Morphological Analysis of Blue Swimming Crab (Portunus pelagicus) Populations From Nine Fishing Grounds in the Philippines through Landmark-based Geometric Morphometrics

Abstract The blue swimming crab (BSC) is one of the Philippines’ major fishery exports. It is a highly valued commodity, having an annual yield of 27,500 metric tons from 2010-2019. The discovery of a putative cryptic species of Portunus pelagicus in previous studies based on cytochrome c oxidase subunit 1 (COI) sequences complicates the assessment of its genetic diversity, which is of importance in designing effective and efficient management plans for this economically-important species. In this study, landmark-based geometric morphometrics was used to examine shape variation between two pre-identified clades of the blue swimming crab Portunus pelagicus. Samples were obtained from various fishing grounds in the Philippines. Shape differences between clades were significant based on multivariate analysis of variance. The distinction was not clear though due to overlaps observed in the canonical variate analysis plot and the considerable misclassification rate. This was attributed to possible effects of sexual dimorphism on morphological analysis of the clades. Although shape variation was observed, the protocols will have to be refined further to effectively diagnose the different clades based on morphology.