EFFECTS OF FEEDING AND STARVATION ON THE METABOLIC-RATE OF THE NECROPHAGOUS ANTARCTIC AMPHIPOD WALDECKIA-OBESA (CHEVREUX, 1905)

The marked seasonality of high latitude marine ecosystems means that t he relationship between nutrition and metabolism is of particular inte rest, for many polar organisms must survive long periods without food. One hundred individuals of the scavenging lysianassoid amphipod Walde ckia obesa (Chevreux, 1905) were collected from Antarctica and then ma intained in cold-water aquaria at the British Antarctic Survey in Camb ridge. One group were fed and then starved for 64 days, during which t ime oxygen consumption fell to 60% of the initial value, and ammonia e xcretion to 20%. The initial decrease in metabolism occurred in about 5 days, after which time ammonia excretion remained roughly constant w hereas oxygen consumption (and hence O:N atomic ratio) oscillated. O:N ratio and proximate composition estimated stoichiometrically from ele mental composition both indicated the use of protein and lipid as meta bolic substrates during starvation. Fed amphipodds exhibited a classic post-prandial increase in metabolism (specific dynamic action, SDA): oxygen consumption and ammonia excretion increased rapidly to a level between 4 and 7.5 times the prefeeding levels, respectively. These are the largest increases of metabolic rate with feeding so far reported for a marine invertebrate and the overall SDA response lasted 8-10 day s. O:N ratios indicated that metabolism 2-4 days after feeding was dom inated by protein metabolism.