Light-limitation on predator-prey interactions: Consequences for metabolism and locomotion of deep-sea cephalopods

present study attempts to correlate the metabolism and locomotory behavior of 25 species of midwater Cephalopoda from California and Hawaii with the m aximal activities of key metabolic enzymes in various locomotory muscle tis sues. Citrate synthase (CS) and octopine dehydrogenase (ODH) activities wer e used as indicators of aerobic and anaerobic metabolic potential respectiv ely. CS activity in mantle muscle is highly correlated with whole-animal ra tes of oxygen consumption, whereas ODH activity in mantle muscle is signifi cantly correlated with a species' ability to buffer the acidic end-products of anaerobic metabolism. Both CS and ODH activities in mantle muscle decli ned strongly with a species' habitat depth. For example, CS and ODH activit ies ranged respectively from 0.04 units g(-1) and 0.03 units g(-1) in the d eep-living squid Joubiniteuthis portieri, to 8.13 units g(-1) and 420 units S-I in the epipelagic squid Sthenoteuthis oualaniensis. The relationships between enzymatic activities and depth are consistent with similar patterns observed for whole-animal oxygen consumption. This pattern is believed to result from a relaxation, among deep-living species, in the need for strong : locomotory abilities for visual predator/prey interactions; the relaxatio n is due to light-limitation in the deep sea. Intraspecific scaling pattern s for ODH activities may, for species that migrate ontogenetically to great depths, reflect the counteracting effects of body size and light on predat or-prey detection distances. When scaled allometrically, enzymatic activiti es for the giant squid, Architeuthis sp., suggest a fairly active aerobic m etabolism but little burst swimming capacity. Interspecific differences in the relative distributions of enzymatic activities in fin, mantle, and arm tissue suggest an increased reliance on fin and arm muscle for locomotion a mong deep-living species. We suggest that, where high-speed locomotion is n ot required, more efficient means of locomotion, such as fin swimming or me dusoid arm propulsion, are more prevalent.