Limited genetic diversity across a broadly connected range in the fished purple stone crab Homalaspis plana

The purple stone crab ( Homalaspis plana ) is a commercially important benthic species along the southeast Pacific coast, with average annual landings reaching approximately 137 tons over the last 26 years. Despite sustained size- and sex-biased artisanal exploitation, little is known about the species’ genetic variation and dispersal patterns. In this study, we analyzed the population genetic structure of H. plana across a ∼3500 km stretch of coastline (20.13°S-39.4°S) using mitochondrial COI sequences and six nuclear microsatellite loci from 222 specimens. Our findings point to a low genetic diversity, placing H. plana in the lower quartile of marine brachyuran species worldwide in terms of haplotype diversity. Microsatellite analyses reveal substantial local self-recruitment and elevated inbreeding levels, yet only minor spatial genetic differentiation was detected, even across a major biogeographic transition zone. These results suggest that persistent fishing pressure and larval retention mechanisms may be driving genetic erosion, even though gene flow appears sufficient to sustain panmixia at larger spatial scales. The interplay between broad-scale connectivity and limited external replenishment underscores the vulnerability of local populations to sustained exploitation and environmental shifts. Our study highlights the need for fisheries management strategies that incorporate connectivity processes and supports the integration of population genetic data into conservation strategies for marine species with complex life histories, especially in the face of changing oceanographic conditions.