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

Abstract

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 (Pg) and molt production (Pe), was 309, 252, 40, and 182, respectively. Annual metabolism (M; 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 (I; 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 (1892 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. © Inter-Research 2006.