Impacts of bioturbation by Venus clam Cyclina sinensis (Gmelin, 1791) on benthic metabolism and sediment nutrient dynamics in a shrimp-clam polyculture pond
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Dynamics of benthic inorganic nutrients are key biogeochemical components of sediment metabolism and ecosystems. This study investigated the roles of the bivalve Cyclina sinensis (Gmelin, 1791) and its influence on benthic metabolism, nutrient fluxes and sediment oxygen consumption (SOC) in a shrimp-clam polyculture system in comparison with shrimp culture ponds without incorporating clams, in Ningbo Zhejiang China. The benthic inorganic nutrients fluxes (ammonium-NH4+, nitrate plus nitrite-NO3-+NO2- and phosphate-PO43-) and SOC were measured across the sediment-water interface with dark incubation experiments. The results showed that there were significantly higher nutrient fluxes from the sediment into the overlying water (p<0.05) in the treatment ponds in the order of NH4+ > PO43- > NO3- + NO2-. The SOC varied significantly (p<0.05) and was three-times higher than that of the control ponds. Water quality (dissolved oxygen, pH, chlorophyll-a and salinity) recorded showed slight variations over time but were not significantly different (p>0.05) between the control and treatment ponds. Sediment organic matter and chlorophyll-a concentration measured in the shrimp-clam ponds varied significantly (p<0.05) as compared to control ponds. The results of this study suggest that the bioturbation activities by C. sinensis promoted the SOC, sediment organic matter degradation and mineralisation process that increased the exchange of nutrients and oxygen uptake between the sediment and the overlying water.
Keywords: Bioturbation, Cyclina sinensis, Nutrient flux, Sediment quality, Shellfish farming