Coral-Symbiodinium association patterns limit community responses to climate change

Background/Question/Methods

The high productivity and biodiversity of coral reef ecosystems is based on the mutualistic relationship between corals and their photosynthetic symbionts, Symbiodinium. This relationship is under stress from local and global factors, such as rapidly increasing temperatures, resulting in concern for the future of coral reef ecosystems. Recent studies have documented patterns of diversity and specificity within coral-Symbiodinium communities, but no studies have coupled empirical data and models to explore how coral-Symbiodinium association patterns influence whole community responses to future climate change. Here we asked the question “How do coral-Symbiodinium association patterns shape community stability under novel environmental conditions driven by climate change?” To address this, we created interaction networks using existing coral-Symbiodinium data to simulate local “extinctions” that represented either the loss of corals or symbionts, or loss of the ability to engage in symbiotic unions. We quantified the stability of coral-Symbiodiniumnetworks to determine which factors are likely to influence community responses to global changes.

Results/Conclusions

We demonstrate that four factors are likely to influence coral-Symbiodinium community responses to climate change, measured as the maintenance of interdependent species despite extinctions (e.g., corals surviving by switching to alternative symbionts). Community stability depended most on generalist corals and symbionts, with simulated communities collapsing most quickly when generalist taxa were removed. Importantly, coral assemblages were 57% more stable if subdominant Symbiodinium contributed to coral fitness and could maintain symbiotic functioning. Moreover, highly mutualistic symbionts contributed more to stability than their environmentally tolerant counterparts, as communities with only mutualistic symbionts were 23% more stable than communities with only tolerant symbionts. Finally, association potential is 35% more stable than species diversity, indicating that impoverished communities have the capacity to recover from environmental disturbances. Together, these results highlight the importance of species characteristics and association patterns in shaping future coral reef communities.