摘要：We assessed the role of planktonic processes, in comparison to allochthonous input from fish cages and sedimentary loss, in the organic carbon (OC) budget of the water column in a semi-enclosed fish-culturing area (culturing red sea bream Pagrus major and yellow tail Seriola quinqueradiata). The sedimentation rate of particulate organic carbon (POC) at the fish-cage station was an average of 1.5 times that at non-cage stations. There was no significant difference in photosynthesis or respiration rates between fish-cage and non-cage stations. Annual allochthonous OC input in the form of leftover feed and fish feces was estimated to be 5 or 10 times that of autochthonous OC input by planktonic photosynthesis. In contrast, POC derived from phytoplankton accounted for a significant part (8 to 61%) of total POC sedimentation. As to sinks of OC in the water column, annual planktonic respiration was twice as high as sedimentary loss at the fish-cage station. The plankton community tended to act as a source of OC in spring and summer and as an OC sink in fall and winter. The present study shows that a significant part of allochthonous and autochthonous OC input is respired by plankton and that the remaining OC input is deposited on the seafloor of fish-culturing areas.
