The Coral Triangle is the world's most biologically diverse marine environment, and the origins of this diversity have been the subject of debate for decades. Biogeographic studies have alternatively argued that this region is a center of (1) origin, (2) overlap, (3) accumulation, or (4) survival. Genetic studies focused on the pattern, distribution, and age of lineage divergence across a broad array of marine fishes and other groups show alternating support for all of these hypotheses, indicating pluralistic origins for the Coral Triangle biodiversity hotspot. While acknowledging multiple causations, the relative contribution of each model is still uncertain. Given the social and economic importance of marine fishes in the Coral Triangle combined with sharp declines in populations and coral reef habitat in this region, understanding the ecological and evolutionary processes shaping biodiversity in the Coral Triangle is more important now than ever. New genomic tools as well as standardized sampling methodologies hold great promise for refining our understanding of the processes driving lineage divergence in the Coral Triangle, providing information essential for effective conservation planning in this region.

THE CORAL TRIANGLE, FROM PATTERN TO PROCESS

Although the name and geographic scope of the Coral Triangle has changed greatly over the past 60 years [1141], it is unquestionably the most diverse marine region on the planet. Defined by the presence of >500 hard coral species [2566] and spanning six Southeast Asian nations, species diversity in a broad range of marine taxa reaches a global maximum in the Coral Triangle with steep declines in diversity moving away from this biodiversity hotspot [200,205,747,1141,2123,2415]. In reef fishes, diversity peaks in the Birds Head region of West Papua, Indonesia [41], with 1511 species in 451 genera and 111 families, 26 species, and 14 families being restricted to this region. Species diversity in fishes can be one to two orders of magnitude higher in the Coral Triangle than peripheral reefs of the Pacific or the Caribbean.