The Vertical Distribution of Pearl Oyster Pinctada fucata martensii Spat in Uchiumi Bay

Abstract

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 were placed from the 1 to 10m at 1m intervals, and the 15, 20 and 30m depths from June 18 to August 22, 1997. The spats were abundantly distributed from the 1 to 10m depth, and most abundant at 6m depth. Few spats were found from the 15 to 30m depth. Although some mechanisms such as water temperature and salinity have been reported in the literature as important environmental factors which determine vertical distribution of bivalve spat in experimental systems, we could not find significant relationships between vertical abundance of P. fucata martensii spat and vertical profiles of some environmental variables. The relationships between the vertical distribution of the spat and the environmental factors in natural environments are thus complicated. The result in the present study is an important information on the vertical distribution pattern of P. fucata martensii spat in natural environmets.