Crown-of-thorns starfish (CoTS) outbreaks rank among the greatest threats to coral throughout the Indo-Pacific. In the future, reefs already stressed by CoTS will be further burdened by overfishing and nutrient loading. Although studies of other interacting coral reef stressors have shown the potential for significant nonlinear effects, how much increases in fishing rate and nutrient input will exacerbate CoTS outbreak severity is still uncertain. Furthermore, the CoTS management literature has focused on the Great Barrier Reef, whereas outbreak damage is rising across the entire Indo-Pacific region. Here, we use a metacommunity model of intermediate complexity to simulate CoTS outbreaks in areas with high anthropogenic stress. We model outbreaks on reefs adjacent to two cities within the range of CoTS that have less prior literature coverage: Cebu City, Philippines, and Jeddah, Saudi Arabia.
Results/Conclusions:
We observe that urban growth can drive complex patterns of multi-stressor interaction, with the relative importance of different reef stressors changing over time. We find that CoTS removal on intermediate spatial scales significantly improves regional-scale coral health, and that combining this with the establishment of a marine protected area can reverse much of the stress brought on by overfishing and nutrient loading. We provide guidelines under which each of four CoTS management strategies (removing CoTS from local areas based on limiting CoTS density, promoting coral recovery, and stopping outbreak spread, as well as prioritization based on an average of those three criteria) is optimal for conservation. We find that coral decline due to overfishing can be sharper on reefs with CoTS, and that nutrification can induce a shift from discrete outbreak waves to continuous CoTS presence. Our work shows the importance of long-term planning for reef management, and highlights how reef stressors can interact in potentially unforeseen ways.
