Mangrove crabs of the genus Scylla are one of the valuable mangrove resources contributing to the viability of the lucrative fisheries in the Philippines.However, there is limited information on the species' population structure in the major fishing grounds.Thus, the present study evaluated population-level morphological variation in carapace morphology among the common Scylla species caught in the commercial fisheries of the Philippines.A total of 644 Scylla specimens were sampled from four major fishing grounds in the Philippines: Lingayen Gulf, Sibuyan Sea (Roxas City), Panguil Bay, and Bislig Bay, which host three Scylla species, namely S. serrata, S. tranquebarica, and S. olivacea.The Scylla carapace morphology was analyzed using landmark-based geometric morphometrics, which examines shape (morphology) variation in the dorsal carapace of Scylla specimens.The analysis of morphological variation involved the application of Generalized Procrustes Analysis (GPA), relative warp analysis, principal component analysis (PCA), canonical variate analysis (CVA), and multivariate statistical tests to assess differential carapace morphology among Scylla populations, sexes, and the three species.The results revealed variation in carapace morphology across Scylla populations, species, and sexes.There was a manifestation of sexual dimorphism in the Scylla males and females, where Scylla males had narrower carapace width, particularly the posterior portion, compared to the Scylla females.The Scylla populations exhibited morphological variation across sampling sites, further distinguishing them and suggesting that they may have adapted to the different environmental conditions at those sites.Variations in fluctuating asymmetry of carapace morphometric traits in Scylla populations also suggested differences in developmental stability among specimens, and these variations are more pronounced in specimens from different environmental conditions at the sampling sites.Thus, the study provided significant data on the population structure of the Scylla species and on their carapace morphological variation across different sampling sites in the Philippines.The application of the geometric morphometric method to analyze carapace morphological variation among Scylla populations, sexes, and species has demonstrated its applicability for discriminating among morphological differences.It also confirms the utility of morphometrics as a cost-effective alternative method in fisheries monitoring, particularly for assessing the stock of mangrove-associated fisheries resources.
Gonzales et al. (Thu,) studied this question.