Production, metabolism and trophic importance of four pelagic amphipods in the Oyashio region, western subarctic Pacific

To estimate the production, metabolism and ingestion of populations of 4 pelagic amphipods (Themisto pacifica, T japonica, Primno abyssalis and Cyphocaris challengeri) in the Oyashio region of the western subarctic Pacific, field time-series data on population structure were combined with laboratory-rearing data. Annual mean biomass, B (mg C m(-2)) was 31.2, 19.6, 17.4, and 36.7 for T pacifica, T japonica, P. abyssalis, and C. challengeri, respectively. Based on size-specific growth rates, annual production, p (mg C m(-2) yr(-1)), computed as the sum of somatic growth (P.) and molt production (P-e), was 309, 252, 40, and 182, respectively. Annual metabolism (M-i mg C m(-2) yr(-1)) was 541, 195, 146, and 258. The annual P:B ratios indicated that the production potential was greatest for T japonica (11.6), followed by T pacifica (9.1), C. challengeri (4.5), and P. abyssalis (2.1). Assuming an assimilation efficiency of 0.90, assimilation (A = P + M) was converted into ingestion (I = A/0.90) for each amphipod. Annual ingestion (1, mg C m-2 yr(-1)) was 941 for T pacifica, 493 for T japonica, 205 for P. abyssalis, and 487 for C. challengeri. The total annual ingestion (=predation) of the 4 amphipods (mg C m(-2) yr(-1)) equals 0.08% of the non-amphipod zooplankton biomass, or 4.5% of their probable daily production in the Oyashio region of the western subarctic Pacific.