Restricted gene flow between Holothuria scabra (Echinodermata : Holothuroidea) populations along the north-east coast of Australia and the Solomon Islands

To describe patterns of gene flow for the fished holothurian species Holothuria scabra 17 to 141 individuals were collected from 8 populations from north-east Australia, the Torres Strait, and the Solomon Islands. Samples were investigated by allozyme electrophoresis of 7 polymorphic loci. Cluster analyses using Rogers' genetic distance identified 3 distinct groups of populations from the north-east coast of Australia, representing samples from the 3 regions Hervey Bay, Upstart Bay and Torres Strait. Populations in the latter region were closely connected to those from the Solomon Islands. F-statistics indicated restrictions in gene flow (average genetic variation between populations, F-ST = 0.088). Hierarchical analyses revealed that 94.7 % of the variation was within sampling locations. Approximately 77 % of the variance among populations was due to differences between regions, and 23 % within regions (most of the latter caused by differences between the 2 Solomon Island populations), Mantel's tests indicated that a high proportion of the variation in genetic distances along the north-east coast of Australia was explained by isolation by distance (Mantel's normalised Z = 0.88). This proportion reduced when the Solomon Islands were included (Z = 0.65). The detection of separate stocks along the north-east coast of Australia is an important finding that has significant consequences for the development of sustainable management plans for this species. Low dispersal may significantly reduce recovery of overfished areas if no local refugia are provided.