Species-specific variation in thermal tolerance in Montipora capitata and Porites compressa corals across two Hawaiian bay habitats

Understanding variation in coral thermal tolerance is critical for predicting coral responses and reef persistence under future ocean conditions. This study investigated thermal performance of two dominant Hawaiian reef-builders, Montipora capitata and Porites compressa , collected from three sites in Kāneʻohe Bay and one site in nearby Kailua Bay (Ulupaʻu). Corals were subjected to a controlled heat-stress assay, and photosynthetic efficiency was measured using Pulse Amplitude Modulation (PAM) fluorometry. Thermal tolerance was quantified as effective dose 30 (ED30), the experimental degree heating week (eDHW) exposure at which corals lost 30% of photosynthetic efficiency. Both species exhibited high thermal tolerance, with ED30 values ranging from 5.93 to 7.21 eDHW and mean values of 6.44 eDHW for M. capitata and 6.70 eDHW for P. compressa . Within Kāneʻohe Bay, thermal performance was similar for both species. In contrast, P. compressa from Ulupaʻu displayed significantly greater tolerance than Kāneʻohe conspecifics and all M. capitata populations. Together, these findings demonstrate that coral thermal tolerance is shaped by environmental history in a species-specific manner. This highlights the importance of selecting both appropriate species and source populations when identifying thermally resilient corals for restoration and conservation strategies in Hawaiʻi.