Feeding reduction, reproductive failure, and mortality in Mytilus edulis during the 1985 'brown tide' in Narragansett Bay, Rhode Island

Abstract

During summer 1985, reduced feeding, reproductive failure and massive mortalities were observed in populations of the blue mussel Mytilus edulis during an extremely dense algal bloom in Narragansett Bay, Rhode Island (USA). Effects of the alga on clearance rates of mussels were tested using natural particulates (NBP) collected from Narragansett Bay during the bloom. Reductions in clearance rate were independent of cell size and extra-cellular exudates of the bloom alga. Experiments repeated with the hard shell clam Mercenaria mercenaria produced similar clearance rate responses. In Narragansett Bay, NBP densities increased from 9 x 10 super(5) cells/ml at seaward stations to above 15 x 10 super(5) cells/ml in the upper bay. High mortality in indigenous mussels was coincident with peak bloom conditions. It is concluded that starvation stress induced by noxious properties of the bloom alga in combination with seasonal effects (reproductive stage, temperature) was the cause of the demise of M. edulis).