Morphometric Variation among Four Local Ruditapes decussatus Populations in Monastir Bay (Eastern Coast, Tunisia)

HIGHLIGHTS

• Ruditapes decussatus from four sites belonging to Monastir bay (Tunisia) was first time analyzed based on morphometry and comparative statistics.

• The site of Ksiba was distinguishable from other sites by larger and heavier specimens.

• The sub-trapezoidal shape was dominant with small- size classes, in most sites.

• The principal component analysis (PCA) revealed different population groups, with two intra-population groups for Sokrine site.

• Allometric relationships showed highly significant correlation with different growth patterns (positive allometric, negative allometric and isometric).

Abstract

In Tunisia, Monastir bay, extending for 38 km along the eastern coast of Tunisia, harbors different species of bivalves such as the clam Ruditapes decussatus, a species of major socio-economic interest. Despite its importance, no studies have been carried out about the morphology of this mollusc in Monastir bay. Thus, the current study aimed to analyze the shell morphological variations in the European clamRuditapes decussatus from Monastir Bay coast. The comparison of the shell shape of individuals from different populations was performed based on samples taken at four different sites (Khniss, Ksiba, Bkalta and Sokrine). Variance analysis of the morphometric indices (elongation, compactness, convexity and density) for the four populations indicated significant differences among sites with (p=0<0.05). Principal component analysis (PCA) revealed two intra-population groups for Sokrine site, supporting an intra-population variation in the shell morphology. Allometric relationships established between linear variables (shell length, height and width) and ponderal variables (total weight, shell weight) as well as the relative growth between variables (isometry vs. allometry) were analyzed. All morphometric relationships were highly significant (P<0.001) with high correlation coefficients (R²: 0.714-0.982), showing positive allometric growth for Bkalta and negative allometric growth for Sokrine. The data obtained will be useful in research studies and have practical application in diverse research fields such as biology, ecology, fisheries assessment and management.

Keywords:
Monastir bay; Ruditapes decussatus; shell morphology; Multivariate analysis; Allometry