RAPID DIGESTION AND ASSIMILATION OF BAIT BY THE DEEP-SEA AMPHIPOD EURYTHENES GRYLLUS

Scavenging lysianassoid amphipods (Eurythenes gryllus) were collected with a newly designed trap to measure digestion rates with timed expos ure to bait in the Canada Basin of the Arctic Ocean (2075 m) and in th e Nares (3521 m) and Sohm Abyssal (4978 m) Plains, northeast Atlantic Ocean. In feeding experiments up to 157 h long, water and organic matt er content were not significantly different in anterior, central and h ind gut regions of individual amphipods, showing that digestion in E. gryllus conforms to the batch reactor feeding model. Ingested bait was rapidly solubilized and water content increased from < 70% to. 90% wi thin 69 h. Digestion rates, calculated from exponential curves fitted to decreases in gut contents for dry matter and various organic compon ents, were very high (2.1-6.5% loss h(-1)) for sardines ingested durin g short (6-11 h) incubation periods in the Canada Basin. Mackerel inge sted by amphipods trapped in the Nares and Sohm Abyssal Plains were di gested at lower rates (0.4-1.0% loss h(-1)) in in situ experiments up to 123 h. Allometric regressions described relationships between body length and calories potentially available for assimilation from one me al by male and female instars. Rapid digestion in opportunistic scaven gers like E. gryllus makes gut capacity available for additional feedi ng when food supply is unpredictable.