The nursery function of shallow nearshore and estuarine benthic habitats for demersal fishes

Abstract

Estuaries and shallow marine nearshore areas are highly productive and valuable ecosystems, which provide numerous habitats for fish and support fundamental ecological links with other environments. Yet only a few studies have focussed on fish community patterns across an estuary and marine nearshore gradient concurrently to determine the nursery value of both environments. This research gap is particularly apparent in southern Africa. The main aim of this study was to assess the relative roles of two permanently open estuaries and the adjacent marine nearshore areas of Algoa Bay, on the south coast of temperate South Africa, as settlement and nursery areas for demersal fishes. Soft-bottom habitats in both the estuaries and the nearshore were dominated by early-life stages (postflexion larvae, settlement stage and young-of-the-year fishes), but a significantly greater density of early-life stage fishes was found in the estuarine environment, highlighting the importance of estuarine habitats for demersal fishes within the Algoa Bay nursery seascape. Settlement and nursery habitats also differed by estuarine-association, with the marine nearshore environment dominated by marine and marine estuarine-opportunists, with core settlement and nursery areas for these species located close to estuary mouths, freshwater outlets and harbours. In contrast, the estuarine environment was dominated by marine estuarine-dependent and estuarine and marine species. This highlights the importance of concurrently sampling habitats in marine nearshore and estuarine environments, which allows for a better understanding of the degree of estuarine dependency of marine fish as well as an understanding of the nursery function of coastal habitats.