Community‐level egg and larval trait interactions with the Amazon River plume determine its role as a dispersal barrier

The Amazon River plume (ARP) functions as a dynamic and porous biogeographic barrier whose permeability to larval dispersal depends on the interplay between species' biological traits and oceanographic processes. Using biophysical modeling combined with a dual analytical framework, namely a multivariate regression tree (MRT) and a generalized additive model (GAM), this study quantifies the factors regulating this permeability for eggs and larvae, taking into account a community‐based approach of broad taxonomic groups present within the regional species pool, including corals, marine gastropods, crustaceans, and fishes in the western tropical Atlantic. Our results reveal a clear hierarchy of controls, with planktonic larval duration (PLD) emerging as the primary determinant, explaining most of the variation in dispersal distances (58%). Diel vertical migration (DVM) was the second biological key factor (11%), modulating whether larvae were locally retained (with DVM) or exported to distant regions (without DVM). Seasonality and the geographic context of spawning habitats further shaped larval interactions with the plume, reinforcing the spatial and temporal complexity of this system. Overall, the ARP acts not as an absolute barrier but as a continuum of permeability, a selective filter that restricts dispersal of eggs and larvae of coastal species with short PLDs and low physiological tolerance, yet facilitates exchange for communities with greater dispersal capacity and behavioral plasticity.