The Rocky Coast Ecosystem

Along Maine's rocky shore, conditions change from hour to hour, day to day, and season to season. Tides rise and fall twice a day, alternately submerging and exposing many intertidal species of organisms. High energy waves break on shore, leaving these organisms to face the full force of these waves. Short summers give way to long stormy, winters that bring with them very cold temperatures.

The rocky shore is divided into several clearly marked zones.

These zones are determined by the tides:

• How long the zone is exposed at low tide and how far thetidal range extends.
• How the organisms are distributed through these zones is based on an individual organism's ability to withstand exposure to air and extreme temperatures.

Because of these changeable, often harsh conditions and the keen competiton for space, only a relatively few species can withstand this environment.

Those that can, however, are typically very abundant. A few of them, such as lichens, algae, and snails, are found in the highest zone, the splash zone, the area above the high tide mark that receives only spray from the pounding waves. These are hardy species that have minimal moisture requirements.

When the tides goes out, organisms that live in the intertidal zone are exposed and risk drying out or overheating. These organisms have evolved strategies to avoid desiccation crabs crawl into damp crevices, mussels clamp their shells shut, and limpets retreat into rock depressions they carve to fit their shells exactly. Then, when the tide comes in, these organisms face the full force of waves crashing on the rocky shore. To avoid being washed away, some seaweeds attach to rocks with thread-like holdfasts, and mussels temporarily anchor themselves to rocks with a strong web of threads.

The subtidal zone, the lowest zone, remains partially submerged at low tide. The organisms in this zone don't have to deal with desiccation like the intertidal organisms do, but they do have to contend with temperature fluctuations and increased crowding in these shallow waters.

Mudflats form close to shore where fine sediments accumulate an ideal habitat for burrowing animals. Most mudflat inhabitants feed on dead organisms and animal wastes carried in with waves, tides, and currents. When mudflat animals and microbes such as bacteria eat wastes, they release nutrients and carbon dioxide. Plants use these byproducts to produce food and oxygen that animals, in turn, consume.