Population dynamics of estuarine amphipods in Cochin backwaters

Abstract

Population dynamics of 11 gammarid amphipod species (belonging to 9 genera), collected from Cochin backwaters, have been studied for the first time, based on an year round collection. The species are : Corophium triaenonyx Stebbing, Photis digitata Barnard, Grandidierella gilesi Chilton, Melita zeylanica Stebbing, Eriopisa chikensis (Chilton), Quadrivisio bengalensis Stebbing, Grandidierella bonnieri Stebbing, Cheiriphotis megacheles Walker, Ampelisca zamboangae Stebbing, Perioculodes longimanus (Bate and Westwood) and Ampelisca cyclops Walker. The highly varying salinities (0 to 36.20 ppt S) are one of the major limiting factors which govern the numerical density and species diversity of these gammarid populations. Except for the 3 high saline species A. Zamboangae, A. cyclops and P. longimanus, which are recorded during late January, all other species contribute substantially to the ecosystem. C. megacheles and G. bonnieri are estuarine and failed to establish themselves. C. triaenonyx is the most widespread species inhabiting all stations with maximum numerical abundance. The coefficient of correlation of different groups with temperature, salinity, dissolved oxygen, C/N ratio and phosphorus revealed that representatives of the families Ampeliscidae, Gammaridae and Photidae are negatively correlated with salinity. Members of the family Corophidae showed some positive correlation with salinity. None of the groups exhibited significant correlation with temperature or with dissolved oxygen. The effect of temperature, salinity and dissolved oxygen on the production of gammarid amphipods was studied by multiple regression analysis. Salinity was found to be the prominent factor controlling the abundance of gammarid amphipods, followed by temperature and dissolved oxygen. The fitted regression was found to be significant at the 1% level (P0.01) only for Station 1