Stepping-stone larval dispersal networks maintain broad-scale connectivity across the Indo-West Pacific

Connectivity between patchy marine habitats through larval dispersal is crucial for the persistence of local populations. Studies of various marine species suggest broad-scale gene flow across the tropical Indo-West Pacific (IWP), presumably facilitated by larval dispersal via stepping-stone habitats. However, the generational timescales and geographic paths involved in such dispersal remain unclear, owing to limited biophysical modelling studies. Here, we quantified connectivity among patchy habitats of the mangrove whelk Terebralia palustris across the IWP using habitat suitability modelling, larval dispersal modelling, and mitochondrial DNA-based population genetic analysis. Our modelling revealed a single larval dispersal network connecting all potential habitats across the IWP. At least 14 generations were required for dispersal via stepping-stone habitats to connect the outer edges of the IWP. The Maldives and Seychelles served as key stepping stones for dispersal, linking the western Indian Ocean and the western Pacific Ocean through monsoon-driven ocean currents. Major haplotypes were shared across 9 regions of the IWP, providing genetic support for a single larval dispersal network. Our findings provide fundamental insights into ecological networks formed by stepping-stone dispersal across the IWP, which maintain broad-scale connectivity of T. palustris and potentially other coastal species.