The distribution of littoral fish associated with eelgrassZostera capensisbeds in the Kariega Estuary, a southern African system with a reversed salinity gradient

Abstract

Eelgrass Zostera capensis has expanded its distribution in the Kariega Estuary mainly in response to the reduced salinity gradient in that system. Seine-net sampling showed that Atherina breviceps, Rhabdosargus holubi, Glossogobius callidus and Mugilidae were the most common fish taxa in the Zostera beds. Fish species richness was maximum in the lower reaches, but highest densities (17,3 individuals·m−2) occurred in the upper reaches. There was increased domination by marine opportunist species in the lower reaches, but estuarine taxa predominated the middle and upper reaches. There was a significant similarity between the species in the middle and upper reaches of the estuary, but not between the lower and middle, or lower and upper reaches. No significant correlation was evident between fish density and salinity, temperature or turbidity. The distributional patterns of most fish associated with Zostera beds in the Kariega Estuary were similar to other estuaries in the Eastern Cape with normal axial salinity gradients, indicating that factors other than salinity influence fish distribution in estuaries.