Review on the fauna and the distributional ecology of pelagic chaetognaths in the southern seas of Japan

Abstract

A review on the fauna and the distributional ecology in the southern seas of Japan in the western North Pacific Ocean are compiled here. Major results are summarized as follows: 1) In total, 30 species with 1 form belonging to 15 genera are listed as the chaetognath fauna with 24 species and 1 form in 12 genera for the epipelagic, 7 species in 5 genera for the mesopelagic, and 4 species in 3 genera for the bathypelagic layers. 2) Some characteristics of chaetognath distribution are : (1) Rare tropical species are found in the coastal waters. (2) Subarctic species such as Parasagitta elegans and Pseudosagitta scrippsae occur in the mesopelagic layer in the Kuroshio area, accompanied by the Intermediate Oyashio Water. Eukrohnia hamata is mainly distributed in the mesopelagic layer in the Kuroshio area and its juveniles often occur in the surface layer. (3) In summer and autumn, Flaccisagitta enflata invades towards inner bays through the coastal waters from the Kuroshio area in the southern seas of Japan. (4) Typical indicator species in this domain are Aidanosagitta crassa in the near-shore water, Zonosagitta nagae in the coastal water, F. enflata in the Kuroshio water and Pterosagitta draco in the offshore-oceanic water. (5) Predominant species in the domain are F. enflata (EN), Mesosagitta minima (MI), Serratosagitta pacifica (PA), Zonosagitta nagae (NA), F. lyra (LY) and A. regularis (RE). The dominant species change seasonally in the inner part of the Kuroshio, winter (MI/PA) ⇒ spring (PA/NA) ⇒ summer (MI/EN) ⇒ autumn (EN/MI), and in the oceanic water south of the Kuroshio, winter (LY/MI/EN) ⇒ spring (PA/MI/EN) ⇒ summer (EN/RE/MI) ⇒ autumn (EN/MI/RE). (6) Data on the autecology of A. crassa and Z. nagae have been accumulated.