Many coral reefs have shifted from coral‐ to macroalgae‐dominated community states, heightening the need to understand resilience of coral communities. Fishing on herbivores often reduces resilience of the coral state, as lower herbivory fosters macroalgal establishment. Despite the acknowledged importance of fishing, relatively little attention has been paid to how fishers change their behavior as macroalgae overgrow reefs, or how the resulting dynamic feedbacks might affect resilience. We address these questions in Moorea, French Polynesia, where local fishers target herbivorous fishes and where shifts to algal dominance have occurred on some lagoon reefs. We quantified fisher preferences for reef habitats where they target various taxa. For the two most ecologically important taxa of herbivores targeted in the fishery, parrotfish (Scaridae) and unicornfish (
Ecological theory predicts that ecosystems with multiple basins of attraction can get locked in an undesired state, which has profound ecological and management implications. Despite their significance, alternative attractors have proven to be challenging to detect and characterize in natural communities. On coral reefs, it has been hypothesized that persistent coral-to-macroalgae “phase shifts” that can result from overfishing of herbivores and/or nutrient enrichment may reflect a regime shift to an alternate attractor, but, to date, the evidence has been equivocal. Our field experiments in Moorea, French Polynesia, revealed the following: (
- Award ID(s):
- 1637396
- PAR ID:
- 10085688
- Publisher / Repository:
- Proceedings of the National Academy of Sciences
- Date Published:
- Journal Name:
- Proceedings of the National Academy of Sciences
- Volume:
- 116
- Issue:
- 10
- ISSN:
- 0027-8424
- Page Range / eLocation ID:
- p. 4372-4381
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Naso ), fishers preferred to harvest from locations with less macroalgae. We incorporated these habitat preferences into a spatially explicit social–ecological model of reef dynamics to explore consequences of changes in fishing behavior for resilience of the coral state, particularly following disturbance. Fishing that targets low‐macroalgae locations typically generates resilience by facilitating local recovery of herbivores and thus of coral in the less‐targeted macroalgae‐dominated patches. However, the resulting movement of fishers across the seascape can sometimes create fragility; if coral loss is widespread, avoidance of macroalgae concentrates fishing in patches having the highest coral cover, resulting in loss of coral via reduced herbivory. Our results emphasize that resilience and coral‐macroalgae regime shifts cannot be understood without considering humans as a dynamic part of the system. -
Abstract Mounting evidence suggests that fishing can be a major driver of coral‐to‐macroalgae regime shifts on tropical reefs. In many small‐scale coral reef fisheries, fishers target herbivorous fishes, which can weaken coral resilience via reduced herbivory on macroalgae that then outcompete corals. Previous models that explored the effects of harvesting herbivores revealed hysteresis in the herbivory–benthic state relationship that results in bistability of coral‐ and macroalgae‐dominated states over some levels of fishing pressure, which has been supported by empirical evidence. However, past models have not accounted for the functional differences among herbivores or how fisher selectivity for different herbivore functional groups may alter the benthic dynamics and resilience. Here, we use a dynamic model that links differential fishing on two key herbivore functional groups to the outcome of competitive dynamics between coral and macroalgae. We show that reef state depends not only on the level of fishing but also on the types of herbivores targeted by fishers. Selectively fishing browsing herbivores that are capable of consuming mature macroalgae (e.g., unicornfish) increases precariousness of the coral state by moving the system close to the coral‐to‐macroalgae tipping point. By contrast, selectively harvesting grazing herbivores that are only capable of preventing macroalgae from becoming established (e.g., parrotfishes) can increase catch yields substantially more before the tipping point is reached. However, this lower precariousness with increasing fishing effort comes at the cost of increasing the range of fishing effort over which coral and macroalgae are bistable; increasing hysteresis makes a regime shift triggered by a disturbance more difficult or impractical to reverse. Our results suggest that management strategies for small‐scale coral reef fisheries should consider how functional differences among harvested herbivores coupled with fisher selectivity influence benthic dynamics in light of the trade‐off between tipping point precariousness and coral recovery dynamics following large disturbances.
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Abstract Nutrient pollution is altering coastal ecosystems worldwide. On coral reefs, excess nutrients can favor the production of algae at the expense of reef‐building corals, yet the role of nutrients in driving community changes such as shifts from coral to macroalgae is not well understood. Here we investigate the potential role of anthropogenic nutrient loading in driving recent coral‐to‐macroalgae phase shifts on reefs in the lagoons surrounding the Pacific island of Moorea, French Polynesia. We use nitrogen (N) tissue content and stable isotopes (δ15N) in an abundant macroalga (
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