Unusual mass shoreward movement of bivalve (Mollusca) Donax scortum Linnaeus along the coastal waters off Calicut - South Eastern Arabian Sea

Abstract

Eutrophication and oxygen depletion are the major factors influencing the responses of benthic organisms in coastal ecosystems. Along the coastal waters of South Eastern Arabian Sea a mass shoreward movement of bivalve Donax scortum (locally referred as “eranthu”) occurred during end phase of summer monsoon upwelling. Possible reasons for this shoreward movement points to the low dissolved oxygen (0.25 ml L^-1) in the bottom waters. Intense blooms of large dinoflagellate species, Noctiluca scintillans were observed a week prior to this event along these coastal waters and the crashing related decaying might have resulted in lower DO values in the region. The study discuss on the deleterious effects of hypoxic conditions caused by summer monsoon algal blooms on benthic fauna of South Eastern Arabian Sea.