Seasonal and temperature effects on osmoregulation by the invasive prawn Palaemon elegans Rathke, 1837 in the Baltic Sea

The effect of season and acclimation temperature on the osmoregulatory ability of the invasive prawn Palaemon elegans in the Baltic Sea was investigated. There was a significant seasonal effect that could be attributed largely to temperature. Decreasing environmental temperature increased haemolymph osmolality (i.e. improved osmoregulatory ability) in field-sampled hyper-regulating prawns. This effect of temperature was confirmed in the laboratory for individuals acclimated to different salinity and temperature regimes. When compared with an English Channel population of P. elegans, individuals of the Baltic population were better at maintaining hyper-osmoregulatory capacity at the lowest temperature tested (2 degrees C), but individuals of the English Channel population were better at maintaining hypo-osmoregulatory capacity at the highest temperature tested (12 degrees C). It is concluded that the low environmental temperatures encountered by P. elegans invading the Baltic will not compromise but may actually further their range expansion in this area.