Figure 1. 1A. Annual variations in sexual stages found in the gonads of P. perna after collection from the Mohammedia (M), Hay El Fath (H) and Bouknadel (B) sites.

Classification of bivalve sexual stages according to Lubet (1959): StIIIC + IIIB, egg-laying; StIIIA, later development (maturation) + morphologically ripe; StI + II, early development; St0 + IIID), resting stage + mussel recently spent. The data correspond to the proportion of approximately 30 individuals collected each month in each site for a given sexual stage. The inter-site variability in the distribution for a sexual stage is illustrated by Tukey’s boxes. * and +p < 0.05 with respect to the distribution found at Bouknadel or Hay El Fath, respectively (Student Newman-Keuls). 1B. Distribution of the different stages in the sexual cycle for the months that were selected for the neurochemical study (July 2010, September (Sep.) 2010, March 2011 and April 2011 (see supplementary Fig. S1 for the full distribution over a year).