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Abstract
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Portunid crabs form the basis of important fisheries in many parts of the world, however, their
population biology is poorly understood. The more than 90 species of the Portunidae are widely
distributed in global oceans often with indistinct boundaries among species, especially in the Indian
Ocean. To clarify the species occurrence and population genetic structure of Portunus pelagicus and
Portunus segnis in Iranian waters, crab specimens were collected from four sites along the Iranian
coast of the Persian Gulf and Oman Sea. For a subset of 40 sampled crabs, the Cytochrome C Oxidase
subunit 1 (COI) was sequenced and compared among the four sites. This analysis identified P. segnis
as the predominant species (39 out of 40 sequenced samples) with the infrequent occurrence of P.
pelagicus (one out of 40 sampled). Genetic diversity analysis for P. segnis samples identified high to
moderate haplotype (0.98) and nucleotide (0.04) diversities. Analysis of molecular variance (AMOVA)
(?ST = 0.09629 P = 0.00673) revealed significant genetic differentiation between two sampling sites
inside the Persian Gulf, at Chabahar and Qeshm which are 500 km apart. Comparisons of the variation
in the carapace morphometrics of 104 male P. segnis among sites using canonical variate analysis
showed significant differences among the four sampling sites (P < 0.0001). Overall, the results revealed
a high degree of morphological and genetic heterogeneity in P. segnis over relatively small spatial scales
in this region of the Indian Ocean. The morphological variability of this species is such that it masked
the sympatric presence of the species, P. pelagicus. It is likely that other cryptic portunid congeners
will be identified in other Indo-Pacific regions given the high level of genetic variability that has been
previously described for P. pelagicus from this region.
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