Metabolism and chemical composition of marine pelagic gastropod molluscs: a synthesis

Metabolism (respiration and ammonia excretion rates) and chemical composition data water content, ash, carbon (C), nitrogen (N) and C:N ratios] of a total of between 6–32 species of pteropods (thecosomes and gymnosomes) and heteropods from ≤500 m depth of the world’s oceans were compiled. Among the independent variables designated (body mass, habitat temperature, sampling depth, taxon), body mass and habitat temperature were significant predictors of metabolism, attributing to 85 % of the variance in respiration rates and 69 % of the variance in ammonia excretion rates. Atomic O:N ratios (respiration:ammonia excretion) ranged from 7.0 to 100 (median 14.5), and no appreciable effects of the variables were detected. A significant negative correlation of C and N compositions and habitat temperature was seen only in the thecosomes. As judged by the concomitant increase in C:N ratios with increasing habitat temperature, a greater deposition of inorganic C (as CaCO₃–C) in the shell of the warmer-living species was suggested. Compared with other zooplankton (copepods, chaetognaths, and euphausiids), the thecosomes were characterized by higher respiration rates per unit body N and larger ash content by having possession of calcareous shells. Because of the shells, C and N composition expressed as % of dry mass of the thecosomes were lower than those of the other zooplankton taxa.