Life in cold oceans: activity dependent on extracellular ion regulation?

It has been hypothesized that a low capacity for extracellular ion (magnesium) regulation in marine crustaceans constrains their cold tolerance and biogeography in the Southern Ocean. This thesis investigates whether there is a relationship between haemolymph magnesium concentration and thermal tolerance in a temperate brachyuran crab (Carcinus maenas, Decapoda, Brachyura, Carcinidae) and in decapod, amphipod and isopod crustaceans from the Southern Ocean. In the sub-Antarctic stone crab Paralomis granulosa (Decapoda, Anomura, Lithodidae) lecithotrophic larvae, juvenile and adult stages were considered. Haemolymph ion composition, cardiovascular variables, locomotory activity, and developmental time were determined. As observed in isopods, life in the extremely cold continental shelf areas of the Antarctic is generally possible despite high haemolymph magnesium concentrations. The findings in P. granulosa render it unlikely that high haemolymph magnesium concentrations are correlated with the absence of this species from extremely cold regions of the Antarctic.