Shoaling of sergestid shrimp Acetes johni (Crustacea Decapoda: Sergestidae) associated with swarming of gammarid amphipods

Abstract

Aggregation of sergestid shrimp Acetes johni and gammarid amphipods was observed at a station (22 degrees 07'N; 67 degrees 03'E) in the northern Arabian Sea during September 1991. Shoaling occurred in the surface layer at night resulting in high zooplankton standing stock (5.81 ml.m/3). The sergestid shrimps and gammarid amphipods formed 94.7% of the zooplankton population, the former constituting more than half of the biomass of the sample. Their numerical abundance decreased with depth. The adaptive significance of swarming behaviour in marine plankton is briefly discussed