The highly heterogeneous Humboldt Current System (HCS) and the 30°S transition zone on the southeast Pacific coast, represent an ideal scenario to test the influence of the environment on the spatial genomic structure in marine near-shore benthic organisms. In this study, we used seascape genomic tools to evaluate the genetic structure of the commercially important ascidian Pyura chilensis, a species that exhibits a low larval transport potential but high anthropogenic dispersal. A recent study in this species recorded significant genetic differentiation across a transition zone around 30°S in putatively adaptive SNPs, but not in neutral ones, suggesting an important role of environmental heterogeneity in driving genetic structure. Here, we aim to understand genomicoceanographic associations in P. chilensis along the Southeastern Pacific coast using two combined seascape genomic approaches. Using 149 individuals from five locations along the HCS, a total of 2,902 SNPs were obtained by Genotyping-By-Sequencing, of which 29-585 were putatively adaptive loci, depending on the method used for detection. In adaptive loci, spatial genetic structure was better correlated with environmental differences along the study area (mainly to Sea Surface Temperature, upwelling-associated variables and productivity) than to the geographic distance between sites. Additionally, results consistently showed the presence of two groups, located north and south of 30°S, which suggest that local adaptation processes seem to allow the maintenance of genomic differentiation and the spatial genomic structure of the species across the 30°S biogeographic transition zone of the Humboldt Current System, overriding the homogenizing effects of gene flow. Most marine taxa, and especially near-shore invertebrates, have free-living larval stages allowing dispersal across heterogeneous environments that lack evident barriers to gene flow 1-3. Dispersal has been often assumed to be an effective mechanism of maintaining connectivity between local populations 4,5. Nonetheless, many species display inconsistent patterns of genetic structure with those predicted from their developmental modes 6-9. For instance, several direct developers are broadly distributed over thousands of kilometers, probably through long-distance dispersal mediated by rafting 6,8,10-13 , while many broadcast-spawners exhibit high levels of genetic structure at narrower geographical scales 2,7,14. Currently, it is widely accepted that evolutionary forces, despite dispersal, can shape the genetic structure of a species across its distribution. Such factors include natural selection, phenotypeenvironmental mismatch and local adaptation, which may override the genetic signatures expected solely on the basis of gene flow 15-17. Understanding how environmental factors influence the contemporary spatial distribution of genomic diversity has become a main goal in evolutionary ecology and biogeography 18-23. Many relevant environmental variables are heterogeneous across a species' distributi...