For the restoration of tides [do they mean “tidal zones” or “tidal areas”?] there is a need for techniques which can reveal features of planktonic larvae of filter feeding macrobenthos, such as bivalves. For understanding and predicting the sources of planctonic larvae, the vertical distribution of larvae is the most important factor, because it affects the drift route. In this study, the optimum range of salinities chosen by the larvae and the vertical movement velocity at each growth stage, from fertilized egg to full-grown stage, was measured using a density-gradient water column apparatus. The results show that trochophore larvae select low salinity water (18～24 psu). D-shaped larvae move toward more saline water (29 psu) in the early stages, and then gradually select lower salinity layers (21～23 psu) as they mature. Results are similar in both dark and light conditions. We derive an empirical equation describing changes in vertical movement velocity at different stages. The temporal changes in the vertical movement of larvae can be simulated by this equation using the values for salinity and vertical movement velocity.

The longarm grenadier, Abyssicola macrochir (Günter), which dominates in a demersal fish assemblage on the upper continental slope from 200 to 500 m off the Pacific coast of northeastern Japan (Tohoku coast), was examined with respect to distribution, age composition, life cycle and feeding habits, in 1999 and 2000. A dense population of A. macrochir was observed off the southern Tohoku coast during autumn, but the population was sparse during other seasons. The population was mainly composed of 0+, 1+ and 2+ fish. GSIs lower than 1.0 were observed throughout the year, suggesting that they were at an immature stage. Major prey organisms were micronekton such as Euphausia pacifica, Sergestes similis and Diaphus theta. These observations suggest that young immature A. macrochir, subtropical demersal fish, use the upper continental slope off the southern Tohoku coast seasonally to feed on highly productive subarctic micronektons in autumn when warm water expands northward from the Kuroshio Extension to the area.

The dinoflagellate Karenia mikimotoi (Miyake et Kominami ex Oda) Hansen is responsible for extensive red tides in western Japan. In order to clarify the mechanism of occurrence of K. mikimotoi red tides in Usuki Bay which is located in the north-western part of Bungo Channel, Japan, field surveys were made in Usuki Bay and adjacent areas during May through September 2003. The initial appearance of K. mikimotoi red tide was observed in Suo-Nada, then the red tide was observed Iyo-Nada, Beppu Bay, and Usuki Bay. The distribution of it extended southward gradually. From result of analysis of the surface water temperature by satellite, the distribution of the red tide area corresponded with the warmer water mass (>25°C). Red tide outbreak in Usuki Bay, accompanied the warmer water mass intrusion into Usuki Bay from Beppu Bay and Iyo-Nada. Furthermore, the red tide of K. mikimotoi in Usuki Bay in August 2003 may have originated from Suo-Nada and warmer, water mass with the red tide intrusion in Usuki Bay.