Genomic data reveals habitat partitioning in massivePoriteson Guam, Micronesia

Abstract

AbstractCorals in marginal reef habitats generally exhibit less bleaching and associated mortality compared to nearby corals in more pristine reef environments. It is unclear, however, if these differences are due to environmental differences, including turbidity, or genomic differences between the coral hosts in these different environments. One particularly interesting case is in the coral genusPorites, which contains numerous morphologically similar massivePoritesspecies inhabiting a wide range of reef habitats, from turbid river deltas and stagnant back reefs to high-energy fore reefs. Here, we generate ddRAD data for 172Poritescorals from river delta and adjacent fore reef populations on Guam to assess the extent of genetic differentiation among massivePoritescorals in these two contrasting environments and throughout the island. Phylogenetic and population genomic analyses identify seven different clades of massivePorites, with the two largest clades predominantly inhabiting either river deltas and fore reefs, respectively. No population structure was detected in the two largest clades, andCladocopiumwas the dominant symbiont genus in all clades and environments. The perceived bleaching resilience of corals in marginal reef environments may therefore be attributed to interspecific differences between morphologically similar species, in addition to potentially mediating environmental differences. Marginal reef environments may therefore not provide a suitable refuge for many reef corals in a heating world, but instead host additional cryptic coral diversity.