Enzymatic activities, metabolic rates and chemical compositions of midwater chaetognaths, medusae and certain nemertean and polychaete worms in relation to habitat depth off California

Metabolic potentials of fourteen species of chaetognaths, were estimated by measuring the activities of citrate synthase (CS) and pyruvate kinase (PK) and correlating these activities with oxygen consumption rates measured on the same individuals. Neither lactate dehydrogenase (LDH) nor any of several -opine dehydrogenases could be detected. CS activities were generally higher than PK activities suggesting that chaetognaths are aerobically poised in their metabolism.;Oxygen consumption rates were measured on 13 species of hydromedusae and 5 species of bathypelagic coronate scyphomedusae. Analysis of all individuals of all species of medusae showed the familiar pattern of decreasing oxygen consumption rate with respect to increasing wet weight of animals. Malate dehydrogenase, CS, LDH, and PK activities were measured on thirty species of medusae. The common allometric scaling phenomenon of decreasing activity in larger size individuals were observed in krebs cycle enzyme activities.;Investigations of metabolic rate, enzyme activity and chemical composition were undertaken on two abundant deep-sea pelagic worms: Nectonemertes mirabilis (Nemertinea; Hoplonemertinea) and Poeobius meseres (Annelida; Polychaeta).;Polychaete worms had the highest oxygen consumption rates, and along with N. mirabilis displayed significant size effects on metabolic rate. Poeobius meseres had the lowest rates of oxygen consumption, and there was no significant relationship of oxygen consumption rate to wet weight. No significant effect of size on the enzymatic activity of CS, LDH or PK was observed in P. meseres or N. mirabilis.;CS activities of pelagic worms showed excellent correlation with metabolic rates. Correlations between CS and oxygen consumption were also good for chaetognaths, however such correlations were poor for medusae.;Neither an apparent decline in metabolic rate nor in metabolic potential can be ascribed to depth of occurrence for pelagic chaetognaths, medusae or worms. This is in contrast to the rapid declines in metabolic rate and metabolic potential with depth that have been observed for pelagic fishes and crustaceans. (Abstract shortened with permission of author.).