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1. Past disturbances and local conditions influence the recovery rates of coral reefs

   https://doi.org/10.1111/gcb.17112  

   Walker, Andrew S; Kratochwill, Chelsey A; van_Woesik, Robert (January 2024, Global Change Biology)

   Abstract Corals are being increasingly subjected to marine heatwaves. Theory suggests that increasing the intensity of disturbances reduces recovery rates, which inspired us to examine the recovery rates of coral cover following marine heatwaves, cyclones, and other disturbances at 1921 study sites, in 58 countries and three oceans, from 1977 to 2020. In the Atlantic Ocean, coral cover has decreased fourfold since the 1970s, and recovery rates following disturbances have been relatively slow, except in the Antilles. By contrast, reefs in the Pacific and Indian Oceans have maintained coral cover and recovery rates over time. There were positive relationships between rates of coral recovery and prior cyclone and heatwave frequency, and negative relationships between rates of coral recovery and macroalgae cover and distance to shore. A recent increase in the variance in recovery rates in some ecoregions of the Pacific and Indian Oceans suggests that some reefs in those ecoregions may be approaching a phase shift. While marine heatwaves are increasing in intensity and frequency, our results suggest that regional and local conditions influence coral recovery rates, and therefore, effective local management efforts can help reefs recover from disturbances. 

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2. Recruitment hotspots and bottlenecks mediate the distribution of corals on a Caribbean reef

   https://doi.org/10.1098/rsbl.2021.0149  

   Edmunds, Peter J. (July 2021, Biology Letters)

   Recruitment hotspots are locations where organisms are added to populations at high rates. On tropical reefs where coral abundance has declined, recruitment hotspots are important because they have the potential to promote population recovery. Around St. John, US Virgin Islands, coral recruitment at five sites revealed a hotspot that has persistent for 14 years. Recruitment created a hotspot in density of juvenile corals that was 600 m southeast of the recruitment hotspot. Neither hotspot led to increased coral cover, thus revealing the stringency of the demographic bottleneck impeding progression of recruits to adult sizes and preventing population growth. Recruitment hotspots in low-density coral populations are valuable targets for conservation and sources of corals for restoration. 

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3. The potential for self-seeding by the coral Pocillopora spp. in Moorea, French Polynesia

   https://doi.org/10.7717/peerj.2544  

   Tsounis, Georgios; Edmunds, Peter J. (January 2016, PeerJ)

   Coral reefs in Moorea, French Polynesia, suffered catastrophic coral mortality through predation by Acanthaster planci from 2006 to 2010, and Cyclone Oli in 2010, yet by 2015 some coral populations were approaching pre-disturbance sizes. Using long-term study plots, we quantified population dynamics of spawning Pocillopora spp. along the north shore of Moorea between 2010 and 2014, and considered evidence that population recovery could be supported by self-seeding. Results scaled up from study plots and settlement tiles suggest that the number of Pocillopora spp. colonies on the outer reef increased 1,890-fold between 2010 and 2014/2015, and in the back reef, 8-fold between 2010 and 2014/2015. Assuming that spawning Pocillopora spp. in Moorea release similar numbers of eggs as con-generics in Hawaii, and fertilization success is similar to other spawning corals, the capacity of Pocillopora spp. to produce larvae was estimated. These estimates suggest that Pocillopora spp. in Moorea produced a large excess of larvae in 2010 and 2014 relative to the number required to produce the recruits found in the back reef and outer reef in 2010 and 2014, even assuming that ∼99.9% of the larvae do not recruit in Moorea. Less than a third of the recruits in one year would have to survive to produce the juvenile Pocillopora spp. found in the back and outer reefs in 2010 and 2014/2015. Our first order approximations reveal the potential for Pocillopora spp. on the north shore of Moorea to produce enough larvae to support local recruitment and population recovery following a catastrophic disturbance. 

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4. Corals survive severe bleaching event in refuges related to taxa, colony size, and water depth

   https://doi.org/10.1038/s41598-024-58980-1  

   Winslow, Erin M; Speare, Kelly E; Adam, Thomas C; Burkepile, Deron E; Hench, James L; Lenihan, Hunter S (December 2024, Scientific Reports)

   Abstract Marine heatwaves are increasing in frequency and duration, threatening tropical reef ecosystems through intensified coral bleaching events. We examined a strikingly variable spatial pattern of bleaching in Moorea, French Polynesia following a heatwave that lasted from November 2018 to July 2019. In July 2019, four months after the onset of bleaching, we surveyed > 5000 individual colonies of the two dominant coral genera,PocilloporaandAcropora, at 10 m and 17 m water depths, at six forereef sites around the island where temperature was measured. We found severe bleaching increased with colony size for both coral genera, butAcroporableached more severely thanPocilloporaoverall. Acroporableached more at 10 m than 17 m, likely due to higher light availability at 10 m compared to 17 m, or greater daily temperature fluctuation at depth. Bleaching inPocilloporacorals did not differ with depth but instead varied with the interaction of colony size and Accumulated Heat Stress (AHS), in that larger colonies (> 30 cm) were more sensitive to AHS than mid-size (10–29 cm) or small colonies (5–9 cm). Our findings provide insight into complex interactions among coral taxa, colony size, and water depth that produce high spatial variation in bleaching and related coral mortality. 

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5. Remnant hollowed out dead coral skeleton branches defer coral community recovery

   https://doi.org/10.1371/journal.pone.0339527  

   Scafidi, Kathryn C; Fouke, Kyle W; Sivaguru, Mayandi; Fouke, Bruce W; Edmunds, Peter J (March 2026, PLOS One)

   Tavakoli-Kolour, Parviz (Ed.)

   Through repeated impacts of ecosystem disturbances, most coral reefs have transitioned to a degraded state with low living coral cover. Until recently, the reefs of Moorea, French Polynesia, have provided an exception to this trend as their coral communities have recovered from sequential disturbances over the last 50 years. Early in 2019, the north shore fore reef at 10-m depth had ~ 75% live coral cover, but was decimated by bleaching to leave 17% coral cover by August 2020 and many kilometers of reef dominated by dead-in-place colonies ofPocilloporaspp. By 2025, coral recovery had not begun because of the chronology of decay affecting deadPocilloporaskeletons. We combine ecological analyses of deadPocilloporacolonies with high-resolution microscopy of aragonite skeletal structure to better understand the fate of these dead branching corals. Bleaching in 2019 created a reef dominated by deadPocilloporacolonies that initially were resilient to breakage and removal. Dead corals were colonized by macroalgae, occupied by a unique assemblage of invertebrates, and deterred coral recruitment as evidenced by coral settlers on settlement tiles but not on dead skeletons. In 2022–2023, three years afterPocilloporacolonies were killed, their remnant hollowed-out branches were first detected. High-resolution microscopy indicates hollowing occurred through bioerosion of dead branches that were scaffolded by encrusting taxa and entrapped sediments. Over 2011–2019, coral communities in Moorea rapidly recovered from devastation, but recovery from the 2019 bleaching has been deferred by the retention of dead corals on reef surfaces, creating the opportunity for erosion to further hollow out and weaken dead coral branches. This study shows how the synergy of well-studied disturbances can create ecological surprises that at best defer community recovery, but at worst portend a different outcome of major disturbance events, preventing recovery of the original coral community. 

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