Using species interactions in the management of Caribbean coral reefs
Across the globe, management and conservation agencies undertake numerous local actions to mitigate losses to coral reef ecosystems and aid in their recovery. While many of these strategies are designed to exploit natural ecological interactions between corals and other reef-associated organisms, only a few interactions are the focus of these approaches despite a suite of relationships that affect corals and likely impact the outcomes of coral reef conservation actions. Additionally, in the wake of major worldwide coral bleaching events in 2014-2016, several studies and news articles have argued that local management actions have little effect on protecting coral reefs from climate change events. In this dissertation, I evaluate how ecological interactions between corals and other reef inhabitants affect the success of current management strategies to better inform the use of local efforts that promote coral reef recovery. To do this, I use a combination of scientific literature review, large-scale observational surveys, and manipulative field experiments to apply ecological theory in this applied context. Reviews of past studies reveal there are numerous interactions that facilitate corals and could be used in the designs of current coral restoration and transplantation efforts, including mutualisms, long-distance facilitation, density-dependence, legacy and biodiversity effects, and trophic interactions (e.g., trophic cascades) (Chapter 1). Because coral predators (‘corallivores’) are considered major threats to reefs worldwide and coral restoration efforts in the Caribbean, I examined the role of corallivores in limiting coral restoration success alone and when combined with physical stress (Chapter 2), the effects of their removals during major climate change events (Chapter 3), and factors controlling corallivore population densities within no-take marine protected areas (Chapter 4). In these studies, I find that chronic, but partial, predation by corallivorous snails increases coral stress that may ultimately hinder coral reef recovery. For instance, partial predation by snails lead to full colony mortality in a third of experimental corals, substantially reduced growth rates by up to 80%, and facilitated algal colonization on small colonies of the endangered staghorn coral (Acropora cervicornis) often used in restoration programs. Although overall tissue loss due to predation was low, removal of corallivorous snails from coral colonies during a warm temperature event significantly reduced the severity of coral bleaching as well as tissue mortality after bleaching, suggesting that tissue loss may considerably underestimate the negative effects of chronic predation and that removal of predation stress increased resistance and recovery (i.e., resilience) to climate change. While manual removals of corallivores is likely to be most feasible for managers at small scales, I found corallivorous snail densities were nearly 50% lower inside no-take marine protected areas within the Florida Keys National Marine Sanctuary, and that snail densities were negatively correlated with two potential predators, black margate (Anisotremus surinamensis) and Caribbean spiny lobster (Panulirus argus), which were both significantly more abundant in protected areas. The research findings presented in this dissertation demonstrate that local strategies can play an important role in coral reef resilience and recovery, and that understanding the ecological interactions between corals and reef-associated organisms is paramount to achieving success in these efforts.
Coral reef ecology
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