POPULATION GENETIC STRUCTURE OF THE WHITE TEATFISH, HOLOTHURIA FUSCOGILVA, IN SOUTH-COAST, KENYA

Abstract

The white teatfish, Holothuria fuscogilva, is widely distributed in coastal areas, around coral reefs and sea grasses in the Indo-Pacific region. In Kenya, the species is distributed in areas of shallow reefs, with higher landings reported from the Gazi-Vanga-Shimoni seascape. The species exhibits density-dependent reproduction with broadcast spawning augmented by low recruitment rates, making it vulnerable to overexploitation. Sea cucumbers are excellent species for regulating water quality through the recycling of nutrients in sediments. Therefore, their ecological importance cannot be overstated. The present study investigated the genetic structure, patterns of effective population size, and effects of fishing pressure on H. fuscogilva populations from Gazi, Shimoni and Vanga sites in south-coast Kenya, using mitochondrial cytochrome oxidase I (COI). A total of 60 individuals, 25 from Gazi, 27 from Shimoni and 8 from Vanga were sampled with 47 individuals yielding high-quality sequences producing 22 haplotypes with high haplotype diversity but low nucleotide diversity (h = 0.922, π = 0.008). Samples from the northernmost site, Gazi had higher genetic diversity (h = 0.933) compared with the Vanga and Shimoni populations. In addition, H. fuscogilva along the south coast of Kenya exhibited a unique clade when compared with individuals from other geographical locations outside the region. The genetic structure was analyzed using Analysis of Molecular Variance (AMOVA) with the highest proportion of variation evident within the populations than, among the populations. The fixation index FST showed a lack of structure among H. fuscogilva (FST = 0.01186, p.value = 0.29069).To visualize past population dynamics and patterns of effective population sizes of H. fuscogilva populations, Mismatch distribution analyses revealed a past population expansion event, while Bayesian skyline plots indicated a gradual demographic growth due to an increase in effective population sizes. The H. fuscogilva populations in the three study sites along Kenya's south coast appear to have genetic connectivity, but no significant genetic structure. The genetic structure estimates and intra-population genetic diversity depict a robust population that can regenerate lost individuals after a fishing event. There is occurrence of population expansion evident from new haplotypes in population and increase in effective population sizes. The Intra-population genetic diversity regenerates the lost individuals after fishing pressure. H. fuscogilva distinction from other species around the world emphasizes the importance of conservation at the local and regional level. Future studies should then be conducted in other areas of the Kenyan coast to provide comprehensive countrywide data critical in formulation of sound harvest strategies and conservation management policies for the H. fuscogilva species