Genetic diversity and connectivity in the East African giant mud crab Scylla serrata: Implications for fisheries management

Abstract

The giant mud crab Scylla serrata provides an important source of income and food to coastal communities in East Africa. However, increasing demand and exploitation due to the growing coastal population, export trade, and tourism industry are threatening the sustainability of the wild stock of this species. Because effective management requires a clear understanding of the connectivity among populations, this study was conducted to assess the genetic diversity and connectivity in the East African mangrove crab S. serrata. A section of 535 base pairs of the cytochrome oxidase subunit I (COI) gene and eight microsatellite loci were analysed from 230 tissue samples of giant mud crabs collected from Kenya, Tanzania, Mozambique, Madagascar, and South Africa. Microsatellite genetic diversity (He) ranged between 0.56 and 0.6. The COI sequences showed 57 different haplotypes associated with low nucleotide diversity (current nucleotide diversity = 0.29%). In addition, the current nucleotide diversity was lower than the historical nucleotide diversity, indicating overexploitation or historical bottlenecks in the recent history of the studied population. Considering that the coastal population is growing rapidly, East African countries should promote sustainable fishing practices and sustainable use of mangrove resources to protect mud crabs and other marine fauna from the increasing pressure of exploitation. While microsatellite loci did not show significant genetic differentiation (p > 0.05), COI sequences revealed significant genetic divergence between sites on the East coast of Madagascar (ECM) and sites on the West coast of Madagascar, mainland East Africa, as well as the Seychelles. Since East African countries agreed to achieve the Convention on Biological Diversity (CBD) target to protect over 10% of their marine areas by 2020, the observed pattern of connectivity and the measured genetic diversity can serve to provide useful information for designing networks of marine protected areas.

Cryptic diversity and limited connectivity in octopuses: Recommendations for fisheries management

“…This is congruent with the results of Tajima’s D-test, Fu’s Fs test, the mismatch distribution analysis and Rogers’ test for sudden population expansion, that suggest demographic growth. This finding is similar to the population expansion reported in the WIO for the African giant mud crab Scylla serrata [66], the skunk clownfish Amphiprion akallopisos [68] and the mangrove whelk Terebralia palustris [30].…”

“…vulgaris showed a moderate level of haplotype diversity ( h ) and a low level of nucleotide diversity ( π ). This pattern has also been reported in other studies in the WIO [30, 66]. The high h and low π might indicate a genetic bottleneck that has caused stochastic extinction of most haplotypes, followed by population expansion [67].…”

“…Similar findings have been reported for Terebralia palustris , for which restricted gene flow was detected between (1) northern Kenya, (2) Kenya, Tanzania and western Madagascar, (3) northeastern Madagascar and (4) southern Madagascar [30]. For the giant mud crab Scylla serrata a significant genetic divergence was found between sites in eastern Madagascar and sites on the West coast of Madagascar, mainland East Africa, as well as the Seychelles [66]. At a smaller scale, a weak genetic structure was detected among populations of Acropora tenuis in Tanzania and Kenya [69].…”

Evaluation of suitable temperature range for post‐harvest processing of mud crabs through cardiac performance

“…The rising demands of live mud crab provide economic opportunities for many regions (Jahan & Islam, ; Paterson & Mann, ; Poole et al, ), and the knowledge about mud crab farming continues to grow (Jiang et al, ; Rumisha, Huyghe, Rapanoel, Mascaux, & Kochzius, ; Waiho et al, ). Here, we described a novel technique for detecting crab ECG through implanting an electrode close to the crab heart.…”

Genetic characterization of the artisanal mud crab fishery in Myanmar

“…A similar pattern of population structure among conspecifics was documented in S . serrata from East Africa, where ocean dynamics impose barriers to gene flow between geographically close populations, while promoting gene flow to further locations [ 37 ]. Likewise, the Asiatic mangrove, Rhizophora mucroanta , showed the most distinct genetic differentiation between the Andaman Sea and the Malacca Strait, which can be explained by the prevailing ocean currents in this region dictating the dispersal of propagules [ 48 ].…”