The vertical distribution of pearl oyster Pinctada fucata martensii spat in Uchiumi Bay

We conducted an experiment to see vertical distribution of the pearl oyster Pinctada fucata martensii spat, in Uchiumi Bay, east side of Bungo Channel , Japan. Since there is an intrusion of Kuroshio Front (Kyucho), the water quality of the bay is strongly affected by the Kyucho. Collectors of spat w ere placed from the 1 to 10 m at 1 m intervals, and the 15, 20 and 30 m dep ths from June 18 to August 22, 1997. The spats were abundantly distributed from the 1 to 10 m depth, and most abundant at 6 m depth. Few spats were fo und from the 15 to 30 m depth. Although some mechanisms such as water tempe rature and salinity have been reported in the literature as important envir onmental factors which determine vertical distribution of bivalve spat in e xperimental systems, we could not find significant relationships between ve rtical abundance of P. fucata martensii spat and vertical profiles of some environmental variables. The relationships between the vertical distributio n of the spat and the environmental factors in natural environments are thu s complicated. The result in the present study is an important information on the vertical distribution pattern of P. fucata martensii spat in natural environmets.