Physiological and ecological study on deep-sea zooplankton

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This study was undertaken to fill the gap of our knowledge about physiological and ecological characteristics of meso/macro zooplankton in mesopelagic and bathypelagic zones of the Oyashio region, western subartic Pacific. Seasonal samplings with vertical closing nets were made down to 3000m to elucidate vertical distribution and life cycle patterns of dominant zooplankton taxa. Live specimens were retrieved for measuring oxygen consumption rates and enzyme assay of electron-transfer-system (ETS). Nucleic acids (RNA, DNA) were determined as an index of nutritional and growth conditions of various zooplankton. The outcome of the study can be summarized as follows ;1.Life cycle modes of representative species of numerically dominant mesozooplankto taxon (ostracods, poecilostomatoid copepods) in the meso/bathypelagic zones were characterized by year-round reproduction and long generation times (1-2 years). Some of them exhibited an ontogenetic vertical migration pattern (upward migration at younger stages). Life-cycles of interzonal large grazing copepods which have diapause phase in meso/bathypelagic zones were fully evaluated. Most of the results were published.2.Oxygen consumption rates of meso/bathypelagic zooplankton (largely copepods) were typically one-half the rates of epipelagic counterparts (note : the effects of temperature and body mass were all removed in this comparison). Of interzonal copepods, oxygen consumption rates of the specimens in diapause were shown to be as low as 30% of the rates at active feeding. The conclusion was further supported by the results of ETS assay. Part of the results was published.3.As judged by RNA/DNA ratios, nutritional/growth conditions of meso/bathypelagic copepods appeared to be less optimal as compared with epipelagic counterparts (note : the effect of body mass was removed, but the effect of temperature could not be removed at present because of the lack of information). Most of the results are to be published.