Production, metabolism and production/biomass (P/B) ratio of Themisto japonica (Crustacea: Amphipoda) in Toyama Bay, southern Japan Sea

Abstract

The production and metabolism of the amphipod <it>Themisto japonica</it> in Toyama Bay, southern Japan Sea, were estimated based on their biomass and population structure data collected from every 2-week samplings from 1 February 1990 through 30 January 1991 (363 days). Over the sampling period, the mean biomass (<it>B</it>) was 370 mg C m^-2. Production (<it>P</it>) was calculated as the sum of somatic (<it>P</it>g) and molt (<it>P</it>e) production (<it>P = P</it>g +<it>P</it>c), and metabolism (<it>M</it>) as the sum of routine metabolism (<it>M</it>rtn) and diel vertical migration (<it>M</it>dvm). Integrating over the entire sampling period, <it>P</it>g and <it>P</it>e were 1934 and 176 mg C m^-2, respectively, and<it>M</it>rtn and <it>M</it>dvm were 4100 and 1778 mg C m^-2, respectively. Mean daily<it>P/B</it> and <it>P</it>g/<it>B</it> ratios were 0.016 and 0.014, respectively, and mean<it>P</it>g/<it>M</it> and <it>P/M</it> ratios were 0.33 and 0.36 respectively. Assuming assimilation efficiency of 0.904, ingestion was computed as 8837 mg C m^-2 per 363 days. For the daily maintenance of growth and metabolism, the<it>T.japonica</it> population needs to ingest an amount of prey which equates to 6.6% of their biomass, or 30% of possible total production of their prey animals (copepods and small euphausiids) in Toyama Bay.