Diet and prey selection in late-stage larvae of five species of fish in a temperate estuarine nursery

Abstract

The plankton assemblage of the permanently open Sundays Estuary in South Africa was sampled seasonally to provide further information on the feeding ecology of the larval stages of fishes in temperate estuaries. Collections were made between winter 2007 and autumn 2009 at eight sites by means of boat-based plankton tows. Physico-chemical variability in the water column was typical for temperate systems. Mean density of larval fishes and zooplankton showed similar seasonal and spatial trends. Gut content analyses were conducted in five dominant larval fish species: Gilchristella aestuaria (Clupeidae), Pomadasys commersonnii (Haemulidae), Monodactylis falciformis (Monodactylidae), Myxus capensis (Mugilidae) and Rhabdosargus holubi (Sparidae). The first record of selective consumption of copepod eggs by G. aestuaria is reported. Insect larvae (chironimids) dominated the diet of some marine fish larvae (M. falciformis and M. capensis). The copepod Pseudodiaptomus hessei formed the largest volume of the diet of P. commersonnii whereas R. holubi selected for the amphipod Corophium triaenonyx, with P. hessei also being a frequently consumed prey item. Seasonal and spatial variability with salinity was evident in the diet. Larvae also showed changes in diet at different stages of development. Pelagic prey species constituted the largest volume of the diet of G. aestuaria whereas all other larvae consumed large volumes of bentho-pelagic prey. All larvae selected P. hessei as a prey item. Myxus capensis and R. holubi also selected this copepod and showed the largest diversity in diet.

Keywords:

• copepod eggs
• insect larvae
• larval fish assemblage
• predation
• seasonality