Sandy Beach Ecosystem

The open coast sandy beach is an ideal area for a study of intertidal zonation. Between the subtidal ocean and the dry land there exists a gradient of environmental conditions. Some important factors include:

a. amount of time area is flooded or exposed.

b. moisture content of sand

c. wave action.

d. coarseness of sand.

e. steepness of beach.

f. temperature.

g. kelp or other seaweed/seagrass detritus.

Make field notes on these conditions during your study. The main data we are collecting are the numbers of animals at different heights of the beach. This will allow us to examine zonation in the sandy beach environment.

One of the advantages of this habitat for research is the paucity of species which live in this environment. Low diversity simplifies our task greatly. We will be recording six types of animals: beach hoppers (Orchestoidea spp.), sand or mole crabs (Emerita), isopods (Excirolana), the bean clam (Donax), bloodworms (Euzonus), and other polychaete worms such as Nephthys.

Beach hoppers burrow during the day and emerge at night to feed on kelp and other detritus. They fight among themselves for food and burrows and are extremely active-- counting them is like counting popcorn as it pops! Much smaller fragments of detritus, called Particulate Organic Matter (POM), and bacteria feeding on Dissolved Organic Matter (DOM) from decaying kelp coat the sand grains. This is the food of the bloodworms who feed like earthworms; moving sand through their guts and digesting away the goodies. They are deep red in color due to hemoglobin in their blood. This pigment allows them to store oxygen and tolerate periods of poor gas exchange during low tide. The bloodworms, in turn, are feed upon by other polychaetes such as the greenish Nephthys. These voracious predators can swim through wet sand. Donax is a suspension or filter feeder. Populations of this clam vary greatly from year to year. Look closely at the shell; often there is a commensal hydroid growing on it. The sand crabs are also filter feeders, straining plankton from the water with their feathery antennae. They burrow into the sand with just the antennae out, facing the surf. (Drop one and watch how fast it digs.) Emerita prefer greater wave action than Euzonus and often is not found on the same beach. Isopods feed on dead sand crabs and sand crab eggs as well as other animal detritus. All of these animals are eaten by shorebirds. But we don't collect shorebird data because they aren't cooperative. Watch for their tracks in the sand.

Sandy beach report

You may get help from a tutor in Guthrie Hall. Use the format for scientific papers but make sure you cover the following issues. Include the following features. Do not answer these questions like a question set 1 through 5. Restructure the material into the format of a scientific paper. Review that format:

I) Introduction: background material & hypotheses. I want a hypothesis for each species.

II) Material & Methods (enough to copy the study)

III) Results :data & observations

IV) Discussion: What’s it mean? What would you like to tell the reader about your study and what should be done next to clarify remaining questions or problems?

V) Conclusion: In a nutshell

1. Diagram a food web of this sandy beach community. (See your lecture text book if you need help with food webs, but don't copy.)

2. Create a set of hypotheses about the likely patterns of vertical distribution of each of these six species in the intertidal. Use the information I've provided. What effect might the removal of kelp from beaches for cosmetic purposes have on beach ecology?

3. Once you have your section's data calculate mean number of individuals of each species by quadrate number. Why do we average by quadrates and NOT by transects? Create a table of these data.

4. Graph your results. Get semi-log graph paper from me or use a computer. By scaling the data in orders of magnitude: 0.1-1, 1-10. 10-100, 100-1000 you can record large differences and subtle differences on the same graph. If you don’t understand semi-log get help from me or someone else, for example a math tutor, rather than guess. LABLE the axes.

5. What patterns of distribution do you notice? Do the observed patterns match your hypotheses? What are some of the surprises (discoveries)?

NOTE: Hypotheses (question 2) should be created BEFORE the study is done. If you didn't do that--then try to construct them without considering what you actually observed in the field. Remember it's OK to be wrong--as long as it makes sense.