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1. On a Reef Far, Far Away: Anthropogenic Impacts Following Extreme Storms Affect Sponge Health and Bacterial Communities

   https://doi.org/10.3389/fmars.2021.608036  

   Shore, Amanda; Sims, Jordan A.; Grimes, Michael; Howe-Kerr, Lauren I.; Grupstra, Carsten G.; Doyle, Shawn M.; Stadler, Lauren; Sylvan, Jason B.; Shamberger, Kathryn E.; Davies, Sarah W.; et al (April 2021, Frontiers in Marine Science)

   null (Ed.)

   Terrestrial runoff can negatively impact marine ecosystems through stressors including excess nutrients, freshwater, sediments, and contaminants. Severe storms, which are increasing with global climate change, generate massive inputs of runoff over short timescales (hours to days); such runoff impacted offshore reefs in the northwest Gulf of Mexico (NW GoM) following severe storms in 2016 and 2017. Several weeks after coastal flooding from these events, NW GoM reef corals, sponges, and other benthic invertebrates ∼185 km offshore experienced mortality (2016 only) and/or sub-lethal stress (both years). To assess the impact of storm-derived runoff on reef filter feeders, we characterized the bacterial communities of two sponges, Agelas clathrodes and Xestospongia muta , from offshore reefs during periods of sub-lethal stress and no stress over a three-year period (2016—2018). Sponge-associated and seawater-associated bacterial communities were altered during both flood years. Additionally, we found evidence of wastewater contamination (based on 16S rRNA gene libraries and quantitative PCR) in offshore sponge samples, but not in seawater samples, following these flood years. Signs of wastewater contamination were absent during the no-flood year. We show that flood events from severe storms have the capacity to reach offshore reef ecosystems and impact resident benthic organisms. Such impacts are most readily detected if baseline data on organismal physiology and associated microbiome composition are available. This highlights the need for molecular and microbial time series of benthic organisms in near- and offshore reef ecosystems, and the continued mitigation of stormwater runoff and climate change impacts. 

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2. Rates of Future Climate Change in the Gulf of Mexico and the Caribbean Sea: Implications for Coral Reef Ecosystems

   https://doi.org/10.1029/2022JG006999  

   Lawman, A. E.; Dee, S. G.; DeLong, K. L.; Correa, A. M. S. (September 2022, Journal of Geophysical Research: Biogeosciences)

   Abstract Rising temperatures and ocean acidification due to anthropogenic climate change pose ominous threats to coral reef ecosystems in the Gulf of Mexico (GoM) and the western Caribbean Sea. Unfortunately, the once structurally complex coral reefs in the GoM and Caribbean have dramatically declined since the 1970s; relatively few coral reefs still exhibit a mean live coral cover of >10%. Additional work is needed to characterize future climate stressors on coral reefs in the GoM and the Caribbean Sea. Here, we use climate model simulations spanning the period of 2015–2100 to partition and assess the individual impacts of climate stressors on corals in the GoM and the western Caribbean Sea. We use a top‐down modeling framework to diagnose future projected changes in thermal stress and ocean acidification and discuss its implications for coral reef ecosystems. We find that ocean temperatures increase by 2°C–3°C over the 21st century, and surpass reported regional bleaching thresholds by mid‐century. Whereas ocean acidification occurs, the rate and magnitude of temperature changes outpace and outweigh the impacts of changes in aragonite saturation state. A framework for quantifying and communicating future risks in the GoM and Caribbean using reef risk projection maps is discussed. Without substantial mitigation efforts, the combined impact of increasing ocean temperatures and acidification are likely to stress most existing corals in the GoM and the Caribbean, with widespread economic and ecological consequences. 

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3. Gene Expression of Endangered Coral (Orbicella spp.) in Flower Garden Banks National Marine Sanctuary After Hurricane Harvey

   https://doi.org/doi.org/10.3389/fmars.2019.00672  

   Wright, Rachel M.; Correa, Adrienne M.; Quigley, Lucinda A.; Santiago-Vázquez, Lory Z.; Shamberger, Kathryn E.; Davies, Sarah W. (November 2019, Frontiers in marine science)

   About 190 km south of the Texas–Louisiana border, the East and West Flower Garden Banks (FGB) have maintained > 50% coral cover with infrequent and minor incidents of disease or bleaching since monitoring began in the 1970s. However, a mortality event, affecting 5.6 ha (2.6% of the area) of the East FGB, occurred in late July 2016 and coincided with storm-generated freshwater runoff extending offshore and over the reef system. To capture the immediate effects of storm-driven freshwater runoff on coral and symbiont physiology, we leveraged the heavy rainfall associated with Hurricane Harvey in late August 2017 by sampling FGB corals at two time points: September 2017, when surface water salinity was reduced (∼34 ppt); and 1 month later when salinity had returned to typical levels (∼36 ppt in October 2017). Tissue samples (N = 47) collected midday were immediately preserved for gene expression profiling from two congeneric coral species (Orbicella faveolata and Orbicella franksi) from the East and West FGB to determine the physiological consequences of storm-derived runoff. In the coral, differences between host species and sampling time points accounted for the majority of differentially expressed genes. Gene ontology enrichment for genes differentially expressed immediately after Hurricane Harvey indicated increases in cellular oxidative stress responses. Although tissue loss was not observed on FGB reefs following Hurricane Harvey, our results suggest that poor water quality following this storm caused FGB corals to experience sub-lethal stress. We also found dramatic expression differences across sampling time points in the coral’s algal symbiont, Breviolum minutum. Some of these differentially expressed genes may be involved in the symbionts’ response to changing environments, including a group of differentially expressed post-transcriptional RNA modification genes. In this study, we cannot disentangle the effects of reduced salinity from the collection time point, so these expression patterns could also be related to seasonality. These findings highlight the urgent need for continued monitoring of these reef systems to establish a baseline for gene expression of healthy corals in the FGB system across seasons, as well as the need for integrated solutions to manage stormwater runoff in the Gulf of Mexico. 

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4. Increased dominance of heat-tolerant symbionts creates resilient coral reefs in near-term ocean warming

   https://doi.org/10.1073/pnas.2202388120  

   Palacio-Castro, Ana M.; Smith, Tyler B.; Brandtneris, Viktor; Snyder, Grace A.; van Hooidonk, Ruben; Maté, Juan L.; Manzello, Derek; Glynn, Peter W.; Fong, Peggy; Baker, Andrew C. (February 2023, Proceedings of the National Academy of Sciences)

   Climate change is radically altering coral reef ecosystems, mainly through increasingly frequent and severe bleaching events. Yet, some reefs have exhibited higher thermal tolerance after bleaching severely the first time. To understand changes in thermal tolerance in the eastern tropical Pacific (ETP), we compiled four decades of temperature, coral cover, coral bleaching, and mortality data, including three mass bleaching events during the 1982 to 1983, 1997 to 1998 and 2015 to 2016 El Niño heatwaves. Higher heat resistance in later bleaching events was detected in the dominant framework-building genus, Pocillopora, while other coral taxa exhibited similar susceptibility across events. Genetic analyses of Pocillopora spp . colonies and their algal symbionts (2014 to 2016) revealed that one of two Pocillopora lineages present in the region ( Pocillopora “ type 1”) increased its association with thermotolerant algal symbionts ( Durusdinium glynnii ) during the 2015 to 2016 heat stress event. This lineage experienced lower bleaching and mortality compared with Pocillopora “type 3”, which did not acquire D. glynnii . Under projected thermal stress, ETP reefs may be able to preserve high coral cover through the 2060s or later, mainly composed of Pocillopora colonies that associate with D. glynnii . However, although the low-diversity, high-cover reefs of the ETP could illustrate a potential functional state for some future reefs, this state may only be temporary unless global greenhouse gas emissions and resultant global warming are curtailed. 

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5. Three decades of degradation lead to diminished impacts of severe hurricanes on Caribbean reefs

   https://doi.org/10.1002/ecy.2587  

   Edmunds, Peter J. (February 2019, Ecology)

   Abstract Major tropical storms are destructive phenomena with large effects on the community dynamics of multiple biomes. On coral reefs, their impacts have been described for decades, leading to the expectation that future storms should have effects similar to those recorded in the past. This expectation relies on the assumption that storm intensities will remain unchanged, and the impacted coral reef communities are similar to those of the recent past; neither assumption is correct. This study quantified the effects of two category five hurricanes on the reefs of St. John,U.S.Virgin Islands, where 31 yr of time‐series analyses reveal chronic coral mortality, increasing macroalgal abundance, and five major hurricanes that caused acute coral mortality. Contextualized by these trends, the effects of the most recent storms, Hurricanes Irma and Maria (September 2017), on coral cover were modest. While mean absolute coral cover declined 1–4% depending on site, these effects were not statistically discernable. Following decades of increasing abundance of macroalgae, this functional group responded to the recent hurricanes with large increases in abundance on both absolute and relative scales. Decades of chronic mortality have changed the coral assemblages of St. John to create degraded communities that are resistant to severe storms. 

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