Genetic diversity is shaped by life history traits and environmental factors across the marine ecoregions of the world (MEOW), a condition that serves as a valuable framework to enhance our understanding of gene flow processes and identifying priority conservation centers among populations in different regions. We investigated the genetic and phylogenetic diversity of 13 decapod crustacean species distributed across the marine ecoregions of Brazil. We hypothesized that ecoregions act as barriers to gene flow, creating distinct population structures and varying genetic diversity levels. We examined how habitat type, bathymetry, geographical distribution, and larval development affect genetic diversity. Mitochondrial markers from 13 species of the four major decapod groups (Anomura, Brachyura, Caridea, and Penaeoidea) were analyzed using nucleotide diversity, haplotype networks, pairwise FST, and linear mixed-effects models (LMER). Results show no significant genetic structuring among ecoregions. Genetic diversity correlates with habitat type (P < 0.05), with species from less impacted areas, especially intertidal zones like rocky shores and estuaries, displaying higher diversity. Phylogenetic diversity (PD) and species richness (SR) varied, with the highest PD in eastern Brazil and the highest SR in southeastern Brazil. Intertidal zones showed the highest genetic diversity, likely due to their complex microhabitats and environmental variability. Our findings indicate that environmental and geographical barriers defined by the ecoregions do not significantly impede genetic connectivity among decapod crustaceans, which suggests that high dispersal potential of larval stages facilitates genetic flow across ecoregions. The results underscore the need for conservation strategies that consider the high genetic connectivity and diversity of marine species across broad spatial scales.
