Genetic Diversity and Population Structure of Scylla spp. Along the Pakistani Coast: Implications for Fisheries Management in the Indian Ocean

Scylla spp., commonly known as mud crabs, are large edible crabs well known for their importance in fisheries.
Previously, both S. serrata and S. olivacea were described from Pakistani waters. Differentiation of both species
based on morphology, however, is difficult, pressing the need for molecular identification. Furthermore, a better
understanding of the genetic diversity and connectivity of mud crabs throughout the Indian Ocean is necessary for
the optimal management of this resource. Sampling of 170 mud crabs was conducted from five different sites along
the Pakistani coast. A fragment of 432 base pairs of the mitochondrial cytochrome oxidase subunit I gene (COI) was
sequenced and aligned with 235 sequences retrieved from GenBank. Population structure in Pakistan was further
analysed using 19 microsatellite loci. Based on the COI sequences, all collected individuals were identified as Scylla
olivacea. In the data set of 392 COI sequences 196 haplotypes were identified. Nucleotide diversity was low,
whereas haplotype diversity was high. Neutrality tests indicated a possible recent population expansion event in
nearly all populations. We detected significant population structure using COI throughout the Indian Ocean.
Population structure within Pakistan was confirmed with microsatellites. Possible explanations for these groupings
are different environmental conditions on both sides of the Pakistani coast and physical barriers to dispersal, such
as the Ganges River outflow and complex current patterns along the Indonesian coast.