Thermally induced coral bleaching is a major cause of reef decline,
though it could be offset by coral adaptation. Here we used three
complementary approaches to identify which environmental gradients drive
local adaptation in two common Florida corals, Porites astreoides and
Agaricia agaricites. Depth is the most important factor for both
species: each contains three genetically distinct lineages segregated by
depth. Additionally, each lineage harbors genetic variation aligning
with other environmental gradients, though elevated temperature is
typically not one of them. In A. agaricites, nitrogen variation predicts
genetic divergence in the deep and mid-depth lineages, while cold
temperature is the most important driver within the shallow lineage.
Nitrogen and cold are also associated with genetic variation in P.
astreoides, and high temperature was highlighted only once in the deep
lineage of P. astreoides. In both species, lineages don’t share
environment-associated groups of SNPs, indicating that lineages adapt
independently. Overall, the locally available genetic variation in our
two corals species seems unlikely to provide thermally adaptive genetic
variants for future warming. Our results map the environmental gradients
that create the strongest genetic barriers for corals, which could serve
as a guide for reef restoration.