Growth, production and productivity of the Arctic sympagic amphipod Gammarus wilkitzkii

The amphipod Gammarus wilkitzkii Birula is one of the major macrofauna species permanently inhabiting the subsurface of Arctic sea ice. It reaches an age of 5 yr with a measured maximum body length of 62.3 mm. The growth of this species is best described by the Gompertz growth function, which gives asymptotic final lengths of 69.2 and 64.6 mm respectively for males and females. Individuals of 46 to 52 mm length show the highest individual production, whereas the length class 31 to 36 mm is the most productive within the investigated population. The somatic P/B ratio (productivity) of the investigated G. wilkitzkii population (0.398 yr–1) is low compared to other amphipod species from boreal and polar regions. This is discussed with respect to the permanent low water temperature, the low energy content of the food, and the high mortality of juveniles under Arctic sea ice. The overall growth performance, ψ, of G. wilkitzkii is not significantly different from other Gammarus species living under boreal conditions. It is therefore assumed that the growth is predominantly determined genetically rather than by environmental conditions.