The genomic characterization of massive Porites in two different environments on Guam, Micronesia

Porites, one of the most prevalent and resilient coral genera on Indo-Pacific reefs, includes an unresolved number of cryptic massive Porites species found in multiple environments. Higher bleaching resistance has been observed across multiple species, including massive Porites, in turbid river deltas compared to nearby fore reefs, however, river deltas are subject to multiple, local anthropogenic stressors. Differential bleaching response may be driven by environment, or intra- or interspecific differences. Here, we use ddRADSeq to identify the number of cryptic species and characterize the population genomics of massive Porites in these two distinct, adjacent habitats on Guam. We detected seven lineages of massive Porites, likely constituting different species. The largest clade predominantly occurs in river deltas while all others predominantly occur on fore reefs, with some more localized than others. The river delta clade exhibited small, yet significant population structure, while the two largest fore reef clades exhibited higher gene flow. Overall, these results indicate that river deltas may provide more limited refuge for corals during bleaching events considering interspecific differences between corals in these habitats and local stressors acting on river deltas.