METABOLIC EFFECTS OF SHORT-TERM STARVATION ON THE BENTHIC AMPHIPOD PONTOPOREIA-AFFINIS LINDSTROM FROM THE NORTHERN BALTIC SEA

Changes induced by a short-term (8 days) starvation period on the meta bolism (VO2, oxygen uptake rate; VNH4, ammonia excretion rate) of the benthic deposit-feeding amphipod Pontoporeia affinis Lindstrom were st udied from a Baltic deep (125 m) open-sea population. The experiments were performed during two different nutritional periods: in March, whi ch represents a period when the benthic environment is deficient of go od quality food, and in June, when the vernal phytoplankton bloom has enriched the sediment with fresh algal material. In March, the VNH4-N of P. affinis is already extremely low, and the resulting VO2:VNH4-N r atios (atomic O:N) high (> 240), indicating an almost exclusive utiliz ation of lipids as the energy source of metabolism. The initial VNH4-N is considerably higher in June and the O:N ratio (mean 54) indicates an equal use of protein and lipid. The VO2 is less affected by starvat ion. The O:N ratio elevates during food deprivation as the animals shi ft their metabolic balance further towards the use of stored lipid. Th e results suggest that the ammonia excretion of P. affinis is an indic ator 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 realist ic results, animals should not be kept too long (over 3 days) without food in the laboratory prior to measurements. Results from additional NH4-N excretion experiments, performed on animals collected from geogr aphically different locations, show marked deviations in rates of ammo nia release, most likely due to differing environmental conditions.