Carbon dioxide fluxes from mariculture ponds with swimming crabs and shrimps in eastern China: The effect of adding razor clams

Abstract

Razor clams (Sinonovacula constricta) are one of the major polyculture species in mariculture ponds, along with swimming crabs (Portunus trituberculatus), in the coastal zones of China, and their effect on CO2 fluxes are poorly studied. CO2 fluxes from mariculture ponds with swimming crabs, kuruma shrimp (Marsupenaeus japonicus) (CS) and mariculture ponds with swimming crabs, kuruma shrimp and razor clams (with different clam densities from low to high, CSB1, CSB2, CSB3, respectively) were measured during the farming season. The CO2 fluxes of CS, CSB1, CSB2, and CSB3 were −25.37, −30.23, −28.81 and −12.18 mg m−2 h−1, respectively. All the ponds acted as CO2 sinks across the water-air interface. Our results showed that water pH was a good indicator of the CO2 flux, and a pH value of 8.24 was the critical value dividing the dataset into influxes or effluxes in the mariculture ponds. Net primary production was also significantly correlated with the CO2 flux and is considered a key driver regulating the CO2 flux. Our findings indicate that the low clam stocking density used in this study could enhance the CO2 sink across the water-air interface by promoting phytoplankton biomass and net primary production, whereas the CO2 sink may be weakened with an increase in clam density due to a decline in phytoplankton biomass and net primary production.