Ocean temperatures have been accelerating at an alarming rate mainly due to anthropogenic fossil fuel emissions. This has led to an increase in the severity and duration of coral bleaching events. Predicted projections for the state of reefs do not take into account the rates of adaptation or acclimatization of corals as these have not as yet been fully documented. To determine any possible changes in thermal tolerances, manipulative experiments were conducted to precisely replicate the initial, pivotal research defining threshold temperatures of corals nearly five decades ago. Statistically higher calcification rates, survivorship, and lower mortality were observed in Montipora capitata, Pocillopora damicornis, and Lobactis scutaria in the present study at 31 °C compared to the original 1970 findings. First whole colony mortality was also observed to occur sooner in 1970 than in 2017 in M. capitata (3 d vs. 15 d respectively), L. scutaria (3 d vs. 17 d), and in P. damicornis (3 d vs. 13 d). Additionally, bleaching occurred sooner in 1970 compared to the 2017 experiment across species. Irradiance was an important factor during the recovery period for mortality but did not significantly alter calcification. Mortality was decreased by 17% with a 50% reduction in irradiance during the recovery period. These findings provide the first evidence of coral acclimatization or adaptation to increasing ocean temperatures for corals collected from the same location and using close replication of the experiment conducted nearly 50 years earlier. An important factor in this increased resistance to elevated temperature may be related to removal of the discharge of treated sewage into Kāne‘ohe Bay and resulting decrease in nitrification and eutrophication. However, this level of increased temperature tolerance may not be occurring rapidly enough to escape the projected increased intensity of bleaching events, as evidenced by the recent 2014 and 2015 high coral mortality in Hawai‘i (34%) and in the tropics worldwide.

Coral reefs are the foundation to our social, cultural, and economic life; however, reefs around the world are currently being threatened by many local and global impacts. Ongoing increases in seawater temperature pose significant threats to the integrity of these valuable ecosystems through extensive coral bleaching events. Therefore, we developed a coral health reference card, the Hawaiian Koʻa (coral) Card, to assess and quantify coral bleaching and to educate the community about its impacts in Hawai‘i. To accurately quantify the change in coral color during bleaching, controlled laboratory studies followed by field validations and surveys were conducted. Colors presented on the Hawaiian Koʻa Card have been linked to physiological state and health (e.g., symbiont density, chlorophyll levels, photosynthetic performance) of common coral species in Hawaiʻi due to bleaching. The Hawaiian Koʻa Card provides a technical solution to inform and improve management of our nearshore resources through collaborative monitoring efforts by community members, educators, researchers, and managers on a state-wide scale, which will assist in determining management efficacy, identifying regions and species of resilience, establishing baselines and focus areas, and developing and executing rapid response plans.

Many corals and reef-dwelling organisms are susceptible to the impacts of storm events, which are typically characterized by large inputs of freshwater, sediment, and nutrients. The majority of storm effects are focused on shallow, nearshore reef flats, as low salinity and sedimentation tend to dissipate with depth and distance from shore. In April 2018, record rainfall on the northern coast of Kaua‘i caused extensive flooding and landslides, introducing large amounts of freshwater and sediment into nearshore reefs. Using benthic and fish transects from 2016–2019 and temperature, sediment, and rainfall data gathered pre- and post-flood, this study aimed to quantify and explicate the effects of flooding on the various biotic populations of two reef habitats at Pila‘a and Hā‘ena, Kaua‘i. Results from the shallow Pila‘a reef suggest sediment and freshwater-associated declines in mean urchin abundance (−52.0%) and increases in mean coral bleaching (+54.5%) at the flood-prone eastern sector. Additionally, decreases in mean urchin (−65.7%) and fish (−42.3%) populations were observed at shallow Hā‘ena transects, but not deep sites, supporting the occurrence of depth-specific affliction. Multivariate community-level analyses affirmed much of these results, showing a significant shift in community structure before and after the flood at both Pila‘a and Hā‘ena. The outcomes of this study are pertinent to strategic design and solution development by local aquatic resource managers, especially as anthropogenic climate change continues to increase the frequency, duration, and intensity of storm events.

No abstract