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.

東北沖太平洋の大陸斜面上部（水深200-500m）において，底魚群集で優占しているテナガダラの分布の季節変化を調べた．10月には高い密度で分布していたが，4月にはほとんど分布していなかった．操業船の漁獲記録から周年の分布密度を調べると，秋季から冬季に多く分布して，冬季から春季にかけて分布密度が減少することがわかった．東北海域に多く分布する10月の標本の年齢を調べると0+，1+，2+がほとんどであった．生殖腺指数は周年1%以下を示し，若齢で未成熟個体が東北海域に分布していると思われた，秋季に東北海域に来遊するテナガダラは，ツノナシオキアミ，キタノサクラエビ，トドハダカといった亜寒帯種のマイクロネクトンを捕食していた．したがって，亜熱帯種であるテナガダラは，亜寒帯種の餌生物を索餌するために，黒潮の勢力が強まる秋季に東北海域へ来遊していることが示唆された．

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.