Incorporating adaptive responses into future projections of coral bleaching

Climate warming threatens to increase mass coral bleaching events, and several studies have projected the demise of tropical coral reefs this century. However, recent evidence indicates corals may be able to respond to thermal stress though adaptive processes (e.g., genetic adaptation, acclimatizati...

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Published in:	Global change biology Vol. 20; no. 1; pp. 125 - 139
Main Authors:	Logan, Cheryl A., Dunne, John P., Eakin, C. Mark, Donner, Simon D.
Format:	Journal Article
Language:	English
Published:	Oxford Blackwell Publishing Ltd 01-01-2014 Wiley-Blackwell
Subjects:	Abiotic stress acclimatization adaptation Adaptation, Physiological Animal and plant ecology Animal, plant and microbial ecology Animals Anthozoa - physiology Applied ecology Biological and medical sciences Climate climate change Climatology. Bioclimatology. Climate change Conservation, protection and management of environment and wildlife coral bleaching Coral Reefs Earth, ocean, space Environmental degradation: ecosystems survey and restoration Exact sciences and technology External geophysics Forecasting Fundamental and applied biological sciences. Psychology General aspects global climate models Global warming Marine Meteorology Models, Theoretical sea surface temperature Temperature Sea surface Climate global climate models Adaptive response Environmental factor Surface temperature coral bleaching Dynamical climatology Climate change Ecological damage Models acclimatization Adaptation sea surface temperature
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Summary:	Climate warming threatens to increase mass coral bleaching events, and several studies have projected the demise of tropical coral reefs this century. However, recent evidence indicates corals may be able to respond to thermal stress though adaptive processes (e.g., genetic adaptation, acclimatization, and symbiont shuffling). How these mechanisms might influence warming‐induced bleaching remains largely unknown. This study compared how different adaptive processes could affect coral bleaching projections. We used the latest bias‐corrected global sea surface temperature (SST) output from the NOAA/GFDL Earth System Model 2 (ESM2M) for the preindustrial period through 2100 to project coral bleaching trajectories. Initial results showed that, in the absence of adaptive processes, application of a preindustrial climatology to the NOAA Coral Reef Watch bleaching prediction method overpredicts the present‐day bleaching frequency. This suggests that corals may have already responded adaptively to some warming over the industrial period. We then modified the prediction method so that the bleaching threshold either permanently increased in response to thermal history (e.g., simulating directional genetic selection) or temporarily increased for 2–10 years in response to a bleaching event (e.g., simulating symbiont shuffling). A bleaching threshold that changes relative to the preceding 60 years of thermal history reduced the frequency of mass bleaching events by 20–80% compared with the ‘no adaptive response’ prediction model by 2100, depending on the emissions scenario. When both types of adaptive responses were applied, up to 14% more reef cells avoided high‐frequency bleaching by 2100. However, temporary increases in bleaching thresholds alone only delayed the occurrence of high‐frequency bleaching by ca. 10 years in all but the lowest emissions scenario. Future research should test the rate and limit of different adaptive responses for coral species across latitudes and ocean basins to determine if and how much corals can respond to increasing thermal stress.
Bibliography:	istex:E559151ECB86914120A5BC6D420C2621D73BAA37 ark:/67375/WNG-1CLTP731-H Cooperative Institute of Climate Science Postdoctoral Program ArticleID:GCB12390 NOAA Coral Reef Conservation Program Figure S1. Percent of global reef cells predicted to experience high-frequency bleaching under RCPs 2.6, 4.5 and 8.5, using the GFDL ESM2M model with (black) and without (gray) a bias correction in the climatological maximum that reduces the frequency of ENSO events in the model (Model 1). An historical climatology (1900-1919) predicts over 50% of global reef cells experiencing severe coral bleaching (more than two bleaching events in 10 years) before the year 2000. A satellite-era climatology (1985-2004) predicts over 50% of global reef cells experiencing high-frequency bleaching by ca. 2030. Results for RCP 6.0 can be found in Fig. .Figure S2. Maps of high-frequency bleaching predictions in model years 2010, 2030, 2050, and 2070 with a 1985-2004 climatology under the moderately high RCP, 6.0 W m−2 by 2100 (black lines in Fig. c). Blue represents a reef location without severe bleaching. Green represents a severe bleaching prediction using the GFDL ESM2M model. Red represents a severe bleaching prediction using bias-corrected ESM2M.Figure S3. Percent of global reef cells predicted to experience high-frequency bleaching in the adaptive response models. Model 2 (a and b) uses a rolling climatological period representative of an adaptive response to recent thermal history over the previous 40, 60, 80, or 100 years. Model 3 (c and d) employs a temporary increase in the bleaching threshold of 1 °C after a bleaching event, which may be representative of a temporary increase in thermal tolerance due to symbiont shuffling or transient community shifts toward more heat-tolerant taxa. Both bleaching models use SST output from the GFDL ESM2M bias-corrected model for the lowest RCP 2.6 (a and c) and moderately low RCP 4.5 (b and d). For comparison, dashed lines in all panels represent the corresponding results from the 'no adaptive response' (Model 1) using the 1985-2004 climatology. Results for RCPs 6.0 and 8.5 can be found in Fig. .Figure S4. Percent of global reef cells predicted to experience high-frequency bleaching for the moderately high RCP (6.0 W m−2 by 2100) using the GFDL ESM2M bias-corrected model with a temporary increase in the Degree Heating Month threshold of 1 °C after a bleaching event and four differing rolling climatology windows (Model 4). For example, this model might represent the additive effect of genetic adaptation to recent thermal history and temporary increases in thermal tolerance due to symbiont shuffling. ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	1354-1013 1365-2486
DOI:	10.1111/gcb.12390