Abirity of Amphiascus sp. (Copepoda, Harpacticoida) to remove fouling diatoms on conchocelis-bearing oyster shells in nori culture

Shell-boring conchocelis of nori Porphyra was incubated for 6 weeks with a harpacticoid copepod Amphiascus sp., which is sometimes observed to propagate in cultivation tanks of the conchocelis, to evaluate the ability of the copepod to remove fouling diatoms on the shells. In the control tank without the copepod, diatoms on the shells increased exponentially and changed the white color of the shells to brown during the experiment. The density of the copepods including nauplii on the shells increased to 5.3 animals/cm(2) for 6 weeks of culture. They suppressed the amount of fouling diatoms to about 1/6 of that in the control tank at the end of the experiment and the shell color was not changed except for the marginal area of the shell. Conchocelis after 6 weeks of culture was significantly longer in the experimental tank than in the control tank although its length was not different between the tanks for the initial 5 weeks. The nutrient concentrations such as PO4 dropped more in the control tank. These results indicate that the copepod can effectively remove fouling diatoms from conchocelis-bearing shells, and so adding this copepod in conchocelis-culture tanks may reduce shell-cleaning labor in nori culture.