Abstract
The unanticipated impacts of consumers in fragmented habitats are frequently a challenge for ecosystem management. On Indo-Pacific coral reefs, crown-of-thorns sea stars (Acanthaster spp.) are coral predators whose outbreaks cause precipitous coral decline. Across large spatial scales, Acanthaster densities are lower in large no-take Marine Protected Areas (MPAs) and reefs subject to limited human exploitation. However, using a combination of observational and manipulative experiments, we found that Acanthaster densities within a network of small, no-take MPAs on reef flats in Fiji were ~2–3.4 times greater inside MPAs than in adjacent fished areas and ~2–2.5 times greater than the upper threshold density indicative of an outbreak. This appeared to result from selective Acanthaster migration to the coral-rich MPAs from fished areas that are coral-poor and dominated by macroalgae. Small MPAs can dramatically increase the cover of foundation species like corals, but may selectively attract coral predators like Acanthaster due to greater food densities within MPAs or because the MPAs are too small to support Acanthaster enemies. As coral cover increases, their chemical and visual cues may concentrate Acanthaster to outbreak densities that cause coral demise, compromising the value of small MPAs. An understanding of predator dynamics as a function of habitat type, size, and fragmentation needs to be incorporated into MPA design and management.
Highlights
The increasing frequency and severity of anthropogenic impacts throughout the global ocean has led to habitat degradation, fragmentation, and trophic downgrading of marine ecosystems worldwide [1, 2]
Predatory sea stars threaten foundation species in small Marine Protected Areas from structurally complex systems dominated by corals to structurally simplified systems dominated by macrolagae [8, 9]
When Acanthaster were released along Marine Protected Areas (MPAs) borders, their directions of initial movement were significantly biased toward the MPA for five of the six borders (p < 0.050, Fig 2), and suggestive of an MPA preference in the remaining contrast
Summary
The increasing frequency and severity of anthropogenic impacts throughout the global ocean has led to habitat degradation, fragmentation, and trophic downgrading of marine ecosystems worldwide [1, 2]. To counter these trends and promote ecosystem recovery and resilience, Marine Protected Areas (MPAs) are increasingly being established–often with broadly defined goals oriented towards the protection of foundation species (e.g., coral, kelp, seagrass, mangroves, etc.) upon which a broad variety of other species depend [3]. Because predators have dramatic direct and indirect impact on community structure and function [1, 16], predicting and mitigating predator-induced disturbances are necessary to safeguard ecosystem integrity and will be increasingly important as global-scale stressors continue to challenge the effectiveness of local management efforts [17, 18]
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