Predation on newly settled bivalves by deposit-feeding amphipods: a Baltic Sea case study

In the Baltic Sea, predation on postlarvae of the infaunal clam Macoma balthica by adults of the 2 most abundant deposit-feeding amphipods, Monoporeia affinis and Pontoporeia femorata, has been considered to be a crucial factor in determining the bivalve's recruitment success. The functional response of adult M. affinis to postlarvae of the bivalve was shown in laboratory experiments to be type III-like, with no levelling off of the number of prey consumed per predator within the postlarval densities tested. Densities included were higher than the highest reported from habitats where both species occur together. In laboratory experiments, adults of P. femorata were also shown to kill M. balthica postlarvae. In neither amphipod species did adults select among sizes of newly settled M. balthica. Juvenile M, affinis were likewise found to kill M. balthica postlarvae. Our results, and a recent field study, confirm the effect of the amphipods on M. balthica postlarvae and their role in controlling bivalve recruitment in Baltic soft sediments. They also support the idea that interactions among juveniles of macrofauna may affect the recruitment success of many benthic species and therefore be important in structuring benthic communities.