Observing the Physiological Stress Responses of Fragmented and Whole Colony Corals in an Artificial Upwelling Experiment

In the face of climate change, coral reefs are now at threat more than ever due to a rise in sea surface temperature. Widespread bleaching events have been observed due to the action of corals expelling their symbiotic algae (zooxanthellae) as a stress response. A call for novel intervention has led researchers to the idea of artificial upwelling (AU). AU has been proposed as a potential mitigation strategy by supplying cooler, nutrient-rich water to shallower reef environments. However, most past experiments have used smaller coral fragments to observe behavior under heat stress. This raises the question of whether these fragments accurately represent the behaviors of whole colonies in a reef community. In this study, three coral species (Montastrea cavernosa, Porites astreoides, and Millepora alcicornis) were exposed to ambient, heated, and heated+AU treatments in mesocosms at the Bermuda Institute of Ocean Sciences. Coral health was monitored using greyscale analysis and PAM fluorometry. Results suggest that AU reduced stress indicators in most species, with an exception to Millepora alcicornis. Fragments and colonies generally exhibited similar trends, supporting the use of fragments in experimental design, though species-specific differences were evident. These findings provide insight into the potential for AU to mitigate coral heat stress under climate change as well as highlight the importance of validating fragment-based studies against whole colonies.

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