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 in slideshow at top of page) leading to coral death and reef degradation. While significant research has been done to understand the mechanisms of thermal tolerance (including Sawall’s previous post-doctoral project in the Red Sea), 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 (image 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. Along with a biogeochemical modeling study conducted by Feng, Sawall conducted a lab-based experiment assessing whether pulses of deeper cold water intrusions into shallow reefs during heat waves could prevent coral bleaching (picture 2.3 and 2.4). Real deep water was collected by the R/V Atlantic Explorer under the supervision of Rod Johnson at the end of two Bermuda Atlantic Time-series Srudy (BATS) cruises. The results of the study have been promising, showing that even short-term (2h/day) intrusions of water from 50-100 m depth decelerated bleaching in corals that were kept at elevated temperatures (Sawall et al. in review). While this study provided an initial indication about the potential utility of artificial upwelling to prevent coral bleaching, making a well-informed decision about its applicability on a broader scale requires more information about the pros and cons of such an intervention. We are currently seeking funding to investigate this topic further, namely to simulate different upwelling scenarios in an outdoor mesocosm experiment.
Students involved in the DFG artificial upwelling project (lab-experiment):