Marine habitats are in decline worldwide, precipitating a strong interest in marine conservation. The use of biogeographic data to designate ecoregions has had significant impacts on terrestrial conservation efforts. However, classification of marine environments into ecoregions has only become available in the last several years, based on biogeographic data supplemented by geomorphology, ocean currents, and water temperatures. Here we use a comparative phylogeographic approach to test for concordant phylogeographic patterns in three closely related species of Tridacna giant clams across the Coral Triangle, the most biodiverse marine region in the world and one of the most threatened.