normal range of oceanic pH. Highly acid water enters the

area from the two rivers, and seepage from the Ocala Limestone aquifer

may also account in part for pH variation (Ingmanson and Ross, 1969).

Figure 5 shows monthly means and ranges of surface water temperature and

salinity from January 1971 to December 1973 (Source: U. S. Coast and

Geodetic Survey, 1970-1974). The minimum and maximum temperatures

occurring during this study were 9.4C in January 1973 and 32.80 in

July 1973. This range is fairly representative for deeper waters at

Figure 4. Fap of the Cedar Keys, Levy County, Florida. Circled
numbers indicate the stations where ophiuroids were
regularly collected. (After U.S. Coast and Geodetic
Survey Chart 1259).

."' '. "> : ", .. "." *^

, v; *.'... ,, 1. '-:.'1.. .*'i^ ,,

F .- . >-
S'-' :


.. . ., 3 .3.'
] ., ',, ' . I --

.i *\
I I r

'- -"" "" m'^ i ,* -" P' '

S"-. |t ,"
* t-- ""-.? .^' ." L ,' \
', . ., .- :.. ,,.. .; ,* .; : *, ..* ',, : \ ,,
.., **"" '-.** '' ; '***:g i :.. o .: ..... "-

.. ^ ".. .. . } -%- .
\1 i

-. -.-.u

/' N
. f .. .". - ", *. NN
" I - .

I ^ I
,1 .


.i'I St.'` '

t- j / 9 -:' t Y %
I: .
Cal- L u0:~ I
:; D (3
L i > _ _ _ _ _

Figure 5. Graph of monthly salinity and temperature means and
ranges, Cedar Key, Florida, January i971 to
December 1973. (Source: U. S. Coast and Geodetic

0o 0 in a
. ' I I I 1 1 1 :,I 1 1 I T I ,

_. .. ,-

S-_ -.-. .- -- _- ---.---

S ----- ----------
--- ---I

--- ----- '---
,---.--,- ---4 -

---- -

--- ---- -- ---t

- --- -/ ".--- --- i -

I i ii- i ---------- ...i i [ .

0 o .- '"
-r- /o . -

Cedar Y:/. but in the present rInveStigatior it wja found that the

water temperature may rise as high a: 34. C and fill to 8C in shallower

areas. The graph demonstrates that temperature varies in a regular and

predictable manner, with a major temperature drop between October and

November of each year and a significant rise once again between March

and May. Monthly variation is least in the summer and greatest in the

winter. While predictable, temperature may still strongly affect

organisms in the area, particularly when a very low or high temperature

coincides with a low spring tide which leaves the grass flats exposed.

Salinity is much less predictable. Although the normal salinity

range (18 to 30 o/oo) is always below that of full seawater, there may

be additional sudden changes in salinity at any time of year, as in

February 1972, when it decreased to 11.8 o/oo. The effect of this drop

on certain organisms in the area was discussed by Stancyk (1973). The

difference in salinity between 1972 and 1973, particularly in the spring

months,deserves attention. Figure 6 shows in detail the salinity changes

for April, May and June of these two years (derived from Figure 5). The

mean monthly salinity for 1972 never dropped below 20 o/oo, and the

April-May-June low was 19.1 o/oo (which actually occurred on July 1, 1972).

The mean salinity in April and May of 1973 was 16.6 o/oo and minima of

less than 14 o/oo were recorded in both months. Such a prolonged and

drastic drop in salinity during the time of year when water temperatures

are rising and salinity is normally much higher could have considerable

impact on the more sedentary inhabitants of the area.

Three stations were selected in order to obtain reasonable numbers

of the ophiuroids under study. Station 1, located in Daughtery Bayou

(Goose Cove~ i: on the southeast side of Cedar Key (Figure 4). There

Figure 6. Comparison of salinity measurements of Cedar Key,
Florida, April June, 1972 and 1973. Open
circles, 1972; closed circles, 1973.





o 1972

Q'i7 3

is no qrasS in thii arj. ini '*i sjubs;r- t i co'mpised of -,il|r, )jnd

(nedran gr-in :ize: 0 3-P 7 mm) with a zhi rJoer l ing la.er of

dc-rltr tus and iiud. The bt toJim 1'i unevenr due to hea.. fteding t.) Stri.n -

a3ys. It is orily e-1osed t e .treerre low tide's., out s particularly

stsceptib l to dues'lc.. 1c di. he.: ? lime: due to lac'. of plant

ccver SLa lor. I ha l :he hl.ghes. dellitle: of O phlph ra lT ,:_ f lo ran_2u

found at Cedar Key, but other amphiurids are common, particu.aily

icrophol is gracillima, Ophiophragmus wurdemani, Amohiodlus sepultus

(see Hendler, 1973), Amphioplus thrombodes, and Hemipholis elonoata.

Station 2 (Figure 4) is a shallow (maximum depth: three meters)

tidal creek on the north side of Seahorse Key. The banks of this

creek consist of oyster bars, and the bottom is well-washed sand and shell.

Most of the oyster bars are exposed by any low tide, but the deeper

portions are exposed only once or twice a year, and on these parts eccur

dense sponge colonies, made up of Hymeniacidon heliophila, Halichondria

sp., and Lissodendoryx isodictyalis. These colonies and the shell

rubble beneath them usually contain large numbers of Ophicthrix anoillata.

The water in the creek sometimes reaches extremely high temperatures

(340C on August 6, 1972), and there is a very strong current whenever

the tide changes. Most of the invertebrates in this area are members of

the sponge or oyster community.

Station 3 (Figure 4) is located on the dense Thalassia flat on

the south side of Seahorse Key, where a large population of Ophioderma

brevispinum occurs. Although this station is exposed at extreme low

tides, the thick grass cover prevents severe desiccation. Because of

exposure to the open Gulf, wave action and salinity are slightly higher


he1'e rh n any other sta tiin. Oph7iophrjqmTi:. fil:.; ran;eu 1Jnlpn iplu

sepultu and Amphiopli thrO'mb~d-Je;, ccur 3t thi: station. but ar-e

less dense than at station 1.


The studies reported herein were carried out between Februar,'

1972 and June 1974. Monthly collections were made at each station from

June 1972 to July 1973, except for station 2, which was also sampled

in May 1972. Attempts were made to obtain a representative sample of

at least 100 individuals of each population,although this was not always

possible for Ophiophragmus filograneus. Collection techniques differed

at each station, depending upon the species sought. Station 1 was

sampled at low tides, and shovelsful of substrate were sieved through

a 3.2 mm mesh sieve. The surface area of substrate taken per shovelful

averaged 0.05 m2, so it was possible to determine the density of

ophiuroids in the area by counting the number of shovelsful of

substrate sieved. At station 2, two 0.1 m2 areas of sponge and shell

were collected and carefully sorted for Ophiothrix angulata. Station 3

was also sampled at low tides, but the density of the grass and the

cryptic nature of Ophioderma brevispinum juveniles made it impossible

to sort samples in the field. Therefore, two areas of 1.0 m2 each were

dug up and placed in tubs, sieved in a preliminary manner in the field

to remove most of the sediment, and the remaining sediment and grass

returned to the laboratory for hand-sorting. Additional collections

of Ophioderma were made with a scallop dredge. Small individuals made

up the same percentage of the population in well-sorted dredge samples

as in the more carefully obtained meter samples. However, dredging could

not ;uppl., er timate, of den i;ty, 1nJ wj; used oni' as a ;uppliemencar/


Recruitment, growth and mortality were determined by size-frequency

diagrams constructed from measurements of the oral frame diameter (OD) of

all individuals in the monthly samples. Oral diameter (Figure 7) was

used as the standard measure because the usual standard, disk diameter,

is too variable in these species. Ophiophragmus filograneus and

Ophiothrix angulata are both capable of contracting the soft disk, and

Ophiophragmus autotomizes and regenerates the disk cover quite easily.

Many animals were collected without the disk cover, or with a newly

regenerated disk cover which belied the actual size of the animal. To

make the results of this study comparable with other studies, disk

diameters and oral diameters of a series of each species were measured

and equivalence values determined. The results are presented in Table 1.

Unless otherwise specified, all measurements in this study will be oral


Growth and mortality for each population werealso estimated by

using values obtained from the size-frequency distributions in a

computer program devised by Ebert (1973). Unless populations contain

discrete size classes or are amenable to marking techniques, it is

difficult to determine these parameters with certainty. The purpose of

the program was to derive secondary growth and mortality estimates and

to supplement findings determined from the monthly samples, to see

if the interpretations of the size-frequency histograms were

plausible. The program was corrected and modified by William Ingram

for uj or the [BIl 370,'165 computer of the Northeast Regional Data

Center at nhe Univer:it, of Florida.

The method uise the following data to estimate a mortality


A -


Figure 7. Oral side of an amphiurid ophiuroid showing the oral
fr'ac (OD) and disk (DD) diameter measurements.
(roUT, Singletary, 1971)


C -

c '4- D C

ea 0

(O C
-- -


mr c 0 <

,0 0 -
*^- *+- o r-

S *- = C o C
'a aaj o
-z M

. Co n Cn

0- s- C C
Co 0


0 0 et3
-o tit

OS.- E
S.s0 'o l tO C

0 0

0i .0r
Ug +-H
CA 0~ 00
0r L
I .0. jIII

corn.st. t rd a r-..d -B.rtj alarnf irow th c:n ant- erne Size of

i rnriviaails t recruiLr n: .' .r) i er3e :1 of the pr.pulation ,r.

:,.re l.3a time, prrefe rabl, .3C: close to a ye.a- from the r.'2 oa

rer.'uitr.'enr t pos',ible (C. t rn e. tir ite of nJat, 'ni, i i:;ie (S ),

i ze of ind l.,idijil at recri.uitrent (S). .anrj e of ind i, .d als of

a kI'Cin age (SN). An approximation of mortality is obt.irne by placing

the derived mortality constant, Z, in the following equation:

Nt = oe

where Nt is the number of individuals in an age class at time t. No is

the number of individuals in the age class at time 0, and e is the

natural log constant, 2.718. Growth is estimated by placing the

derived Brody-Bertalanffy growth constant, K, in the following equation:

St = S (l-e-Kt)

The derivation of the formulae for determining the constants is discussed

by Ebert (1973).

To find growth and mortality constants from only two measurements

of the population, the program must make several assumptions. The most

basic are 1) mortality rate is constant (all ages included in the

population have the same mortality rate); and 2) the population under-

goes Brody-3Brtalanffy growth, which implies that there is no lag phase

or period of exponential growth of a linear dimension. Other assumptions

are: 3) the species has a stable population with a stationary age

distribution over the period sampled; 4) recruitment is confined to one

month a year; 5) rates of growth and mortality are constant during a

year; 6) estimated mean individual size is the parametric value of mean

size; and 7) individuals ear;':'.-c their asymptotic size so the

largest individual is a reasonable E timLte of mj.:;c..ni i;

At Cedar Key, nmny of these a;s-mpions do not hold strictly true.

They are most important if one has only two measurements of mean

individual size in a population. Supplementary data can be used to

modify the assumptions and still derive good estimates of the

necessary input for the method. Thus, if mortality rate was variable,

the prediction of longevity would be distorted. This error would be unde-

tectable unless one knew when mortality was higher, and could adjust

the estimate accordingly. Similarly, variation in growth rate with

age or season could also reduce the accuracy of the method. Seasonal

variation in growth rate can be circumvented by choosing the times of

measurement as close to a year apart as possible, so that they encompass

periods of both fast and slow growth. The effect of these potential

errors on the present study will be discussed later. Populations of

organisms which live one or two years are not stationary and stable

unless they have constant recruitment, and then they do not fit the

assumption of one recruitment period per year. In such cases, population

parameters are predictable if a single age class can be discerned and

followed throughout the year, and the mean individual size of that age

class only used as input into the method. As will be seen,such a

modification was necessary for both Ophiothrix and Ophiophragmus.

Gonad development, based on a gonad index, was examined in 10

males and 10 females from each monthly sample. These individuals

varied between OD 3.34-5.53 mm for Ophioderma brevispinum, 1.78-3.12 mm

for Ophiophragmus filograneus and 1.42-3.48 mm for Ophiothrix angulata.

The gonads of Ophioderma and Ophiophragmus are multiple, with 200-400

in mature Ophioderma and 100-200 in Ophiophragmus. There are just two

large gonads per interradius in Ophiothrix angulata. The gonads were

dissected away from the disl and arrm which were subsequently

decalcified in acetic acid 12.5 r) for 24 hour; Oiss, arm;, and gonads

were then placed in 5 < 10 cm glassine enielope5, dried overnight at 80'C

and weighed to 0.1 myi on a flettler H'S analytical balance. Because of

the small weights of these dried tissue;, tbani envelopes were also

weighed to eliminate error due to water absorption bj the envelopes.

A gonad index value was calculated by determining the percentage of total

tissue dry weight made up by the gonads.

Since it was difficult to tell by inspection or gonad index when

Ophiophragmus filograneus spawned, five females were kept each month for

sectioning and histological analysis. Ovaries from these females were

preserved in Bouin's solution and transferred to alcohol after several

days. They were then embedded in Paraplast, sectioned at 7-10 microns

and stained with Delafield's hematoxylin and eosin. For each female the

diameter of the longest axis of 20 oocytes sectioned through the nucleolus

was measured. The first 20 suitably sectioned oocytes were measured without

discrimination as to size in order to obtain an unbiased sampling of the

oocyte sizes present in the ovary. Occasional oocytes dissected from live

material are 0.2 mm in diameter, but most of the large oocytes measured

had a diameter of about 0.18 mm. The largest oocyte diameters in the

sectioned material averaged about 0.165-0.170 mm. This 7-10% difference

in size is probably due to shrinkage in the preserved material.

Egg numbers for Ophioderma and Ophiophragmus were determined as

described in Stancyk (1973) by counting subsamples from interradii. A

different method was used for Ophiothrix, which has large numbers of small

eggs. Since the average egg size of Ophiothrix is .09 mm. the volume of

an egg can be determined by the formula V = 4/3nr to tie 5.24 10 Imm A

sample of ten ferIae 'ihl~othrir ranuirng in size from OD 2.02-.-I.S mm

ere coi ie.:ted and their qonrad .ere removed and blotted. The .clume of

the gonads for each female was determined by the amount of water they

displaced. This volume was divided by the volume of a single egg to

give an estimate of the number of eggs per female. Since the gonads also

contain smaller oocytes and empty places, the figures derived by this

method are probably high. This is less important in Ophiothrix than the

other species, since an error of 20,000 eggs is only about 20% of the

total egg number.

To compare metabolic rates between species and at different tempera-

tures, rates of oxygen consumption were measured in a Gilson Differential

Respirometer between March and June, 1973. Individuals of each species

were acclimated for two weeks at temperatures between 15 and 30C.

Drained wet weight of the animals was measured and oxygen consumption

determined as ml 02/gram wet weight-hr. Eight individuals were run at

one time, and were placed in 50 ml flasks containing 25 ml of millepore-

filtered seawater, with a piece of gauze saturated with 10% KOH in a

sidearm of the flask to absorb CO2. After the animals were placed in the

flasks, they were allowed to equilibrate for one hour before readings

were begun. Readings were taken every two hours for eight hours, but

only the last six hours were used in determining the oxygen consumption.

Since all three species normally avoid light, the experiments were run in

the dark. Different series of animals were acclimated to different temp-

atures and were used only at those temperatures. All temperatures in

this paper refer to water temperature.


Densities, Monthly Collections

Density (individuals/m2) of each species at each collection time is

shown in Table 2. At station 2, Ophiothrix angulata is abundant, with

densities ranging from 1740/m2 in May 1973 to 365/m2 in July 1972, and

with only one individual in the July 1973 collection. This fluctuation

in density at one station follows a pattern, and Ophiothrix is signifi-

cantly less dense (p = 0.05) from July to November than at the other

times of the year. Ophioderma brevispinum is less dense than

Ophiothrix, with numbers ranging from 49/m2 in June 1973 to 17/m2 in

October 1972, but its density also varies in a regular manner. However,

while Ophiothrix grows rarer in the summer months, Ophioderma is less

abundant in the winter. The density at station 3 drops from a mean of

41.8/n2 in the spring and summer to a lower value of 30.8/m2 in the

colder months of September to February. The difference between these

means is significant at a 95% confidence level. The density of

Ophiophra gus filograneus at station 1 fluctuates from 8.33/m2 in

September 1972 to 31.6/m2 in December 1972, but the fluctuation is

irregular and there is no significant difference between concentrations

during the sampling period.

The stations sampled were chosen because they were found to have the

greatest densities of the species under study, hut each species occurred

elsewhere. High numbers of Ophiothrix angulata were found only in the

Table 2. Densities of ophiuroids during monthly
collections at Cedar Key

Density (individuals/m2

Ophiothrix Ophiophragmus
angulata filograneus





Mean and
standard error 970+130




37. + 2.0







tidal creel at station 2 and a few sponge beds on deeper shell bottoms.

Ophiothrix is therefore e..tremely dense in a patchily distributed

habitat, but can be found in densities of less than li, m elsewhere,

clinging to floating objects or solitary tunicates. Ophioderma

brevispinum is very widespread, but its greatest densities occur on the

grass flats where station 3 was located. Ophiophraqmus filoqraneuus

is most abundant in bare sandy bottoms such as station 1, but can be

found in densities up to 10m" in the softer substrates on the grass flats.

Figure 8 is a size-frequency histogram for collection; of Ophiothrix

angulata at station 2, from June 1972 to June 1973. A collection in

July 1973 yielded only one Indi.idual. In 1972, there were two timTes of

relatively, high recruitment. The first occurred in April or Ma,, and

the large new. ;ize class can be seen in June at 00 0 75-1.5 rm, making

up 69% of the total population. The second major peal occurs in August,

at size 0 5-0 75 mm, and males up 16. of the population. There is

additional low recruitment during the rest of the year, at least until

April, 1973. Howe..er, there was no repeated heavy settlement in the

spring of 1973, and by July the population had disappeared.

The curved lines in Figure 8 are appro-imate growth lines of different

settling classes, estimated bi epe. Most of the growth of a newly

settled group tool place within one year It i probable that few members

of any one group survive for more than one year, although some of the

larger animals (as in June, 1972) mad, be two rears old. The total growth

of a settling class was about 2.5 mmn OD/year, or 0.21 nm.'month. However,

the graph shows that most of this growth took place only in the warrier

months, and slowed or stopped from Decerner to March, when mean water

temperature w.*s below about' 20:'C. Growth rates before and after this

time were approximately the same, as discerned by the equality of 'he


\ \. o,

- J.L L> L' ,


-" I
o o


\ 0

I !... .
{>- >1 ,
1 \ r o

\ \ -- -- +
^"^--'^ iT"':" ^
\ IJ -- :

(1IU .^~l'W "~ --'0t

slopes of the lines. There may t.e some slcwing in somatic growth

in the larger animals, as can be seen in the slopes of the top two lines

from flarch-June. 1973 If growth were constant, maximum size of 3.85 nmm

would be reached in about 1.5 years.

Figure 9 is the size-frequency .raph for col elections of Ophiophr.agmus

filograneus from station 1, June 1972 to July 1973. ?ecruitment at any

time seemed low, about 3.4% of the population. It appeared to take

place several times a year, with individuals of OD less than 1 mm being

found in September, February, and July. The presence of individuals

between 1.0 and 1.5 mm at nearly all times of year indicates a much more

constant recruitment than just the three months stated. However, the

small sample sizes in monthly collections makes it difficult to

estimate the size or number of settling classes, especially when the

animals are small. Approximate growth, indicated by lines, shows that most

individuals lived less than one year. Growth rate estimates are about

0.12 mmn OD/month, with little reduction in growth rate during the winter.

Assuming this rate is constant, an age of about 2 years for growth to

maximum size of 3.41 mm can be calculated. The fact that the percentage

of the population made up by a settling class increases with size

indicates that there is probably a sampling error which caused an under-

estimate of the number of small individuals in the population. In

addition, the small sample sizes make it difficult to distinguish older

classes, so growth determinations are approximations of real growth.

The size-frequency histogram of Ophioderma brevisoinum collected

from May 1972 to June 1973 at station 3 is shown in Figure 10. Two

distinct younger classes can be distinguished, and the lines follow

their growth through the ,ear. The younger grouo appeared at OD 1.07 mm

in July 1972, and reached an average of 2.75 mrr by the ne

z 12

I *1-lr

-u, .1*
c .~'~ -

n N C














~I -J

A ii




Q. 0

z E

-c '4

o =N

N >


.grC.Jth rae of 1i Fr.mon,:h. The second small size class was visible

in May 1972 at Gf 2.i) mm, and had grown into the main population at

3.2 mm by October, for a calculated growth rate of 0.2 mm/month over the

summer and fall. Recruitment was fairly low, or about 6-8% of the total

population. In this population, as in 0phiothrix angulata, growth

stopped from October through March, when the water temperature was below

250C. Note that from October 1972 on, except for January (1 individual),

there were no individuals of large size (OD greater than 5.5. mm) in

the population; in fact, in December there were none over 5.0 mm. In

later months, they reappeared, but not in as great numbers as before


Estimates of Survivorship, Growth and Mortality

After modification of the basic program of Ebert (1973) and evaluation

of the necessary assumptions, values of the parameters necessary to

estimate survivorship, growth and mortality were selected from the popula-

tion histograms in Figures 8-10. The values chosen for each species and

the resultant growth (K) and mortality (Z) constants are shown in

Table 3. Since Ophiothrix angulata and Ophiophragmus filograneus both

have relatively constant recruitment, a settling class was chosen for

these species which could be followed throughout the year, and any

individuals not in that class were not included in the average individual

size calculations. The two estimates of average individual size in the

populations were made as far apart as possible, so that growth figures

encompass both fast and slow growth periods.

Calculated survivorship values of the ophiuroids in this study are

listed in Table 4. According to the method used, a settling class of


o- 0 E
0 0-- -
I cCc n

km@ C
C 1 .i 49
0I '' -

E4) cMC

Eo c 0

0 a))
s-E 0
C"0 L -O O
o-' c 8 c 10

Sc 11 C0


UN4C .C 0C Ct
0 U 00
+4E aO S a a o

CL 0 O V E
o eo n E

4i Li C t-

tiC)..0 0 0

cta- 4 i c >
Cts -ifl -U 0

2cm a,
S II 0 ci *

1 I- >


Table 4. Survivorship values of estuarine ophiuroids, determined
from computer-generated estimates.

Age Ophiothrix Ophiophragmus
(vPers) anniil1t; fi1nnr~nInJR

hrp v zn i n Iir

0 1.000 1.000 1.000
1 0.000 0.043 0.823
2 0.002 0.677
3 0.000 0.557
4 0.458
5 0.376
6 0.310
7 0.255
8 0.210
9 0.173
10 0.142
15 0.054
20 0.020
25 0.007

Johiotrir ides not have an, individual: survive for more th3n cne ,ear,

ar.o t.e mortal it, constant, i, 1 high. 18.35 (Table 3). Ophiop r.aimus

is alo short-lived, and only ', of a ettlingr cla;s survi ve until the

neCt ,ear, 0.,. until the third year The mortality constant for

Ophiophrar.r. u is 3. 15. OphloodenmT has j mor-talit constant of 0 195 ar.d

is fairly long-lived, with 14% of a settling class still alive after 10

,ears, and 1% surviving until 23 years of age.

Growth curves for each species are plotted in Figures 11 to 13.

Figure 11 shows that Ophiothrix, with a growth constant of 1.56, reaches

a size of OD 3.0 mm in its first year; the largest individual found,

3.85 mm, could not have been more than 4 years old. The program thus

predicts that Ophiothrix is a short-lived, fast-growing species, with

few individuals surviving for more than a year. Ophiophragmus also

appears to be fast-growing (Figure 12) with a growth constant of 1.21,

and reaching an oral diameter of 2.7 mm in its first year. The largest

individual captured (3.41 mm) could be as old as 5 years. Ophioderma

is slower-growing (Figure 13), with a growth constant of 0.25, and takes

about 9 years to reach a size of 6.0 mm. The method predicts that the

largest individuals found may be as old as 25-28 years.


Fecundity, egg size, size and age at first reproduction, developmental

type and sex ratio for each species are given in Table 5. Many of these

data are derived from Stancyk (1973). Age at first reproduction was

determined by finding the smallest individuals with large oocytes in the

monthly samples and fitting them to the computer-generated growth curves

for each species. Size at first reproduction in Ophiothrix angulata was

difficult to determine, because any individual which could be sexed


Figure 11. Estimated growth curve for Ophiothrix angulata.

I 2 3 4 5 6

Figure 12. Estimated growth curve for Ophiophragmus filograneus.



E 5-0-



%40- !./


2 6 10 14 18 22 26

Figure 13. Estimated growth curve for Ophioderma brevispinum.

* .- '
: C 0"^
-c. cg *ZN




4-* u

't -a
-- C

- Cr
f0 f

0- C








C -

4. 0


s .c





.0 E

3C C

C. Q ^

> -

C -





* C



- to

r ,. r

c J
Ld -
C) '1)



h en


C t

m us,
e t
Lt C-.

CO 0 00
c- en

contained many large oocytes. However, the gonad Volume of

individuals between OD 2.0 and 2.5 mm was the same, and began to

increase in individuals larger then 2.5 mm. This size was therefore

chosen as the earliest size of oocyte proliferation prior to spawning.

The table shows that Ophiothrix, which has planktotrophic develop-

ment, has by far the highest egg number and the smallest eggs. The

other two species, which have modified development, have larger and

fewer eggs. The two species with the largest egg numbers (Ophiothrix

and Ophiophragmus) begin to reproduce within their first year of life,

while Ophioderma does not begin to reproduce until 2-3 years old. None

of the sex ratios are significantly different from 1:1, so it appears

that males and females are equal in all three species. A gonad index

(% total decalcified dry weight made up by gonads) was used to

determine when spawning took place. Figures 14 to 16 show the gonad

index change over 1 year in each species. In Ophiothrix angulata

(Figure 14) gonad index varied little over the year. There were peaks

in September and November, 1972, and in April-May, 1973. These are

associated with increases in the standard deviation about the mean and

therefore increases in the range of variability of the monthly samples.

It appears that some fraction of the population was nearing spawning

condition at these times. This is interpreted as a demonstration that

spawning is asynchronous, and some fraction of the population is in

spawning condition at any time of year; the peaks merely represent the

maturation of a large settling class. Note in Figure 8 that recruitment

occurred throughout the year, with peaks in June and August.

Figure 14. Mean and standard deviation of gonad indices of
Ophiothrix angulata, July 1972 to June 1973. Gonad
index = % of total dry weight made up by gonads.



1 -------------- --~c--- -------

I g


0 1

0 2
1---*---> --r
0 0
S- Z

1 -------.0..----

I i

c n

IM 3nSS.l V, O i. o.O (.%)

The opposite case appeared in O.phodermn bre ioinun (Figure 151.

The gcnad: miade up less than 25:. of the total dr, tissuec weight until

April, when they rapidly inc:reised to about 32.. By June, they decreased

to abOut 18,, and they .tayed at about 15-2c' the rest of the ,ear. i u th

a minor peal in rNovember. it appears that Ophiodermi spawns S'nchronoul1.,

in ta) with The possibility of some ilcr-lenel :Fpuning during the uTr;ler

and fall. Note that the recruitment shown in Figure 9 is fairly discrete,

and iniic.tes that settlement takes place over a short time, once a year.

There is no significant difference between the gonad indices for any

month in the Ophiophragmus filograneus samples (Figure 16). The means

varied from 15 to 27%, but at several times of year there were some

individuals in the sample with gonad percentages over 40%, particularly

in the spring and summer. This lack of difference suggeststhat some

fraction of the population is nearing spawning condition at any time of

year. To clarify this picture somewhat, sectioned ovaries from five

females per month were examined. The proportion of oocytes of varying

diameters making up the ovary contents are shown in Figure 17. Large

oocytes (0.17-0.2 mm) were present at nearly all times of the year.

However, there was a significant change in their proportion between

October and November 1972, February and March 1973, and May and July

1973. The polymodal distribution of oocyte diameters at all times of

year indicates that there was constant growth of oocytes throughout the

year. The decrease in large oocyte percentage at the three times of

year discussed above suggests spawning of three different settling

classes which made up a larger part of the population, but spawning was

probably continuous at a lower level. The frequency of recruitment of

small size classes (Figure 10) also indicate; constant' spanning lote

Figure 15. Mean and standard deviation of gonad indices of
Ophioderma brevispinum, July 1972 to June 1973. Gonad
index = % of total dry weight made up by gonads.

~--- C I---

I -i-----

uE i

I--- -- ----- ----- |----- ------ -----
60 .
6 m s ko o o
I.P 3SSI311 AC iW1O1 JO (J,)

'- I-w

Figure 16. Mean and standard deviation of gonad indices of
Ophiophragmus filograneus, July 1972 to June 1973.
Gonad index = % of total dry weight made up by


I .



I- ---0--


I C I---


M 3 010 0 0

I A ans s ii A e o -rTio -0 0 1,


I. ,

Figure 17. Polygons showing frequency of primary oocyte diameters
in the ovaries of Ophiophragmus filoaraneus, September
1972 to July 1973. Circles indicate mean diameter for
each month.

0 10 015

that while spawning took place year-round in Ophiothrix and

C'phic'im, there was a major peak in all three species in spring

and early summer.


Oxygen consumption of the three species used in this study was

examined at various temperatures, from 150 to 300C. In all species,

total 02 consumption increased logarithmically with the size of the

animal. Figure 18 shows the relation of oxygen consumption to

temperature for the three species used in this study. As might be

expected, 02 consumption increased with increasing temperature, and

between 150 and 25C there was no difference among the means of the

three species. At 30C, the respiration rate of Ophiothrix was twice as

high as the other two species. Even with the small sample sizes used

(N=8) the difference was significant at the 99.999% confidence level.

There was no difference between Ophioderma and Ophiophragmus at 30C.

It appears that Ophiothrix is much more temperature-sensitive than

the other two species, particularly at temperatures above 250C. Note

in Table 2 that the densities of Ophiothrix at station 2 decreased

drastically in July, and did not increase to a higher level until


0= Oph O erma
Q: Optitfl.rix
O C;i C ;.c -.

i I 120 I '25

.. I I

Figure 18. Oxygen consumption of three estuarine ophiuroids at
different temperatures. Results are expressed as means
surrounded by 95% confidence intervals.

0 12




| 0-06-

! O -



I I '-30


Population Dynamics

It is not unusual to find high densities of ophiuroids;

Vevers (1952) found 340 Ophiothrix fragilis /m2 off Great Britain,

and amphiurids have been reported as high as 1,516/m2 off southern

California (Barnard and Ziesenhenne, 1961). This study shows that

density changes over the year in both Ophioderma brevispinum and

Ophiothrix angulata, and that in both species, the larger (older)

individuals disappear (see Figures 8 and 10). The absence of large

Ophioderma in the winter has two possible explanations. Local fishermen

feel that some Ophioderma leave the grass flats for deeper waters in the

winter because they find large numbers of them in their crab traps.

However, most of the trapping is done in the winter, and dredge hauls have

indicated that Ophioderma occurs in deeper water year-round. That they

would concentrate around a bait source is not surprising, and Allee (1927)

recorded that they would grasp and hold a baited hook. The other

explanation is that the large individuals are members of the oldest year

class, post-reproductives, who die with the coming of cold. In Figure 10

they comprise between 3 and 5% of the population. This corresponds

rather closely with the figures derived from the estimate of survivorship.

Ophiothrix angulata has its lowest density in the summer, and most

individuals larger than the size class recruited in April (OD 1.6 mm)

are absent by the end of September (Figure 8). In light of this

disappearance of older individuals, it is worthwhile to consider the data

on o.ygCn consumption in some detail. The mean respiration rate for

each species betuceen 22' and 25"C does not differ greatly from those

of ophiurolds reported in the literature, all of which fall between

0.03 and 0.102 ml 02'/g wet weight.h, .with a mean of 0.058 0.019 ml

0,,"g wet weighC/h (llicol, 1960; Euchanan, 196.4, Farmanfarm an, 1 66;

Pentreath, 1971; Singletary, 1971. Hendler, 1973). However, Ophlothri

has a greatly increased metabolic rate at higher environmental

temperatures, while the other two species show a less rapid rise.

Temperatures at 30C are not uncommon at Cedar Key; in fact, the

mean temperature in July for the last three years (1971-1974) has been

at or above 300C (Figure 5) and values of 34C have been recorded at

station 2 several times since 1969. Thus, the Ophiothrix population

may be subject to some temperature stress each summer. Older individuals

might die more easily because they have lost their energy reserves to

reproduction in June, and are thus unable to cope with increased metabolic

costs associated with high temperatures. Smaller individuals have the

necessary reserves, or can resorb unspawned gametes (Boolootian, 1966).

The surrer die-off is probably a regular phenomenon, as it occurred in

both 1972 and 1973 (Figure 8).

The rates of population growth and survivorship derived from the

method of Ebert (1973) appear to approximate the actual growth

(Figures 8-10). Variation between the two is chiefly due to poor fit

of the assumptions of the method to the real populations. In benthic

invertebrate populations, mortality is probably not constant in all age

groups. Thorson (1950, 1966) discussed the biological and Kinne (1964)

the physical aspects of high mortality in young agess of benthic

invertebrates. However, this high mortality would occur before the

animals reach a large enough size to appear in mn, samples. High

mortality of older individuals ,culd c.auj'( the program to predict a

longer time to reach ma .ifmuim si :e zhan is actually necessary. Tr.u;,

the program predicts a little over two years for both Ophiophragmus

and Ophiothrix to attain maximum size, while Figures 8 and 9 indicate

that this growth may occur in 0.8 to 1.5 years.

There is no adjustment in the model for a decrease in somatic

growth rate with the onset of sexual maturity and gonad growth.

Hendler (1973) demonstrated that in Amphioplus abditus there was an

inverse relation between gonad growth and annual somatic growth, somatic

growth being correlated with temperatures above 120C and gonad growth

with lower temperatures. He also showed that gonad development can be

fairly rapid. In a semelparous species (one which spawns only one time)

with a 1-1.5 year life span, growth to a large size could occur during

the warmer parts of the year. Storage of nutrients or gonad growth

could take place when temperatures were low, particularly if the species

fed year-around, regardless of temperature. Stancyk (1970) found no

cessation of feeding below 25C by any ophiuroids at Cedar Key, although

somatic growth stopped between 20 and 250C. The major spawning peaks

in the spring and early summer in both Ophiothrix and Ophiophragmus,

following periods of reduced somatic growth in winter, indicate

that large parts of the populations of these two short-lived species

followed this pattern. Somatic growth to a given size, followed

by rapid gonad growth and continued reduced somatic growth may be a

general pattern in semelparous species. Buchanan (1967) found a similar

pattern over three years in Amphiura filiformis, and Singletary (1971)

found rapid gonad development in Micropholis gracillima. In any case,

the variation in growth will reduce the closeness of fit of the growth

estimates to actual growth rates in the short-lived species.

Ophiodermi brevispinum, lie many other long-1 i'ed forms (Fell,

1966; Swin, 1966), has two to three years of somatic growth before

re3Ching mature j. Somatic growth then continues at a nore gradual

rate, stopping each Winter when temperatures decrease. Gonad growth

occurs gralual ly over the winter, and most of tre population spawns

in the Spring. This pattern was described for Gorcornocephalus caryi

by Patent (196'?), and for Amphiura iga i and Ophioderma lo Iongicuda

by Fenau, (1970, 1972). Because variation in growth is spread1 D over

long period of time, the predictive metrho fits the actual population

grown of Ophiod.erTia better than the other two species.

The variation in growth increment is low between the three species

10.12 to 0 2 T mi'r'onth 00) although the patterns of annual growth vary

great wnich could suggest that roughly the same percentage of incoming

energy is partitioned to somatic growth by all three species. This does

not necessarily imply that they are all putting the same amount into

maintenance and reproduce tion. In fact, the data on respiration suggest

that Ophiothrit may have to expend more energy during part of the year

than the other species.

Means of obtaining life history values from actual marking in pop-

ulations of soft-bodied or fragile benthic invertebrates have not been

devised, so the method used here is quite useful in refining and

verifying field results. Given the modifications of the assumptions

discussed previously, the final program appears to appro imatea the Inown

parameters of the three ophriuroid populations, 3nd therefore its values

for parameters otherwise unobtainable (survivorship. mortality) are

good first estimates of the actual populat"'n values The method is

most helpful in determining the dynamics of the slow-growing Ophlodermj.

since age i:,sse; could only oe followed for about 10% of their life span.

The r.eults ;how that the ophiuroids studied have two basic life

hi;tor; ) pjc rns (e\clulinU reproductive mode). One species (Ophioderma

bre'vispirnum) ta'e: two or three ,ears to reach maturity, then spawns

repeatedly for up to 25 years (iteroparity). This resembles the more

common case in ophiuroids: slow growth, iteroparity, and a long life of

10-15 years (Fell, 1966; Swan, 1966; Buchanan, 1964). Fenaux (personal

communication) has found that Ophioderma longicauda in the Mediterranean

may live up to 30 years, which compares favorably with my findings for

Ophioderma brevispinum.

J- The other two species (Ophiophragmus filograneus, Ophiothrix angulata)

grow to maturity in a year or less, spa.,i all reproductive products in one

season, and die. Such rapid maturation is unusual in ophiuroids.

Buchanan (1964, 1967) found that Amphiura filiformis reaches maturity in

three years and dies. Fell (1966) noted that Ophiura texturata takes two

years and Taylor (1958, from Singletary, 1971) found that Ophiothrix

fragilis and Ophiopholis aculeata reach maturity in about 1 1/2 years.

Singletary (1971) found three species of amphiurids in Biscayne Bay which

matured in less than a year. In fact, Micropholis gracillima, which also

occurs at Cedar Key, reached sexual maturity two months after settling.

Buchanan (1964) attributes the fast growth of Amphiura filiformis to its

high-energy suspension-feeding habit. However, it may be that these

species with rapid maturation are also susceptible to periods of high

mortality, as are Ophiothrix and Ophiophragmus.

Several theoretical papers on life history pattern and the environment

have been published (Murphy, 1968; Gadgil and Bossert, 1970; Calow, 1973;

Schaffer, 1974). All reach the same basic conclusion: if adult mortality

is high or ariible, there will be selection for semelparity with a short

life, if there ;i high mortal ity in pre-reproducti es or incrEased

positi, e feedback on reproductive process with age (increased fertility

or .lar iajl, decreased rep'oductive O costs), there will be selection for

Iteroparit and long life. The ophiuroidL eaminred in this Stud fit.

both patterns. Ophiothrl, anqulata adult, are l killed during periods of

high temperature. Also, the evidence presented indicates that pre-

reproducti'.e: do not survive periods of low salinity, since spawning

occurred in spring 19:'2, but there was no recruitment. Ophiothrix

clearly has a !.emelparous strategy.

Ophioderma bre.ispinum has iteroparous development and a long life,

and the adults are well-adapted to physical variations in the environment

(Stancyk,1970). They appear to have low mortality from predation. I

know of no organisms who eat Ophioderma brevispinum except for two sea

stars, Luidia clathrata and L. alternate, which do not occur in the

same grassflat habitat (Stancyk, 1974).

Ophiophragmus filograneus is also well-adapted to environmental

fluctuation (Stancyk, 1970; Turner, 1974; Thomas, 1961), and in light

of its somewhat lower fecundity, might also be expected to have a long

iteroparous life. However, heavy mortality in adults due to predation

is possible in this species, although the predators are unidentified.

In any given collection of Ophiophragmus, between 20 and 30% of the

adults showed evidence of disk regeneration, and 100% of thd animals had

some of the arms partially regenerated. In the laboratory, hermit crabs

of several species and young blue crass, Callinectes sapidus, rapidly

devoured the exposed arms of buried Ophiophranrrus If such predation

causes high adult mortality, the semelparous development of this specieS

n')ht t e.-plainred. Even if this is not true, Schaffer (1974) found in

certain cajs= that increases in ferul1:; or postbreeding growth and

survival could result in either an iteroparous or semelparous equilibrium

life history, and the mode could not be predicted. It is possible that

Ophiophragmus fits such a pattern.


The relationship between egg number, egg size and developmental type

has been discussed by numerous authors (Thorson, 1950; Mileikovsky, 1971;

Schoener, 1972; Stancyk, 1973). Hendler (1973) summarized the known

information for ophiuroids. In general, species with brooded or ovovivi-

parous development have few eggs of large size; species with modified

development (direct demersal, vitellaria) have moderate numbers of eggs

of medium size; and species with planktotrophic development have many

small eggs. Out of 39 ophiuroid species for which egg numbers are known,

for example, only five do not fit and the development of three of these

is unknown. The species studied here do fit the expected pattern:

Ophioderma brevispinum and Ophiophragmus are well within the range for

abbreviated development; in fact, 0. filograneus approaches the egg

size and number of Amphioplus abditus, which has direct demersal develop-

ment (Hendler, 1973). Ophiothrix has egg numbers at the lower range of

those produced by most planktotrophic species. Perhaps production of

a planktotrophic larva which will metamorphose in a short time causes a

reduction in the numbers of eggs that can be produced, because there is a

higher energy cost involved in building each egg.

The abbreviated development of all three species is interesting in

light of a theoretcial model proposed by Vance (1973), which predicts that

only the extremes of the possible range of egg size and type of nutrition,

planktotrophy and lecithrtroph would be e.slurionarily stable.

Abbrejiated development is an energetically e,.pensi.e way to maintain

restricted di:persal. Howei er, when ternporal -ariation in the adult

environment was included, Vance (1l974, found that disturbance faored

an intermediate strategy with large eggs, a long benthic prefeeding

development and 3 1horL plan Lotrophic stage. Functionally, that

tpe of development is analogous to the .1tellaria or short-li ed

plankOttroph found in the Ced3r ',i oph'uroids Vance's conclulionS

were based on the result; of simulation : which employed arbitrary

parameter values, 3o it is noteworthy that they predict a L;rategq

close to that followed by these ophiuroids.

Dispersal has the chief advantage of allowing rapid colonization

and exploitation of disturbed habitats (Vance, 1974). Strathmann (1974)

stated that factors favoring dispersal include variations in success

of settling of larvae entering an area, in mortality in the benthic stage,

in gamete production, in spawning losses, and in survival of early stages

released in an area. In Vance's (1974) model dispersal becomes important

in the evolution of reproductive mode only if benthic development is a

more efficient means of juvenile production; that is, complete benthic

development would be selected if it were not necessary to have dispersal

for colonization (and recolonization) of disturbed environments. This may

be the case in Ophiophragmus. Chia (1971) tentatively demonstrated that

direct development may be energetically cheaper than planktotrophy, and

at times of environmental fluctuation in an area like Cedar Key, benthic

development certainly results in greater juvenile production than plankto-

trophy. Finally, Vance (1974) indicated that dispe'oal confers 3 greater

advantage on planktotrophy when the energy 3.ailable For reproduction is

low. The possibility exists that Ophlothrl, has plarktor.oph:, because it

is mo:t :en iti e to en>ironrental .,3riat ion and c-ut spend more ererJ~

for ri.,inlteranc e, leading le;: for reproduction.

Tnorson (1?SO, I66) and l ilei;o:: y (1971i) attempted to correlate

the occurrence or abbreliated deelo?.nient in benthi: invertebrates with

the en.ironmrent Hendler (1973. p. 161i reviewed the situation in


Clearly, the assemblage of abbreviated developers is not syste-
matically cohesive. Similarity in size of eggs, larvae, and
post-larvae as well as the related similarity in the number and
mass of gametes produced and the rate of development indicate
that they are ecologically and physiologically convergent.
Apparently the abbreviated developers have been selected from
different stocks and combine some of the advantages and dis-
advantages of viviparous and planktotrophic development to suit
a specific larval "niche".

In Cedar Key, Stancyk (1973) argued that this larval niche helps

reduce mortality in an unpredictably variable environment: the susceptible

young stage has a better chance of getting out of the variable pelagic

conditions and into the more stable substrate before a lethal environmental

perturbation can take place. Carriker (1967) expressed the idea that

abbreviated development provides an advantage by reducing dispersal so

that young stages can settle in an environment of proven suitability to

adults, often their own parents. Reduced or local dispersal of this sort

would certainly not be an advantage to a species like Ophiothrix, where

the population (and a single individual's genotype) would be eliminated

if summer temperatures were high and the local salinity was low. Hendler

(1973) demonstrated that the directly-developing eggs of Amphioplus abditus

fared poorly in low salinities, but were normally kept out of such stress

by being demersal and remaining in the higher salinity bottom layer.

That environmental .riabilitt can affect recruitment was clearly

deontra;tted bV Cpfjo:hr( andnuiaja in Che :pring of 1973. Gonad index

aot.l InrJicjte that many individual sp:.ri.ned in the spring (ad ir. the spring

of !972), but recruitment. ,ca very lov (Ficure S) tbecaue the lowi

salinit- in Ilarch and April (Fi.Jurei- 5 and 6) urndouttedly ll1d most cf

the larvae.

Finally, the reilt.l.,nf hip between lor.goq ity, :pawnirinq eriojd.:ity and

..rv 1ir rirn tl vi t ariarbili:.,' nrust c e..amrrned. Few O'rhiuroids nav- very

long tbircijln se.a...-ns ( oPoo tlrn, i.5). ko...e.,er, Gui 1 (1961) found

that OCphioLth l quinqu:mr,:culata breeds :,ear roud, uIth peaks in the

spring and fall. Fell (1946) stated that th, viviparous Axiognathus

(Amphipholis) squamatus probably breeds all year round, and Singletary

(1971) found this to be the case for Micropholis gracillima in Biscayne

Bay. J. S. Pearse (personal communication) noted that Ophiocoma scol-

opI n,-i'na from the Red Sea also breeds year-round. The advantage of a

long spawning period in a variable environment is clear: if some

individuals are spawning at any time of year, the possibility is increased

that some larvae will encounter a beneficial environment and settle

successfully. Thus itisnot surprising to find Oohiothrix angulata and

Ophiohr2agmus filograneus with continual spawning. However, having a

long breeding season is not advantageous to the individual and its genes,

carried in its offspring, unless it can spawn more than once itself. Not

only will multiple spawning increase the chances for some of an individual's

offspring to encounter a suitable pelagic environemnt, but Strathmann

(1974) predicted that species with short-lived larvae, particularly

pelagic nonfeeding larvae would have a higher i-:i.J.:-nce of multiple

spawnings if .there is selection for spread of larvae. It is logical,

therefore, that Ophioderma not only spawns cer" sc tral ,car'. but rnja

spawn heavily once, then at a reduced rate 'or a long.:- period each year

(Gra.e, 1916). r:e'I.,cn (1921) stated that Ophiothrix angulata releases

all of it, or:c..te it .vire; however, the few 0. angulata that spawned in

my laboratory did not release all of their oocytes, and sections of gonads

showed oocytes of several diameters, which indicates multiple spawning

in a species that only lives 1 to 1 1/2 years. Ophiophrag s filograneus

gonad sections (Figure 17) also reveal several sizes of oocytes. Note

that the short-lived species had the longest spawning seasons. This may

be an adaptation to avoid intermittent variability, or it may simply be

a result of continual recruitment, so that some individuals are reaching

maturity at all times of year.

In conclusion, this study provides empirical evidence which supports

both recent models concerning the relationship of life history strategies

and the environment, and recent theoretical work on reproductive

strategies. The ophiuroids examined exhibit different life history

strategies, each providing them with high fitness in an unpredictably

variable environment.

1 Ophiothrix angulata is a widespread species similar to the fugitive

species described by Hutchinson (1951). It is short-lived, with high

fecundity, has a short-lived planktotrophic larva (allowing relatively

high dispersal), and is relatively intolerant of environmental fluctuations

in both adult and larval stages. The strategy of this species is to

colonize and recolonize disturbed areas after local extinction.

Ophioderma brevisoinum is long-lived, with low fecundity and moderate

dispersal via a vitellaria larva. It is tolerant of environmental

fluctuations as an adult, and the larvae are able to avoid most

fluctuations by metamorphosing quickly. The strategy of this species is

to survive in a given area through all environmental stresses. By having

a vitellaria larva, Ophioderma maintains high larval survival while

retainlr; imited dispersal bil it,', and is thus modera.ely widespread

S'ph'a mij loc ioraneu; i3 ;hor t-l ved, with moderate fe-cund lt/.

It protbablj ha3 little or no dispersal, .assuinq that it undergoe:

direct deter;al development. Its distritutional r3nqe i' small. There

is not enough Inon about adJ!it mortal it, to accuratel- define the

strategy, but it appear: that there has tern selection for high

surji' l in bot h adul t' 3nd joung, :0: th3 tihe population can maintain

itself in the face of almost any environmental stress, and therefore

need not retain dispersal mechanisms.

It is tempting to suggest that some of these species are r-selected

and others selected; however, Gadgil and Solbrig (1972) point out that

the definition of r and K selection is relative, and depends on

differences in allocation of resources, not on birth rate. Categorization

of these species into r and K selection is not necessary, as MacArthur

(1973) pointed out that this division, while fairly natural, is not the

only alternative. It would be better to say that the life history

patterns seen here are the result of selection to maximize fitness in a

variable environment, and the patterns vary with species because each

has a different genetic background upon which selection acts.


1. The life history strategies of three ophiuroids with different modes

of reproduction, all inhabiting the unpredictably variable polyhaline

estuary at Cedar Key, Florida, were studied by means of monthly collections

and laboratory experiments from May 1972 to June 1974. Ophioderma

brevispinum has a vitellaria larva, Ophiothrix angulata has a short-lived

planktotrophic pluteus, and Ophiophragmus filograneus probably has direct

demersal development.

2. The population density of Ophioderma brevispinum drops during the

colder months (September to February), and that of Ophiothrix angulata

drops in the summer when mean temperatures are above 300C. Analysis of

monthly collections shows that the older (larger) individuals in both

cases disappear from the study area, either because of death due to

temperature stresses (both species) or migration to deeper water (0.


3. Monthly collections indicate that spring recruitment of young

Ophiothrix angulata was high in 1972 and low in 1973, when unusually

low salinities occurred. The other species were unaffected by this

salinity reduction.

4. Size-frequency analyses show that Ophiothrix angulata and

Ophiophagmus filograneus are fast-growing, with constant recruitment

under favorable conditions. Ophioderma brevispinum is slower-growing,

and has a peak of recruitment in the spring and early summer.

5. Estimates of gror Cth, mortal i y and sur. i *orshlp confirm that

Ophirothrri angul at and Ophiophraomu fi lograneu: 1 ive .about 1 1 1/2

years a-di mature in less than one ,E.3r. Ophioderri.3 brv i spinum i Ve

20-25 years and matures in 2-3 ,ears.

6. Study of gonad indice.: of .aii three rpeciEs and sectioned coaries

of Ophiophragmus filograneus show that some members of the Ophiothrix

angulata and Ophiophragmus populations spawn at all times of year,

with a peak in the spring. Ophioderma brevispinum spawning peaks in

the spring, with continued low-level spawning into the summer. All

three species probably have multiple spawning by individuals.

7. Respiration measurements at temperatures between 15-30C indicate

that Ophiothrix angulata is more temperature-sensitive than the others at

higher environmental temperatures (300C). This may explain the

mortality of older individuals in the summer.

8. Ophiothrix angulata, with semelparity, a short life and a relatively

narrow environmental tolerance range in both young and adult stages,

appears to be a fugitive species, selected for high dispersal and the

ability to colonize and recolonize disturbed habitats after extinction.

9. Ophiophragmus filograneus is semelparous and short-lived with a broad

tolerance of the range of environmental conditions. It appears to be

selected for high survival of both adult and young stages through most

environmental fluctuations, and has a reduced dispersal ability.

10. Ophioderma brevispinum is long-lived and iteroparous, and seems to be

selected for survival of environmental variability as an adult, with

adaptations in the larval stage to help avoid environmental fluctuations

while retaining some degree of dispersal.


11. The life hit'.or. tri.tegies of these three ophiuroids provide

empirical evidicne ,i:ch supports theoretical predications of life

history and reproductive strategies in disturbed or variable environ-



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Stephen Edward Stancyk was born on April 8, 1946, in Denver,

Colorado. In 1954, he moved to Lakewood, Colorado, and was graduated

from Lakewood High School in 1964. He entered the University of

Colorado at Boulder in 1964, and was graduated with a Bachelor of Arts,

majoring in biology, in June 1968. In September 1958, he began studies

toward the Master of Science degree in zoology at the University of

Florida, and was awarded that degree in December 1970. He has since

been working toward the degree of Doctor of Philosophy, also at the

University of Florida. From January 1969, through August 1973, he

worked as a graduate assistant in the Department of Zoology, and from

September 1973 to June 1974, as a half-time instructor in the Division

of Biological Sciences.

Mr. Stancyk is a member of the Phi Sigma Society, the Society of

Sigma Xi, the Ecological Society of America, and the American Society

of Zoologists.

I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.

rFanT J. S. Ma oro, Jr., chairman
Professor of ology

I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.


Jofn W. Brookbank
Professor of Zoology

I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.

Thortas C. Enmmel
Associate Professor of Zoology

I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.

Ariel E. Lugo
Assistant Professor of Botany

This dissertation was submitted to the Graduate Faculty of the Depart-
ment of Zoology in the College of Arts and Sciences and to the Graduate
Council, and was accepted as partial fulfillment of the requirements
for the degree of Doctor of Philosophy.

August, 1974

Dean, Graduate School

8 t

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