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

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Abstract
The production and metabolism of the amphipod Themisto japonica 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 (B) was 370 mg C m-2. Production (P) was calculated as the sum of somatic (Pg) and molt (Pe) production (P = Pg +Pc), and metabolism (M) as the sum of routine metabolism (Mrtn) and diel vertical migration (Mdvm). Integrating over the entire sampling period, Pg and Pe were 1934 and 176 mg C m-2, respectively, andMrtn and Mdvm were 4100 and 1778 mg C m-2, respectively. Mean dailyP/B and Pg/B ratios were 0.016 and 0.014, respectively, and meanPg/M and P/M 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, theT.japonica 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.

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