Distribution of the Organisms in the aquatic Habitat and their Adaptive Features

1. Splash zone/Shore organisms: On rocky shores, periwinkles and shore slaters are found in the area that water splashes when waves break (also called splash zone). Barnacles, oysters, mussels and limpets are found on the intertidal zone of the rocks. Anemones, sponges and seaweeds are found on sheltered parts of rocks. Sea urchins, sea cucumbers and seaweeds are found in rock crevices. Most of these organisms have adhesive structures so as to be able to withstand wave and tide action.

Examples:

(i) Sargassum (a seaweed) is attached to rocks by holdfasts. see below

(ii) Barnacles are cemented to the rocks

(iii) Limpets have feet with which they hold unto rocks.

Sandy shore organisms include starfish, ghost crabs, bivalves and annelids. Their major adaptation is to burrow into the sand so as to escape being washed away by waves and tides.

(i) The shell of the starfish prevents it from drying up and it has tube feet which enable it to hold onto rocks.

(ii) Periwinkles have lungs to breath and foot for attachment.

(iii) The ghost crab has gills for breathing in water and a spongy structure for breathing on land.

(iv) Crabs can burrow into the mud quickly to protect themselves against predators, strong waves and tides.

2. Intertidal organisms: These include bivalves, mollusks, barnacles, anemones, worms, etc. These organisms face the challenge of exposure and drying out. To overcome this;

(i) Barnacles, mollusks and worms on rocky areas withdraw into their shells or tubes which hold some water.

(ii) Bivalves have special feet for digging into the sand or mud.

3. Sub-tidal organisms:These include lobsters, crayfish and fishes like the sting ray and sole.
   lobsters

The sting ray’s body is flattened from top to bottom and so it lives on the sea floor. The sole is also flat, it lies on its lower side and has both eyes on the upper side. These fishes lie buried in the sandy sea floor and hunt for small animals there.

The lobsters and crayfish have claws for seizing prey.

4. Benthic organisms:These are mainly consumers and decomposers. Fishes that live in the deep sea are adapted to live under conditions of great pressure. Some have expandable mouths and stomachs for swallowing large prey. Most live on dead remains of organisms from surface waters above.
   

The open waters support planktons and nektons.

Planktons are microscopic organisms which float, drift or swim slowly on the surface waters. They include producers like diatoms and seaweeds and consumers such as protozoa,  copepods, worms, larvae and mollusks. Adaptations of planktons that help them stay afloat include; oil globules inside the body; gas-filled external floats and bubble rafts; external spines and hair which (provide friction and prevent sinking).

Nektons are actively swimming animals e.g. fishes, whales, prawns and squids. Adaptive features of fishes include;

(i) a streamlined muscular body coupled with fins which help them move swiftly in water.

(ii) bony fishes have gas-filled swim bladders which help them to move to different depths in water.

(iii) Sharks and dogfish have the ability to retain urea in their body to cope with high salinity.

(iv) The herring take in salt water to maintain osmotic balance between their tissue fluids and the salt water.

(v) Some bony fishes possess salt secreting glands in their gills for osmoregulation.