Primary production mechanism in a bay with cultivation of pearl oyster Pinctada fucata martensi (Dunker)

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The object of this study was to clarify the primary production mechanism in the bay where pearl oysters Pinctada fucata martensi (Dunker) were cultivated. The results obtained were as follows : 1) the amount of predation of P.fucata martensi on phytoplankton in summer was 0.11 mug/hr/g of wet weight, 2) P.fucata martensi filtrated 171/hr/individual (43g) of sea water in summer, 3) 0.5 mug/l of chlorophyll a increased with the Kyucho in the bay, 4) a mitigation hypothesis, that P.fucata martensi indirectly favored the growth of phytoplankton by filtrating sea water, was induced based on the comparison of the increase by the pump up mechanism and the decrease by predation of P.fucata martensi predation, 5) the concentrations of P04-P and NH4-N increased in the filtrated sea water, 6) growth substances existed in the filtrated sea water by P.fucata martensi.It was found that while P.fucata martensi favored the growth of phytoplankton in the bay it also hindered its growth by its predation. This is a mitigation effect of P.fucata martensi on its predation on phytoplankton.These results indicated an important prey-predatory relationship in an aquatic ecosystem.