Oceanographic connectivity strongly restricts future range expansions of critical ecosystem structuring species

Climate change is anticipated to profoundly shift the distribution of marine biodiversity, yet the extent to which species can track suitable habitats remains unknown. In particular, oceanographic connectivity, the exchange of individuals mediated by ocean currents, can play a crucial role in dispersal and future range dynamics. Here, we integrate species distribution models and biophysical models to quantify the extent to which oceanographic connectivity can restrict future range expansions of marine forests of seagrasses and brown macroalgae under contrasting climate change scenarios. Our results show substantial range contractions for both groups, particularly under high emissions. Despite the potential for broad poleward range expansions that could partially offset range constrictions, oceanographic connectivity emerges as a major limiting factor, restricting potential expansion areas of newly suitable habitats by up to 8-fold for seagrasses and by 6.7-fold for brown macroalgae. These restrictions may push up to 90% of species into experiencing negative net habitat changes. Notably, connectivity barriers are well-defined at the global scale, and particularly strong in regions projected to hold extensive future suitable habitat, including the Okhotsk Sea, New Zealand, and the Arctic. Overall, our findings emphasize the need for conservation and management strategies that explicitly integrate both changing habitat suitability and oceanographic connectivity to provide the most accurate and actionable guidance for protecting marine forests in a changing climate.