Low genetic diversity in the endangered marine alga Silvetia siliquosa (Ochrophyta: Fucaceae) and the implication to conservation

Abstract

Although significant research efforts have been targeted toward conservation and management of endangered terrestrial flora and fauna, attempts have been limited to conserve threatened seaweeds. Silvetia siliquosa is an ecologically and commercially vital brown alga that is uniquely distributed in the Yellow-Bohai Sea and along the southwest coast of Korea. A massive decline in its distribution range and biomass from the mid-1990s onward indicates that this species has become endangered. In the present study, we used nuclear internal transcribed spacer and concatenated mitochondrial cytochrome oxidase I subunit+intergenic spacer to estimate the genetic diversity, population connectivity, and degree of genetic differentiation of S. siliquosa in China and Korea. The molecular results exhibited strikingly low levels of haplotype/ribotype and nucleotide diversity in S. siliquosa populations, with only three mitochondrial haplotypes and nuclear ribotypes detected in 136 and 143 specimens, respectively. The analysis of molecular variance revealed 85%–95% of genetic variance among populations. Population differentiation coefficient (F_ST) and gene flow (N_m) suggested that two populations (JIN and GWA) along the southern coast of Korea are highly divergent from the others, with weak genetic exchange. No significant genetic differentiation was observed among populations either in China or along the geographically proximate west coast of Korea. Thus, four independent management units were designated for sustainable management: the LII and RUS populations in China, the YEO and CHA populations along the west coast of Korea, and each of the GWA and JIN populations along the south coast of Korea. We suggest that artificial cultivation and transplantation of S. siliquosa are the effective approaches for restoration and conservation.