SEASONAL-VARIATION IN ABUNDANCE AND DIET OF THE SAND GOBY POMATOSCHISTUS-MINUTUS (PALLAS) IN A NORTHERN BALTIC ARCHIPELAGO

In shallow, soft-bottom benthic communities meiofauna is as important as macrofauna, with regard to both biomass and production. Shallow bottoms are also important as feeding habitats for the sand goby Pomatoschistus minutus and meiofauna accounts for a considerable part of their diet. Population dynamics, diet and potential predation effect on the infauna by P. minutus were studied in a shallow (1-1.5 m) sandy area in the northwestern part of Aland, northern Baltic Sea (May-October, 1989). The predation efficiency of the fish was studied in aquaria with Ostracoda, Corophium volutator, Neomysis integer and Macoma balthica as prey. The abundance of P minutus resembled that of other areas in the Baltic and neighbouring seas. The lowest density was found in October (0.5 ind/m2), while the highest abundance (11.2 ind/M2) was recorded in September. The diet of P. minutus varied seasonally and with increasing fish size. Small individuals (< 40 mm) consumed mainly meiofauna, while larger fish (> 40 mm) ate mostly macrofauna. The experiments showed that P. minutus is an effective predator on both meio- and macrofauna, since all prey populations were significantly reduced in the fish treatment.