E.T. A LOCAL WAY OF LEARNING
Title: ROCKY SHORE ECOSYSTEM
Author: Jane Ducey
Eulalie R. Rivera Elementary School
Grade Level: 4-12
1. Energy 1. Social Studies
2. Ecosystem 2. Science
3. Carrying Capacity 3. Language Arts
4. Clean Water 4. Art
7. Land Use
8. Values and Attitudes
Student shall identify the zonation of the beach and tell which animals and
plants are found where and why. Student shall explain the adaptations that have
taken place to enable the organism to live where it does. Student shall become
familiar with the transectt" technique.
The carbonate beach rock exposed in the intertidal zone may either be abrupt or
be interspersed with sandy mini beaches, providing nooks in which plants and
animals are found. This is also the place where tide pools are common. There
is a zonation where you may expect to find particular animals and plants.
Microscopic algae serves as food for many animals whose "mouth" is on the
bottom. For others the ever renewing splash of water brings new source of food
with each wave: they have "mouths" on the top. Most are anchored securely
against the wave action. Most have great tolerance for extremes of salinity and
temperature--if it rains-a tide pool is almost fresh water--if the wave action
is low the pool dries up and salinity and temperature go way up. Butwatch your
step, those black tar balls are still soft. .
Sneakers to walk in water for foot protection, sketch pad and pencil.
In class preparation:
Introduce as many casts of crabs and dead shells of other animals you expect to
find. See movies, look at books of rocky shore and intertidal plants and
animals. Note that some "exoskeleton" animals (crab, lobster) must cast their
hard outer covering to grow, whereas other shells (snail, conch, clam) grow an
additional section of their shell when they become crowded in the present one.
Note the hermit crab, who has no shell on his own posterior and must drag around
the dead shell of another, usually a West Indian top shell, to protect his soft
"tail". This requires a regular search for a slightly larger shell as the
ROCKY SHORE ECOSYSTEM
Activities at the site:
Note the color change from black, at the top of the rock (blue-green algae) to
pink at the water's edge. On the high rocks and on grass and weeds are the
beaded periwinkles (Tectarius muricatus). This is a marine snail which shows
extreme adaptation. On the high beach during a dry season the animal pulls
himself deep in his shell to preserve moisture, seals off his door operculumm)
and also seals his shell rim to the rocky substrate. It has been shown to be
able to live for 18 months in this dried up state and still revive when put into
1. Mark a shell with a dot of red finger nail polish, draw a ring on the rock
around the snail with the same polish. Come back, days, weeks, later and see
how much the snail moved. (Check him out a year later). The snail stays within a
radius of a few feet. Pour some water on a patch of snails and watch for a
while. (Almost immediately they begin to move a little).
2. What does the periwinkle eat? Scrape some of the "black" (blue-green algae)
off the rock, wet it, and look at it under a microscope. (Looks like a golf
3. How does the snail reproduce? (Lays eggs at the water's edge so the surge can
take the hatchlinqs (Veligers) into the sea (plankton). This is probably the
longest trip Tectarius makes from the high beach.
4. Make an estimate of the number of snails (probably the greatest resident of
the rocky shore in numbers). This is done by making a transect. Pull a line,
as perpendicular to the shore as you can, from the high beach to the water's
edge. Using a square measure (a stiff wire bent to close a square) of known
size--foot, quarter meter--flip it over and over down the beach and count the
snails in every fifth (or another interval, depending upon the width of the
beach) square. Multiply the total by the number of squares in all.
Example: If you counted five squares and there were 25 in all, you will multiply
the total number of snails counted by five to estimate the whole strip. Don't
overlook all the immature snails stuck tightly underneath the rocky outcrops.
5. Closer to the water line you find a pointed shell with zigzag lines
(Littorina ziczac). At the splash line another snail, the nerite or tooth shell
is found. N. peloronta has a red mark (bleeding tooth) the other two do not.
These snails are edible if you have the patience.
6. Just below the water line is the West Indian top shell of "wilk" (Cittarium
pica) and is of a size such that a few make a worthwhile meal. The above are
7. At the high water mark you will find a meat eater, Purpera patula. If
prodded the animal will excrete a smelly white substance which stains skin
purple. Put the Purpera in a pool with other snails and watch them leave.
8. Find some limpets and some keyhole limpets--why do you think they are so
named? Also at the splash zone you will see an animal not changed since the
beginning of time. It is the chiton and there are three, depending upon the
kind of girdle it has. The animal looks like it's stuck in a rock hollow
forever. It has eight separate plates in its shell. Don't paint it with
polish--it has pores on the top of its shell.
9. Look for casts of crabs (Grapsus grapsus) with their claws still gripped to
the rock to pull themselves out. Those short-spined sea eggs are rock boring,
red or black, urchins (Echinometra lucunter) and they dig the hole they are
sitting in. Barnacles may be feeding if the water is surging over them.
They whip out their feeding "plumes" to catch whatever is in the water.
10. Slightly lower on the beach you will find two other urchins, the white one
you can safely pick up (Tripneustes) and the long spined black one (Diadema)
Note the weed and shell bits the white one has stuck on his shell: how does it
do this? (Has tube feet between the spines). Pick it up and hold it at the
water level. Feel the tube feet with the suction cups hold on to you-in this
way the animal avoids being swept by the surf.
The five zones are the surf zone, pink zone, green zone, yellow zone and the
black zone, according to Lewis. From land to sea, below the black zone and
still above the high water mark is the yellow zone which has a thick film of
algae. It is here that the nerites are found. The green zone is covered by
coralline algae and is smooth--here you will find Purpera. The pink zone
extends between the mean low water mark and the mean high water mark (area of
the wilks). The pink is also an encrustation of coralline algae. In the surf
zone are the algae Halimeda, Dictyota, Padina, Laurencia, Turbinaria and
STa ain ass5rS
Tide pools have a changing community as the big waves bring new fish or give
access for others to return to the sea. Tiny hermits scurry around. Frequently
an octopus gets carried into the pool by a big surge of water. Observina his
color change (chromatophores) you can see how good they are at camouflaging
themselves. Also observe the use of appendages curled up to 'walk' and the
precise timing to catch the next big wave to get back into the sea.
Guidebook to the Geology and Ecology of St. Croix
H. Gray Multer and-Lee C. Gerhard
West Indies Laboratory