Associate Professor Rutgers University New Brunswick, New Jersey, United States
While reducing emissions is critical to the continued persistence of reefs, local conditions have been shown to interact synergistically with climate change to negatively impact coral cover and overall reef health. Effectively managed marine protected area (MPA) networks must therefore address both local and global threats. In particular, these networks should aim to reduce stressors locally while harnessing natural environmental variation to facilitate evolutionary rescue at the regional scale. To that end, we analyzed the distribution of existing MPAs in three major coral reef regions, the Caribbean, Southwest Pacific (SWP), and the Coral Triangle (CT), to compare the temperature and connectivity characteristics of MPA sites to those without protection (non-MPA sites). Next, we used an eco-evolutionary model to test the efficacy of various spatial arrangements of MPAs in each region to identify strategies that best supported evolving coral populations under projected warming (RCP4.5).
First, we found that existing MPA and non-MPA sites differ significantly in certain temperature and connectivity metrics. Most strikingly, the Caribbean MPA network is hotter than the rest of the region while MPA networks in the SWP and CT are colder relative to non-MPA sites in their respective regions. These temperature differences likely corresponds to differences in the thermal optima of incoming larvae which implies varying evolutionary rescue potential among MPA and non-MPA sites. Next, using our eco-evolutionary model, we found that all MPA strategies were similarly effective in supporting overall coral cover, although the best-performing strategies depended on the region and focal time period. While protecting cold sites, or refugia, led to the highest cover during decline, protecting hot sites led to the highest cover at the end of the simulations. Randomly selecting sites maintained coral cover through time and avoided stark trade-offs during the decline and recovery periods that were evident in other strategies. This is likely because the random strategy supports coral cover across a range of temperatures, in addition to both sources and sinks of coral larvae. In doing so, a random network maintains multiple adaptation pathways: local adaptation, demographic rescue, and evolutionary rescue.