Population structure and life cycle of the mesopelagic ostracodConchoecia pseudodiscophorain Toyama Bay, southern Japan Sea

✍ Scribed by T. Ikeda; A. Imamura

• Publisher: Springer-Verlag
• Year: 1992
• Tongue: English
• Weight: 683 KB
• Volume: 113
• Category: Article
• ISSN: 0025-3162
• DOI: 10.1007/bf00349703

✦ Synopsis

The population structure and life cycle of the mesopelagic ostracod Conchoecia pseudodiscophora Rudjakov in Toyama Bay, southern Japan Sea, were investigated using a time-series of samples collected during 0 to 500 m vertical hausls with twin-type Norpac nets (0.35 and 0.10 mm mesh) over one full year (1 February 1990 to 30 January 1991). Additional samples were also collected with a single-type closing Norpac net (0.06 mm mesh) to examine the vertical distribution patterns of eggs and all instars of this species. The proportion of gravid females present indicated that reproduction of C. pseudodiscophora continues throughout the year, but peaks in April July. Eggs and Instars I and II were distributed below 500 m, while the more advanced instars were most abundant in the 350 to 500 m stratum by both day and night. Based on the abundance peaks of each instar in the time-series samples, development times were estimated to be 2.5, 4, 3, 7 and 11 mo for Instars III, IV, V, VI, and VII, respectively. Thus, a total of 30 mo is required for newly spawned eggs to hatch and reach adulthood. Stomach-fullness indexes revealed no seasonality in the feeding activity of any instar stage, but that feeding activity was low in older instars, particularly in adult males. The present results are compared with those for a few other ostracod species, in an attempt to characterize the life cycle of C. pseudodiscophora inhabiting waters of "subzero" temperature in the mesopelagic zone of the Japan Sea.

The present study examines the life cycle of Conchoecia pseudodiscophora, including breeding season, developmental time of each instar, and life span. The study is based on material from time-series samples over one full year at an offshore station in Toyama Bay, southern Japan Sea.