Nursery function of red-algal dominated reef in temperate Algoa Bay, South Africa

Abstract

Abstract Structurally complex macroalgae within coastal seascapes are important as nursery areas for many marine fish species. This study examines the nursery role of a mosaic of red algae dominated habitats in a shallow (< 5 m), sheltered rocky cove in warm-temperate Algoa Bay, South Africa. As an indicator of nursery function within the cove we assessed and mapped macroalgal communities, the resource seascape (epiphytes and invertebrates), as well as fish assemblages (abundance, size structure and species richness) in different subtidal habitat patches. We also looked at the trophic ecology of dominant juvenile fish species within the cove. Red algae, particularly canopy forming Plocamium spp. and lower growing Laurencia spp. dominated subtidal high and low profile reef respectively, with the lower intertidal dominated by coralline turf. Algal complexity (canopy height) was negatively correlated with the biomass of resources, with the biomass of epiphytic algae highest on coralline turf and the abundance of amphipods and polychaetes highest on low growing Laurencia and corralline turf. Laurencia, epiphytes, polychaetes and amphipods were important food sources for juvenile sparids. Although results from this study indicate that lower complexity algae likely provide more food for juvenile sparids, the high abundance of juvenile sparids in Plocamium dominated high profile reef indicates that canopy-forming Plocamium likely provides more shelter from predation than lower complexity algal reef habitats. This shows that macroalgal habitats comprising several functional forms have the potential to support higher juvenile diversity and abundance through both food provision and protection.