The response of Grandidierella lignorum (Barnard) (Crustacea: Amphipoda) to episodic flooding in three eastern Cape estuaries

Abstract

The response of the euryhaline amphipod Grandidierella lignorumto changing freshwater inflow was investigated in three estuaries with differing river discharges. In the Kariega and Keiskamma estuaries an increase in the density of G. lignorum was correlated with an increase in river inflow. The sharp reduction in salinity during flooding is suggested as a possible trigger which stimulates G. lignorum to rise into the water column. The position of stations along the Kariega and Keiskamma estuaries, together with seasonal effects, also influenced G. lignorum abundance. In the Great Fish estuary, which has a continuous large freshwater input, changes in the abundance of G. lignorum were not correlated with inflow. Possible reasons for this anomalous situation, as well as the biological implications of becoming part of the zooplankton during flooding, are discussed.