Benthic Respiration and Nutrient Release Associated with Net Cage Fish and Longline Oyster Aquaculture in the Geoje-Tongyeong Coastal Waters in Korea

Abstract

Sediment oxygen demand (SOD) and benthic nutrient fluxes were measured at five sites using an in situ benthic chamber: fish farm (FF), oyster farm (OF), Tongyeong Marine Science Station (TMSS), and two controls (FF-C and OF-C) June 27–July 1, 2017, to assess the impact of aquaculture on coastal waters of southern Korea. The net oxygen production rate of the epiphyte community attached to farming facilities was also measured using an oxygen microsensor to quantify the potential contribution of organic matter to bottom sediment. The SODs at the FF and OF were − 155.2 ± 0.2 m−2 day−1 and − 88.6 ± 0.1 m−2 day−1 respectively, more than twice those of the control sites (FF-C and OF-C). The benthic fluxes of ammonium and phosphate at the fish farm were 12.7 mmol m−2 day−1 and 3.3 mmol m−2 day−1, respectively, which were ~ 10 times higher than those of the control sites and ~ 1.5 times higher than at the OF site. The benthic N and P fluxes accounted for 128% and 501%, respectively, at FF and 89% and 70% of N and P requirements, respectively, at OF for primary production. This suggests that aquaculture activities result in an excess supply of nutrients to the water column, thereby inducing eutrophication in the coastal ecosystem. Potentially, the net production of organic carbon by the epiphyte community yielded about 65 mmol C m−2 day−1, which suggests that organic matter produced by epiphytic communities substantially contributed to benthic respiration. Thus, the commercial finfish and oyster farms increased SOD and benthic nutrient flux, but at a conservatively managed aquaculture (TMSS), there were minimal benthic impacts.