Review on the fauna and the distributional ecology of pelagic chaetognaths in Sagami and Suruga Bays

A review on the fauna of chaetognaths in Sagami and Suruga Bays, located on the Pacific coast of central Japan, was compiled here. Hitherto 30 species have been found in the bays, with 27 species occurring in both bays. The chaetognath fauna is composed of a small number of coastal species and a large number of oceanic species introduced mainly from the Kuroshio Current and North Pacific Intermediate Water. The three vertical zones (epipelagic, upper mesopelagic and lower mesopelagic zone) are recognized, corresponding to the vertical structure of water masses. However, undescribed species have been collected from deep water in recent studies, suggesting the existence of unknown benthopelagic fauna in the bays. The seasonal change of abundance and species composition is remarkable in the epipelagic zone; a coastal species and some oceanic species dominate in spring-summer and autumn-winter, respectively. There are marked differences between previous studies in the months of peak abundance and the magnitude of peaks. For a better understanding of the mechanisms causing such variations, it is necessary to investigate long-term seasonal changes on the basis of observations of the physical and biological environment, as well as study the population dynamics, life history, and interspecific relationships of chaetognaths.