Coral Thermal Tolerance and Global Warming 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, picture 2.1) leading to coral death and reef degradation. While comparatively much research has been done to understand the mechanisms of thermal tolerance, the current focus of the MABEE Lab is to find solutions to mitigate the effects of global warming on corals. The need for immediate and ambitious action plans to mitigate global warming-related reef loss has become a high priority, in particular after the most recent devastating global coral bleaching event (2014-2017). Such plans may include novel interventions, such as assisted evolution, reef shading, or artificial upwelling (AU). The MABEE Lab is one of very few labs that explores the potential utility of artificial upwelling, a geoengineering technology that uplifts cooler deep water to the warm surface waters during heat stress events (picture 2.2). This management tool could offer a localized mid-term solution to allow corals a more gradual adjustment to global warming.

Together with Yuming Feng at GEOMAR, Helmholtz Center for Ocean Research, Kiel, Germany, we received a research grant of DFG (German Research Foundation, 2017-2019) that allowed us to conduct preliminary work on the effect of AU. The MABEE lab conducted a laboratory-based experiment assessing whether pulses of deeper cold water intrusions into shallow reefs during heat waves could prevent coral bleaching (pictures 2.3 & 2.4) using deep water collected by the R/V Atlantic Explorer at depths of 50 and 100m (Sawall et al 2020, see also) While this study provided a first indication about the potential utility of artificial upwelling to prevent coral bleaching, much more information is required about the pros and cons of this intervention to make a well-informed decision about its applicability. We are currently seeking funding to investigate this topic further, namely to simulating different upwelling scenarios in an outdoor mesocosm experiment.

Students involved in the DFG artificial upwelling project (lab-experiment):

• Moronke Harris (B. Sc., of Guelph, Canada, 2018). Presentation of results on the ASLO Ocean Science Meeting, San Diego 2020 and 14th International Coral Reef Symposium, Bremen, Germany, 2021. More information about Moronke in the Currents issue June 2020.
• Hannah Lampit (undergraduate, Newcastle Univ., UK, 2018).