ENZYMATIC-ACTIVITIES AND METABOLIC RATES OF PELAGIC CHAETOGNATHS - LACK OF DEPTH-RELATED DECLINES

Metabolic potentials of 16 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. Furthermore, CS activities were generally higher than PK activities, suggesting that chaetognaths are aerobically poised in their metabolism. Metabolic rates and enzyme activities were examined with regard to body size and minimum depths of occurrence. There was an overall decline in both oxygen consumption and enzyme activities with body mass in interspecific comparisons. The highest CS and PK activities were measured in individuals of the bathypelagic species Caecosagitta macrocephala. The lowest enzyme activities measured in a southern California chaetognath were in the mesopelagic species Pseudosagitta maxima. The lowest overall PK activity was measured in the antarctic species Pseudosagitta gazellae. In contrast to the rapid declines in metabolic potential with depth that have been observed for pelagic fish and crustaceans, no decline in metabolic rate nor in enzyme activities can be ascribed to depth of occurrence for pelagic chaetognaths. Below depths of several hundred meters, chaetognaths have metabolic rates comparable to those of meso- and bathypelagic fish and crustaceans.