The following is an outline for a field lesson that aims to explore the interesting habitat of floating docks and wharf pilings. (Go here for a scanned copy of the handout provided for the 2000 MIZ class field lesson, including discussion questions and a species list).
1. Begin by simply having your group explore the habitat by pulling up the tires. (Or if the dock is not floating, be sure to visit it when the organisms are exposed.)
2. After introducing the group to the exciting but bewildering assortment of living things on the dock, have them discuss the environmental parameters of the habitat (e.g. temperature, salinity, desiccation/tidal changes, wave forces and direction) and how these may differ from other habitats. Discuss which parameters may vary within the habitat and how/why.
3. To more clearly illustrate how differences in physical parameters may affect tire communities, have teams of two or three people survey a few tires on two sides of the dock with different hydrodynamic conditions. Pick a handful of target species that show clear differences between the two sides, and have the teams make counts of these species on the tires they survey. Teams that focus on different target organisms can report back to the group, and in this way the group will be exposed to patterns in distribution without being overwhelmed by the diversity of the communities. We found obvious differences in the abundance of several species that were relatively easy to identify and count. The outside tires harbored significantly more limpets, mussels, and large barnacles. The inside tires had a greater abundance of Metridium anemones, Chelyosoma tunicates, and Serpulid worms.
4. Ask the group to think about the different lifestyles of the float inhabitants: modes of locomotion, feeding, reproduction and how the organisms protect themselves in the environment. Discuss any patterns of organism distribution on the substrate. Are certain animals clustered at certain levels (depths) along the floats? What evidence is there of animal interactions within the habitat, such as space competition or commensalism?
5. We suggest conducting simple exercises in the field, such as temperature recordings and the Life Saver dissolution experiment, to better understand the variations in environmental parameters within your habitat and how they relate to the organism distribution patterns you have observed.
A few additional suggestions:
* Expect surprises. Given the diversity of organisms that typically inhabit floating docks, one can't expect to be able to identify everything. Bring a local field guidebook to aid in identifications and to provide additional information about the natural history of the organisms you discover. An excellent field guide for the Pacific Northwest is Eugene N. Kozloff's, Seashore Life of the Northern Pacific Coast, published by the University of Washington Press.
* Be careful to leave the habitat as undisturbed as possible. Do not unnecessarily remove organisms (particularly sessile animals.) Resubmerge the substrate/animals as soon as you are finished looking at them. Many of the organisms (such as sponges) will not survive if exposed to air for too long.