Genetic diversity is crucial for species’ maintenance and persistence, yet is often overlooked in conservation studies. Species diversity is more often reported due to practical constraints, but it is unknown if these measures of diversity are correlated. In marine invertebrates, adults are often sessile or sedentary and populations exchange genes via dispersal of gametes and larvae. Species with a larval period are expected to have more connected populations than those without larval dispersal. We assessed the relationship between measures of species and genetic diversity, and between dispersal ability and connectivity. We compiled data on genetic patterns and life history traits in nine species across five phyla. Sampling sites spanned 600 km in the northwest Mediterranean Sea and focused on a 50 km area near Marseilles, France. Comparative population genetic approaches yielded three main results. (1) Species without larvae showed higher levels of genetic structure than species with free-living larvae but the role of larval type (lecithotrophic or planktotrophic) was negligible. (2) A narrow area around Marseilles, subject to offshore advection, limited genetic connectivity in most species. (3) We identified sites with significant positive contributions to overall genetic diversity across all species, corresponding with areas near low human population densities. In contrast, high levels of human activity corresponded with a negative contribution to overall genetic diversity. Genetic diversity within species was positively and significantly linearly related with local species diversity. Our study suggests that local contribution to overall genetic diversity should be taken into account for future conservation strategies.