Abstract
Seven species of two genera of pelagic chaetognaths ( Eukrohnia hamata, E. bathypelagica, E. fowleri, Sagitta elegans, S. macrocephala, S. scrippsae. and S. zetsios) were collected at Ocean Station P (50°N, 145°W) from February 1980 to January 1981. The most abundant species, E. hamata, E. bathypelagica, E. fowleri, and S. elegans comprised 71.0, 18.0, 7.2, and 3.8%, respectively, of the chaetognaths in the upper 2000 m. S. elegans inhabits the epipelagic layer (0 to 200 m), E. hamata the epipelagic and upper mesopelagic layers, E. bathypelagica the mesopelagic layer (200 to 1000 m), S. macrocephala the lower mesopelagic and bathypelagic layers (500 to 2000 m), and E. fowleri the layer below 1000 m. E. hamata and S. elegans both had three spawning periods during the year, separated by distinct gaps in both presence of mature individuals and appearance of new juveniles. Generation lengths were 8 to 10 months for E. hamata and 6 to 10 months for S. elegans. Factors that produce the overlapping, two-thirds year generations remain to be demonstrated. Mean growth rates determined by following their cohorts were 2.5 to 3.0 mm per month for E. hamata and 5 to 6 mm per month for S. elegans. Breeding and development were continuous through the year for E. bathypelagica and E. fowleri.
Published Version
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