Association of early stage fishes with surf diatom Anaulus australis accumulations in a warm temperate surf zone, South Africa

Abstract

Surf zones are recognised as important nursery habitats for early stage fishes worldwide, but microhabitat opportunities for feeding and refuge are not well studied. Surf diatoms accumulate in high densities, discolouring the water and offering potential refuge and feeding opportunities. The aim of this study was to investigate the association of early stage fishes with surf diatom Anaulus australis accumulations in the Sundays Beach surf zone on the South African southeast coast. Early stage fishes were sampled within and outside of visible A. australis accumulations using a 4.5 × 1.5 m larval fish seine net with 500 μm mesh. Over 22 sampling trips, 338 replicate samples were collected. Species diversity, the overall catch per unit effort (CPUE) and that of the dominant species Chelon richardsonii, Diplodus capensis, Rhabdosargus globiceps and R. holubi, were significantly higher within accumulations compared to outside. Postflexion larvae and early juveniles occurred in significantly higher numbers within accumulations, indicating that fishes were actively selecting A. australis accumulations. Generalized linear models revealed that temperature, dissolved oxygen (mg l−1), turbidity and A. australis biomass (μg Chl a l−1) were the most significant variables correlated with the overall CPUE and that of dominant species. Since A. australis accumulations have a patchy distribution in the surf zone, it is suggested that early stage fishes are opportunistically using this resource when and where it occurs as both a feeding and refuge area. Understanding the role of microhabitats for early stage fishes is essential for understanding survival and life history strategies within the mosaic of coastal nursery areas.