Microalgal food of the ribbed mussel Aulacomya atra (Molina, 1782) in Golfo Nuevo (Patagonia, Argentina)

Stomach contents of the ribbed mussel Aulacomya atra and phytoplankton samples from the west coast of Golfo Nuevo (Chubut Province, Argentina) were analyzed monthly between August 1997 and December 1998. Twenty-five taxa of microalgae ranging from 9 to 231 mu m in size were found in stomach contents along with other miscellaneous items. A marked seasonal variation of microalgal food was not observed in Aulacomya atra. Diatoms such as Paralia sulcata and Thalassiosira sp. were observed year round. Variation in the benthic to total species ratio revealed that during most of the year benthic and pelagic microalgae contributed equally to the diet of the ribbed mussel. In contrast, during dinoflagellate blooms, as occurred during late spring and summer, dinoflagellate cells dominated the ribbed mussel stomach contents. This finding is of special importance in relation to the recurrent blooms of the PSP causative agent, Alexandrium tamarense, in the Golfo Nuevo.