Adaptations of Animals in Rocky Shores

Adaptations to resist wave action The crashing wave action against the rocks is an important factor limiting the variety of organisms on rocky shores. Because organisms would either swept away or broken apart by the pounding waves.

Bivalves, barnacles, sponges and mussels Secrete a kind of cement or posses byssus(a tuff of strong filaments) for attachment on the substratum.

Barnacles and chitons

Limpets, chitons and periwinkles posses a suctorial foot for attachment by suction.

Crabs are generally flattened in shape and have powerful legs for gripping the rocks. They seeks shelters from the waves in rock crevices or under rocks.

Sea slaters can run very fast to avoid the waves and splashes.

Adaptations to withstand desiccation at low tides Organisms in the littoral zone are exposed to the air and direct sunshine twice a day at low tides. Exposed organisms face the risks of dehydration.

Most sedentary animals enclosing themselves in the shells and trapping a small amount of water within the shell. The shells are impermeable and thus reduce water loss by evaporation.

Mobile animals such as crabs hide in the rock crevices or simply move into rock pools. Sea urchins, sea anemous and sponges grow in rock pools where they are submerged in water even at low tides. Sea anemones also aggregate to from a mass of individuals to reduce water loss.

Adaptation for gas exchange Most animals inhabiting the littoral zone are marine in nature. Their respiratory surfaces or gills are very susceptible to desiccation in air. Intertidal organisms tend to enclose their respiratory organs in a protective cavity to prevent them from drying out.

Rocky oysters, chitons and limpets, which have gills in the mantle cavity (a space inside body), are kept moist and protected by the shells. Gas exchange usually only occurs in the presence of water. Small amount of water is often trapped so the gas exchange still occur in low tides.

Gastropods have great difficulties in keeping the gills moist. They are adapted by reduction of the gills and modification of the mantle cavity as a lung for aerial respiration.

Adaptations to salinity Rocky shores may be flooded by fresh water. This creates stress to organisms that are only adapted to the marine enviroment.

The only adaptation reported in barnacles and molluscs is to closed up their valves opercular.

Most of them show no mechanism to tolerate salinity changes. This explains the occasional reports about sudden mortality of intertidal organisms after heavy rain.

Adaptations for feeding Mussels and barnacles are filter-feeder. They obtain food by filtering minute food particles suspended in water.

Chitons, limpets and gastropods possess a radula(a strip of membrane with longtiudinal rows or teeth)for browsing the algae on rock surfaces. These intertidal animals have to expose their bodies when they feed. To avoid disciccation,most of themfeed only during high tides when they are submerged

Crabs and sea slaters feed at low tides. They are detrtivores which can feed on any food washed in by the tides.

Adaptation for reproduction Most of the littoral organisms are sedentary and depend on water for dispersal of eggs or larvae. They usually produce a large amount of gamates in sheltered places or attached to seaweeds.

This prevent the gametes from being wash away by tides and waves. Their breeding cycles are usually synchronized with the occurrence of spring tides. The spring tides cover a large area of the shore and this increases the chance of fertilization.

For the crabs, they carry the eggs on the abdomen until the early stage of egg development is completed. This increase the survivorship of the larve.