Marine Biology (2+1)

5.Salinity

Salinity

Since most of the organisms in the intertidal sandy shore live beneath the sand surface, salinity of the interstitial water is a very important factor. Salinity of the interstitial water usually approximates to that of the sea, except at the surface layers where the values may be high, owing to evaporation, or low as a result of freshwater influence. Further, the water held in the interstices is a salt water which has a higher density than freshwater flowing on the surface or percolated through the sand. It is observed that even when a stream of freshwater passed over the surface of the intertidal sand, there would be a little effect on the salinity of the interstitial water at a depth of 25-30 cm, where it approaches the seawater. In this case, the animals living near the surface will have to burrow themselves to deeper levels to escape the adverse effects of lowered salinity. Many sandy shore organisms like the burrowing prawn Callianasa and Upogebia, which have only very narrow salinity tolerance (stenohaline), resort to this method.