Clearing a path to resilience: removal of dead coral skeletons mitigates downstream impacts of marine heatwaves on coral reefs

Ecological disturbance regimes are shifting and leaving behind novel legacies, like the remnant structures of dead foundation species, which have poorly known impacts on ecosystem resilience. On coral reefs, the primary source of mass coral mortality has historically been powerful tropical storms that kill corals and remove their skeletons from the reef. More recently, there has been a rise in the prevalence of other disturbances, like marine heatwaves that cause coral bleaching or outbreaks of coral predators, both of which kill corals but leave their structurally complex skeletons intact. We explored how the physical environment created by standing dead coral skeletons influences the outcomes of spatial competition between corals and macroalgae, relative to when dead skeletons are removed. Following a marine heatwave, we removed dead skeletons from reef patches then used underwater photogrammetry and AI-powered image analysis to quantify trajectories of coral and macroalgae, which constitute alternative community states in this system. We found several lines of evidence indicating that dead skeletons act as an alternative substrate type that facilitates the buildup of macroalgae and drives the continued loss of live coral after disturbance. More encouragingly, however, we also found that removing dead skeletons can mitigate these adverse effects. Our findings identify a promising avenue to manage for coral reef resilience and reveal how changing disturbance regimes can create novel physical environments that sway the outcomes of spatial competition.

Presentation Preference: Oral

Primary Presenter: Kai Kopecky, University of Colorado Boulder (kai.kopecky@colorado.edu)

Authors:

Kai Kopecky, Environmental Data Science Innovation & Inclusion Lab  (kai.kopecky@colorado.edu)

Gaia Pavoni, Visual Computing Lab ISTI-CNR  (gaiapavoni@isti.cnr.it)

Massimiliano Corsini, Visual Computing Lab ISTI-CNR  (massimiliano.corsini@isti.cnr.it)

Andrew Brooks, Coastal Research Center, Marine Science Institute, University of California Santa Barbara  (ajbrooks@ucsb.edu)

Bartholomew Difiore, Gulf of Maine Research Institute  (bdifiore@gmri.org)

Fabio Menna, University of Sassari  (fmenna@uniss.it)

Erica Nocerino, University of Sassari  (enocerino@uniss.it)