Abstract
Complex histories of chronic and acute sea surface temperature (SST) stresses are expected to trigger taxon- and location-specific responses that will ultimately lead to novel coral communities. The 2016 El Niño-Southern Oscillation provided an opportunity to examine large-scale and recent environmental histories on emerging patterns in 226 coral communities distributed across 12 countries from East Africa to Fiji. Six main coral communities were identified that largely varied across a gradient of Acropora to massive Porites dominance. Bleaching intensity was taxon-specific and was associated with complex interactions among the 20 environmental variables that we examined. Coral community structure was better aligned with the historical temperature patterns between 1985 and 2015 than the 2016 extreme temperature event. Additionally, bleaching responses observed during 2016 differed from historical reports during past warm years. Consequently, coral communities present in 2016 are likely to have been reorganized by both long-term community change and acclimation mechanisms. For example, less disturbed sites with cooler baseline temperatures, higher mean historical SST background variability, and infrequent extreme warm temperature stresses were associated with Acropora-dominated communities, while more disturbed sites with lower historical SST background variability and frequent acute warm stress were dominated by stress-resistant massive Porites corals. Overall, the combination of taxon-specific responses, community-level reorganization over time, geographic variation, and multiple environmental stressors suggest complex responses and a diversity of future coral communities that can help contextualize management priorities and activities.
Highlights
The spatial and taxonomic responses of corals to stressful exposure events will determine the future resilience and persistence of coral reefs in the face of rapid climate change (Hughes et al 2017, 2018a)
We evaluated a number of geographic, environmental, habitat, and fisheries management variables and calculated a suite of sea surface temperature (SST) characteristics to determine how thermal stress metrics differentially affect corals (Table 1)
Where sites have been studied over time, there is an ongoing replacement of sensitive corals and associated symbiotic taxa by weedy and stresstolerant coral taxa and heat-resistant symbionts (Darling et al 2013, Edmunds et al 2014, McClanahan et al 2014, Palumbi et al 2014)
Summary
The spatial and taxonomic responses of corals to stressful exposure events will determine the future resilience and persistence of coral reefs in the face of rapid climate change (Hughes et al 2017, 2018a). Monitoring and evaluating a variety of thermal impacts over gradients of geography, ecologies, and time is critical to identify and guide management interventions to safeguard species and coral reef communities threatened by climate change. We evaluated how coral taxa and communities responded to a variety of acute thermal exposure metrics in the context of a site’s historical SSTs. The study was undertaken on a broad spatial scale to evaluate the geographic context of responses. We evaluated a variety of possible thermal stress metrics to better understand their potential impacts on coral taxa and communities. We hypothesized that coral community composition and responses to thermal stress would be influenced by historical SST patterns, and bleaching responses would be taxa-specific, contextual, and interactive with a variety of potential environmental stresses
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