The spiny lobster Palinurus gilchristi is endemic to the deep shelf waters along the southern coast of South Africa, where it supports a commercial fishery. Mark-recapture studies and phenotypic differences suggest there are 2 populations of this species along the coast, but it is unknown if the observed differences have arisen because of low gene flow and subsequent genetic differentiation. To investigate population structure and the physical processes that may have influenced gene flow, a portion of the mitochondrial DNA control region was sequenced for 187 lobsters across the entire range of the species. An analysis of molecular variance showed no significant genetic difference between the 2 putative populations. A mismatch distribution and Fu's F S test indicated that this species has undergone a fairly recent demographic expansion (population size and geographic range). The genetic structure of this species could be panmictic due to a high amount of gene flow between the 2 regions during the larval stage, when the larvae are carried downstream by the Agulhas Current. Furthermore, the lack of genetic differences between the 2 putative populations could be the result of a recent demographic expansion accompanied by low diversity of haplotypes produced by a leading edge effect from the expansion.
This study examines the fine‐scale population genetic structure and phylogeography of the spiny lobster Panulirus homarus in the Western Indian Ocean. A seascape genetics approach was used to relate the observed genetic structure based on 21 microsatellite loci to ocean circulation patterns, and to determine the influence of latitude, sea surface temperature (SST), and ocean turbidity (KD490) on population‐level processes. At a geospatial level, the genetic clusters recovered corresponded to three putative subspecies, P. h. rubellus from the SW Indian Ocean, P. h. megasculptus from the NW Indian Ocean, and P. h. homarus from the tropical region in‐between. Virtual passive Lagrangian particles advected using satellite‐derived ocean surface currents were used to simulate larval dispersal. In the SW Indian Ocean, the dispersion of particles tracked over a 4‐month period provided insight into a steep genetic gradient observed at the Delagoa Bight, which separates P. h. rubellus and P. h. homarus. South of the contact zone, particles were advected southwestwards by prevailing boundary currents or were retained in nearshore eddies close to release locations. Some particles released in southeast Madagascar dispersed across the Mozambique Channel and reached the African shelf. Dispersal was characterized by high seasonal and inter‐annual variability, and a large proportion of particles were dispersed far offshore and presumably lost. In the NW Indian Ocean, particles were retained within the Arabian Sea. Larval retention and self‐recruitment in the Arabian Sea could explain the recent genetic divergence between P. h. megasculptus and P. h. homarus. Geographic distance and minimum SST were significantly associated with genetic differentiation in multivariate analysis, suggesting that larval tolerance to SST plays a role in shaping the population structure of P. homarus.
Long-term movement patterns of deep-water rock lobster Palinurus gilchristi were investigated off the south coast of South Africa using tag recapture data. Over a 12 yr period (1988 to 1999), 30 043 lobsters were tagged at 5 sites. From west to east, these were Cape Agulhas, West and East Agulhas Bank, Mossel Bay to Port Elizabeth, and Port Alfred. The overall recapture rate was 7.51%, with individuals remaining at large for up to 10.3 yr. Overall, 547 (25.8%) tagged lobsters of both sexes moved > 20 km within or between sites. We hypothesized that counter-current migration of juveniles would occur to redress downstream dispersal of phyllosoma larvae by the westerly flowing Agulhas Current. The vast majority of migrants (72.6%) did prove to be immature (carapace length < 72 mm) and did migrate eastwards against the prevailing flow of the Agulhas Current. The Cape Agulhas population (at the western extreme) comprised juveniles only. Over 97% migrated > 50 km, either southeastwards offshore to the West and East Agulhas Bank sites (106 lobsters, covering a mean distance of 154 km), or eastwards alongshore to the Mossel Bay to Port Elizabeth site near the center of the range (33 lobsters, 461 km). The fastest 5% of migrants moved at 0.43 to 0.78 km d -1
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