Life history, distribution, seasonal variability and feeding of the pelagic chaetognath Sagitta elegans in the Subarctic Pacific : A review

Sagitta elegans Verrill is the dominant epipelagic chaetognath species in Pacific Subarctic Waters. In this paper, the seasonal variability, horizontal distribu tion, vertical distribution, diel migration, breeding, life cycles, gut contents and feed ing activity of S. elegans are reviewed. The southern-most records of this species in the Pacific Ocean is in the southern Japan Sea near the Tsushima Strait and in Sagami Bay where warm Tsushima and Kuroshio Currents, respectively, cover the surface layer. Diel vertical migration of S. elegans has been observed in various water masses and adults show migration of a larger scale compared to that seen in smaller animals. S. elegans is distributed as deep as 1000 m or more in the Japan Sea and the vertical dispersal of this species is facilitated by the absence of competi tors such as Eukrohnia hamata, E. bathypelagica, E. fowleri and S. macrocephala. The number of generations produced each year increases with the distance from the north pole. Generation times are 4-5 months in Dabob Bay, 6-10 months at Ocean Station P and 10-12 months in Toyama Bay, respectively. Copepods are the predom inant prey of S. elegans regardless of water mass. The percentage of secondary pro duction consumed daily by S. elegans was 10% in the Bering Sea and 4% in the Western Gyre during the summer.