Biomass of plankton and macrobenthos and benthic species diversity in relation to environmental gradients in a nationwide coastal survey

Abstract Using Korean coastal survey data, we examined the relationships between plankton and benthic biomass and environmental parameters. The nitrate in coastal waters was mainly derived from the influx of fresh water, whereas much of the ammonium originated from decomposing organic matter in the sediments and river discharge. Phytoplankton and zooplankton concentrations were positively related to the amount of suspended particulate matter (SPM), but decline when SPM becomes high (> 10 ppm). Particulate organic carbon (POC) comprised about 40% of the SPM, suggesting that organic matters associated with river-borne sediments and re-suspended particles are a large source of coastal water POC. Zooplankton abundance was more closely related to the distribution of phytoplankton than to that of POC. Benthic biomass showed a dome-shaped relationship with the water column POC concentration, but no clear relationship with sediment POC distribution. The biodiversity of macrobenthic animals gradually decreases when POC exceeds 1% of the sediment weight. Reduction of siltation and POC could lead to enhanced benthic–pelagic coupling via increased plankton biomass and productivity, as well as overall increased benthic diversity in coastal environments.