Dead Coral Skeletons Can Slow Reef Recovery by Sheltering Algae

Researchers used mathematical modeling to show that dead coral skeletons left behind by certain types of disturbances can make coral reefs more vulnerable to regime shifts from coral-dominated to algae-dominated states by providing shelter for competing algae. The researchers developed a mathematical model to explore the consequences of structure-removing and structure-retaining disturbances, simulating how the fraction of reef space occupied by key interacting benthic space holders (corals, macroalgae) changes following these two types of disturbance events. Dead coral skeletons substantially diminished coral resilience if they provided macroalgae refuge from herbivory. Material legacies broadened the range of herbivore biomass over which coral and macroalgae states are bistable. Structure-retaining disturbances can move reef systems into regions where coral and macroalgal states become bistable, triggering shifts to algae dominance. The presence of dead skeletons effectively reduces herbivores' capacity to control macroalgae without changing the actual number of herbivores present. The research shows that the type of disturbance matters as much as its intensity for coral reef recovery. As climate change increases both severe storms and marine heatwaves, understanding how different disturbance types affect reef resilience could inform conservation strategies and help predict which reefs are most vulnerable to permanent shifts to algae-dominated states.

Citation

Kopecky, Kai L.; Stier, Adrian C.; Schmitt, Russell J.; Holbrook, Sally J.; Moeller, Holly V. (2023). Material legacies can degrade resilience: Structure‐retaining disturbances promote regime shifts on coral reefs. Ecology.

"Dead coral skeletons substantially diminished coral resilience if they provided macroalgae refuge from herbivory."

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