Genetic diversity is the raw foundation for evolutionary potential. When genetic diversity is significantly reduced, the risk of extinction is heightened considerably. The long-snouted seahorse (Hippocampus guttulatus) is one of two seahorse species occurring in the Northeast Atlantic. The population living in the Ria Formosa (South Portugal) declined dramatically by 2008, prompting fears of greatly reduced genetic diversity, reduced effective population size, and possibly a genetic bottleneck. This study tests this hypothesis using samples from eight microsatellite loci taken from 2001 and 2013, either side of the 2008 decline. The data suggests that the population has not lost its genetic diversity, nor experienced a genetic bottleneck. Effective population size has seemingly increased but whether these results have been affected by sample size is not clear. However, plausible effective population size is approaching the threshold to retain evolutionary potential in perpetuity. We found that overall relatedness had doubled between 2001 to 2013, leading to questions of future inbreeding. Several explanations are proposed for these results, such as plausible gene flow and the duration of the demographic decline. Given results presented here, recommendations for more precise estimates are given that may be able to highlight discrepancies between this study and other relevant literature, but also in light of a more recent demographic decline.
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