Abstract
The greenfish sea cucumber Stichopus chloronotus is an economically and ecologically important sea cucumber species throughout its range. This species is widely distributed, inhabiting coral reefs of the Indo-Pacific Ocean. Our study evaluated population genetic structure and levels of genetic diversity in southern Japan. A total of 180 individuals were collected from eight locations from Okinawa and Okinoerabu Islands and sequenced using mitochondrial 16S ribosomal DNA (16S) and nuclear histone H3 (H3) gene. Only three 16S haplotypes were detected (518 bp) with haplotype diversity ranging from 0 to 0.56 and nucleotide diversity from 0 to 0.1%. H3 showed no variation among the studied locations. It is plausible that such results could be due to a shift to asexual reproduction. Additionally, the presence of the species on the east coast of Okinawa could only be detected in one location and all individuals consisted of a single haplotype. Genetic differences between the east and west coasts of Okinawa have been noticed in other coral reef organisms, and attributed to either ecological or biogeographical historical differences between the coasts due to differing levels of isolation during Pleistocene ice ages. Results from the present study should inform management and conservation policies of S. chloronotus in southern Japan.
Highlights
Sea cucumbers belong to class Holothuroidea of phylum Echinodermata and play an important and essential part in maintaining and structuring the marine ecosystem
Statistics on fisheries/fishing activities for sea cucumbers are unavailable for many countries as most fisheries organizations still record invertebrate catch as ‘others.’ some organizations such as the Secretariat of the Pacific Community (SPC) and the Food and Agriculture Organization of the United Nations (FAO) have made efforts to make records available for invertebrates including sea cucumbers
We examine whether S. chloronotus on the east and west coasts of Okinawa are genetically differentiated as has been observed in a number of recent studies on other sea cucumber (Soliman, Fernandez-Silva & Reimer, 2016) and other invertebrate species (White, Reimer & Lorion, 2016)
Summary
Sea cucumbers (holothurians) belong to class Holothuroidea of phylum Echinodermata and play an important and essential part in maintaining and structuring the marine ecosystem. The species Stichopus chloronotus Brandt, 1835 (greenfish sea cucumber), belonging to the family Stichopodidae, is a member of such highly commercial marine sea cucumber fisheries This species is a widely distributed across most of the tropical Indo-Pacific region, from the Western Indian Ocean to the Central Pacific, and from southern Japan to northern Australia (Purcell et al, 2012). Based on recent increasing commercial pressure in Okinawa, we expect that locations near to large human populations may show reduced S. chloronotus genetic diversity, as well as a potential shift to asexual reproduction due to reduced water quality, as was previously observed in H. edulis (Soliman, Fernandez-Silva & Reimer, 2016)
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