28 Apr 2014

Ichthyo- and zooplankton dynamics associated with accumulations of Anaulus australis in a warm temperate South African surf-zone.

The dynamics between larval fish, zooplankton and a surf zone diatom, Anaulus australis, on a warm temperate surf zone were investigated in this study. A modified beach seine net was used to sample planktonic surf zone communities within and adjacent to A. australis accumulations. Differences in larval fish and zooplankton species composition, abundance were observed between A. australis accumulations and the diet was analysed to further clarify associations.

inant fish species collected during the study included the important linefish the cape stumpnose, (Rhabdosargus holubi) cape sole, (Heteromycteris capensis), blackhand sole (Solea turbynei) and the estuarine round herring (Gilchristella aestuaria). Species belonging to the Mugilidae family were significantly higher in abundance within accumulations however numbers collected during the present study were lower than that recorded in previous studies. Biomass of A. australis ranged from 3.0 to 931.6 µg chl a l-1. The presence of accumulations of A. australis has however not shown to be inducing a significant increase in larval fish abundance. Dominant zooplankton species included Eurydice spp. and Gastrosaccus psammodytes. Greater zooplankton abundances were recorded within accumulations. Due to the patchy nature of A. australis, primarily driven by rip currents, accumulations are thought to serve as opportunistic food sources for larval fishes.