Environmental hypoxia and haemocyanin between-individual variability in Norway lobsters Nephrops norvegicus (L.)

The extent to which exposure to environmental hypoxia (PO₂=8, 6, and 4 kPa, approximately 40%, 30%, and 20% saturation, respectively) resulted in an increase in the concentration of the respiratory pigment haemocyanin (Hc]) in individuals of the Norway lobster Nephrops norvegicus depended crucially on the initial Hc] as well as the intensity of the hypoxia itself. While mean Hc] did increase with decreasing PO₂ (and the variation decreased), for individuals with relatively high initial Hc] there was no change or even a decrease observed. The greatest hypoxia-related increases in Hc] were observed in the individuals with the lowest initial Hc]. Consequently the notion of an 'optimum' Hc] for a given level of oxygenation was postulated. The changes in Hc] recorded took place over a considerably shorter time scale (hours rather than days) than has been observed in previous studies. It was not possible to correlate environmental PO₂ and median Hc] in the field. However, it was interesting that the Hc] frequency distribution curve for lobsters collected from a site that had been markedly hypoxic (PO₂=8.0 kPa, approximately 40% saturation) until a few days before sampling was almost exactly the same shape (i.e. leptokurtic) and position (i.e. similar median) to that obtained when lobsters were exposed to PO₂=8.0 kPa in the laboratory. Although it would have been desirable to investigate the effect of hypoxia on the frequency distribution of a physiological trait, in this case Hc], it was not possible due to insufficient sample size, even though the sample sizes employed were considerably larger than those normally used in physiological investigations.