Interactions Among Organisms:
Life Along the Shore
Communities that live on shorelines are affected by plant productivity, which in turn is affected by salinity and temperature conditions, as are all marine communities. Interactions among plants and animals along the shore result in zones, stripes, and patches of organisms that are obvious even to a casual observer.
On most rocky intertidal shores, four fairly well defined zones of organisms can be found. Isopods, limpets and littorine snails inhabit the uppermost zone; below them we find shore crabs, Fucus (a brown algae), barnacles and other limpet species. Lower still, we find mussels, goose barnacles, chitons and predatory snails. The lowest zone, exposed only rarely by the lowest tides, may consist mainly of seaweeds, sponges, sea slugs, anemones, and other creatures. Generally speaking, the organisms of the lower most belts are least resistant to exposure to air, sunlight and rain, whereas those in the uppermost zones are most resistant to exposure.
Many physical factors can blur the boundaries of the organisms in intertidal zones. As a result the zones can be shifted higher or lower on the shore, or be broadened or narrowed. Where exposed rocks are washed by surf, intertidal organisms range higher onto the shore than in sheltered areas nearby. Algae can survive at higher elevations on the shaded north sides of boulders than on sunny south sides. Nevertheless, the belts of organisms living together are often very sharply defined.
The boundaries of these zones are caused by both environmental and biological factors. The organisms of intertidal zones, as all other organisms, must find a suitable habitat to live. This habitat, or niche, must have both the correct environmental conditions (sunlight, water, air) as well as a reasonable level of competition between the other species of organisms that inhabit the same area. Every organism living in the intertidal zone has managed to find suitable living conditions.
Comprehension Questions:
Answer the following questions in complete sentences.
1. What two things affect plant productivity?
2. What is the result when plants and animals interact along the shore?
3. There are _____ fairly well defined zones of organisms that can be found in intertidal zones.
4. Name two organisms that inhabit the uppermost zone.
5. Name two organisms that inhabit the second uppermost zone.
6. Name two organisms that inhabit the second lowest zone.
7. Name two organisms that inhabit the lowermost zone.
8. What three factors are organisms of the lower most belts least resistant to?
9. Name the two physical factors that can blur the boundaries of the organisms in intertidal zones.
10. Explain the statement: A niche must have both the correct environmental and biological conditions.