EFFECTS OF SHORT-TERM HYPOXIA ON METABOLISM AND HEMOCYANIN OXYGEN-TRANSPORT IN THE PRAWNS PALAEMON ADSPERSUS AND PALAEMONETES VARIANS

In summer, high temperatures are combined with severe nocturnal hypoxi a in the shallow water of Danish fjords. Under these conditions, the p rawns Palaemonetes varians (Leach) and Palaemon adspersus (Rathke) are spatially separated, with the former occupying the areas of highest t emperature and lowest oxygen tension. If kept together, P. adspersus s hows aggressive behaviour towards P. varians. Aerobic/anaerobic respir ation and haemocyanin characteristics were measured in laboratory expe riments (24 degrees C, 14 ppt). Although the 2 species have similar me tabolic rates, P. varians survives severe hypoxia better and has a low er P-c (critical oxygen tension, below which respiration is partly or fully anaerobic) than P. adspersus. Both species accumulate high level s of lactate during anaerobiosis and remove it at similar rates. The h aemocyanin concentration and total oxygen carrying capacity (0.78 +/- 0.25 mmol l(-1) and 2.25 +/- 0.56 vol%) of P. varians was higher than P. adspersus (0.28 +/- 0.07 mmol l(-1) and 1.14 +/- 0.15 vol%). Haemoc yanin oxygen affinity was always higher in P. varians regardless of pH , but the Bohr factor (-1.44 and -1.46) and cooperativity (n(50): 2.61 +/- 0.20 and 2.82 +/- 0.49) were similar for P. varians and P. adsper sus, respectively. P. varians is thus better adapted to severe hypoxia than P. adspersus.