Seascape Connectivity Shapes Genetic and Species β-Diversity in Tropical Reef Fishes

Habitat configuration governs the movement of organisms across landscapes, thereby shaping both population structure and community assembly. While theoretical and empirical studies have assessed how habitat connectivity simultaneously influences intra- and interspecific diversity, direct comparisons across contrasting biogeographic regions remain limited. Here, we investigate patterns of genetic and species β-diversity in tropical reef fishes across two ocean basins with distinct spatial configurations: the Caribbean Sea and the Western Indian Ocean. Using a comparative framework based on species occurrence data from five fish families and single nucleotide polymorphism (SNP) data from 19 species, we detected significant isolation by distance at both population and community levels in the Western Indian Ocean, but only at the community level in the Caribbean Sea. Additionally, genetic and species β-diversity were positively correlated among species in the Western Indian Ocean, but not in the Caribbean Sea. Together, these results suggest that the shorter inter-reef distances of the Caribbean Sea promote higher connectivity, leading to a decoupling of intra- and interspecific β-diversity patterns.