Connectivity differs by orders of magnitude among co-distributed corals, affecting spatial scales of eco-evolutionary processes.

Reef building corals are declining worldwide, yet the processes driving population connectivity remain poorly understood. Using complementary analyses, we provide quantitative estimates of ecologically relevant dispersal and evolutionarily important gene flow in co-distributed coral species on the Great Barrier Reef. We find dispersal distances across meters (23 to 102 meters) in the brooding and across kilometers (21 to 52 kilometers) in the broadcast spawning , consistent with expectations based on their reproductive modes. Similarly, while gene flow rates averaged over the past ~400,000 generations are very low among populations, populations are well connected. As a result, estimates of genetic diversity across multiple metrics and population sizes are smaller in compared to . These results highlight the importance of spatial scales and reproductive modes in predicting coral adaptive responses and underscore the value of considering spatial connections between target populations in conservation and restoration.