How does salinity influence the swimming speed of the estuarine calanoid copepod Eurytemora affinis?
Résumé
Michalek et al. (Michalek et al., 2010) report that, in the absence of food, increase in salinity (i.e. 5, 15, 25 and 30) steadily decreased the instantaneous speed of Eurytemora affinis reproductive stages (male, non-ovigerous female and ovigerous female). This contradicts previous observations conducted on individuals obtained from a laboratory culture in the presence of food, i.e. a mixture of Isochrysis galbana and Nanochloropsis oculata, showing an increase in overall swimming activity, speed and path complexity for males and non-ovigerous females, but not for ovigerous females (Seuront, 2006). To account for this discrepancy, Michalek et al. (Michalek et al., 2010) stressed the importance of the experimental conditions employed for observations, but barely discussed the implications of their findings in an ecological context as was done by Seuront (Seuront, 2006, see their Figure 6). It is agreed that it is difficult to compare behavioural responses of copepods originating from a continuous culture (Seuront, 2006) and from the field (Michalek et ...