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1. The Costs and Benefits of Environmental Memory for Reef-Building Corals Coping with Recurring Marine Heatwaves

   https://doi.org/10.1093/icb/icac074  

   Brown, Kristen T; Barott, Katie L (June 2022, Integrative and Comparative Biology)

   Abstract Marine heatwaves are occurring more frequently as climate change intensifies, resulting in global mass coral bleaching events several times per decade. Despite the time between marine heatwaves decreasing, there is evidence that reef-building corals can develop increased bleaching resistance across repetitive marine heatwaves. This phenomenon of acclimatization via environmental memory may be an important strategy to ensure coral persistence; however, we still understand very little about the apparent acclimatization or, conversely, sensitization (i.e., stress accumulation or weakening) of reef-building corals to consecutive heatwaves and its implications for the trajectory and resilience of coral reefs. Here, we highlight that not only will some corals become stress hardened via marine heatwaves, but many other individuals will suffer sensitization during repeat heatwaves that further exacerbates their stress response during repeat events and depresses fitness. Under current and predicted climate change, it is necessary to gain a better understanding of the acclimatization vs. sensitization trajectories of different species and individuals on the reef, as well as identify whether changes in bleaching susceptibility relates to physiological acclimatization, trade-offs with other biological processes, and ultimately coral persistence in the Anthropocene. 

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2. Twenty years of change in benthic communities across the Belizean Barrier Reef

   https://doi.org/10.1371/journal.pone.0249155  

   Alves, Catherine; Valdivia, Abel; Aronson, Richard B.; Bood, Nadia; Castillo, Karl D.; Cox, Courtney; Fieseler, Clare; Locklear, Zachary; McField, Melanie; Mudge, Laura; et al (January 2022, PLOS ONE)

   Coen, Loren D. (Ed.)

   Disease, storms, ocean warming, and pollution have caused the mass mortality of reef-building corals across the Caribbean over the last four decades. Subsequently, stony corals have been replaced by macroalgae, bacterial mats, and invertebrates including soft corals and sponges, causing changes to the functioning of Caribbean reef ecosystems. Here we describe changes in the absolute cover of benthic reef taxa, including corals, gorgonians, sponges, and algae, at 15 fore-reef sites (12–15m depth) across the Belizean Barrier Reef (BBR) from 1997 to 2016. We also tested whether Marine Protected Areas (MPAs), in which fishing was prohibited but likely still occurred, mitigated these changes. Additionally, we determined whether ocean-temperature anomalies (measured via satellite) or local human impacts (estimated using the Human Influence Index, HII) were related to changes in benthic community structure. We observed a reduction in the cover of reef-building corals, including the long-lived, massive corals Orbicella spp. (from 13 to 2%), and an increase in fleshy and corticated macroalgae across most sites. These and other changes to the benthic communities were unaffected by local protection. The covers of hard-coral taxa, including Acropora spp., Montastraea cavernosa , Orbicella spp., and Porites spp., were negatively related to the frequency of ocean-temperature anomalies. Only gorgonian cover was related, negatively, to our metric of the magnitude of local impacts (HII). Our results suggest that benthic communities along the BBR have experienced disturbances that are beyond the capacity of the current management structure to mitigate. We recommend that managers devote greater resources and capacity to enforcing and expanding existing marine protected areas and to mitigating local stressors, and most importantly, that government, industry, and the public act immediately to reduce global carbon emissions. 

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3. Historical and modern data sources reveal long-term declines in Caribbean coral reef water quality

   https://doi.org/10.32942/X2S103  

   Cramer, Katie; Alvarez-Filip, Lorenzo; Carilli, Jessica; McField, Melanie; Tewfik, Alexander; Whaley, Zachary; McClenachan, Loren (June 2026, EcoEvoRxiv)

   Although it is suspected that the widespread death of Caribbean corals is associated with declining reef water quality from land-based pollution, this link has been difficult to quantify due to a dearth of reef water quality data. To assess the role of land-based pollution in recent coral declines, we synthesized paleoecological, historical, and modern data on reef water quality across the Caribbean region from 1970-2021. We focused on two aspects of water quality that have been most consistently collected in the Caribbean and have been shown to have direct impacts on corals: nutrients (nitrogen and phosphorous) and water clarity. We analyzed trends in water quality across the wider Caribbean and within individual well-studied countries or reefs, providing insights into how the differing histories of land use and contrasting oceanographic conditions have influenced the varying trajectories of reef water quality change and ecosystem health. On a regional scale, nutrient concentrations had already exceeded established thresholds beyond which coral health was compromised by the 1970s, nutrient levels increased and water clarity decreased between the 1970s-2000, and nitrogen to phosphorous ratios were negatively correlated with coral cover. Case study sites revealed that coral cover declines were often related to water quality declines even in marine protected areas and at offshore reefs previously thought to be less influenced by land-based pollution. This synthesis of long-term historical data confirms the urgent need to mitigate land-based pollution to improve reef health and resilience in the face of increasing alteration of coastal zones and climate change impacts. 

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4. Assessing the potential for demographic restoration and assisted evolution to build climate resilience in coral reefs

   https://doi.org/10.1002/eap.2650  

   DeFilippo, Lukas B.; McManus, Lisa C.; Schindler, Daniel E.; Pinsky, Malin L.; Colton, Madhavi A.; Fox, Helen E.; Tekwa, E. W.; Palumbi, Stephen R.; Essington, Timothy E.; Webster, Michael M. (October 2022, Ecological Applications)

   Abstract Interest is growing in developing conservation strategies to restore and maintain coral reef ecosystems in the face of mounting anthropogenic stressors, particularly climate warming and associated mass bleaching events. One such approach is to propagate coral coloniesex situand transplant them to degraded reef areas to augment habitat for reef‐dependent fauna, prevent colonization from spatial competitors, and enhance coral reproductive output. In addition to such “demographic restoration” efforts, manipulating the thermal tolerance of outplanted colonies through assisted relocation, selective breeding, or genetic engineering is being considered for enhancing rates of evolutionary adaptation to warming. Although research into such “assisted evolution” strategies has been growing, their expected performance remains unclear. We evaluated the potential outcomes of demographic restoration and assisted evolution in climate change scenarios using an eco‐evolutionary simulation model. We found that supplementing reefs with pre‐existing genotypes (demographic restoration) offers little climate resilience benefits unless input levels are large and maintained for centuries. Supplementation with thermally resistant colonies was successful at improving coral cover at lower input levels, but only if maintained for at least a century. Overall, we found that, although demographic restoration and assisted evolution have the potential to improve long‐term coral cover, both approaches had a limited impact in preventing severe declines under climate change scenarios. Conversely, with sufficient natural genetic variance and time, corals could readily adapt to warming temperatures, suggesting that restoration approaches focused on building genetic variance may outperform those based solely on introducing heat‐tolerant genotypes. 

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5. Asynchronous effects of heat stress on growth rates of massive corals and damselfish in the Red Sea

   https://doi.org/10.1371/journal.pone.0316247  

   Zahid, Fiza; Gajdzik, Laura; Korsmeyer, Keith E; Cotton, Jordyn D; Coker, Daren J; Berumen, Michael L; DeCarlo, Thomas M (January 2025, PLOS ONE)

   Mayfield, Anderson B (Ed.)

   Climate change is imposing multiple stressors on marine life, leading to a restructuring of ecological communities as species exhibit differential sensitivities to these stressors. With the ocean warming and wind patterns shifting, processes that drive thermal variations in coastal regions, such as marine heatwaves and upwelling events, can change in frequency, timing, duration, and severity. These changes in environmental parameters can physiologically impact organisms residing in these habitats. Here, we investigate the synchrony of coral and reef fish responses to environmental disturbance in the Red Sea, including an unprecedented combination of heat stress and upwelling that led to mass coral bleaching in 2015. We developed cross-dated growth chronologies from otoliths of 156 individuals of two planktivorous damselfish species,Pomacentrus sulfureusandAmblyglyphidodon flavilatus, and from skeletal cores of 48Poritesspp. coral colonies. During and immediately after the 2015 upwelling and bleaching event, damselfishes exhibited a positive growth anomaly but corals displayed reduced growth. Yet, after 2015–2016, these patterns were reversed with damselfishes showing a decline in growth and corals rebounding to pre-disturbance growth rates. Our results reveal an asynchronous response between corals and reef fish, with corals succumbing to the direct effects of heat stress, and then quickly recovering when the heat stress subsided—at least, for those corals that survived the bleaching event. Conversely, damselfish growth temporarily benefited from the events of 2015, potentially due to the increased metabolic demand from increased temperature and increased food supply from the upwelling event, before declining over four years, possibly related to indirect effects associated with habitat degradation following coral mortality. Overall, our study highlights the increasingly complex, often asynchronous, ecological ramifications of climate extremes on the diverse species assemblages of coral reefs. 

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