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 exposure to bait in the Canada Basin of the Arctic Ocean (2075 m) and in the Nares (3521 m) and Sohm Abyssal (4978 m) Plains, northeast Atlantic Ocean. In feeding experiments up to 157 h long, water and organic matter content were not significantly different in anterior, central and hind 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% within 69 h. Digestion rates, calculated from exponential curves fitted to decreases in gut contents for dry matter and various organic components, were very high (2.1–6.5% loss h⁻¹) for sardines ingested during short (6–11 h) incubation periods in the Canada Basin. Mackerel ingested by amphipods trapped in the Nares and Sohm Abyssal Plains were digested 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 meal by male and female instars. Rapid digestion in opportunistic scavengers like E. gryllus makes gut capacity available for additional feeding when food supply is unpredictable.