Metabolic effects of short-term starvation on the benthic amphipod Pontoporeia affinis Lindström from the northern Baltic Sea

Abstract

Changes induced by a short-term (8 days) starvation period on the metabolism (VO 2, oxygen uptake rate; VNH 4, ammonia excretion rate) of the benthic deposit-feeding amphipod Pontoporeia affinis Lindström were studied from a Baltic deep (125 m) open-sea population. The experiments were performed during two different nutritional periods: in March, which represents a period when the benthic environment is deficient of good quality food, and in June, when the vernal phytoplankton bloom has enriched the sediment with fresh algal material. In March, the VNH 4-N of P. affinis is already extremely low, and the resulting VO 2:VNH 4-N ratios (atomic O:N) high (> 240), indicating an almost exclusive utilization of lipids as the energy source of metabolism. The initial VNH 4-N is considerably higher in June and the O:N ratio (mean 54) indicates an equal use of protein and lipid. The VO 2 is less affected by starvation. The O:N ratio elevates during food deprivation as the animals shift their metabolic balance further towards the use of stored lipid. The results suggest that the ammonia excretion of P. Affinis is an indicator of more-or-less recent feeding history of individuals, and the O:N ratio is a potential index for the condition of these animals as it reflects the nutritional state of the benthic environment; for realistic results, animals should not be kept too long (over 3 days) without food in the laboratory prior to measurements. Results from additional NH 4-N excretion experiments, performed on animals collected from geographically different locations, show marked deviations in rates of ammonia release, most likely due to differing environmental conditions.