Changes in the macrobenthic community structure associated with finfish farming in Richards Bay Estuary, South Africa

Abstract

Globally, aquaculture has shown the potential to boost economic activity and enhance food security. However, controversy exists around large-scale finfish farming, with objections centred around potential environmental issues (especially eutrophication). Given this, the effects of a trial dusky kob (Argyrosomus japonicus) fish farm established in Richards Bay Estuary on the macrobenthic community were studied from 2016–2018. Water quality, sediment nutrient levels and macrobenthic community data were collected along a gradient away from the fish farm for twelve months during fish farm operations and nine months after operations ceased. Results show that high nutrient concentrations at the fish farm site caused low dissolved oxygen concentrations, confirming sediment eutrophication in the immediate vicinity. The macrobenthic community structure revealed a separation between fish farm sites and those further away, which confirmed the localised effect of fish farming on the benthic community. Opportunistic taxa such as Pilargidae and Spionidae polychaetes, including Sigambra spp. and Prionospio spp., dominated at the fish farm sites. Nevertheless, a measured, long-term reversal of this process was observed during the recovery period. The study concluded that fish farm activities had a localised and reversible impact on the benthic habitat quality and the macrobenthic community.