Northwestern Hawaiian Islands Connectivity
Ecosystem Monitoring Studies
Coral Health Assessment Program
Maps and Data
Science Management Integration and Communications
Science Terms Glossary
Coral reef health and response of corals to climate change
The Research Problem
The health of coral reefs along the entire Hawaiian Archipelago is vitally important to our marine ecosystems. There are many factors that affect the health of our reefs. These include local factors such as sedimentation, nutrification, overfishing, coastal construction, invasive species, and overuse that affect specific sites and there are global problems that influence reefs worldwide. Concerns over coral bleaching caused by temperature increases and ocean acidification due to oceanic uptake of atmospheric CO2 originating from human activities such as burning of fossil fuels and land-use changes have been increasing. . These issues have raised serious concerns regarding their adverse effects on corals and calcifying communities.
To address ocean acidification on coral reefs we conducted manipulative experiments to determine the effects of ocean acidification on marine organisms, while developing a predictive model to test various assumptions and scenarios surrounding the possible effects of global climate change, and advance the understanding of climate change effects on corals through the development of coral calcification hypotheses.
Our experiments showed that an increase in ocean acidification will result in a decrease in recruitment and growth of crustose coralline algae by over 90% before the end of the century. Additionally, a reduction in calcification in Hawaiian corals by 20-30% will occur as well as a further net loss of calcium carbonate (CaCO3) material. The “proton flux hypothesis” offers an explanation for the reduction in calcification caused by ocean acidification and other phenomena associated with increasing acidification. The model is a radical departure from previous thought, but is consistent with existing observations and provides new insights for future studies. Additionally, our Coral Mortality and Bleaching Output (COMBO) model shows patterns of seasonal temperature and temperature anomalies in both the Northwestern and Main Hawaiian Islands, and Johnston Atoll. Projected changes over time show higher initial decline in coral cover at high latitude before synergistic effects are accounted for. Synergistic impacts of increased temperature and acidification will further reduce coral growth. The projected impact of the two factors acting in unison increases with decreasing latitude in the Hawai‘i region.
We evaluated the relative biological “health” and “value” of the coral reefs of the Northwestern Hawaiian Islands in the context of the entire Hawaiian Archipelago. Sufficient data on five vitally important biological indicators (reef fish biomass, reef fish endemicity, total living coral cover, population of the endangered Hawaiian monk seal (Monachus schauinslandi), and the number of female green sea turtles (Chelonia mydas) nesting annually on each island) were used to develop a simple integrated scoring and ranking scheme. The scoring shows that the ecological status of the Main Hawaiian Islands is extremely poor and that the Northwestern Hawaiian Islands represent a valuable biological resource that is pristine in comparison to the Main Hawaiian Islands. A sensitivity analysis revealed that all five biological metrics show essentially the same pattern, suggesting that numerous biological characteristics of ecosystems are impacted in a similar manner under anthropogenic stress.
Simulating present and future temperature and CO2 conditions helps us understand what corals and other marine organisms will be facing in the future. Developing predictive models using our experimental data allow us to test various assumptions and scenarios surrounding the possible effects of global climate change on coral reefs. By currently understanding what we face in the future we can initiate solutions to combat this rapidly advancing adversary.