Physiological plasticity is key to the presence of the isopod Idotea baltica (Pallas) in the Baltic Sea

Abstract

The low salinity of the Baltic Sea presents a physiological challenge to marine species. The marine isopod Idotea baltica is notably dominant among the shallow sublittoral of the Baltic Sea in association with Fucus vesiculosus, with permanent populations documented in salinities as low as 3psu. To investigate the role of physiological plasticity in the successful colonisation of the Baltic by I. baltica three populations from the Swedish coast were here studied, one from the Kattegat (Malmö) and two from the Baltic Sea (Kalmar and Öregrund). These three sites cover the geographic range of this species within the Baltic Sea on the Swedish coast, and also the salinity range of this species within the Baltic Sea (10–5psu). Individuals from these populations were exposed in the laboratory to a fully crossed experiment with the factors salinity and food source, to test for differences in the physiology of these populations under different conditions that may indicate local adaptation, or no differences that indicate physiological plasticity to differing salinity and food source. Metabolic rate, growth and thermal tolerance responses did not differ between the three populations across salinity treatments after a 12week exposure. The results of this study indicate that the physiology of adult I. baltica is highly plastic with regard to salinity; this plasticity is likely to have facilitated their colonisation of the Baltic Sea.