Factors affecting the distribution of the amphipod Corophium volutator in two estuaries in South-east England

The distribution of Corophium 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 volutator were 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 of C. volutator and the median particle size of the sediment nor the mud content. There was a significant but weak negative correlation between the abundance of C. volutator and the polychaete Nereis diversicolor. The aggregation of C. volutator in 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 hats, displacement of swimming amphipods by the flood tide further upstream and into semi-enclosed areas would occur. Their dispersal behaviour places C. volutator in 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. (C) 1997 Academic Press Limited.