Coral reefs are under serious threat in the Anthropocene. Terrestrial based stressors, including nutrient runoff, sedimentation from flood events, and pollution can influence disease on coral reefs. Seagrass meadows, mangroves, and wetlands are critically important buffers to these land-based stressors that increase disease outbreaks on coral reefs. Despite the potential importance of these ecosystems for reef health, human activities have rapidly degraded their extent worldwide in recent history. We sought to quantify the co-occurrence of these ecosystems with coral reefs and the potential for ecosystem services to mitigate disease risk. To first establish current and historical extents of these ecosystems globally, we conducted a literature search to identify existing databases of global distributions of different coastal ecosystems (coral reefs, mangroves, saltmarshes, and seagrass meadows) for both contemporary and historical years. From these databases, we were able to calculate co-occurrence of these ecosystems over the period of 1996 to 2016. Then, we conducted a meta-analysis to systematically identify and quantify ecosystem services provided by mangroves, seagrasses, and saltmarshes. Incorporating both the global extents and meta-analysis, along with known drivers of coral disease, we were able to model the risk of disease given different stressors over a twenty year period.
Results/Conclusions
We found that, overall, 15% of coral reefs co-occur with at least one coastal ecosystem. From our identified datasets, this figure remained relatively constant over the period of 1996 to 2016, though co-occurrence with individual ecosystems can show losses up to 17% of their 1996 overlap. For most ecosystems, we identified ecosystem services that can indirectly affect disease, including mitigation of terrestrial runoff, sediment capture, and nutrient capture. For seagrass ecosystems, we found evidence that seagrass has been linked to reduced levels of disease on coral reefs. One major uncertainty we identified in our meta-analysis is how the services from different ecosystems interact to mitigate different stressors and disease. By modeling different hypothesized interactions (additive, antagonistic, and synergistic), we found that co-occurrence of reefs with multiple coastal ecosystems is likely to be a stronger buffer than any single ecosystem as strong antagonistic interactions would be required to negate the services of multiple ecosystems. This information can inform management and restoration of coral reefs and coastal ecosystems as combined efforts to restore more than a single ecosystem may prove to be more resilient than single ecosystems alone.