Climate change-related disturbances in 2024 drive the largest known population of elkhorn coral (Acropora palmata) in Barbados to the brink of extirpation

Climate change-related disturbances in 2024 drive the largest known population of elkhorn coral (Acropora palmata) in Barbados to the brink of extirpation | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Climate change-related disturbances in 2024 drive the largest known population of elkhorn coral (Acropora palmata) in Barbados to the brink of extirpation Henri Vallès, Kristen Clarke, Annabel J. Cox, Robert Bourne, Julian Walcott, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8750412/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 9 You are reading this latest preprint version Abstract Climate change is leading to global increases in frequency and severity of marine heatwaves, increasingly contributing to coral reef degradation. In 2024, Barbados was impacted by the passage of Hurricane Beryl and the most severe marine heatwave to date. Here, we report on the fate of the largest known population of the foundational Caribbean reef building coral, Acropora palmata , in Barbados in the face of such disturbances. Between June 2024 and March 2025, we tagged, measured and monitored (biweekly to monthly) the health status of 33–41 A. palmata colonies at Mullins Reef on Barbados’ west coast. On July 1, Hurricane Beryl passed south of Barbados, causing the loss of 36.4% of tagged colonies. On August 4 and September 2 2024, average daily cumulative heat stress reached four and eight Degree Heating Weeks (DHW), respectively, peaking on November 12 at an unprecedented 24.2 DHW. After Beryl, tagged colonies that were not destroyed remained healthy until September 16, when some started to show bleaching signs. By October 29, all colonies were fully bleached and by December 18 most colonies had died. By February 14 2025, only one colony remained alive; it had regained full coloration, but lost > 50% of its live tissue. The collapse of the most important A. palmata population on the west coast, coupled with the devastating impact of Hurricane Beryl on the south coast, provide a stark warning that A. palmata might have now reached functional extinction in Barbados, abruptly ending two decades of slow A. palmata recovery. coral bleaching heatwave hurricanes local extirpation Acroporids climate change Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Climate change is resulting in a global increase in the frequency and/or severity of marine heatwaves (Smith et al. 2025) and tropical hurricanes (Knutson et al. 2020; Knutson et al. 2021). Since the 1980s, marine heatwaves and hurricanes have played an increasingly important role in the degradation of coral reefs in the wider Caribbean (Gardner et al. 2005; Wilkinson and Souter 2008; Eakin et al. 2010; Cetina-Heredia and Allende-Arandía 2023; Gonzalez-Barrios et al. 2023; Lenton et al. 2025). Corals differ markedly in life-history traits (Darling et al. 2012) that are linked to differences in their vulnerability to thermal-induced bleaching mortality (Loya et al. 2001; Mizerek et al. 2018) and/or storm-induced mortality due to colony dislodgement (Madin et al. 2014). These differences have strongly contributed to driving shifts in the composition of the surviving coral assemblages over time that undermine the structure and function of these systems (Hughes et al. 2018; Estrada-Saldívar et al. 2019) and their ability to provide a wide range of critical ecosystem services (Eddy et al. 2021; Smith et al. 2025). The increasing frequency and severity of such episodic disturbances is now impacting even the more resilient coral species (Byrne et al. 2025; Doherty et al. 2025). In the Caribbean, which already suffers from relatively low functional and taxonomic coral diversity (Bellwood et al. 2004), and where such climate-related stressors often interact with chronic local stressors such as poor water quality and overfishing, this is driving coral reefs ever closer to a long-term regime shift to an algal-dominated or degraded state (Lenton et al. 2025). Elkhorn coral, Acropora palmata (Lamarck, 1816), is one of the foundational reef building corals of Caribbean reefs, historically being the main reef framework constructor and inhabitant of the shallow reef crest zone of many of the region’s fringing reefs (Goreau 1959; Gladfelter 1982; Cramer et al. 2021). As such it played a crucial ecological role through the provision of complex three dimensional physical structure that benefits other reef organisms (Lirman 1999), and was responsible for mediating the wave energy attenuation effect of reefs that protects coastlines (Toth et al. 2023). More recent paleoecological evidence supports that the abundance of A. palmata (and that of the only other Caribbean acroporid species, A. cervicornis , Lamarck, 1816) across the region dropped considerably around the mid 1950s and 1960s, likely due to human-induced local stressors such as coastal run off affecting water quality (Cramer et al. 2020). A. palmata populations underwent further rapid declines primarily due to a Caribbean-wide episode of White Band Disease in the late 1970s and early 1980s, with hurricanes also playing an important, but more localized role, in this decline (Aronson and Precht 2001). Subsequently, A. palmata has demonstrated high vulnerability to both thermal-induced bleaching mortality and storm-induced mortality in the region (Wilkinson and Souter 2008). Although there have been some reports of A. palmata population recovery across the Caribbean in recent decades (Macintyre and Toscano 2007; Zubillaga et al. 2007; Muller et al. 2013; Larson et al. 2014; Croquer et al. 2016), Caribbean acroporids are still considered critically endangered (Gutierrez et al. 2024). In Barbados, like other countries across the Caribbean, A. palmata has historically been a dominant reef framework constructor (Lewis 1984; Macintyre et al. 2007). Its last remnant shallow water populations on the west coast of the island declined sometime during the 1900’s, likely primarily due to sedimentation driven by island-scale deforestation and tropical storms (Lewis 1984), in a time line consistent with Cramer et al. (2020)’s paleoecological region-wide study. By the time regular monitoring of Barbados reefs began in the early 1980s, A. palmata (and A. cervicornis ) were relatively rare. However, MacLean and Oxenford (2016) provided strong evidence that A. palmata populations were recovering in 2015 in Barbados. MacLean and Oxenford (2016) exhaustively surveyed 46 shallow fringing reefs along the entire west coast of Barbados in 2015 and recorded a total of 707 A. palmata colonies, present in 57% of the reefs surveyed. Importantly, one reef located towards the northern end of the west coast, the Mullins Reef, accounted for 68% of all the A. palmata colonies found (482 colonies) and exhibited the highest colony density (137 colonies per hectare). More detailed subsequent surveys at Mullins Reef in 2016 by Oxenford et al. (2024) yielded a revised total abundance estimate of 599 A. palmata colonies, i.e. 72% of all reported colonies on the west coast’s fringing reefs between 2015 and 2016. Moreover, this A. palmata population included many large mature colonies, with in situ confirmation of active spawning taking place in 2017 (Oxenford et al. 2024). Finally, genetic analyses confirmed the presence of at least eight different A. palmata genets at Mullins Reef, which largely exceeded the genotypic diversity found in a few other shallow reefs surveyed in the south and west coasts of Barbados in 2016 (Oxenford et al. 2024). These different lines of evidence jointly support that the thriving A. palmata population at Mullins Reef in 2015 and 2016 likely played a particularly important role as a source population in the recovery of this species in Barbados at that time. The above characteristics motivated the use of A. palmata colonies from the Mullins Reef as donor material in the context of an A. palmata coral restoration project in Barbados in 2024. This effort also led to the frequent monitoring of a representative fraction of this population from June 2024 onward, for the first time since 2016. However, 2024 was a year with a relatively high number of major hurricanes in the Caribbean (five in total; NOAA’s National Hurricane Center at https://www.nhc.noaa.gov/ ) of which one, Hurricane Beryl, made history as the earliest Category 5 hurricane on record in the Atlantic Basin (Beven II et al. 2025). Hurricane Beryl cut through the Windward Islands on July 1st 2024, passing approximately 200 km south of Barbados as a Category 4 hurricane, making landfall on the Grenadian island of Carriacou, and becoming a Category 5 hurricance on July 2nd 2024 (Fig. 1 A) (Beven II et al. 2025). Although Barbados was not in the direct path of the hurricane, the south and west coastal and nearshore environments of the island were heavily affected by storm surge, which breached the Bridgetown fishing harbour wall, severely damaging hundreds of fishing vessels as well as the Bridgetown harbour cruise ship terminal (Beven II et al. 2025). Moreover, between 2023 and 2024 the world experienced the hottest marine heatwave on record, amplified by El Niño conditions (Jiang et al. 2024; Smith et al. 2025), which translated into the highest cumulative temperature stress (as degree heating weeks (DHW)) on record for the Windward Islands, peaking in November 2024 for this subregion (Fig. 1 B). The 2023–2024 marine heatwave resulted in the 4th global mass coral bleaching event (Goreau and Hayes 2024; Reimer et al. 2024), with multiple reports confirming mass coral bleaching and mortality throughout the wider Caribbean (Mejias-Rivera and Courtney 2024; Muniz-Castillo et al. 2024; Neely et al. 2024; Prato-Valderrama et al. 2024; Doherty et al. 2025), including a report from the Windward Island of Martinique during this period (Bon et al. 2025). The few recently published reports support that most remaining populations of A. palmata have suffered extensive bleaching-induced mortality across the region, further threatening the long-term persistence of this critically endangered species (Neely et al. 2024; Birkart and Alvarez-Filip 2025; Manzello et al. 2025), although some locations were not as severely affected (Neely et al. 2024). In Barbados, A. palmata populations at Mullins and several other reefs did suffer bleaching in 2023, but they recovered well thereafter (pers obs), likely because the heatwave did not reach its peak in the Windward Islands until 2024 (Fig. 1 B). Here, we report on the fate of the A. palmata population at Mullins Reef in the face of the passage of Hurricane Beryl and the 2023–2024 heatwave in 2024, when it was most severe in the subregion, and provide some notes on impacts on other A. palmata populations in Barbados around the same time. Because Barbados is located in the most southeastern range of the wider Caribbean, east of the Lesser Antilles Island chain, we hope that our data will contribute to filling a geographic gap on the direct and most recent impact of climate change-related events on A. palmata populations across the entire range of this species. Methods On June 19 2024, 33 haphazardly selected A. palmata colonies of the population at Mullins Reef were tagged for monitoring (Fig. 2 ). These colonies were located at depths of 1.0 m to 2.5 m, the depth range that hosted the majority of the A. palmata population (Fig. 2 ). On July 21 2024, an additional 20 colonies were tagged after the passage of Hurricane Beryl (Fig. 2 ). The depth of each colony was estimated using a SCUBA depth gauge to the nearest 0.1 m and the maximum height of each colony from the benthic substrate was estimated to the nearest cm using a marked rod. The tagged colonies were surveyed approximately biweekly via SCUBA until January 2025, and at least monthly thereafter until March 2025. During each survey, top-down photographs of every colony were taken. A one-metre reference rod marked at 10 cm intervals was included in each photograph as a reference scale. These images were later analysed in ImageJ (Abramoff et al. 2004) to calculate additional colony size metrics and colony health status. Additional colony size metrics included colony length (longest planar dimension), colony width (longest planar dimension perpendicular to length) and colony total planar area. Colony health status included percent area that is dead out of the colony’s total planar area (i.e. % dead surface) and the pigmentation status of the live tissue. The latter was categorized as fully pigmented, bleached, or dead. Fully pigmented implied that the colony had live tissue and that such live tissue exhibited conspicuous and bright brownish colouration. Bleached implied that the colony had live tissue, but such tissue had either lost some pigmentation (relative to the initial baseline colouration photographs of June 2024) or completely lacked any pigmentation (fully bleached). Dead colonies exhibited no live tissue, which was evidenced by turf algae overgrowth of the coral skeleton. In situ sea surface temperature readings were obtained from a HOBO Water Temp Pro v2 Logger (U22-001) deployed at a depth of 4 m on a fringing reef site located midway along the west coast of Barbados. Shallow sea surface temperature profiles are very similar along the west coast of Barbados, so the data generated at this central site will be sufficiently representative of the temperature experienced at Mullins Reef. Degree Heating Weeks (DHW), a measure of cumulative heat stress, were derived from NOAA’s Coral Reef Watch Windward Caribbean Islands Time Series, accessed via the National Environmental Satellite, Data, and Information Service (NESDIS; https://www.nesdis.noaa.gov/ ). Daily in situ sea surface temperature readings and DHW estimates were averaged over each biweekly period preceding a colony survey and these averages were displayed graphically. Colony size metrics and colony depth were described graphically as size frequency distributions. Potential differences in colony size dimensions among different sets of tagged colonies were assessed using Mann-Whitney tests. Potential associations between colony size metrics and depth were assessed using Spearman’s rank correlation tests. Changes in colony health metrics over time were summarized and displayed graphically as percentage of colonies under each pigmentation status and as boxplots of dead surface area estimates across colonies over time. Analyses were conducted in R (R Core Team 2025) and plots were generated using ggplot (Wickham 2016) and MS Excel. Results and Discussion Impact of Hurricane Beryl The initial 33 A. palmata colonies tagged before the passage of Hurricane Beryl had an average length of 89.7 cm ± 9.4 (standard error), an average width of 70.3 cm ± 5.8 (Fig. 3 B), an average height of 34.0 cm ± 4.0 (Fig. 3 C), and were found at an average depth of 1.8 m ± 0.1 (Fig. 3 D). These dimensions align well with the large size category (longest top-down planar dimension of 50–100 cm) of Oxenford et al. (2024), which accounted for 25% of the 586 colonies measured in 2016 at Mullins Reef, with only 12.5% of the colonies being larger (> 100 cm) at that time. It also suggests that A. palmata colonies had increased considerably in size since 2016, when the population was dominated (63%) by considerably smaller colonies (< 50 cm) (Oxenford et al. 2024). Satellite imagery data from 2016 and 2023 also supports that the population in 2023 was at least as abundant as, and likely more abundant than, in 2016 (Fig S1 ). However, unlike Oxenford et al. (2024)’s study, our colony sampling was not specifically designed to fully characterize the colony abundance and size class distribution of the entire population at Mullins Reef, so this temporal comparison warrants caution. Colony height was significantly positively correlated with depth (Spearman rank correlation test: r s =0.30, p = 0.032), but this was not the case for colony width (r s =0.17, p = 0.211) nor length (r s =0.18, p = 0.192). A positive correlation between colony height and depth is expected given the shallow depth range of the reef crest that was surveyed in this study (1.0-2.5 m), which will necessarily limit colony height growth in this fast growing species (Gladfelter et al. 1978). The swells generated by the storm surge of Hurricane Beryl led to the complete dislodgement and loss of 12 (36.4%) of the initial 33 colonies on July 1st 2024. The tagged colonies lost to Beryl did not differ significantly in height, width, or length from the tagged colonies that survived (Mann-Whitney tests: X 2 ≤0.48, df = 1, p ≥ 0.487) (Fig. 3 A-C). However, they were significantly shallower (average: 1.3 m ± 0.1, n = 12) than the survivor ones (2.1 m ± 0.1, n = 21) (Mann-Whitney test: X 2 =14.81, df = 1, p ≤ 0.001; Fig. 3 D) and located on the reef crest zone closer to shore (Fig. 2 ). Subsequent surveys confirmed the disappearence of most (tagged and non-tagged) colonies at this depth (Clarke 2025). Fringing reefs significantly reduce wave energy and height, with the reef crest playing a dominant role in wave energy dissipation (Ferrario et al. 2014), which helps explain why the shallower colonies were much more heavily impacted by the wave-breaking energy derived from the storm surge than their deeper counterparts. The survival of a relatively large fraction of the A. palmata population at Mullins Reef through Hurricane Beryl was facilitated by the location of the reef, which lies in the northern section of the west coast (Fig. 2 ). Because Hurricane Beryl travelled south of Barbados (Fig. 1 A), it had a much stronger impact on the south coast than on the west coast, resulting in substantial infrastructure damage and vessel losses in the south (Beven II et al. 2025). In that regard, the second largest known population of A. palmata at the time, located at greater average depths (> 2.5 m) near a popular surfing area of the south coast (Drill Hall), approximately 3 km south of the Bridgetown Harbour, was completely eradicated by the passage of Beryl (Clarke 2025). It is thus likely that any remaining patches of A. palmata colonies that had survived Beryl’s passage were primarily confined to the west and north coasts of Barbados, with the Mullins Reef continuing to host one of the most important populations right after Beryl. A. palmata has historically dominated shallow high wave energy reef environments in the Caribbean (Cramer et al. 2020; Cramer et al. 2021), and its fast growth rates and branching shape are well adapted to undergo wave-induced fragmentation (Gladfelter et al. 1978; Lirman 2000). However, these life traits also make it particularly susceptible to impacts by tropical storms and so increases in storm frequency and/or intensity have been repeatedly identifed as important contributing factors to its long-term demise across the region (Woodley et al. 1981; Gardner et al. 2005; Macintyre et al. 2007; Wilkinson and Souter 2008; Hernández-Delgado et al. 2024), even though individual storms will impact reefs at more localized spatial scales than other regional disturbances such as marine heatwaves and disease outbreaks. In line with this, our study highlights that Hurricane Beryl had already drastically reduced standing A. palmata populations in Barbados before the 2023–2024 regional marine heatwave reached its peak severity in 2024. Impact of the 2024 heatwave The additional 20 colonies that were tagged at Mullins Reef post-Beryl to replace and supplement the ones lost to Beryl did not differ from the initially tagged colonies that survived Beryl in either height, width, or length (Mann-Whitney tests: X 2 ≤0.08, df = 1, p ≥ 0.784) (Fig. 3 A-C). However, they were minimally but significantly shallower (average: 1.9 m ± 0.1) than the initially tagged survivors (average: 2.1 m ± 0.1) (Mann-Whitney test: X 2 =14.81, df = 1, p ≤ 0.001) (Fig. 3 D) and were also closer to shore (Fig. 2 ). In situ daily sea surface water temperature on the west coast of Barbados during 2024 were the highest on record, exceeding that of 2005, 2010 and 2023, which were years that also showed unsually high temperatures over the last two decades (Fig S2 ) and during which mass coral bleaching events were reported in Barbados (Oxenford et al. 2008; Oxenford and Vallès 2016; Irvine et al. 2025). The 2024 in situ temperature measurements for Barbados were generally within the range of minimum and maximum values estimated by NOAA Coral Reef Watch for the Windward Caribbean Islands (Fig S2 ), supporting that such satellite temperature data adequately inform on the nearshore marine environment of Barbados, which is not always the case across Caribbean reefs (Margaritis et al. 2025). During the biweekly period up to July 8, average in situ daily sea surface temperature was 29.3 degrees Celsius and continued to gradually increase thereafter, reaching peak values in the October 15 biweekly period of 30.8 degrees Celsius (Fig. 4 A). It gradually dropped thereafter, reaching 29.5 degrees Celsius during the December 4 period and 28.1 degrees Celsius during the January 31 period (Fig. 4 A). Cumulative heat stress, expressed as average daily degree heating weeks, exceeded the four-week bleaching threshold and eight-week bleaching-induced mortality theshold during the August 6 and September 2 biweekly periods, respectively, reaching a peak of 24.2 DHW during the November 12 biweekly period and gradually decreasing thereafter (Fig. 4 A). On July 8, a week after the passage of Beryl, all the tagged colonies were fully pigmented and had very low levels of tissue mortality (average: <2% of dead surface area); these health metrics remained relatively similar through September 2 (Fig. 4 B-C; Fig. 5 A). By September 16 some colonies (17%) started to show signs of bleaching (partial loss of original pigmentation) and by October 1 all colonies showed signs of bleaching in varying degrees. By October 29 all colonies were fully bleached (complete loss of pigmentation; Fig. 4 B; Fig. 5 B-D), which coincided with the first record of increases in tissue mortality (Fig. 3 B; Fig. 5 B-D). By November 12 some colonies (15%) had fully died (Fig. 3 B; Fig. 5 B-D). By December 4, a period of unusually high wave energy led to the dislodgement and loss of a further four of the tagged colonies (10%) (Fig. 3 B). December 4 coincided with a dramatic increase in tissue mortality that led to more than one third (38%) of colonies fully dying (Fig. 3 B-D; Fig. 5 B-F). By December 18, the majority of the tagged colonies (70%) had completely died after bleaching, with just three bleached tagged colonies surviving but showing varied levels of tissue mortality (Fig. 3 B-C). On January 3, only two bleached tagged colonies were still alive with high levels of tissue mortality (average: >50% of dead surface area) (Fig. 3 B-C). On January 31, one of the two colonies had regained full pigmentation while the other one remained bleached (Fig. 3 B-C). By February 14, only the colony that had regained full pigmentation during the preceding period remained alive (Fig. 3 B-C). Overall, out of the 41 tagged healthy colonies monitored post-Beryl (July 8, 2024 - March 12, 2025), 36 (88%) died due to thermal-induced bleaching, four (10%) were lost to high wave action, and one (2%) survived, but suffered high tissue mortality. Photographic evidence of the wider Mullins Reef population mirrored the fate of the tagged colonies and confirmed the near complete extirpation of its entire A. palmata population (Fig S3). The unprecedented cumulative heat stress experienced in the last half of 2024 (reaching as high as 24.2 DHW) led to the final collapse of the A. palmata population at Mullins Reef. This was the case even though this population undoubtedly exhibited a substantial degree of thermal tolerance, having survived previous heatwaves, including those of 2005, 2010 and 2023, which exceeded the 14 DHW (Fig. 1 B) that has been suggested as the general upper thermal threshold of A. palmata (Birkart and Alvarez-Filip 2025). Our findings support Williams et al. (2017), who suggested that thermal tolerance thresholds for A. palmata likely vary geographically. They also suggested that A. palmata populations, at least in the upper Florida Keys, do not become increasingly thermally tolerant following repeated severe thermal stress exposures, findings that concord with our own observations in Barbados, despite the previously documented relatively high genotypic diversity at our site in 2016 (Oxenford et al. 2024). Although such genetic diversity was not reassessed in 2024, conspicous differences in colony morphology (pers obs) suggested that much of it remained at the site. Our findings also echo those reported by others across the region as a result of the extreme heatwave experienced over 2023–2024. For example Thompson et al. (2025) witnessed the extirpation of A. palmata populations in the Dry Tortugas (Florida Keys), and Manzello et al. (2025) report the functional extinction of A. palmata (and A. cervicornis ) throughout the Florida Keys. Likewise, Birkart and Alvarez-Filip (2025) report that A. palmata vanished from the Puerto Morelos reefscape and concluded that this species suffered catastrophic mass mortality across its entire shallow water distribution range in the Greater Caribbean. The observation by Williams et al. (2017) supported by our own observations that A. palmata does not improve heat tolerance with successive exposure to heatwaves contrasts with adaptive responses (acclimitization) observed in some other coral species (e.g. Guest et al. 2012), including an Indo-Pacific acroporid ( A. digitifera ) (e.g. Humanes et al. 2022). Of note, several rapid surveys on other shallow reefs on the west coast of Barbados in November 2024 identified a few small patches of surviving A. palmata colonies that were not bleached (unpublished data), highlighting the existence of some uniquely heat-resistant phenotypes and providing a glimmer of hope. Whether such heat-resistance is driven by the coral host genotype, the symbiont identity and/or reef-scale environmental factors remains to be determined (e.g. Karp et al. 2025). Conclusion The likely extirpation of A. palmata populations on the south coast due to Hurricane Beryl, coupled with the subsequent bleaching-induced loss of the A. palmata population at Mullins Reef, a population that exhibited the highest abundance and density on the west coast and included many sexually reproductive individuals, suggest that A. palmata might now be functionally extinct in Barbados, an island that is primarily self-recruiting (Cowen et al. 2006). Overall, this mirrors other reports of extirpation and functional extinction of A. palmata from across the Caribbean suggesting that the slow recovery of this now endangered species over recent decades has endured a major setback. This underscores the urgent need to biopreserve the few and uniquely heat-resistant phenotypes left in Barbados and other islands and engage in their assisted recovery to prevent loss of this valuable foundational species (Muller et al. 2025). Declarations Acknowledgments We thank N. Hand-Lennon, J. A. Silverman, K. Shulman, E. Paquette and C. Pierre for helping locate surviving A. palmata colonies in November 2024. We thank K. Alleyne, S. Alleyne, J. Weekes, and S. Palmer for their assistance with various aspects of this work. This work was partially funded by the project entitled “ Wave Attenuation: Natural solutions with elkhorn coral (WANSEC): Exploring the lattice turbulence of Acropora palmata thickets in wave attenuation and sediment deposition as a device for coastal protection ”, project # EbA3_039 of the Caribbean Biodiversity Fund (CBF), co-financed by the International Climate Inititative (IKI) of the German Federal Ministry for Environment, Nature Conservation, and Nuclear Safety through KfW. Authors contributions Conceptualization and Methodology: HV; Supervision: AJC; Investigation: KC, AJC, RB, HAO; Data curation: AJC, KC, HV; Formal analysis: HV, KC; Visualization: HV, AJC, KC; Writing-original draft preparation: HV, KC; Writing-review and editing: HV, HAO, JW, KC, AJC, RB; Funding acquisition: HV, JW, HAO. 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Coral Reefs 26:765-773 MacLean R, Oxenford HA (2016) Mapping the return of acroporid corals on fringing reefs along the west coast of Barbados. Centre for Resource Management and Environmental Studies (CERMES). Faculty of Science and Technology, The University of the West Indies, Cave Hill Campus, Barbados. CERMES Technical report No 80, 56 pages Madin JS, Baird AH, Dornelas M, Connolly SR (2014) Mechanical vulnerability explains size-dependent mortality of reef corals. Ecol Lett 17:1008-1015 Manzello DP, Cunning R, Karp RF, Baker AC, Bartels E, Bonhag R, Borreil A, Bourque A, Brown KT, Bruckner AW, Corbett B, D'Alessandro M, Dahlgren C, Dilworth J, Geiger E, Gilliam DS, Gomez M, Hanson G, Harrell C, Hesley D, Huebner LK, Kenkel CD, Koch HR, Kuehl J, Kuffner IB, Ladd MC, Lee SP, Lesneski KC, Lewan A, Lirman D, Liu G, Matsuda SB, Montoya-Maya PH, Moore J, Muller EM, Nedimyer K, Parkinson JE, Ruzicka R, Spadaro J, Spady BL, Stein J, Unsworth JD, Walter C, Wen ADE, Williams DE, Williams SD, Williamson OM (2025) Heat-driven functional extinction of Caribbean Acropora corals from Florida's coral reef. Science 390:361-366 Margaritis G, Kent EC, Foster GL (2025) Intercomparison of satellite-derived SST with logger data in the Caribbean-Implications for coral reef monitoring. Plos Clim 4:e0000480 Mejias-Rivera CL, Courtney TA (2024) Ocean warming, heat stress, and coral bleaching in Puerto Rico. 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Commun Biol 7:1452 Neely KL, Nowicki RJ, Dobler MA, Chaparro AA, Miller SM, Toth KA (2024) Too hot to handle? The impact of the 2023 marine heatwave on Florida Keys coral. Front Mar Sci 11:1489273 Oxenford HA, Vallès H (2016) Transient turbid water mass reduces temperature-induced coral bleaching and mortality in Barbados. PeerJ 4:e2118 Oxenford HA, Suckoo RB, Cox AM, Cox AJ (2024) Assisted recovery of elkhorn coral ( Acropora palmata ) on a fringing reef in Barbados: A pilot study 2016-2019. Final Report 2020. Centre for Resource Management and Environmental Studies, The University of the West Indies, Cave Hill Campus, Barbados. CERMES Technical Report No. 109, Barbados, 51 pages Oxenford HA, Roach R, Brathwaite A, Nurse L, Goodridge R, Hinds F, Baldwin K, Finney C (2008) Quantitative observations of a major coral bleaching event in Barbados, Southeastern Caribbean. Clim Change 87:435-449 Prato-Valderrama J, Mejía-Rentería JC, Forbes M, Santos-Martinez A, Castaño D, Schuhmann PW (2024) Extreme temperatures in 2023 generate mass coral reef bleaching in the western Caribbean, Seaflower Biosphere Reserve. Bull Mar Sci 100:793-794 R Core Team (2025) R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. Version 4.5.0. https://www.R-project.org/, pages Reimer JD, Peixoto RS, Davies SW, Traylor-Knowles N, Short ML, Cabral-Tena RA, Burt JA, Pessoa I, Banaszak AT, Winters RS, Moore T, Schoepf V, Kaullysing D, Calderon-Aguilera LE, Wörheide G, Harding S, Munbodhe V, Mayfield A, Ainsworth T, Vardi T, Eakin CM, Pratchett MS, Voolstra CR (2024) The fourth global coral bleaching event: Where do we go from here? Coral Reefs 43:1121-1125 Smith KE, Sen Gupta A, Burrows MT, Filbee-Dexter K, Hobday AJ, Holbrook NJ, Malan N, Moore PJ, Oliver ECJ, Thomsen MS, Wernberg T, Zhao Z, Smale DA (2025) Ocean extremes as a stress test for marine ecosystems and society. Nat Clim Chang 15:231-235 Thompson AM, Stathakopoulos A, Hollister KJ, Lynch AM, Holder JC, Kuffner IB (2025) Acute heat stress and the extirpation of a threatened coral species from a remote, subtropical reef system. Coral Reefs 44:1023-1030 Toth LT, Storlazzi CD, Kuffner IB, Quataert E, Reyns J, McCall R, Stathakopoulos A, Hillis-Starr Z, Holloway NH, Ewen KA, Pollock CG, Code T, Aronson RB (2023) The potential for coral reef restoration to mitigate coastal flooding as sea levels rise. Nat Commun 14:2313 Wickham H (2016) ggplot2: Elegant graphics for data analysis. Springer-Verlag New York Wilkinson C, Souter D (2008) Status of Caribbean coral reefs after bleaching and hurricanes in 2005. Global Coral Reef Monitoring Network, and Reef and Rainforest Research Centre, Townsville, Australia Williams DE, Miller MW, Bright AJ, Pausch RE, Valdivia A (2017) Thermal stress exposure, bleaching response, and mortality in the threatened coral Acropora palmata . Mar Pollut Bull 124:189-197 Woodley JD, Chornesky EA, Clifford PA, Jackson JB, Kaufman LS, Knowlton N, Lang JC, Pearson MP, Porter JW, Rooney MC, Rylaarsdam KW, Tunnicliffe VJ, Wahle CM, Wulff JL, Curtis AS, Dallmeyer MD, Jupp BP, Koehl MA, Neigel J, Sides EM (1981) Hurricane Allen's impact on Jamaican coral reefs. Science 214:749-755 Zubillaga AL, Márquez LM, Cróquer A, Bastidas C (2007) Ecological and genetic data indicate recovery of the endangered coral Acropora palmata in Los Roques, Southern Caribbean. Coral Reefs 27:63-72 Additional Declarations No competing interests reported. Supplementary Files SIforAcroporaarticle.pdf SIA.palmatacharacteristicsandtimeseriesincolonyhealthandmortalityandSST.xlsx Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 27 Mar, 2026 Reviews received at journal 04 Mar, 2026 Reviews received at journal 27 Feb, 2026 Reviewers agreed at journal 10 Feb, 2026 Reviewers agreed at journal 10 Feb, 2026 Reviewers invited by journal 09 Feb, 2026 Editor assigned by journal 04 Feb, 2026 Submission checks completed at journal 03 Feb, 2026 First submitted to journal 31 Jan, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8750412","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":589218168,"identity":"298a5ef1-9adb-4971-baa0-b2af72e5bd97","order_by":0,"name":"Henri Vallès","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABHklEQVRIiWNgGAWjYBACAxCRAMR87EDiA4gnwdh44AGQZgOx8WlhY2ZgYJwB0dJwIIGQFgaoFmYeBogysBYGHFrM2XuPfXjAcFiejZn58GebGrvEfulmkC2HE/sYmA/e5sHUYtlzLnkGUIFhGzNbmnTOseTEmXMOQrS0MbAlW2PRYnAjxxjolzTGNmYeM+bcBmZjgxuJYC25bQw8ZtLYtNx/A9Zi38bM//mzZUO9sT1CC/83rFpu8IC02CQCbWGQZmw4LGcggbCFDauWMyCHGdgkA/1iJtlz7LicBNgWg/R6oIix5RwsWo6fMWb8USFh28/e/PjDj5pqHv4Z6Q8ffKiwNpZvb3544w2WUIZoxCrCjEv5KBgFo2AUjAJCAAC5pV8OuIujiQAAAABJRU5ErkJggg==","orcid":"","institution":"University of the West Indies","correspondingAuthor":true,"prefix":"","firstName":"Henri","middleName":"","lastName":"Vallès","suffix":""},{"id":589218169,"identity":"d73e9968-2572-435b-b24d-5575ad7d3241","order_by":1,"name":"Kristen Clarke","email":"","orcid":"","institution":"University of the West Indies","correspondingAuthor":false,"prefix":"","firstName":"Kristen","middleName":"","lastName":"Clarke","suffix":""},{"id":589218170,"identity":"18204e78-2219-4c48-9c06-f1ef7d443fad","order_by":2,"name":"Annabel J. Cox","email":"","orcid":"","institution":"University of the West Indies","correspondingAuthor":false,"prefix":"","firstName":"Annabel","middleName":"J.","lastName":"Cox","suffix":""},{"id":589218171,"identity":"0d1b0a48-c973-470b-8d8b-e74601074293","order_by":3,"name":"Robert Bourne","email":"","orcid":"","institution":"University of the West Indies","correspondingAuthor":false,"prefix":"","firstName":"Robert","middleName":"","lastName":"Bourne","suffix":""},{"id":589218172,"identity":"43352006-3a0a-4a1c-adcf-08cbd0104ba5","order_by":4,"name":"Julian Walcott","email":"","orcid":"","institution":"University of the West Indies","correspondingAuthor":false,"prefix":"","firstName":"Julian","middleName":"","lastName":"Walcott","suffix":""},{"id":589218173,"identity":"a9b3fe6f-2836-4a11-88da-9706d48382b9","order_by":5,"name":"Hazel A. Oxenford","email":"","orcid":"","institution":"University of the West Indies","correspondingAuthor":false,"prefix":"","firstName":"Hazel","middleName":"A.","lastName":"Oxenford","suffix":""}],"badges":[],"createdAt":"2026-01-31 13:54:15","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8750412/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8750412/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":102571013,"identity":"38929a07-b8c0-4a94-9d4e-1ba9611e4d31","added_by":"auto","created_at":"2026-02-13 07:11:25","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":362260,"visible":true,"origin":"","legend":"\u003cp\u003eClimate-change related disturbances affecting Barbados. A) Modified satellite imagery of the Windward Islands including Barbados (red circle) showing the trajectory of Hurricane Beryl (red/orange dotted line) and its location (red start) and associated water vapor cover on July 1\u003csup\u003est\u003c/sup\u003e 2024; original image source: Zoom Earth (\u003ca href=\"https://zoom.earth\"\u003ehttps://zoom.earth\u003c/a\u003e); B) Average daily Degree Heating Weeks (DHW) for the Windward Islands for the months of May to December for the years corresponding to global (1998; 2010; 2014-2017; 2023-2024) and regional (2005) mass coral bleaching events; dotted vertical black lines indicate four and eight DHWs; data source: NOAA Coral Reef Watch accessed via the National Environmental Satellite, Data and Information Service (NESDIS; https://www.nesdis.noaa.gov/).\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8750412/v1/292069d5d4eb0f7e6d32ef08.png"},{"id":102571044,"identity":"9cd68e37-600b-4bd4-ab28-27b355b0d301","added_by":"auto","created_at":"2026-02-13 07:11:48","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":796451,"visible":true,"origin":"","legend":"\u003cp\u003eLocation of 53 \u003cem\u003eA. palmata\u003c/em\u003e colonies at Mullins Reef in Barbados that were tagged before (white and red circles) and after (orange circles) the passage of Hurricane Beryl, identifying those that were lost to Hurricane Beryl (red circles). The location of Mullins Reef on the west coast of Barbados is shown in the inset. Original image source: Google EarthPro.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8750412/v1/d279c22244981da0a43593c2.png"},{"id":102570969,"identity":"0fb31fca-1e6a-45b0-a9cf-36db23d2467b","added_by":"auto","created_at":"2026-02-13 07:11:00","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":115288,"visible":true,"origin":"","legend":"\u003cp\u003eFrequency distributions of 53 \u003cem\u003eA. palmata\u003c/em\u003ecolonies at Mullins Reef that were tagged before and after the passage of Hurricane Beryl, identifying those that were lost to Hurricane Beryl, for A) colony maximum length; B) colony maximum width; C) colony maximum height, and D) colony depth.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8750412/v1/09bbeba3b9c628f11c933676.png"},{"id":102570974,"identity":"c524fde9-4e8f-4d4c-81e1-c1e3994a4bdd","added_by":"auto","created_at":"2026-02-13 07:11:01","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":185312,"visible":true,"origin":"","legend":"\u003cp\u003eTime series of sea surface temperature metrics and coral health metrics from the tagged \u003cem\u003eA. palmata\u003c/em\u003e colonies at Mullins Reef that survived the passage of Hurricane Beryl between July 8 2024 and March 2025. A) Biweekly average daily sea surface temperature (derived \u003cem\u003ein situ\u003c/em\u003e from a \u0026nbsp;central site on Barbados’ west coast; black line) and associated average daily Degree Heating Weeks for the Windward Islands (blue bars); B) Percent of tagged \u003cem\u003eA. palmata\u003c/em\u003e colonies allocated to four different health status categories over time; C) Boxplots of dead surface area estimates for the tagged \u003cem\u003eA. palmata\u003c/em\u003e colonies and corresponding mean dead surface area (across tagged colonies) (red line) over time. Dashed vertical black lines in A) indicate four and eight DHWs.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-8750412/v1/858fe85726b61aa5be153151.png"},{"id":102571008,"identity":"2c28fbcb-e606-4059-93df-0dace74534c6","added_by":"auto","created_at":"2026-02-13 07:11:19","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1390136,"visible":true,"origin":"","legend":"\u003cp\u003eProgression of a selected tagged \u003cem\u003eA. palmata\u003c/em\u003e colony from the Mullins Reef population, as it transitions from alive and fully pigmented to completely dead between July 8 and November 11, 2024. A) fully pigmented (July 8); B) early signs of bleaching, with partial discolouration visible (September 16); C) partially bleached with significant loss of pigment (October 1); D) fully bleached with small spots of algal growth; E) increased mortality and widespread algal growth (October 29); F) fully dead with extensive algal growth covering the colony (November 11).\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-8750412/v1/9ed2f7b50370912381a0a760.png"},{"id":102571241,"identity":"6a50404e-971b-4e95-9a76-36f6df154006","added_by":"auto","created_at":"2026-02-13 07:12:17","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3870632,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8750412/v1/a105f17f-d50e-41fd-8b1f-c37ce9a642b0.pdf"},{"id":102570961,"identity":"9d8a1cd0-1a94-498a-8e29-45fb65a5ed36","added_by":"auto","created_at":"2026-02-13 07:10:58","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":1219766,"visible":true,"origin":"","legend":"","description":"","filename":"SIforAcroporaarticle.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8750412/v1/84f8eeceeec13dc116b497b8.pdf"},{"id":102571020,"identity":"7971a5ef-6431-4a28-ae00-ee8a9e102768","added_by":"auto","created_at":"2026-02-13 07:11:29","extension":"xlsx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":14212,"visible":true,"origin":"","legend":"","description":"","filename":"SIA.palmatacharacteristicsandtimeseriesincolonyhealthandmortalityandSST.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-8750412/v1/586112c2f182f310dcf73d50.xlsx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Climate change-related disturbances in 2024 drive the largest known population of elkhorn coral (Acropora palmata) in Barbados to the brink of extirpation","fulltext":[{"header":"Introduction","content":"\u003cp\u003eClimate change is resulting in a global increase in the frequency and/or severity of marine heatwaves (Smith et al. 2025) and tropical hurricanes (Knutson et al. 2020; Knutson et al. 2021). Since the 1980s, marine heatwaves and hurricanes have played an increasingly important role in the degradation of coral reefs in the wider Caribbean (Gardner et al. 2005; Wilkinson and Souter 2008; Eakin et al. 2010; Cetina-Heredia and Allende-Arand\u0026iacute;a 2023; Gonzalez-Barrios et al. 2023; Lenton et al. 2025).\u003c/p\u003e \u003cp\u003eCorals differ markedly in life-history traits (Darling et al. 2012) that are linked to differences in their vulnerability to thermal-induced bleaching mortality (Loya et al. 2001; Mizerek et al. 2018) and/or storm-induced mortality due to colony dislodgement (Madin et al. 2014). These differences have strongly contributed to driving shifts in the composition of the surviving coral assemblages over time that undermine the structure and function of these systems (Hughes et al. 2018; Estrada-Sald\u0026iacute;var et al. 2019) and their ability to provide a wide range of critical ecosystem services (Eddy et al. 2021; Smith et al. 2025). The increasing frequency and severity of such episodic disturbances is now impacting even the more resilient coral species (Byrne et al. 2025; Doherty et al. 2025). In the Caribbean, which already suffers from relatively low functional and taxonomic coral diversity (Bellwood et al. 2004), and where such climate-related stressors often interact with chronic local stressors such as poor water quality and overfishing, this is driving coral reefs ever closer to a long-term regime shift to an algal-dominated or degraded state (Lenton et al. 2025).\u003c/p\u003e \u003cp\u003eElkhorn coral, \u003cem\u003eAcropora palmata\u003c/em\u003e (Lamarck, 1816), is one of the foundational reef building corals of Caribbean reefs, historically being the main reef framework constructor and inhabitant of the shallow reef crest zone of many of the region\u0026rsquo;s fringing reefs (Goreau 1959; Gladfelter 1982; Cramer et al. 2021). As such it played a crucial ecological role through the provision of complex three dimensional physical structure that benefits other reef organisms (Lirman 1999), and was responsible for mediating the wave energy attenuation effect of reefs that protects coastlines (Toth et al. 2023). More recent paleoecological evidence supports that the abundance of \u003cem\u003eA. palmata\u003c/em\u003e (and that of the only other Caribbean acroporid species, \u003cem\u003eA. cervicornis\u003c/em\u003e, Lamarck, 1816) across the region dropped considerably around the mid 1950s and 1960s, likely due to human-induced local stressors such as coastal run off affecting water quality (Cramer et al. 2020). \u003cem\u003eA. palmata\u003c/em\u003e populations underwent further rapid declines primarily due to a Caribbean-wide episode of White Band Disease in the late 1970s and early 1980s, with hurricanes also playing an important, but more localized role, in this decline (Aronson and Precht 2001). Subsequently, \u003cem\u003eA. palmata\u003c/em\u003e has demonstrated high vulnerability to both thermal-induced bleaching mortality and storm-induced mortality in the region (Wilkinson and Souter 2008). Although there have been some reports of \u003cem\u003eA. palmata\u003c/em\u003e population recovery across the Caribbean in recent decades (Macintyre and Toscano 2007; Zubillaga et al. 2007; Muller et al. 2013; Larson et al. 2014; Croquer et al. 2016), Caribbean acroporids are still considered critically endangered (Gutierrez et al. 2024).\u003c/p\u003e \u003cp\u003eIn Barbados, like other countries across the Caribbean, \u003cem\u003eA. palmata\u003c/em\u003e has historically been a dominant reef framework constructor (Lewis 1984; Macintyre et al. 2007). Its last remnant shallow water populations on the west coast of the island declined sometime during the 1900\u0026rsquo;s, likely primarily due to sedimentation driven by island-scale deforestation and tropical storms (Lewis 1984), in a time line consistent with Cramer et al. (2020)\u0026rsquo;s paleoecological region-wide study. By the time regular monitoring of Barbados reefs began in the early 1980s, \u003cem\u003eA. palmata\u003c/em\u003e (and \u003cem\u003eA. cervicornis\u003c/em\u003e) were relatively rare.\u003c/p\u003e \u003cp\u003eHowever, MacLean and Oxenford (2016) provided strong evidence that \u003cem\u003eA. palmata\u003c/em\u003e populations were recovering in 2015 in Barbados. MacLean and Oxenford (2016) exhaustively surveyed 46 shallow fringing reefs along the entire west coast of Barbados in 2015 and recorded a total of 707 \u003cem\u003eA. palmata\u003c/em\u003e colonies, present in 57% of the reefs surveyed. Importantly, one reef located towards the northern end of the west coast, the Mullins Reef, accounted for 68% of all the \u003cem\u003eA. palmata\u003c/em\u003e colonies found (482 colonies) and exhibited the highest colony density (137 colonies per hectare). More detailed subsequent surveys at Mullins Reef in 2016 by Oxenford et al. (2024) yielded a revised total abundance estimate of 599 \u003cem\u003eA. palmata\u003c/em\u003e colonies, i.e. 72% of all reported colonies on the west coast\u0026rsquo;s fringing reefs between 2015 and 2016. Moreover, this \u003cem\u003eA. palmata\u003c/em\u003e population included many large mature colonies, with \u003cem\u003ein situ\u003c/em\u003e confirmation of active spawning taking place in 2017 (Oxenford et al. 2024). Finally, genetic analyses confirmed the presence of at least eight different \u003cem\u003eA. palmata\u003c/em\u003e genets at Mullins Reef, which largely exceeded the genotypic diversity found in a few other shallow reefs surveyed in the south and west coasts of Barbados in 2016 (Oxenford et al. 2024). These different lines of evidence jointly support that the thriving \u003cem\u003eA. palmata\u003c/em\u003e population at Mullins Reef in 2015 and 2016 likely played a particularly important role as a source population in the recovery of this species in Barbados at that time.\u003c/p\u003e \u003cp\u003eThe above characteristics motivated the use of \u003cem\u003eA. palmata\u003c/em\u003e colonies from the Mullins Reef as donor material in the context of an \u003cem\u003eA. palmata\u003c/em\u003e coral restoration project in Barbados in 2024. This effort also led to the frequent monitoring of a representative fraction of this population from June 2024 onward, for the first time since 2016.\u003c/p\u003e \u003cp\u003eHowever, 2024 was a year with a relatively high number of major hurricanes in the Caribbean (five in total; NOAA\u0026rsquo;s National Hurricane Center at \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://www.nhc.noaa.gov/\u003c/span\u003e\u003cspan address=\"https://www.nhc.noaa.gov/\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e) of which one, Hurricane Beryl, made history as the earliest Category 5 hurricane on record in the Atlantic Basin (Beven II et al. 2025). Hurricane Beryl cut through the Windward Islands on July 1st 2024, passing approximately 200 km south of Barbados as a Category 4 hurricane, making landfall on the Grenadian island of Carriacou, and becoming a Category 5 hurricance on July 2nd 2024 (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e1\u003c/span\u003eA) (Beven II et al. 2025). Although Barbados was not in the direct path of the hurricane, the south and west coastal and nearshore environments of the island were heavily affected by storm surge, which breached the Bridgetown fishing harbour wall, severely damaging hundreds of fishing vessels as well as the Bridgetown harbour cruise ship terminal (Beven II et al. 2025).\u003c/p\u003e \u003cp\u003eMoreover, between 2023 and 2024 the world experienced the hottest marine heatwave on record, amplified by El Ni\u0026ntilde;o conditions (Jiang et al. 2024; Smith et al. 2025), which translated into the highest cumulative temperature stress (as degree heating weeks (DHW)) on record for the Windward Islands, peaking in November 2024 for this subregion (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e1\u003c/span\u003eB). The 2023\u0026ndash;2024 marine heatwave resulted in the 4th global mass coral bleaching event (Goreau and Hayes 2024; Reimer et al. 2024), with multiple reports confirming mass coral bleaching and mortality throughout the wider Caribbean (Mejias-Rivera and Courtney 2024; Muniz-Castillo et al. 2024; Neely et al. 2024; Prato-Valderrama et al. 2024; Doherty et al. 2025), including a report from the Windward Island of Martinique during this period (Bon et al. 2025). The few recently published reports support that most remaining populations of \u003cem\u003eA. palmata\u003c/em\u003e have suffered extensive bleaching-induced mortality across the region, further threatening the long-term persistence of this critically endangered species (Neely et al. 2024; Birkart and Alvarez-Filip 2025; Manzello et al. 2025), although some locations were not as severely affected (Neely et al. 2024). In Barbados, \u003cem\u003eA. palmata\u003c/em\u003e populations at Mullins and several other reefs did suffer bleaching in 2023, but they recovered well thereafter (pers obs), likely because the heatwave did not reach its peak in the Windward Islands until 2024 (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e1\u003c/span\u003eB).\u003c/p\u003e \u003cp\u003eHere, we report on the fate of the \u003cem\u003eA. palmata\u003c/em\u003e population at Mullins Reef in the face of the passage of Hurricane Beryl and the 2023\u0026ndash;2024 heatwave in 2024, when it was most severe in the subregion, and provide some notes on impacts on other \u003cem\u003eA. palmata\u003c/em\u003e populations in Barbados around the same time. Because Barbados is located in the most southeastern range of the wider Caribbean, east of the Lesser Antilles Island chain, we hope that our data will contribute to filling a geographic gap on the direct and most recent impact of climate change-related events on \u003cem\u003eA. palmata\u003c/em\u003e populations across the entire range of this species.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003eOn June 19 2024, 33 haphazardly selected \u003cem\u003eA. palmata\u003c/em\u003e colonies of the population at Mullins Reef were tagged for monitoring (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003e). These colonies were located at depths of 1.0 m to 2.5 m, the depth range that hosted the majority of the \u003cem\u003eA. palmata\u003c/em\u003e population (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003e). On July 21 2024, an additional 20 colonies were tagged after the passage of Hurricane Beryl (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe depth of each colony was estimated using a SCUBA depth gauge to the nearest 0.1 m and the maximum height of each colony from the benthic substrate was estimated to the nearest cm using a marked rod. The tagged colonies were surveyed approximately biweekly via SCUBA until January 2025, and at least monthly thereafter until March 2025. During each survey, top-down photographs of every colony were taken. A one-metre reference rod marked at 10 cm intervals was included in each photograph as a reference scale. These images were later analysed in ImageJ (Abramoff et al. 2004) to calculate additional colony size metrics and colony health status. Additional colony size metrics included colony length (longest planar dimension), colony width (longest planar dimension perpendicular to length) and colony total planar area. Colony health status included percent area that is dead out of the colony\u0026rsquo;s total planar area (i.e. % dead surface) and the pigmentation status of the live tissue. The latter was categorized as fully pigmented, bleached, or dead. Fully pigmented implied that the colony had live tissue and that such live tissue exhibited conspicuous and bright brownish colouration. Bleached implied that the colony had live tissue, but such tissue had either lost some pigmentation (relative to the initial baseline colouration photographs of June 2024) or completely lacked any pigmentation (fully bleached). Dead colonies exhibited no live tissue, which was evidenced by turf algae overgrowth of the coral skeleton.\u003c/p\u003e \u003cp\u003e \u003cem\u003eIn situ\u003c/em\u003e sea surface temperature readings were obtained from a HOBO Water Temp Pro v2 Logger (U22-001) deployed at a depth of 4 m on a fringing reef site located midway along the west coast of Barbados. Shallow sea surface temperature profiles are very similar along the west coast of Barbados, so the data generated at this central site will be sufficiently representative of the temperature experienced at Mullins Reef. Degree Heating Weeks (DHW), a measure of cumulative heat stress, were derived from NOAA\u0026rsquo;s Coral Reef Watch Windward Caribbean Islands Time Series, accessed via the National Environmental Satellite, Data, and Information Service (NESDIS; \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://www.nesdis.noaa.gov/\u003c/span\u003e\u003cspan address=\"https://www.nesdis.noaa.gov/\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e). Daily \u003cem\u003ein situ\u003c/em\u003e sea surface temperature readings and DHW estimates were averaged over each biweekly period preceding a colony survey and these averages were displayed graphically.\u003c/p\u003e \u003cp\u003eColony size metrics and colony depth were described graphically as size frequency distributions. Potential differences in colony size dimensions among different sets of tagged colonies were assessed using Mann-Whitney tests. Potential associations between colony size metrics and depth were assessed using Spearman\u0026rsquo;s rank correlation tests. Changes in colony health metrics over time were summarized and displayed graphically as percentage of colonies under each pigmentation status and as boxplots of dead surface area estimates across colonies over time. Analyses were conducted in R (R Core Team 2025) and plots were generated using ggplot (Wickham 2016) and MS Excel.\u003c/p\u003e"},{"header":"Results and Discussion","content":"\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eImpact of Hurricane Beryl\u003c/h2\u003e \u003cp\u003eThe initial 33 \u003cem\u003eA. palmata\u003c/em\u003e colonies tagged before the passage of Hurricane Beryl had an average length of 89.7 cm\u0026thinsp;\u0026plusmn;\u0026thinsp;9.4 (standard error), an average width of 70.3 cm\u0026thinsp;\u0026plusmn;\u0026thinsp;5.8 (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003eB), an average height of 34.0 cm\u0026thinsp;\u0026plusmn;\u0026thinsp;4.0 (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003eC), and were found at an average depth of 1.8 m\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1 (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003eD). These dimensions align well with the large size category (longest top-down planar dimension of 50\u0026ndash;100 cm) of Oxenford et al. (2024), which accounted for 25% of the 586 colonies measured in 2016 at Mullins Reef, with only 12.5% of the colonies being larger (\u0026gt;\u0026thinsp;100 cm) at that time. It also suggests that \u003cem\u003eA. palmata\u003c/em\u003e colonies had increased considerably in size since 2016, when the population was dominated (63%) by considerably smaller colonies (\u0026lt;\u0026thinsp;50 cm) (Oxenford et al. 2024). Satellite imagery data from 2016 and 2023 also supports that the population in 2023 was at least as abundant as, and likely more abundant than, in 2016 (Fig \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). However, unlike Oxenford et al. (2024)\u0026rsquo;s study, our colony sampling was not specifically designed to fully characterize the colony abundance and size class distribution of the entire population at Mullins Reef, so this temporal comparison warrants caution.\u003c/p\u003e \u003cp\u003eColony height was significantly positively correlated with depth (Spearman rank correlation test: r\u003csub\u003es\u003c/sub\u003e=0.30, p\u0026thinsp;=\u0026thinsp;0.032), but this was not the case for colony width (r\u003csub\u003es\u003c/sub\u003e=0.17, p\u0026thinsp;=\u0026thinsp;0.211) nor length (r\u003csub\u003es\u003c/sub\u003e=0.18, p\u0026thinsp;=\u0026thinsp;0.192). A positive correlation between colony height and depth is expected given the shallow depth range of the reef crest that was surveyed in this study (1.0-2.5 m), which will necessarily limit colony height growth in this fast growing species (Gladfelter et al. 1978).\u003c/p\u003e \u003cp\u003eThe swells generated by the storm surge of Hurricane Beryl led to the complete dislodgement and loss of 12 (36.4%) of the initial 33 colonies on July 1st 2024. The tagged colonies lost to Beryl did not differ significantly in height, width, or length from the tagged colonies that survived (Mann-Whitney tests: X\u003csup\u003e2\u003c/sup\u003e \u0026le;0.48, df\u0026thinsp;=\u0026thinsp;1, p\u0026thinsp;\u0026ge;\u0026thinsp;0.487) (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003eA-C). However, they were significantly shallower (average: 1.3 m\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1, n\u0026thinsp;=\u0026thinsp;12) than the survivor ones (2.1 m\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1, n\u0026thinsp;=\u0026thinsp;21) (Mann-Whitney test: X\u003csup\u003e2\u003c/sup\u003e =14.81, df\u0026thinsp;=\u0026thinsp;1, p\u0026thinsp;\u0026le;\u0026thinsp;0.001; Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003eD) and located on the reef crest zone closer to shore (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Subsequent surveys confirmed the disappearence of most (tagged and non-tagged) colonies at this depth (Clarke 2025). Fringing reefs significantly reduce wave energy and height, with the reef crest playing a dominant role in wave energy dissipation (Ferrario et al. 2014), which helps explain why the shallower colonies were much more heavily impacted by the wave-breaking energy derived from the storm surge than their deeper counterparts.\u003c/p\u003e \u003cp\u003eThe survival of a relatively large fraction of the \u003cem\u003eA. palmata\u003c/em\u003e population at Mullins Reef through Hurricane Beryl was facilitated by the location of the reef, which lies in the northern section of the west coast (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Because Hurricane Beryl travelled south of Barbados (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e1\u003c/span\u003eA), it had a much stronger impact on the south coast than on the west coast, resulting in substantial infrastructure damage and vessel losses in the south (Beven II et al. 2025). In that regard, the second largest known population of \u003cem\u003eA. palmata\u003c/em\u003e at the time, located at greater average depths (\u0026gt;\u0026thinsp;2.5 m) near a popular surfing area of the south coast (Drill Hall), approximately 3 km south of the Bridgetown Harbour, was completely eradicated by the passage of Beryl (Clarke 2025). It is thus likely that any remaining patches of \u003cem\u003eA. palmata\u003c/em\u003e colonies that had survived Beryl\u0026rsquo;s passage were primarily confined to the west and north coasts of Barbados, with the Mullins Reef continuing to host one of the most important populations right after Beryl.\u003c/p\u003e \u003cp\u003e \u003cem\u003eA. palmata\u003c/em\u003e has historically dominated shallow high wave energy reef environments in the Caribbean (Cramer et al. 2020; Cramer et al. 2021), and its fast growth rates and branching shape are well adapted to undergo wave-induced fragmentation (Gladfelter et al. 1978; Lirman 2000). However, these life traits also make it particularly susceptible to impacts by tropical storms and so increases in storm frequency and/or intensity have been repeatedly identifed as important contributing factors to its long-term demise across the region (Woodley et al. 1981; Gardner et al. 2005; Macintyre et al. 2007; Wilkinson and Souter 2008; Hern\u0026aacute;ndez-Delgado et al. 2024), even though individual storms will impact reefs at more localized spatial scales than other regional disturbances such as marine heatwaves and disease outbreaks. In line with this, our study highlights that Hurricane Beryl had already drastically reduced standing \u003cem\u003eA. palmata\u003c/em\u003e populations in Barbados before the 2023\u0026ndash;2024 regional marine heatwave reached its peak severity in 2024.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eImpact of the 2024 heatwave\u003c/h3\u003e\n\u003cp\u003eThe additional 20 colonies that were tagged at Mullins Reef post-Beryl to replace and supplement the ones lost to Beryl did not differ from the initially tagged colonies that survived Beryl in either height, width, or length (Mann-Whitney tests: X\u003csup\u003e2\u003c/sup\u003e \u0026le;0.08, df\u0026thinsp;=\u0026thinsp;1, p\u0026thinsp;\u0026ge;\u0026thinsp;0.784) (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003eA-C). However, they were minimally but significantly shallower (average: 1.9 m\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1) than the initially tagged survivors (average: 2.1 m\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1) (Mann-Whitney test: X\u003csup\u003e2\u003c/sup\u003e =14.81, df\u0026thinsp;=\u0026thinsp;1, p\u0026thinsp;\u0026le;\u0026thinsp;0.001) (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003eD) and were also closer to shore (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cem\u003eIn situ\u003c/em\u003e daily sea surface water temperature on the west coast of Barbados during 2024 were the highest on record, exceeding that of 2005, 2010 and 2023, which were years that also showed unsually high temperatures over the last two decades (Fig \u003cspan refid=\"MOESM2\" class=\"InternalRef\"\u003eS2\u003c/span\u003e) and during which mass coral bleaching events were reported in Barbados (Oxenford et al. 2008; Oxenford and Vall\u0026egrave;s 2016; Irvine et al. 2025). The 2024 \u003cem\u003ein situ\u003c/em\u003e temperature measurements for Barbados were generally within the range of minimum and maximum values estimated by NOAA Coral Reef Watch for the Windward Caribbean Islands (Fig \u003cspan refid=\"MOESM2\" class=\"InternalRef\"\u003eS2\u003c/span\u003e), supporting that such satellite temperature data adequately inform on the nearshore marine environment of Barbados, which is not always the case across Caribbean reefs (Margaritis et al. 2025).\u003c/p\u003e \u003cp\u003eDuring the biweekly period up to July 8, average \u003cem\u003ein situ\u003c/em\u003e daily sea surface temperature was 29.3 degrees Celsius and continued to gradually increase thereafter, reaching peak values in the October 15 biweekly period of 30.8 degrees Celsius (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e4\u003c/span\u003eA). It gradually dropped thereafter, reaching 29.5 degrees Celsius during the December 4 period and 28.1 degrees Celsius during the January 31 period (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e4\u003c/span\u003eA). Cumulative heat stress, expressed as average daily degree heating weeks, exceeded the four-week bleaching threshold and eight-week bleaching-induced mortality theshold during the August 6 and September 2 biweekly periods, respectively, reaching a peak of 24.2 DHW during the November 12 biweekly period and gradually decreasing thereafter (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e4\u003c/span\u003eA).\u003c/p\u003e \u003cp\u003eOn July 8, a week after the passage of Beryl, all the tagged colonies were fully pigmented and had very low levels of tissue mortality (average: \u0026lt;2% of dead surface area); these health metrics remained relatively similar through September 2 (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e4\u003c/span\u003eB-C; Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e5\u003c/span\u003eA). By September 16 some colonies (17%) started to show signs of bleaching (partial loss of original pigmentation) and by October 1 all colonies showed signs of bleaching in varying degrees. By October 29 all colonies were fully bleached (complete loss of pigmentation; Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e4\u003c/span\u003eB; Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e5\u003c/span\u003eB-D), which coincided with the first record of increases in tissue mortality (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003eB; Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e5\u003c/span\u003eB-D). By November 12 some colonies (15%) had fully died (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003eB; Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e5\u003c/span\u003eB-D). By December 4, a period of unusually high wave energy led to the dislodgement and loss of a further four of the tagged colonies (10%) (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003eB). December 4 coincided with a dramatic increase in tissue mortality that led to more than one third (38%) of colonies fully dying (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003eB-D; Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e5\u003c/span\u003eB-F). By December 18, the majority of the tagged colonies (70%) had completely died after bleaching, with just three bleached tagged colonies surviving but showing varied levels of tissue mortality (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003eB-C). On January 3, only two bleached tagged colonies were still alive with high levels of tissue mortality (average: \u0026gt;50% of dead surface area) (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003eB-C). On January 31, one of the two colonies had regained full pigmentation while the other one remained bleached (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003eB-C). By February 14, only the colony that had regained full pigmentation during the preceding period remained alive (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003eB-C).\u003c/p\u003e \u003cp\u003eOverall, out of the 41 tagged healthy colonies monitored post-Beryl (July 8, 2024 - March 12, 2025), 36 (88%) died due to thermal-induced bleaching, four (10%) were lost to high wave action, and one (2%) survived, but suffered high tissue mortality. Photographic evidence of the wider Mullins Reef population mirrored the fate of the tagged colonies and confirmed the near complete extirpation of its entire \u003cem\u003eA. palmata\u003c/em\u003e population (Fig S3).\u003c/p\u003e \u003cp\u003eThe unprecedented cumulative heat stress experienced in the last half of 2024 (reaching as high as 24.2 DHW) led to the final collapse of the \u003cem\u003eA. palmata\u003c/em\u003e population at Mullins Reef. This was the case even though this population undoubtedly exhibited a substantial degree of thermal tolerance, having survived previous heatwaves, including those of 2005, 2010 and 2023, which exceeded the 14 DHW (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e1\u003c/span\u003eB) that has been suggested as the general upper thermal threshold of \u003cem\u003eA. palmata\u003c/em\u003e (Birkart and Alvarez-Filip 2025). Our findings support Williams et al. (2017), who suggested that thermal tolerance thresholds for \u003cem\u003eA. palmata\u003c/em\u003e likely vary geographically. They also suggested that \u003cem\u003eA. palmata\u003c/em\u003e populations, at least in the upper Florida Keys, do not become increasingly thermally tolerant following repeated severe thermal stress exposures, findings that concord with our own observations in Barbados, despite the previously documented relatively high genotypic diversity at our site in 2016 (Oxenford et al. 2024). Although such genetic diversity was not reassessed in 2024, conspicous differences in colony morphology (pers obs) suggested that much of it remained at the site. Our findings also echo those reported by others across the region as a result of the extreme heatwave experienced over 2023\u0026ndash;2024. For example Thompson et al. (2025) witnessed the extirpation of \u003cem\u003eA. palmata\u003c/em\u003e populations in the Dry Tortugas (Florida Keys), and Manzello et al. (2025) report the functional extinction of \u003cem\u003eA. palmata\u003c/em\u003e (and \u003cem\u003eA. cervicornis\u003c/em\u003e) throughout the Florida Keys. Likewise, Birkart and Alvarez-Filip (2025) report that \u003cem\u003eA. palmata\u003c/em\u003e vanished from the Puerto Morelos reefscape and concluded that this species suffered catastrophic mass mortality across its entire shallow water distribution range in the Greater Caribbean. The observation by Williams et al. (2017) supported by our own observations that \u003cem\u003eA. palmata\u003c/em\u003e does not improve heat tolerance with successive exposure to heatwaves contrasts with adaptive responses (acclimitization) observed in some other coral species (e.g. Guest et al. 2012), including an Indo-Pacific acroporid (\u003cem\u003eA. digitifera\u003c/em\u003e) (e.g. Humanes et al. 2022).\u003c/p\u003e \u003cp\u003eOf note, several rapid surveys on other shallow reefs on the west coast of Barbados in November 2024 identified a few small patches of surviving \u003cem\u003eA. palmata\u003c/em\u003e colonies that were not bleached (unpublished data), highlighting the existence of some uniquely heat-resistant phenotypes and providing a glimmer of hope. Whether such heat-resistance is driven by the coral host genotype, the symbiont identity and/or reef-scale environmental factors remains to be determined (e.g. Karp et al. 2025).\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThe likely extirpation of \u003cem\u003eA. palmata\u003c/em\u003e populations on the south coast due to Hurricane Beryl, coupled with the subsequent bleaching-induced loss of the \u003cem\u003eA. palmata\u003c/em\u003e population at Mullins Reef, a population that exhibited the highest abundance and density on the west coast and included many sexually reproductive individuals, suggest that \u003cem\u003eA. palmata\u003c/em\u003e might now be functionally extinct in Barbados, an island that is primarily self-recruiting (Cowen et al. 2006). Overall, this mirrors other reports of extirpation and functional extinction of \u003cem\u003eA. palmata\u003c/em\u003e from across the Caribbean suggesting that the slow recovery of this now endangered species over recent decades has endured a major setback. This underscores the urgent need to biopreserve the few and uniquely heat-resistant phenotypes left in Barbados and other islands and engage in their assisted recovery to prevent loss of this valuable foundational species (Muller et al. 2025).\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe thank N. Hand-Lennon, J. A. Silverman, K. Shulman, E. Paquette and C. Pierre for helping locate surviving \u003cem\u003eA. palmata\u003c/em\u003e colonies in November 2024. We thank K. Alleyne, S. Alleyne, J. Weekes, and S. Palmer for their assistance with various aspects of this work. This work was partially funded by the project entitled “\u003cem\u003eWave Attenuation: Natural solutions with elkhorn coral (WANSEC): Exploring the lattice turbulence of Acropora palmata thickets in wave attenuation and sediment deposition as a device for coastal protection\u003c/em\u003e”, project # EbA3_039 of the Caribbean Biodiversity Fund (CBF), co-financed by the International Climate Inititative (IKI) of the German Federal Ministry for Environment, Nature Conservation, and Nuclear Safety through KfW.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eConceptualization and Methodology: HV; Supervision: AJC; Investigation: KC, AJC, RB, HAO; Data curation: AJC, KC, HV; Formal analysis: HV, KC; Visualization: HV, AJC, KC; Writing-original draft preparation: HV, KC; Writing-review and editing: HV, HAO, JW, KC, AJC, RB; Funding acquisition: HV, JW, HAO.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors have no competing interests to declare that are relevant to the content of this article\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAbramoff MD, Magalhaes PJ, Ram SJ (2004) Image processing with ImageJ. 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Coral Reefs 27:63-72\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"coral-reefs","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"core","sideBox":"Learn more about [Coral Reefs](http://link.springer.com/journal/338)","snPcode":"338","submissionUrl":"https://submission.nature.com/new-submission/338/3","title":"Coral Reefs","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"coral bleaching, heatwave, hurricanes, local extirpation, Acroporids, climate change","lastPublishedDoi":"10.21203/rs.3.rs-8750412/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8750412/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eClimate change is leading to global increases in frequency and severity of marine heatwaves, increasingly contributing to coral reef degradation. In 2024, Barbados was impacted by the passage of Hurricane Beryl and the most severe marine heatwave to date. Here, we report on the fate of the largest known population of the foundational Caribbean reef building coral, \u003cem\u003eAcropora palmata\u003c/em\u003e, in Barbados in the face of such disturbances. Between June 2024 and March 2025, we tagged, measured and monitored (biweekly to monthly) the health status of 33\u0026ndash;41 \u003cem\u003eA. palmata\u003c/em\u003e colonies at Mullins Reef on Barbados\u0026rsquo; west coast. On July 1, Hurricane Beryl passed south of Barbados, causing the loss of 36.4% of tagged colonies. On August 4 and September 2 2024, average daily cumulative heat stress reached four and eight Degree Heating Weeks (DHW), respectively, peaking on November 12 at an unprecedented 24.2 DHW. After Beryl, tagged colonies that were not destroyed remained healthy until September 16, when some started to show bleaching signs. By October 29, all colonies were fully bleached and by December 18 most colonies had died. By February 14 2025, only one colony remained alive; it had regained full coloration, but lost\u0026thinsp;\u0026gt;\u0026thinsp;50% of its live tissue. The collapse of the most important \u003cem\u003eA. palmata\u003c/em\u003e population on the west coast, coupled with the devastating impact of Hurricane Beryl on the south coast, provide a stark warning that \u003cem\u003eA. palmata\u003c/em\u003e might have now reached functional extinction in Barbados, abruptly ending two decades of slow \u003cem\u003eA. palmata\u003c/em\u003e recovery.\u003c/p\u003e","manuscriptTitle":"Climate change-related disturbances in 2024 drive the largest known population of elkhorn coral (Acropora palmata) in Barbados to the brink of extirpation","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-13 07:09:04","doi":"10.21203/rs.3.rs-8750412/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-03-27T21:55:28+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-03-04T20:18:02+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-02-27T16:52:58+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"244584687168155342023107436843447621069","date":"2026-02-10T21:11:50+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"205970121204454971164803622026641530324","date":"2026-02-10T19:49:19+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-02-09T19:43:29+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-02-05T03:23:09+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-02-03T13:50:18+00:00","index":"","fulltext":""},{"type":"submitted","content":"Coral Reefs","date":"2026-01-31T13:45:29+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"coral-reefs","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"core","sideBox":"Learn more about [Coral Reefs](http://link.springer.com/journal/338)","snPcode":"338","submissionUrl":"https://submission.nature.com/new-submission/338/3","title":"Coral Reefs","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"85d7fb37-3b59-4dd3-9be6-eabd55b572e2","owner":[],"postedDate":"February 13th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-13T00:24:13+00:00","versionOfRecord":[],"versionCreatedAt":"2026-02-13 07:09:04","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8750412","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8750412","identity":"rs-8750412","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}