Advantages To Living In Intertidal Zones

There are a number of advantages to living in a tide pool ecosystem.

• Algae and other intertidal plants grow in the abundant sunlight and support an entire food chain of animals.
• Constant wave action supplies the tide pool with nutrients and oxygen.
• Food is abundant.
• A varied substrate provides hiding places and surfaces to cling to.

Challenges To Living In The Intertidal Zone

The rapidly changing conditions of a tide pool make survival a challenge. Exposure to surf and sun varies considerably.

• Plentiful sunlight, which helps intertidal plant life grow quickly, can also rapidly dry up precious moisture and increase the water temperature.
• Waves that bring in much-needed nutrients and moisture can also carry unprotected animals out to sea.
• As the tides rise and fall, the salinity (salt concentration) constantly changes. Animals living in the intertidal zone must be able to tolerate wide salinity variations.
• If sufficient nutrients are available, intertidal animals reproduce rapidly, so they constantly compete for space, light, and food.
• Animals are also exposed to predators while the tide is out.

Adaptations To The Variable Environment

Small animals that live in the splash zone can avoid desiccation by closing their shells tightly to seal in moisture.

Some animals, like crabs and marine snails and bivalves, have thick, tough outer coverings to slow evaporation. Others, such as mussels and leaf barnacles, cluster together to reduce individual exposure.

One main problem intertidal animals face is the constant pounding of waves. These animals have developed different adaptations to keep from being washed away. Some, like sea stars, cling fast to the rocky surfaces; others find shelter in crevices or hide under thick mats of seaweed when the tide is out.

Most intertidal life centers in the low intertidal level, which normally remains under water. Most of these inhabitants can only tolerate exposure to air for short periods. It is here and in the subtidal zone (below the intertidal) that marine plants provide fish and invertebrates with protective cover and food.

Animal Adaptations To Intertidal Life

Tide pool animals and plants are well adapted to the intertidal zones. Some adaptations include:

• The ochre sea star can tolerate a longer time period exposed to air than many other sea stars. They regularly withstand up to eight hours of exposure during low tides. In laboratory conditions, they have tolerated up to 50 hours out of the water with little harm. Yet, they are not found in high intertidal pools due to their lack of ability to withstand high water temperatures or low oxygen levels.
• Some abalones, limpets, and turban snails can smell approaching ochre stars and will move away to avoid being eaten.
• Sea cucumbers have few known predators, other than humans and sea stars. If disturbed, some species may eviscerate (expel their entrails), leaving the entrails to the predator while the sea cucumber escapes. Its organs will regenerate after several days.
• When the tide is out, periwinkle snails cluster in crevices, secrete a gluelike mucus to stick to the rock's surface, and withdraw into their shells to avoid drying out.
• Many fishes that inhabit tide pools, such as tide pool sculpin and young opaleyes, can breathe air at the surface—an adaptation that enables them to survive in oxygen poor water when the tide is out.

Tide Pool Food Chains

A food chain is a diagram showing "who eats what" in an ecosystem. A single tide pool contains many food chains. Algae and other plants are eaten by plant-eating zooplankton; this plankton is eaten by larger, carnivorous plankton; these are eaten by a mussel, barnacle or other marine invertebrate; the mussel is then eaten by an ochre star, which may be eaten by a gull or a sea otter.

All the food chains in an ecosystem can be interconnected to form a food web, a complex diagram showing all the interconnecting predator-prey relationships in an ecosystem.

Many marine animals rely on tide pools for food and other resources. Gulls and other seabirds, as well as some mammals, forage in tide pools. Tide pools even serve as "nurseries" for some fish species.