Metabolism and chemical composition of marine pelagic amphipods: synthesis toward a global bathymetric model

Respiration and ammonia excretion data and chemical composition data water content, ash, carbon (C), nitrogen (N) and C:N ratios] of 18–32 amphipods (hyperiids and gammarids) from the epipelagic through bathypelagic zones of the world’s oceans were compiled. The independent variables including body mass, habitat temperature and mid-sampling depth were all significant predictors of respiration, accounting for 65–83 % of the variance in the data, while the former two variables were significant predictors of ammonia excretion, accounting for 64–77 % of the variance. Atomic O:N ratios (respiration:ammonia excretion) ranged from 11 to 74 (median 21.5). C composition was negatively correlated with habitat temperature, but water contents, ash, N, and the C:N ratio were uncorrelated with the three independent variables. As judged by C:N ratios, protein was considered to be the major organic component of most pelagic amphipods. However, some amphipods from >500 m depth exhibited high C:N ratios (>10) suggesting a large deposition of lipids in the body. Comparison of the present results with global bathymetric models of euphausiids and pelagic copepods revealed that respiration rates of the pelagic amphipods were near-equal to the rates of euphausiids but greater than the rates of pelagic copepods, reflecting taxon-specific body morphology and swimming behavior among the three taxa. As a marked feature of body chemical composition, the pelagic amphipods exhibited extremely high ash content (mean 25 % of DM) due to their possession of a robust exoskeleton.