Marine Biology

Place of collection

The animals and plants on the seashore are not distributed haphazardly; each kind occupies a well-defined zone. What we find on seashore will depend not only on the state of the tide but also on the type of shore. Seashores can be roughly classified rocky, shingle, muddy and sandy.

Shingle or pebble beaches are covered by smooth rounded stones. These cannot retain water between them and waves constantly roll them about so that life cannot settle on them and shingle beaches are therefore barren and not worth any attention.  

Sandy beaches are exposed to surf (waves), these waves like the upper layers of sand in a cloud of abrasive particles. This scouring action is harmful to life and only those which can take refuge by burrowing can survive. A sandy beach therefore looks apparently barren until one starts digging. We can then find typical sand dwelling animals like the ghost crab (Ocypode), mole crab (Emerita), cockle (Cariata), razor shell (Solen) and wedge clam (Donax) among others.

Mud consists of very fine particles, which can accumulate only where there is restricted wave action. The fine size of mud particles enables easy burrowing and also prevents drying up of mud even at the surface. Typical mud dwellers are the sea anemones (Para condylacten), tapertry clam (Paphia), lug worm (Arenicola) etc.

Rocky shores may be either in the form of steep cliffs running down into the sea or extensive flat slopes with many fissures and crevices. There we may also include man-made stones or concrete structure as such as marinas and wharf piles for example. In contrast to mud flats and sandy beaches where  animals  can easily burrowe, rocky shores which are exposed to strong wave action can provide shelter only to animals or plants which can cling to the rocky surface. Typical rock dwellers are the Acorn barnacles (Balanus), Periwinkle (Littornia), Oyster (Ostrea), Mussel (Perna), hydroides (Obelia), bryozoans (Membranipora), rock sea anemones and sea weeds such as Ulva, Entermorpha, Padina and so on.

On the  rocky shores, we have the limpet (Cellana), the sea hare (Aplysia), many gastropod snails and most types of sea weeds. A large variety of life forms are unable to tolerate  desiccation like fishes, octopi and sea slugs are found in rocky pools, which retain some water even at ebb tide.

Although we have classified the seashores into rocky, sandy and muddy, we may also have mixed shores, having two or all three components. Then a sandy beach open into mud flats at a lower level and also have rounded stones or boulders on it. Such places provided ideal collecting sites as they have all the three components of the seashore.

At some places in India for example in the Gulf of Kutch (Port Okha, Pirotan island), south eastern coast near Rameswaram, Lakshadweep islands and Andman & Nicobar islands, we have extensive coral reefs...

Marshes occurring in patches in many of our creeks and estuaries and in vast areas like Sunderbans of Bengal, are typically inhabited by mangroves – terrestrial trees which have secondarily invaded the sea, very successfully.