Effects of climate change on marine biodiversity on the western Atlantic coast

The current climate crisis, driven by greenhouse gas emissions, threatens global biodiversity, including that in marine ecosystems. However, projections for the western Atlantic Ocean that jointly quantify species richness and endemism while accounting for spatially biased and incomplete occurrence data remain limited. We addressed this gap across the western Atlantic from 57°S to 40°N, within 1500 km of the coast and on the continental shelf in waters shallower than 150 m. Using broad taxonomic coverage across vertebrates, invertebrates, and algae, we modeled biodiversity metrics directly as species richness and the corrected weighted endemism index (WEIc), applied uniform sampling from sampling effort (USSE) to minimize the effects of spatially biased and incomplete occurrence records on predictions, and tested multiple algorithms to project these metrics under Shared Socioeconomic Pathway (SSP) scenarios SSP2-4.5 and SSP5-8.5 for 2050 and 2100. The results indicated a significant reduction in species richness and endemism, with up to 69% of the study area projected to experience a reduction of more than 5% in species richness under the high-emissions scenarios. The most affected areas included the coast of Florida, the Gulf of Mexico, the Caribbean, the northern region of South America, and southern Brazil. The decrease in endemism was equally concerning, with significant reductions predicted in areas of high diversity, threatening species adapted to specific ecological niches and increasing the risk of local extinctions. Vertebrates and invertebrates showed the greatest reductions in richness in the Gulf of Mexico, the Caribbean, northeastern Brazil, and northern Argentina. For algae, the most significant decreases were predicted for Florida and southern Brazil. This loss of biodiversity could compromise the resilience of marine ecosystems and the availability of fishery resources, highlighting the urgent need for coordinated global actions.