Coral Thermal Tolerance and Heat Stress Mitigation Strategies

Global warming is considered to be the most severe threat to coral reefs. This is evident in an increase of frequency and severity of global coral bleaching events (loss of coral symbionts due to heat stress) leading to coral death and reef degradation. The current focus of the MABEE lab is to find ways to mitigate the impact of global warming on corals by either strengthening corals to resist marine heat waves (ENCORE project) or by altering the environment to reduce thermal stress (AU Coral project).

AU Coral (NSF-funded #2320629, since 2023, lead-PI: Sawall): The MABEE lab is one of very few labs that explores the potential utility of artificial upwelling (AU), a geoengineering technology that uplifts cooler deep water to the warm surface waters during heat stress events. This reef management tool could offer a localized mid-term solution to allow corals a more gradual adjustment to global warming. The overarching goal of theAU Coral project is to provide an understanding about how AU could be used for surface water cooling by identifying AU scenarios (depth, duration) that mitigate coral bleaching effectively, while imposing minimal risk of unwanted side effects. Here we focus on creating daily short-term thermal refugia (pulsed AU for a few hours a day) with waters from the intermediate and lower euphotic zone (30-100 m). Using the BMMF facility, we investigate immediate and lasting effects (legacy) of AU on coral physiology during heat stress. Furthermore, we assess reef community responses to heat stress and to heat stress + AU. 

Lab participants: Chloe Carbonne, Janna Hynds, Jacob Welter, Teagan Roome, Elli Dunleavy, and various undergraduate students in Bermuda and Tempe. 

Collaborators: Liza Roger (ASU), Maysa Ito (GEOMAR, GER), ASU proteomics core facility and team 

ENCORE - Phase 3 (funded by Heising-Simons Foundation International, start May 2026): The overall goal of this collaborative project is to address coral resilience, acclimatization, and adaptation to a warming ocean. The focus of the 3rd phase of this multi-year program is to understand whether surviving corals become more heat-tolerant over time and whether this resilience can be passed on to their offspring. These insights are critical for predicting the future of coral reefs in a warming ocean.

Building on earlier phases, we have shown that heat waves can act as a form of natural selection, favoring more resilient corals, and have identified key differences in vulnerability and tolerance among species. We also established a unique resource: reef corals with known heat-stress histories and successfully reared large numbers of their offspring. In the current phase, we investigate whether heat tolerance is temporary, lasting, or inherited, and whether it comes with hidden costs such as reduced growth or reproduction. By tracking both adult corals and their offspring over multiple years and across contrasting reef environments (Bermuda and Thailand), we anticipate novel insight into the mechanisms, limits, and trade-offs of coral adaptation to climate change.

To address these questions, a combination of in-situ and experimental manipulation studies using mesocosms (e.g., BMMF) and / or aquaria is used, in conjunction with physiological measurements and molecular analyses. The study is conducted in collaboration with Marlene Wall (University of Vienna) and colleagues at the Phuket Marine Biological Station (Thailand).

PIs: Yvonne Sawall, Marlene Wall (University of Vienna, Austria)  

Lab participants: New post-doc to be hired by fall 2026, Janna Hynds, Teagan Roome, undergraduate students and short-term visiting graduate students.

AU Reef (DFG-funded, 2017-2019). This award allowed to conduct some preliminary studies on the potential use of artificial upwelling (AU) during heat stress on coral physiology (manipulation experiment, Sawall et al. 2020, see also ) and on surface waters biogeochemistry (modelling approach, Feng et al. 2020). 

Lead-PI: Yuming Feng (GEOMAR, GER)

Collaborators: Yvonne Sawall, Marlene Wall (GEOMAR, GER), Mario Lebrato (BCSS, Mozambique)

ENCORE - Phase 2 (HSFI-funded, 2022-25). This award investigated coral resilience and adaptation to ocean warming in reefs of Bermuda, Hawaiʻi, and the Cayman Islands. It examined acute heat response, recovery and legacy effects in adult corals assessing whether heat stress leads to long-term weakening or increased resilience (“stress hardening”). Furthermore, it investigated heat stress responses in early life stages of corals, and the role microbial communities play in the resilience of recruits. 

PIs: Yvonne Sawall, Samantha de Putron (BIOS), Gretchen Goodbody-Gringley (CCMI), Hollie Putnam (URI)

Lab participants and others: Brett Jameson (postdoc), Florence Fields (PhD student URI), undergraduate students and short-term visiting graduate students.