Field sampling
We selected Pseudodiploria strigosa (Dana, 1846) as the coral host species because it is widely distributed across the Bermuda platform. In Bermuda, a high-latitude subtropical coral reef system, corals are exposed to a wide annual range in temperature fluctuations and reef-zone specific thermal regimes ranging from more fluctuating profiles in the inner lagoon patch reefs and milder conditions in the outer reefs (de Putron and Smith 2011a; Courtney et al. 2017, 2020; Lima et al. 2020; Wong et al. 2021). The reef zones sampled were approximately 8 km apart (Lima et al. 2020) and P. strigosa is a broadcast spawner; therefore, there is a high likelihood that gene flow between the coral hosts colonizing inner and outer reefs is maintained and that the host genetics is not structured into different populations. Indeed, studies on other species have indicated high genetic exchange among reef sites in Bermuda (Serrano et al. 2014, 2016). The sampling period occurred between May 18th and May 22nd, 2017, late spring in the northern hemisphere, when environmental conditions between the two reef zones, especially temperature, are similar. The environmental gradient assessed here are based on the knowledge that these two reef zones are exposed to different regimes on a seasonal basis, with the most striking fluctuations occurring in the winter and summer months (de Putron and Smith 2011b; Smith et al. 2013; Courtney et al. 2017). Therefore, we selected this period to capture a potential long-term acclimatization of the coral holobiont to their reef zones, and not their immediate response to acute temperature fluctuations. The mucus from P. strigosa was collected from six colonies from the inner and outer reef zones (n = 12 colonies total) to describe the natural spatial variability in the coral microbiome (Lima et al. 2020, 2022). After the mucus sampling, each coral colony was collected using a hammer and chisel to be used in the experiments to assess heat resistance. The colonies (n = 12 total, 6 from each reef zone) were carefully placed in a cooler with seawater and transported to the Bermuda Institute of Ocean Sciences. The collections were performed via SCUBA diving at 4-6m depth.