Review on the fauna and the distributional ecology of pelagic chaetoganaths in the Japan Sea

Abstract

A review on the fauna and the distributional ecology of pelagic chaetognaths in the Japan Sea was compiled here. The Japan Sea is a marginal sea surrounded by the Asian Continent and the Japanese Islands and characterized by limited connectivity to other seas through the four shallow straits (The Tsushima, Tsugaru, Soya and Mamiya). Major results are summarized as follows: 1) In total, 22 species with 1 form belonging to 11 genera are listed as the epipelagic chaetognath fauna. 2) Some characteristics of chaetognath distribution are: (1) Only Parasagitta elegans and not Pseudosagitta scrippsae or Eukrohnia hamata occur of the subarctic species. (2) Flassisagitta hexaptera, Krohnitta subtilis, Mesosagitta decipiens, M. neodecipiens and Pseudosagitta lyra, which are mainly distributed in the mesopelagic layer in the Kuroshio Current region, appear rarely in the surface layer. (3) The dominant species in the epi-and mesopelagic layers in subarctic regions is only P. elegans, and its distribution extends into the mesopelagic layer in the Tsushima Warm Current region. (4) In the Tsushima Warm Current region, the dominant species are Mesosagitta minima, Zonosagitta nagae, Flassisagitta enflata and Serratosagitta pacifica, and a seasonal shift is apparent: M. minima (in winter), P. elegans (in spring), Z. nagae (in summer), M. minima (in autumn). (5) The northern limit of Aidanosagitta crassa, distributed in near-shore waters, is found in Mutsu Bay on the Japanese side, but not at such a northern latitude on the continental side. (6) Rare subtropical species occur increasingly after the 1990’s, accompanied by the rise of water temperature.