Morphological Differentiation Among Geographically Close Populations of the Green Crab Carcinus Aestuarii Nardo, 1847 (brachyura, Carcinidae) from the Tunisian Coast

In the present study, we assessed patterns of morphological variation among populations of the Mediterranean green crab Carcinus aestuarii Nardo, 1847 from the Tunisian coast. Eleven morphometric traits were measured on 464 specimens from nine sites, and the pattern of morphological variation among sites was assessed using multivariate approach. Non-parametric MANOVA (NPMANOVA) and non-metric Multidimensional Scaling (MDS) analyses revealed statistically significant differences among the studied locations for both sexes proving that natural variability of the measured traits differs clearly between locations. Canonical discriminant analysis (CDA), on the other hand, showed that over 36\% of individuals could be assigned to their location of origin on the basis of their morphology. Correct assignment of individuals to their location was much higher (over 63\%) when sites were combined into three regional groups and marked morphological differentiation was found in both sexes. A positive correlation was noted between the squared Mahalanobis distances (D-2) and the geographic distances for both male and female green crab populations suggesting isolation by distance. The results obtained indicate that morphological divergence among populations of the green crab can occur over shorter distances than expected based on dispersal potential. Possible drivers of the observed pattern of morphological variation are discussed.