Climate change is affecting corals on a backdrop of many other anthropogenic stressors such as sedimentation, overfishing, trampling by snorkelers and divers, and nutrient loading. It is important that we understand why some corals species are more susceptible than others to these local and global stressors to gain a better idea of what future reefs may look like. The goals of my research are to provide a framework to model future species composition, abundance, and available habitat for future coral reefs. With these models, scientists, managers, and policy makers can prioritize areas that are subject to the most immediate and dangerous threats and discuss strategies to minimize local and climate change effects in those areas.
Winners and Losers: Hawaiian Corals
Previous work has shown ocean warming and acidification reduces coral growth and increases coral bleaching (through the loss of algal symbionts); however, responses are not uniform within and between coral species. This suggests some individuals may not be affected by end-of-century climate change scenarios. To gain a better understanding of the future of coral reefs in Hawaiʻi, I conducted a series of laboratory experiments to determine the relative susceptibility of five abundant species including the endemic finger coral (Porites compressa), lace coral (Pocillopora damicornis), rice coral (Montipora capitata), crust coral (Leptastrea purpurea) and mushroom coral (Fungia scutaria) to future climate change conditions.
Overall, I found that ocean warming had a greater negative impact on coral growth compared to ocean acidification. The crust coral showed no detectable response in growth to increased temperatures and acidity, revealing this species may be more resistant to climate change. Ocean acidification also did not appear to effect growth in rice corals. However, the other four coral species all had lower growth rates under ocean warming conditions, and the endemic finger coral was found to be the most susceptible coral species to these climate change stressors.
Reef recruitment and biodiversity
In collaboration with NOAA Coral Reef Ecosystem Program, I am currently assessing the effects of ocean acidification and warming on reef recruitment and biodiversity using Autonomous Reef Monitoring Structures (ARMS).
Coral Bleaching Assessment and Monitoring
Corals reefs of the Hawaiian Islands have experienced three bleaching events: 1996, 2014, and 2015. The severity and extent of this bleaching event may pose a significant threat to the integrity of this unique ecosystem.
Our recent paper describes the July 2014 flooding event and the Sept bleaching event. Also, we discuss the comparison of these most recent events with previous: bleaching events (1996 and 2014) and freshwater kills (1965, 1988, and 2014). Overall, the freshwater flooding event reduced coral cover in the northern part of Kāneʻohe Bay by 22.5%. A subsequent major bleaching event during Sept 2014 caused extensive coral bleaching and mortality throughout the bay and further reduced coral cover in the freshwater “kill” area by 60.0 %. The high temperature bleaching event only caused a 1.0 % reduction in live coral throughout the portion of the bay not directly impacted by the freshwater event. Thus the combined impact of the low salinity event and the thermal bleaching event appears to be more than simply additive.
I am currently assessing the resiliency of this unique ecosystem to these consecutive bleaching events in collaboration with CRAMP and USGS.