Factors Affecting the Distribution of the AmphipodCorophium volutatorin Two Estuaries in South-east England

The distribution ofCorophium volutator(Pallas) in the estuaries of the Rivers Blackwater and Crouch in South-east England was examined by taking samples of mud from 137 sites at approximately 0•5 m below mean high water of neap tidal level.Corophium volutatorwere approximately twice as abundant in creeks and semi-enclosed bays than on the open mud flats, a difference that was significant statistically. There was no correlation between the abundance ofC. volutatorand the median particle size of the sediment nor the mud content. There was a significant but weak negative correlation between the abundance ofC. volutatorand the polychaeteNereis diversicolor. The aggregation ofC. volutatorin the creeks and bays was attributed to their dispersal behaviour of swimming on the flood tide, which would sweep the amphipods into such areas where the tide rises but does not flow laterally. On the open mud flats, displacement of swimming amphipods by the flood tide further upstream and into semi-enclosed areas would occur. Their dispersal behaviour placesC. volutatorin the creeks and bays within the saltmarsh vegetation, where their bioturbatory feeding habits may be responsible, in part, for the significant loss of pioneer zone vegetation that occurs there.