Increased disease prevalence in a warming peripheral reef setting (Abu Dhabi, Persian/Arabian Gulf)

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Bauman, John A. Burt, Mike McWilliams, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8330824/v1 This work is licensed under a CC BY 4.0 License Status: Under Revision Version 1 posted 9 You are reading this latest preprint version Abstract Coral reefs in the Persian/ Arabian Gulf (PAG) are subject to extreme heat stress. Moreover, effects of temperature induced bleaching on local coral assemblages are being further compounded by coral disease. This manuscript explores taxonomic and seasonal variation in disease prevalence, at Ras Ghanada, Abu Dhabi, from 2010–2024. Thirty-two image-based surveys were conducted across winter, spring and summer seasons which looked at active diseases, partial mortality, bleaching, encroachment by neighboring biota and general health from images. Seafloor temperature was also recorded across the monitoring period. Elevated disease prevalence in 2013, 2019, 2021, and 2024 followed marked summer heat stress with significant coral bleaching. Disease was most prevalent in winter after summer thermal stress. Porites harrisoni showed highest disease prevalence, while species within the genus Dipsastraea spp. were more resilient. Acropora spp. suffered moderate disease prevalence after bleaching and disappeared from Ras Ghanada after 2015 likely as a result of both stressors. Relative prevalence of diseases increased from 1.42% in 2010 to 5.66% of all corals in 2024. Coral diseases on PAG marginal reefs are chronic stressors that contribute to community shifts and structural loss. Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Scleractinian corals are subject to a wide range of diseases (Harvell et al. 1999; Woodley et al. 2016; Precht et al. 2016) that have become one of the leading causes of community change in the Caribbean basin since the 1980s (Harvell et al. 1999; Aronson & Precht 2001; Gardner et al. 2003; Precht et al. 2020). Coral diseases are also posing an increasing threat in the Indo-Pacific (Willis et al. 2004; Hobbs et al. 2015) and are increasingly affecting reefs in the Persian/Arabian Gulf (PAG; Riegl 2002; Bruckner & Riegl 2015; Aeby et al. 2020; Howells et al. 2020). New diseases and disease epizootics have arisen over the past decades (i.e., stony coral tissue disease, SCTLD (Precht et al. 2016; Brandt et al. 2021)) which has caused widespread mortality and community collapse across the tropics (Papke et al. 2024; Swaminathan et al. 2024). However, pinpointing pathogens has proven elusive (Vega Thurber et al. 2020; Papke et al. 2024). There is growing evidence that many coral diseases may be secondary manifestations of environmental stresses (Thurber et al. 2017; Ricci et al. 2022). High temperatures, pollution (Harvell et al. 2007; Precht et al., 2020), and sedimentation (Haapkyla et al. 2011; Hazraty-Kari et al. 2021) have all been linked to outbreaks of coral disease. High-latitude regions, such as the northern Caribbean, have been hot-spots for devastating disease outbreaks (Weil 2006; Van Woesik & Randall 2017; Precht et al. 2020). In a warming climate, coral reefs globally may be subject to similar disease-inducing heat stress (Harvell et al. 2007; Howells et al. 2020). Thermal stress on coral reefs does not always manifest as bleaching events, but diseases can be a primary sign or result of thermal stress (Howells et al. 2020). Impacts of coral epizootics can be dramatic and can displace species and genera from entire regions. This was most dramatically demonstrated by the Caribbean-wide die-back of Acropora in the 1970s and 80s (McClanahan & Muthiga 1998; Miller et al. 2002). Similarly, declines were also seen in the PAG where local species richness was reduced from 34 to 27 after bleaching-related coral disease outbreaks in 1996 and 1998 (Riegl 2002). The PAG is a high latitude, largely enclosed peripheral sea where corals exist under harsh environmental conditions, such as extreme temperature fluctuations (> 20°C annually), high maximum temperatures (> 36°C), hypersalinity, and intermittent high levels of turbidity (Riegl 1999; Coles 2003; Sheppard et al. 2010; Riegl et al. 2012; Burt 2019; Riegl Jr. et al. 2024). Major thermal heat events have been recorded repeatedly over the last three decades, in 1996, 1998, 2002, 2010, 2012, 2017, 2018, and 2021, each corresponding with mass bleaching and partial recovery (Riegl 2002; Bauman et al. 2010; Riegl & Purkis 2012, 2015; Burt 2019; Burt 2024; Riegl Jr. et al. 2024). Long term temperature records show peak summer sea temperatures have increased steadily, with maxima frequently exceeding 35.7°C in recent years (Riegl Jr. et al. 2024). In addition to frequent thermal stress, the region’s coral communities have been degraded through chronic pressures imposed by coastal urbanization and industrialization (Burt 2024). These combined acute and chronic stressors have contributed to the persistent decline in live coral cover and shifts in benthic community structure throughout much of the southern PAG (Riegl et al. 2012; Burt 2019; Riegl Jr. et al. 2024) This study explores temporal patterns of disease prevalence at Ras Ghanada, Abu Dhabi, historically one of southeastern PAG’s largest and most diverse coral reefs. Coral health status was monitored annually for the period from 2010–2024 along with temperatures measured on the reef. Coral reefs in the southeastern PAG (Abu Dhabi, United Arab Emirates) are vulnerable to near-field stressors due to the proximity of coastal urbanization as well as to far-field stressors like increased atmospheric heat content as these corals exist near their upper thermal physiological limit (Burt 2024). This makes them prone to repeated bleaching (Lough et al. 2018; Paparella et al. 2019) and, so observations suggest (Aeby et al. 2020), likely also to disease outbreaks. Although impacts have been noted, research on coral disease in the PAG remains limited, with only four documented types of coral diseases (Arabian Yellow Band; Black Band; White Syndrome; Pink Line Disease (Riegl et al. 2012)) and little quantification of long-term patterns and impacts in and around the Arabian Peninsula (Riegl et al. 2012; Bruckner & Riegl 2015). Methods Study Site Surveys were conducted at Ras Ghanada Marine Protected Area (MPA) in Abu Dhabi, United Arab Emirates, located in the southern Persian/Arabian Gulf (PAG). At Ras Ghanada, one of the southern PAG’s largest contiguous reef areas exists adjacent to large seagrass beds and a mangrove system. The reefal area is made up mostly by thin (~ 1m) Porites spp. framework between 5-8m depth, which over the years lost the majority of live coral tissues (Fig. 1 ). This region experiences extreme environmental conditions, including high summer temperatures and elevated salinity levels (Sheppard et al. 2010; Burt 2019). Ras Ghanada’s reef and adjacent marine associated habitats are neighbored by Khalifa Port and Al Taweelah power and desalination plant. Data Collection From January 2010 to September 2024, roughly sixty downward-facing photo transect images (~ 1-1.5 m 2 each) were collected three times each year—January, May, and September - at locations haphazardly chosen on the reef, except in 2014, 2015, 2018, 2019, 2020 and 2021. No surveys were conducted in 2014 or 2018, surveys in 2015 and 2019 were conducted only in September and in 2020 only in January. In 2021 surveys were conducted in May and September. Seafloor temperature data were obtained for each survey year beginning in 2010 using VEMCO and HOBO temperature loggers affixed to the reef at depth of 7-8m (1m tidal range). Since the sampling was seasonal (January falling into the coldest period, i.e. winter, May being before the hottest season, i.e. spring, and September being at the end of the hot season, i.e. summer) data analysis grouped the sampling periods into winter, spring and summer. Data Analysis Only high-quality photographs with clear focus and proper framing were considered in this study (Fig. 1 ). From each survey year, thirty randomly chosen images (ten per season) were used for analysis to ensure consistent temporal replication across the study period. Every visible coral colony was identified to the species level when morphological characteristics were sufficiently distinct. Coral health status was assessed by documenting signs of active disease (i.e., such as tissue loss, discoloration, and lesions with defined margins), partial mortality (i.e., including partially recovered lesions, visible mortality, and permanent tissue loss), and bleaching (Fig. 1 ). Colonies that exhibited active disease or bleaching at the time of observation were classified as unhealthy, while those that appeared normal in tissue and coloration were categorized as healthy regardless of partial mortality presence. Three major diseases are known in the PAG (Arabian Yellow Band, Black Band, White Syndromes; Riegl et al. 2012; Bruckner & Riegl 2015). Encroachment was defined as any physical interaction between a coral colony and adjacent benthic organisms that could potentially inhibit colony growth (Fig. 1 ). Each colony was assessed for direct contact along its perimeter, and the encroaching organism was categorized into one of five groups (corals, invertebrates, crustose coralline algae, turf algae, and cyanobacteria). Contact was recorded as presence or absence per colony, and percentages were later calculated to reflect the proportion of colonies encroached by categories in each year. Quantifying encroachment provided an insight into the secondary effects of disease, highlighting cascading effects on community dynamics and reef composition in the southern PAG. Coral disease prevalence was calculated as the proportion of colonies showing active signs of disease. Seasonal and annual prevalence values were summarized with means, standard deviations, and sample sizes. Seasonal patterns in disease prevalence were visualized with boxplots (Fig. 3 ) with overlaid points representing individual years. Temporal trends in coral counts and disease prevalence were assessed using General Additive Models (GAMs) with smoothing splines fitted to year. A Gaussian GAM was used to model annual changes in total coral counts, and a Generalized Liner Model (GLM) was used for disease prevalence from 2010 to 2024 (Fig. 2 A). Seasonal disease prevalence trends were analyzed using binomial GAMs for Winter, Summer, and Spring seasons, with the proportion of diseased corals modeled as a function of year. All GAMs were fitted using the mgcv package (Wood 2017) with basis dimension k = 5 or 6. They were then evaluated using a GAM check to assess model fit and ensure appropriate smoothing. No signs of undersmoothing were detected (k-index > 1, p > 0.5 for all models). To compare disease prevalence between 2010 and 2024, a binomial proportion test was applied. Long-term linear trends in disease prevalence were also assessed using Generalized Linear Models (GLMs). Non-parametric Kruskal-Wallis tests were used to detect seasonal differences in active disease and bleaching prevalence. To examine temperature and disease relationships, annual disease prevalence was compared with corresponding maximum reef temperatures for each year (Fig. 4 ). GLMs were fitted to assess temporal trends for each disease type. Species-specific disease counts, total colonies, and encroachment patterns were analyzed and presented in tables and figures. All statistical analyses were done using R v4.2.2 (R Core Team, 2022) and packages including tidyverse (Wickham & Grolemund 2017; Wickham et al. 2019), mgcv (Wood 2017), stats, and janitor. Raw survey and temperature files were imported and reshaped using readr and dplyr from magrittr (Bache 2022), table sanitizing tools in janitor (Firke 2023) and dates parsed and binned using lubridate (Spinu et al. 2023). Graphics were generated in ggplot2 (Wickham 2016), with axis scaling and formatting from library scales (Wickham & Seidel 2022) and assembled with patchwork (Pedersen 2020). Context maps were produced using ArcGIS Pro (ESRI, 2024). Results Dataset Overview Thirty-two surveys were conducted between 2010–2024 in January, May, and September.. Cumulative species richness over the entire study period was 34 species, with dominant species Platygyra daedalea, Porites harrisoni, Dipsastraea spp. In 2010, average coral cover was approximately 56.2%, comprising mostly P. daedalea (22.6%), P. harrisoni (37.8%) and Dipsastraea spp. (25%). Coral abundance declined significantly over time, with a GAM indicating a nonlinear trend (edf = 4.46, F = 125.1, p < 0.001, deviance explained = 98.8%; Fig. 2 A). Prevalence of coral disease increased over the same period, although there was substantial temporal variation (Fig. 2 A), with a binomial GLM indicating a strong significance (β = 0.0408 ± 0.0173 SE, z = 2.36, p = 0.018). This suggests disease occurrence was episodic and likely driven by environmental stressors such as thermal anomalies, as demonstrated by their close temporal association (Fig. 2 A). Temperature effects The corals in Ras Ghanada were exposed to maximum summertime temperatures exceeding 35 \(\:℃\) nearly every year throughout the course of this study (Fig. 4 ). The widest temperature range was encountered in 2012, with the highest temperature recorded at 36 \(\:℃\) (35.96 \(\:℃\) ) (above coral bleaching limit) and lowest at 17.6 \(\:℃\) (17.58 \(\:℃\) ), giving a range of > 18 \(\:℃\) . 2011, 2012, 2015, 2017, 2018,2020, 2021, 2023 and 2024 all experienced peak temperatures above 35 \(\:℃\) which mark heat events that approached or exceeded the physiological thermal thresholds for corals in the PAG (35.7 \(\:℃\) ; one day bleaching threshold; Riegl et al. 2011) and caused extensive coral bleaching. Seasonal Patterns Coral health varied across seasons, with both disease and bleaching prevalence showing clear temporal trends. Disease prevalence increased from summer to winter (Table 1 ). Bleaching preceded disease prevalence, peaking during the warmest months of the year (Table 1 ). Average mean disease prevalence was highest during winter (January, 5.14% of all corals), followed by spring (May, 4.03%) and summer (September, 3.24%). Bleaching showed highest prevalence in summer (21.2%), while winter (0.23%) and spring (0.4%) had minimal bleaching (Table 1 ). A Kruskal-Wallis test revealed statistically significant differences in bleaching prevalence (Chi²= 522.35, df = 2, p < 2.2e-16) and disease prevalence (Chi²= 9.71, df = 2, p = 0.007801) among seasons. Table 1 – Average mean prevalence (%) of diseases and bleaching across winter, spring and summer surveys from 2010 to 2024. Large standard deviations reflect that neither diseases nor bleaching occurs every year. Season Mean Disease Prevalence % Mean Bleaching Prevalence % Spring (May) 4.03 ± 19.7 0.4 ± 6.34 Summer (September) 3.24 ± 17.7 21.2 ± 40.9 Winter (January) 5.14 ± 22.1 0.23 ± 4.83 Long-term trajectory Disease prevalence (all corals in all seasons across the year) increased by about 4% from 1.42 ± 11.8% in 2010 to 5.66 ± 23.2% in 2024. This trend was supported by a binomial GLM that indicated a significant positive increase in disease prevalence between 2010 to 2024 (β = 0.0408 ± 0.0173 SE, z = 2.36 p = 0.018). Disease prevalence peaked in years following heat events, specifically 2019 and 2021; both of which exceeded coral thermal thresholds the year prior (Figs. 2 A & B, 4). Two diseases (Arabian Yellow Band = AYB, White Syndrome = WS) were common across the entire survey period with one (Black Band Disease = BB) being encountered only in one year. At the survey’s onset, AYB was about twice as frequent as WS, but from 2019 onward, WS became more frequent (Figs. 2 B & 4 ). Species-specific differences in disease prevalence Clear differences with regards to disease prevalence were observed among the coral taxa. The most abundant genus within the dataset, Dipsastraea spp., exhibited relatively low disease prevalence (0.9% of all colonies across all years) but moderate levels of partial mortality (~ 19%). Platygyra daedalea showed moderate levels of disease (4.7%) and high prevalence of partial mortality (35%), indicating repeated stress events and partial recovery over time. The most vulnerable dominant species with about 13% of colonies showing disease and more than 60% of colonies showing partial mortality was Porites harrisoni , an apparently highly susceptible species. Although Acropora species were less common in this dataset and disappeared altogether around 2015, they showed disease susceptibility when present (~ 5%), but one third (34%) showed evidence of partial mortality suggesting that disease and heat stress contributed to their local loss. Encroachment interactions Encroachment across the study period reflects both competition and impacts of environmental stressors, specifically disease prevalence and temperature stress. Coral-to-coral interactions were initially the most common form of encroachment (in earlier years such as 2010, roughly 90% of all interactions, Table 2 ). This reflected the higher coral cover prior to widespread coral morality. However, with repeated diseases and thermal stress, coral mortality allowed other benthic competitors to increase. Crustose Coralline Algae (CCA) and turf algae increased in years following mass bleaching and disease outbreaks. Cyanobacterial encroachment remained uncommon throughout the dataset but in later years became slightly more common. The decline of coral-to-coral interaction reflects the severe reduction of coral cover. These patterns underline how disease and temperature stress not only drive mortality but also reshape competitive interactions and the broader benthic communities of Ras Ghanada and other reefs within the region. Table 2 Percent of coral colonies encroached upon by different benthic groups in 2010 and 2024, highlighting shifts in competitive interactions over time. Encroachment category 2010 (%) 2024 (%) Cyanobacteria 0 0 Turf Algae 0 50.2 Crustose Coraline Algae (CCA) 8.56 40.0 Corals 90.8 4.88 Invertebrates 0.68 4.88 Discussion Temperature–disease relationships are complex and depend on the disease or the thermal metrics considered (Rosenburg & Ben-Haim 2002; Jones et al. 2004; Miller & Richardson 2015). In this study, the most relevant indicator was the annual maximum water temperature, which reflects the acute thermal stress endured by corals at Ras Ghanada and the southern PAG in general. Years that reached or exceeded bleaching threshold temperatures (35.7°C) were typically followed by increased disease prevalence in the subsequent surveys. Elevated temperatures can accelerate some coral diseases (e.g., black band), while others may manifest slowly or with a delay following bleaching related stress (Bruno et al. 2007; Harvell et al. 2007; Miller & Richardson 2011; Thurber et al. 2017; Howells et al. 2020). The observed winter peaks in disease prevalence likely represent a lagged biological response, where colonies weakened or bleached during the extreme summer temperatures later develop lesions or tissue necrosis even under cooler conditions. This pattern is supported by the temporal consistency between years of peak summer temperature and subsequent increases in disease prevalence. Live coral cover decreased from approximately 56.2% in 2010 to well below 10% (4.08%; variance = 10.64, SD = 3.26 ) in 2024 at Ras Ghanada. This trajectory mirrors regional trends across the southern PAG, where reefs have similarly shifted to degraded states often dominated by turf algae and/or crustose coralline algae (Grizzle et al. 2016; Burt et al. 2019; Bejarano et al. 2022; Riegl Jr. et al. 2024). Colony counts in the photo-transect dataset also declined sharply, reflecting both a reduction in the number of coral colonies and reductions in size. While multiple stressors may have contributed to this decline, recurrent bleaching events show a high coincidence with disease frequency, while other local pressures such as sedimentation and turbidity were considered of less importance (also because no relevant data were available). Coral disease acted as an additional compounding stressor, often following bleaching events and extending coral morality into the winter months. Together these acute and chronic pressures have driven the degradation of Ras Ghanada and the southern PAG. The delayed manifestation of disease following thermal events aligns with patterns that have been observed across the Indo-Pacific, Great Barrier Reef, and the Caribbean, where heat induced stress weakened the corals’ immunity and facilitated disease outbreaks (Bruno et al. 2007; Harvell et al. 2007; Miller & Richardson 2011). The similarity of these responses across geographically and thermally distinct regions suggests that the physiological mechanisms linking temperature and disease are globally consistent. As such, reefs in the PAG can serve as a natural model for future trajectories for reef communities as ocean temperatures continue to rise. The prevalence of disease varied among species. Poritids seemed highly vulnerable to disease outbreaks in the PAG, similar to regions like the Indo-Pacific (Raymundo et al. 2005). However, the local loss of Acropora species and the persistence of other taxa ( Porites spp., Platygyra daedalea, Dipsastraea spp.) shifted the relative contribution of each genus to overall disease prevalence. Specifically, Porites harrisoni exhibited the highest proportion of disease prevalence. Most Porites harrisoni colonies throughout the dataset showed clear signs of partial mortality that were either heat related and/ or caused by disease. Acropora species in the PAG were extremely sensitive to heat and disease, similar to elsewhere (Aeby et al. 2020; Precht et al. 2020). No Acropora were recorded after 2015, reflecting local extirpation due to a combination of bleaching a disease susceptibility. Many Acropora colonies observed before 2015 showed tissue loss or active lesions, indicating that disease likely accelerated post bleaching mortality. Dipsastraea spp. had relatively low disease prevalence but had a high level of partial mortality (a potential sign of having overcome disease), indicating that prevalence (frequency of infection) and severity (extent of tissue loss) varied among genera and/or species. This may suggest that Dipsastraea spp. are more likely to die directly from bleaching than ensuing diseases. Platygyra daedalea had moderate disease incidence. Many P. daedalea colonies exhibited visible partial mortality. Whether the mortality was due to a combination of both disease and heat stress or one or the other, the species showed strong evidence of recovery from either bleaching or disease. The incidence of benthic competition, as measured by encroachment, substantially changed during this study. At the beginning of the survey (2010), coral-to-coral interaction was about 90% but later declined to < 5% (2024, Table 2 ). This is primarily attributed to widespread coral loss which demonstrates the influence of disease mortality on competition among the benthos. Also, the disease-mediated loss of branching corals, which were major contributors to the reef framework, and the reduced frequency of massive corals, led to a lack of habitat heterogeneity. The increase of encroachment by other benthic organisms like CCA and turf algae reflects the shifts in the benthic community following coral decline (McCook 1999; Norström et al. 2009; Riegl Jr. et al. 2024). This study provides a continuous long-term assessment of disease prevalence within the southern PAG and demonstrates clear links between temperature stress, coral disease, and shifts in coral assemblages at Ras Ghanada. By combining annual monitoring with species level health assessments, it establishes a baseline of disease prevalence at a region where long term records are not readily available. These findings emphasize the need for continued monitoring of temperature, disease, mortality and benthic community structure to better predict and manage persistence of the now very few corals remaining in the PAG and other thermally challenged systems. More generally, the results show that coral disease is becoming an increasingly important driver of community change in the Persian/ Arabian Gulf – one of the few regions outside of the Caribbean where long term records now show disease contributing to larger scale coral loss. Declarations Author Contribution BJR analyzed and wrote manuscript. MSP, JAB, AGB assisted in review of manuscript. Manuel Ploner made map of UAE. Acknowledgements: This paper is part of BJR’s MPhil thesis at JCU. BJR and AGB were supported by ONR grant N000142512019. BJR analyzed and wrote manuscript. MSP, JAB, AGB assisted in review of manuscript. Manuel Ploner made map of UAE. 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Riegl B, Bruckner A, Samimi-Namin K, Purkis S (2012) Diseases, harmful algal blooms (HABs) and their effects on Gulf coral populations. In: Riegl B, Purkis S (eds) Coral Reefs of the Gulf. Springer, New York, pp 107–125. Riegl B, Purkis S (2015) Coral population dynamics across consecutive mass mortality events. Glob Change Biol 21:3995–4005. Riegl B, Johnston M, Purkis S, Howells E, Burt J, Steiner SC, Bauman A (2018) Population collapse dynamics in Acropora downingi, an Arabian/Persian Gulf ecosystem-engineering coral, linked to rising temperature. Glob Change Biol 24:2447–2462. Riegl Jr B, Bauman A, Hadj-Hamou J et al. (2024) A decade of benthic changes on coral reefs in the southern Persian/Arabian Gulf (2010–2020). Coral Reefs 43:1647–1657. Rosenberg E, Ben-Haim Y (2002) Microbial diseases of corals and global warming. Environ Microbiol 4:318–326. R Core Team (2022) R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. https://www.R-project.org/ Sheppard CRC, Al-Husiani M, Al-Jamali F et al. (2010) The Gulf: a young sea in decline. Mar Pollut Bull 60:13–38. Spinu V, Grolemund G, Wickham H (2023) lubridate: Make dealing with dates a little easier. R package version 1.9.3. https://CRAN.R-project.org/package=lubridate Swaminathan SD, Lafferty KD, Knight NS, Altieri AH (2024) Stony coral tissue loss disease indirectly alters reef communities. Sci Adv 10:eadk6808. Thurber RV, Payet JP, Thurber AR, Correa AM (2017) Virus–host interactions and their roles in coral reef health and disease. Nat Rev Microbiol 15:205–216. Van Woesik R, Randall CJ (2017) Coral disease hotspots in the Caribbean. Ecosphere 8:e01814. Vega Thurber R, Mydlarz LD, Brandt M et al. (2020) Deciphering coral disease dynamics: integrating host, microbiome, and the changing environment. Front Ecol Evol 8:575927. Weil E, Smith G, Gil-Agudelo DL (2006) Status and progress in coral reef disease research. Dis Aquat Org 69:1–7. Wickham H (2016) ggplot2: Elegant graphics for data analysis. Springer-Verlag, New York. Wickham H, Averick M, Bryan J et al. (2019) Welcome to the tidyverse. J Open Source Softw 4:1686. Wickham H, Grolemund G (2017) R for Data Science: Import, tidy, transform, visualize, and model data. O’Reilly Media, Sebastopol, CA. Wickham H, Seidel DP (2022) scales: Scale functions for visualization. R package version 1.2.1. https://CRAN.R-project.org/package=scales Willis BL, Page CA, Dinsdale EA (2004) Coral disease on the Great Barrier Reef. In: Rosenberg E, Loya Y (eds) Coral Health and Disease. Springer, Berlin, pp 69–104. Wood SN (2017) Generalized Additive Models: An Introduction with R. 2nd edn. Chapman & Hall/CRC, Boca Raton. Woodley CM, Downs CA, Bruckner AW, Porter JW, Galloway SB (eds) (2016) Diseases of Coral. Wiley Blackwell. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Revision Version 1 posted Editorial decision: Revision requested 29 Apr, 2026 Reviews received at journal 20 Apr, 2026 Reviewers agreed at journal 08 Apr, 2026 Reviews received at journal 18 Mar, 2026 Reviewers agreed at journal 19 Feb, 2026 Reviewers invited by journal 17 Feb, 2026 Editor assigned by journal 19 Dec, 2025 Submission checks completed at journal 14 Dec, 2025 First submitted to journal 10 Dec, 2025 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. We do this by developing innovative software and high quality services for the global research community. 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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-8330824","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":592938522,"identity":"d34098e4-5311-4c99-8bca-1b72ebce5b48","order_by":0,"name":"Bernhard Jr. Riegl","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAyklEQVRIiWNgGAWjYDACZiB++MdGDsQ+8IBoLYkNacZgLQlE25TYcDixAcQgSot5O/PhF4k70tLnhx1+CLTFTk63gYAWmcNsaRaJZ2xyN95OMwBqSTY2O0BAiwQzj5lBAlta7sbZCSAtBxK3EdbC/w2o5XC64ez0D8Rq4WF+kNh2OEFeOodoW9jMGBLOpBlukM4pOJBgQIxf+A8//vChwkZefnb6ZiDDTo6gFiBgkwCRBmCVBoSVgwDzBxAp30Cc6lEwCkbBKBiBAABT8kW3az9f9QAAAABJRU5ErkJggg==","orcid":"","institution":"James Cook University","correspondingAuthor":true,"prefix":"","firstName":"Bernhard","middleName":"Jr.","lastName":"R","suffix":"Jr."},{"id":592938524,"identity":"88cc575f-805a-444d-bce0-830ae141d41b","order_by":1,"name":"Andrew G. Bauman","email":"","orcid":"","institution":"National Coral Reef Institute, Nova Southeastern University","correspondingAuthor":false,"prefix":"","firstName":"Andrew","middleName":"G.","lastName":"Bauman","suffix":""},{"id":592938525,"identity":"ea3edd1e-ced9-489a-85a1-9b45f354f296","order_by":2,"name":"John A. Burt","email":"","orcid":"","institution":"New York University Abu Dhabi","correspondingAuthor":false,"prefix":"","firstName":"John","middleName":"A.","lastName":"Burt","suffix":""},{"id":592938526,"identity":"52b4c82a-321e-4c9b-acc9-939e8ec3c26d","order_by":3,"name":"Mike McWilliams","email":"","orcid":"","institution":"James Cook University","correspondingAuthor":false,"prefix":"","firstName":"Mike","middleName":"","lastName":"McWilliams","suffix":""},{"id":592938527,"identity":"113d3b91-7916-476d-ab6e-9e57e10ec4ac","order_by":4,"name":"Morgan S. Pratchett","email":"","orcid":"","institution":"James Cook University","correspondingAuthor":false,"prefix":"","firstName":"Morgan","middleName":"S.","lastName":"Pratchett","suffix":""}],"badges":[],"createdAt":"2025-12-10 21:08:04","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8330824/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8330824/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":103166770,"identity":"2b28cd3f-571d-42f2-9021-6ddf4e895346","added_by":"auto","created_at":"2026-02-22 12:42:20","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1999933,"visible":true,"origin":"","legend":"\u003cp\u003e(A) Map of the southern Persian/Arabian Gulf showing the Ras Ghanada Marine Protected Area (red dot) in Abu Dhabi, United Arab Emirates. (B \u0026amp; C)\u003cstrong\u003e \u003c/strong\u003eExamples of photo types used. (B) Standard transect photograph used for most surveys, showing consistent ~1-1.5 m\u003csup\u003e2\u003c/sup\u003e benthic coverage. (C) Alternative image type used in some periods when transect photos were unavailable, providing supplemental coverage. Examples of coral health classifications. (D) Coral colony showing signs of \u003cstrong\u003epartial mortality\u003c/strong\u003e. (G) Coral colony showing \u003cstrong\u003eactive disease\u003c/strong\u003e, characterized by fresh tissue loss, discoloration, and clearly defined lesion margins. Examples of additional health indicators and \u003cstrong\u003eencroachment\u003c/strong\u003e. (E, H \u0026amp; I) Coral colonies with visible \u003cstrong\u003eencroachment\u003c/strong\u003e by benthic competitors (i.e., (E) crustose coralline algae (CCA), (H) turf algae, (I) invertebrates, (H) other corals). (F) Coral colonies exhibiting bleaching, characterized by pale or white tissue color. Colonies B-E and H-I are all mostly healthy corals. In (F \u0026amp; G) a visibly diseased and bleached corals are present and would be recorded as unhealthy and recorded as diseased or bleached.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-8330824/v1/4ad7cfdaef12da26cb5d68ea.png"},{"id":103504366,"identity":"245823f7-35c5-40eb-9f6e-ada2876bf94e","added_by":"auto","created_at":"2026-02-26 13:19:30","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":260595,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eA \u0026amp; B-\u003c/strong\u003e (\u003cstrong\u003eA\u003c/strong\u003e) Annual counts of observed coral colonies (blue line) and disease prevalence (red line) at Ras Ghanada from 2010 to 2024. Vertical dashed lines (orange) represent years in which coral bleaching threshold (35.7 \u003cstrong\u003e°C)\u003c/strong\u003e \u0026nbsp;was reached or exceeded. Although coral colonies decreased over time disease prevalence fluctuated, following known thermal stress events. (\u003cstrong\u003eB\u003c/strong\u003e) Observed coral disease types at Ras Ghanada by year (Arabian Yellow Band = Orange, Black Band = Blue, White Syndrome = Green). Asterisks (*) represent years when bleaching affected more than 10% of coral colonies surveyed.\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8330824/v1/6d18882480a17136259efac7.jpeg"},{"id":103504314,"identity":"4f9edfbc-550e-42a9-ba2b-36f9d627985c","added_by":"auto","created_at":"2026-02-26 13:19:09","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":40082,"visible":true,"origin":"","legend":"\u003cp\u003eSeasonal variation in disease prevalence at Ras Ghanada. Winter surveys recorded the highest disease levels; summer surveys showed the lowest. A Kruskal-Wallis test revealed a significant difference in active disease prevalence among seasons (χ² = 6.6122, df = 2, \u003cem\u003ep\u003c/em\u003e = 0.03666).\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-8330824/v1/d69920de4507975c29049eb8.png"},{"id":103166767,"identity":"36b0f92e-bc85-4ef7-b7b8-2886ae2113dc","added_by":"auto","created_at":"2026-02-22 12:42:20","extension":"jpeg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":275290,"visible":true,"origin":"","legend":"\u003cp\u003eAnnual prevalence of Arabian Yellow Band (AYB, green), White Syndrome (WS, blue), and Black Band (BB, orange) diseases at Ras Ghanada (2010–2024), with corresponding annual maximum sea surface temperature (SST; red dashed line). Generalized linear model (GLM) fits are shown for each disease (AYB: \u003cem\u003eR²\u003c/em\u003e = 0.16, \u003cem\u003eF\u003c/em\u003e= 1.89, \u003cem\u003ep\u003c/em\u003e = 0.199; WS: \u003cem\u003eR²\u003c/em\u003e = 0.28, \u003cem\u003eF\u003c/em\u003e = 3.42, \u003cem\u003ep\u003c/em\u003e= 0.097; BB: model not fitted due to low occurrence).\u003c/p\u003e","description":"","filename":"floatimage4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8330824/v1/a8f94273a38cf185e6f62ffe.jpeg"},{"id":103166771,"identity":"ae4f00f2-0741-4d17-9e4c-16678ea5e051","added_by":"auto","created_at":"2026-02-22 12:42:20","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":52293,"visible":true,"origin":"","legend":"\u003cp\u003eSpecies specific prevalence of coral disease at Ras Ghanada (2010-204). Bars show the percentage of colonies within each taxon exhibiting active disease at the time of survey. Numbers in parentheses indicate the total number of colonies analyzed (n).\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-8330824/v1/351d4a2a7acb2572c7e105e8.png"},{"id":103509234,"identity":"f43e0f08-af8a-42dc-a7b9-bb3ff4cd173a","added_by":"auto","created_at":"2026-02-26 13:57:31","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3202485,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8330824/v1/2b6b10be-1acf-4804-9be5-6a774bb35c98.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Increased disease prevalence in a warming peripheral reef setting (Abu Dhabi, Persian/Arabian Gulf)","fulltext":[{"header":"Introduction","content":"\u003cp\u003eScleractinian corals are subject to a wide range of diseases (Harvell et al. 1999; Woodley et al. 2016; Precht et al. 2016) that have become one of the leading causes of community change in the Caribbean basin since the 1980s (Harvell et al. 1999; Aronson \u0026amp; Precht 2001; Gardner et al. 2003; Precht et al. 2020). Coral diseases are also posing an increasing threat in the Indo-Pacific (Willis et al. 2004; Hobbs et al. 2015) and are increasingly affecting reefs in the Persian/Arabian Gulf (PAG; Riegl 2002; Bruckner \u0026amp; Riegl 2015; Aeby et al. 2020; Howells et al. 2020). New diseases and disease epizootics have arisen over the past decades (i.e., stony coral tissue disease, SCTLD (Precht et al. 2016; Brandt et al. 2021)) which has caused widespread mortality and community collapse across the tropics (Papke et al. 2024; Swaminathan et al. 2024). However, pinpointing pathogens has proven elusive (Vega Thurber et al. 2020; Papke et al. 2024). There is growing evidence that many coral diseases may be secondary manifestations of environmental stresses (Thurber et al. 2017; Ricci et al. 2022). High temperatures, pollution (Harvell et al. 2007; Precht et al., 2020), and sedimentation (Haapkyla et al. 2011; Hazraty-Kari et al. 2021) have all been linked to outbreaks of coral disease.\u003c/p\u003e \u003cp\u003eHigh-latitude regions, such as the northern Caribbean, have been hot-spots for devastating disease outbreaks (Weil 2006; Van Woesik \u0026amp; Randall 2017; Precht et al. 2020). In a warming climate, coral reefs globally may be subject to similar disease-inducing heat stress (Harvell et al. 2007; Howells et al. 2020). Thermal stress on coral reefs does not always manifest as bleaching events, but diseases can be a primary sign or result of thermal stress (Howells et al. 2020). Impacts of coral epizootics can be dramatic and can displace species and genera from entire regions. This was most dramatically demonstrated by the Caribbean-wide die-back of \u003cem\u003eAcropora\u003c/em\u003e in the 1970s and 80s (McClanahan \u0026amp; Muthiga 1998; Miller et al. 2002). Similarly, declines were also seen in the PAG where local species richness was reduced from 34 to 27 after bleaching-related coral disease outbreaks in 1996 and 1998 (Riegl 2002).\u003c/p\u003e \u003cp\u003eThe PAG is a high latitude, largely enclosed peripheral sea where corals exist under harsh environmental conditions, such as extreme temperature fluctuations (\u0026gt;\u0026thinsp;20\u0026deg;C annually), high maximum temperatures (\u0026gt;\u0026thinsp;36\u0026deg;C), hypersalinity, and intermittent high levels of turbidity (Riegl 1999; Coles 2003; Sheppard et al. 2010; Riegl et al. 2012; Burt 2019; Riegl Jr. et al. 2024). Major thermal heat events have been recorded repeatedly over the last three decades, in 1996, 1998, 2002, 2010, 2012, 2017, 2018, and 2021, each corresponding with mass bleaching and partial recovery (Riegl 2002; Bauman et al. 2010; Riegl \u0026amp; Purkis 2012, 2015; Burt 2019; Burt 2024; Riegl Jr. et al. 2024). Long term temperature records show peak summer sea temperatures have increased steadily, with maxima frequently exceeding 35.7\u0026deg;C in recent years (Riegl Jr. et al. 2024). In addition to frequent thermal stress, the region\u0026rsquo;s coral communities have been degraded through chronic pressures imposed by coastal urbanization and industrialization (Burt 2024). These combined acute and chronic stressors have contributed to the persistent decline in live coral cover and shifts in benthic community structure throughout much of the southern PAG (Riegl et al. 2012; Burt 2019; Riegl Jr. et al. 2024)\u003c/p\u003e \u003cp\u003eThis study explores temporal patterns of disease prevalence at Ras Ghanada, Abu Dhabi, historically one of southeastern PAG\u0026rsquo;s largest and most diverse coral reefs. Coral health status was monitored annually for the period from 2010\u0026ndash;2024 along with temperatures measured on the reef. Coral reefs in the southeastern PAG (Abu Dhabi, United Arab Emirates) are vulnerable to near-field stressors due to the proximity of coastal urbanization as well as to far-field stressors like increased atmospheric heat content as these corals exist near their upper thermal physiological limit (Burt 2024). This makes them prone to repeated bleaching (Lough et al. 2018; Paparella et al. 2019) and, so observations suggest (Aeby et al. 2020), likely also to disease outbreaks. Although impacts have been noted, research on coral disease in the PAG remains limited, with only four documented types of coral diseases (Arabian Yellow Band; Black Band; White Syndrome; Pink Line Disease (Riegl et al. 2012)) and little quantification of long-term patterns and impacts in and around the Arabian Peninsula (Riegl et al. 2012; Bruckner \u0026amp; Riegl 2015).\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStudy Site\u003c/h2\u003e \u003cp\u003eSurveys were conducted at Ras Ghanada Marine Protected Area (MPA) in Abu Dhabi, United Arab Emirates, located in the southern Persian/Arabian Gulf (PAG). At Ras Ghanada, one of the southern PAG\u0026rsquo;s largest contiguous reef areas exists adjacent to large seagrass beds and a mangrove system. The reefal area is made up mostly by thin (~\u0026thinsp;1m) \u003cem\u003ePorites\u003c/em\u003e spp. framework between 5-8m depth, which over the years lost the majority of live coral tissues (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). This region experiences extreme environmental conditions, including high summer temperatures and elevated salinity levels (Sheppard et al. 2010; Burt 2019). Ras Ghanada\u0026rsquo;s reef and adjacent marine associated habitats are neighbored by Khalifa Port and Al Taweelah power and desalination plant.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eData Collection\u003c/h3\u003e\n\u003cp\u003eFrom January 2010 to September 2024, roughly sixty downward-facing photo transect images (~\u0026thinsp;1-1.5 m\u003csup\u003e2\u003c/sup\u003e each) were collected three times each year\u0026mdash;January, May, and September - at locations haphazardly chosen on the reef, except in 2014, 2015, 2018, 2019, 2020 and 2021. No surveys were conducted in 2014 or 2018, surveys in 2015 and 2019 were conducted only in September and in 2020 only in January. In 2021 surveys were conducted in May and September. Seafloor temperature data were obtained for each survey year beginning in 2010 using VEMCO and HOBO temperature loggers affixed to the reef at depth of 7-8m (1m tidal range). Since the sampling was seasonal (January falling into the coldest period, i.e. winter, May being before the hottest season, i.e. spring, and September being at the end of the hot season, i.e. summer) data analysis grouped the sampling periods into winter, spring and summer.\u003c/p\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eData Analysis\u003c/h2\u003e \u003cp\u003eOnly high-quality photographs with clear focus and proper framing were considered in this study (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). From each survey year, thirty randomly chosen images (ten per season) were used for analysis to ensure consistent temporal replication across the study period. Every visible coral colony was identified to the species level when morphological characteristics were sufficiently distinct. Coral health status was assessed by documenting signs of active disease (i.e., such as tissue loss, discoloration, and lesions with defined margins), partial mortality (i.e., including partially recovered lesions, visible mortality, and permanent tissue loss), and bleaching (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Colonies that exhibited active disease or bleaching at the time of observation were classified as unhealthy, while those that appeared normal in tissue and coloration were categorized as healthy regardless of partial mortality presence. Three major diseases are known in the PAG (Arabian Yellow Band, Black Band, White Syndromes; Riegl et al. 2012; Bruckner \u0026amp; Riegl 2015). Encroachment was defined as any physical interaction between a coral colony and adjacent benthic organisms that could potentially inhibit colony growth (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Each colony was assessed for direct contact along its perimeter, and the encroaching organism was categorized into one of five groups (corals, invertebrates, crustose coralline algae, turf algae, and cyanobacteria). Contact was recorded as presence or absence per colony, and percentages were later calculated to reflect the proportion of colonies encroached by categories in each year. Quantifying encroachment provided an insight into the secondary effects of disease, highlighting cascading effects on community dynamics and reef composition in the southern PAG.\u003c/p\u003e \u003cp\u003eCoral disease prevalence was calculated as the proportion of colonies showing active signs of disease. Seasonal and annual prevalence values were summarized with means, standard deviations, and sample sizes. Seasonal patterns in disease prevalence were visualized with boxplots (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) with overlaid points representing individual years. Temporal trends in coral counts and disease prevalence were assessed using General Additive Models (GAMs) with smoothing splines fitted to year. A Gaussian GAM was used to model annual changes in total coral counts, and a Generalized Liner Model (GLM) was used for disease prevalence from 2010 to 2024 (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA). Seasonal disease prevalence trends were analyzed using binomial GAMs for Winter, Summer, and Spring seasons, with the proportion of diseased corals modeled as a function of year. All GAMs were fitted using the mgcv package (Wood 2017) with basis dimension k\u0026thinsp;=\u0026thinsp;5 or 6. They were then evaluated using a GAM check to assess model fit and ensure appropriate smoothing. No signs of undersmoothing were detected (k-index\u0026thinsp;\u0026gt;\u0026thinsp;1, p\u0026thinsp;\u0026gt;\u0026thinsp;0.5 for all models). To compare disease prevalence between 2010 and 2024, a binomial proportion test was applied. Long-term linear trends in disease prevalence were also assessed using Generalized Linear Models (GLMs). Non-parametric Kruskal-Wallis tests were used to detect seasonal differences in active disease and bleaching prevalence. To examine temperature and disease relationships, annual disease prevalence was compared with corresponding maximum reef temperatures for each year (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). GLMs were fitted to assess temporal trends for each disease type. Species-specific disease counts, total colonies, and encroachment patterns were analyzed and presented in tables and figures.\u003c/p\u003e \u003cp\u003eAll statistical analyses were done using R v4.2.2 (R Core Team, 2022) and packages including tidyverse (Wickham \u0026amp; Grolemund 2017; Wickham et al. 2019), mgcv (Wood 2017), stats, and janitor. Raw survey and temperature files were imported and reshaped using readr and dplyr from magrittr (Bache 2022), table sanitizing tools in janitor (Firke 2023) and dates parsed and binned using lubridate (Spinu et al. 2023). Graphics were generated in ggplot2 (Wickham 2016), with axis scaling and formatting from library scales (Wickham \u0026amp; Seidel 2022) and assembled with patchwork (Pedersen 2020). Context maps were produced using ArcGIS Pro (ESRI, 2024).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eDataset Overview\u003c/h2\u003e \u003cp\u003eThirty-two surveys were conducted between 2010\u0026ndash;2024 in January, May, and September.. Cumulative species richness over the entire study period was 34 species, with dominant species \u003cem\u003ePlatygyra daedalea, Porites harrisoni, Dipsastraea\u003c/em\u003e spp. In 2010, average coral cover was approximately 56.2%, comprising mostly \u003cem\u003eP. daedalea\u003c/em\u003e (22.6%), \u003cem\u003eP. harrisoni\u003c/em\u003e (37.8%) and \u003cem\u003eDipsastraea\u003c/em\u003e spp. (25%). Coral abundance declined significantly over time, with a GAM indicating a nonlinear trend (edf\u0026thinsp;=\u0026thinsp;4.46, F\u0026thinsp;=\u0026thinsp;125.1, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001, deviance explained\u0026thinsp;=\u0026thinsp;98.8%; Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA). Prevalence of coral disease increased over the same period, although there was substantial temporal variation (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA), with a binomial GLM indicating a strong significance (β\u0026thinsp;=\u0026thinsp;0.0408\u0026thinsp;\u0026plusmn;\u0026thinsp;0.0173 SE, z\u0026thinsp;=\u0026thinsp;2.36, p\u0026thinsp;=\u0026thinsp;0.018). This suggests disease occurrence was episodic and likely driven by environmental stressors such as thermal anomalies, as demonstrated by their close temporal association (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eTemperature effects\u003c/h2\u003e \u003cp\u003eThe corals in Ras Ghanada were exposed to maximum summertime temperatures exceeding 35\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:℃\\)\u003c/span\u003e\u003c/span\u003e nearly every year throughout the course of this study (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). The widest temperature range was encountered in 2012, with the highest temperature recorded at 36\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:℃\\)\u003c/span\u003e\u003c/span\u003e (35.96\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:℃\\)\u003c/span\u003e\u003c/span\u003e) (above coral bleaching limit) and lowest at 17.6\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:℃\\)\u003c/span\u003e\u003c/span\u003e (17.58\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:℃\\)\u003c/span\u003e\u003c/span\u003e), giving a range of \u0026gt;\u0026thinsp;18\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:℃\\)\u003c/span\u003e\u003c/span\u003e. 2011, 2012, 2015, 2017, 2018,2020, 2021, 2023 and 2024 all experienced peak temperatures above 35\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:℃\\)\u003c/span\u003e\u003c/span\u003e which mark heat events that approached or exceeded the physiological thermal thresholds for corals in the PAG (35.7\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:℃\\)\u003c/span\u003e\u003c/span\u003e; one day bleaching threshold; Riegl et al. 2011) and caused extensive coral bleaching.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eSeasonal Patterns\u003c/h3\u003e\n\u003cp\u003eCoral health varied across seasons, with both disease and bleaching prevalence showing clear temporal trends. Disease prevalence increased from summer to winter (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Bleaching preceded disease prevalence, peaking during the warmest months of the year (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Average mean disease prevalence was highest during winter (January, 5.14% of all corals), followed by spring (May, 4.03%) and summer (September, 3.24%). Bleaching showed highest prevalence in summer (21.2%), while winter (0.23%) and spring (0.4%) had minimal bleaching (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). A Kruskal-Wallis test revealed statistically significant differences in bleaching prevalence (Chi\u0026sup2;= 522.35, df\u0026thinsp;=\u0026thinsp;2, p\u0026thinsp;\u0026lt;\u0026thinsp;2.2e-16) and disease prevalence (Chi\u0026sup2;= 9.71, df\u0026thinsp;=\u0026thinsp;2, p\u0026thinsp;=\u0026thinsp;0.007801) among seasons.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003e\u0026ndash; Average mean prevalence (%) of diseases and bleaching across winter, spring and summer surveys from 2010 to 2024. Large standard deviations reflect that neither diseases nor bleaching occurs every year.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSeason\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMean Disease Prevalence %\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMean Bleaching Prevalence %\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSpring (May)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e4.03\u0026thinsp;\u0026plusmn;\u0026thinsp;19.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.4\u0026thinsp;\u0026plusmn;\u0026thinsp;6.34\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSummer (September)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e3.24\u0026thinsp;\u0026plusmn;\u0026thinsp;17.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e21.2\u0026thinsp;\u0026plusmn;\u0026thinsp;40.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWinter (January)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e5.14\u0026thinsp;\u0026plusmn;\u0026thinsp;22.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.23\u0026thinsp;\u0026plusmn;\u0026thinsp;4.83\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eLong-term trajectory\u003c/h3\u003e\n\u003cp\u003eDisease prevalence (all corals in all seasons across the year) increased by about 4% from 1.42\u0026thinsp;\u0026plusmn;\u0026thinsp;11.8% in 2010 to 5.66\u0026thinsp;\u0026plusmn;\u0026thinsp;23.2% in 2024. This trend was supported by a binomial GLM that indicated a significant positive increase in disease prevalence between 2010 to 2024 (β\u0026thinsp;=\u0026thinsp;0.0408\u0026thinsp;\u0026plusmn;\u0026thinsp;0.0173 SE, z\u0026thinsp;=\u0026thinsp;2.36 \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.018). Disease prevalence peaked in years following heat events, specifically 2019 and 2021; both of which exceeded coral thermal thresholds the year prior (Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA \u0026amp; B, 4).\u003c/p\u003e \u003cp\u003eTwo diseases (Arabian Yellow Band\u0026thinsp;=\u0026thinsp;AYB, White Syndrome\u0026thinsp;=\u0026thinsp;WS) were common across the entire survey period with one (Black Band Disease\u0026thinsp;=\u0026thinsp;BB) being encountered only in one year. At the survey\u0026rsquo;s onset, AYB was about twice as frequent as WS, but from 2019 onward, WS became more frequent (Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB \u0026amp; \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eSpecies-specific differences in disease prevalence\u003c/h2\u003e \u003cp\u003eClear differences with regards to disease prevalence were observed among the coral taxa. The most abundant genus within the dataset, \u003cem\u003eDipsastraea\u003c/em\u003e spp., exhibited relatively low disease prevalence (0.9% of all colonies across all years) but moderate levels of partial mortality (~\u0026thinsp;19%). \u003cem\u003ePlatygyra daedalea\u003c/em\u003e showed moderate levels of disease (4.7%) and high prevalence of partial mortality (35%), indicating repeated stress events and partial recovery over time. The most vulnerable dominant species with about 13% of colonies showing disease and more than 60% of colonies showing partial mortality was \u003cem\u003ePorites harrisoni\u003c/em\u003e, an apparently highly susceptible species. Although \u003cem\u003eAcropora\u003c/em\u003e species were less common in this dataset and disappeared altogether around 2015, they showed disease susceptibility when present (~\u0026thinsp;5%), but one third (34%) showed evidence of partial mortality suggesting that disease and heat stress contributed to their local loss.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eEncroachment interactions\u003c/h2\u003e \u003cp\u003eEncroachment across the study period reflects both competition and impacts of environmental stressors, specifically disease prevalence and temperature stress. Coral-to-coral interactions were initially the most common form of encroachment (in earlier years such as 2010, roughly 90% of all interactions, Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). This reflected the higher coral cover prior to widespread coral morality. However, with repeated diseases and thermal stress, coral mortality allowed other benthic competitors to increase. Crustose Coralline Algae (CCA) and turf algae increased in years following mass bleaching and disease outbreaks. Cyanobacterial encroachment remained uncommon throughout the dataset but in later years became slightly more common. The decline of coral-to-coral interaction reflects the severe reduction of coral cover. These patterns underline how disease and temperature stress not only drive mortality but also reshape competitive interactions and the broader benthic communities of Ras Ghanada and other reefs within the region.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ePercent of coral colonies encroached upon by different benthic groups in 2010 and 2024, highlighting shifts in competitive interactions over time.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEncroachment category\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2010 (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2024 (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCyanobacteria\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTurf Algae\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e50.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCrustose Coraline Algae (CCA)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e8.56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e40.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCorals\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e90.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4.88\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eInvertebrates\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.68\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4.88\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eTemperature\u0026ndash;disease relationships are complex and depend on the disease or the thermal metrics considered (Rosenburg \u0026amp; Ben-Haim 2002; Jones et al. 2004; Miller \u0026amp; Richardson 2015). In this study, the most relevant indicator was the annual maximum water temperature, which reflects the acute thermal stress endured by corals at Ras Ghanada and the southern PAG in general. Years that reached or exceeded bleaching threshold temperatures (35.7\u0026deg;C) were typically followed by increased disease prevalence in the subsequent surveys. Elevated temperatures can accelerate some coral diseases (e.g., black band), while others may manifest slowly or with a delay following bleaching related stress (Bruno et al. 2007; Harvell et al. 2007; Miller \u0026amp; Richardson 2011; Thurber et al. 2017; Howells et al. 2020). The observed winter peaks in disease prevalence likely represent a lagged biological response, where colonies weakened or bleached during the extreme summer temperatures later develop lesions or tissue necrosis even under cooler conditions. This pattern is supported by the temporal consistency between years of peak summer temperature and subsequent increases in disease prevalence.\u003c/p\u003e \u003cp\u003eLive coral cover decreased from approximately 56.2% in 2010 to well below 10% (4.08%; variance\u0026thinsp;=\u0026thinsp;10.64, SD\u0026thinsp;=\u0026thinsp;3.26 ) in 2024 at Ras Ghanada. This trajectory mirrors regional trends across the southern PAG, where reefs have similarly shifted to degraded states often dominated by turf algae and/or crustose coralline algae (Grizzle et al. 2016; Burt et al. 2019; Bejarano et al. 2022; Riegl Jr. et al. 2024). Colony counts in the photo-transect dataset also declined sharply, reflecting both a reduction in the number of coral colonies and reductions in size. While multiple stressors may have contributed to this decline, recurrent bleaching events show a high coincidence with disease frequency, while other local pressures such as sedimentation and turbidity were considered of less importance (also because no relevant data were available). Coral disease acted as an additional compounding stressor, often following bleaching events and extending coral morality into the winter months. Together these acute and chronic pressures have driven the degradation of Ras Ghanada and the southern PAG.\u003c/p\u003e \u003cp\u003eThe delayed manifestation of disease following thermal events aligns with patterns that have been observed across the Indo-Pacific, Great Barrier Reef, and the Caribbean, where heat induced stress weakened the corals\u0026rsquo; immunity and facilitated disease outbreaks (Bruno et al. 2007; Harvell et al. 2007; Miller \u0026amp; Richardson 2011). The similarity of these responses across geographically and thermally distinct regions suggests that the physiological mechanisms linking temperature and disease are globally consistent. As such, reefs in the PAG can serve as a natural model for future trajectories for reef communities as ocean temperatures continue to rise.\u003c/p\u003e \u003cp\u003eThe prevalence of disease varied among species. Poritids seemed highly vulnerable to disease outbreaks in the PAG, similar to regions like the Indo-Pacific (Raymundo et al. 2005). However, the local loss of \u003cem\u003eAcropora\u003c/em\u003e species and the persistence of other taxa (\u003cem\u003ePorites\u003c/em\u003e spp., \u003cem\u003ePlatygyra daedalea, Dipsastraea\u003c/em\u003e spp.) shifted the relative contribution of each genus to overall disease prevalence. Specifically, \u003cem\u003ePorites harrisoni\u003c/em\u003e exhibited the highest proportion of disease prevalence. Most \u003cem\u003ePorites harrisoni\u003c/em\u003e colonies throughout the dataset showed clear signs of partial mortality that were either heat related and/ or caused by disease. \u003cem\u003eAcropora\u003c/em\u003e species in the PAG were extremely sensitive to heat and disease, similar to elsewhere (Aeby et al. 2020; Precht et al. 2020). No \u003cem\u003eAcropora\u003c/em\u003e were recorded after 2015, reflecting local extirpation due to a combination of bleaching a disease susceptibility. Many \u003cem\u003eAcropora\u003c/em\u003e colonies observed before 2015 showed tissue loss or active lesions, indicating that disease likely accelerated post bleaching mortality. \u003cem\u003eDipsastraea\u003c/em\u003e spp. had relatively low disease prevalence but had a high level of partial mortality (a potential sign of having overcome disease), indicating that prevalence (frequency of infection) and severity (extent of tissue loss) varied among genera and/or species. This may suggest that \u003cem\u003eDipsastraea\u003c/em\u003e spp. are more likely to die directly from bleaching than ensuing diseases. \u003cem\u003ePlatygyra daedalea\u003c/em\u003e had moderate disease incidence. Many \u003cem\u003eP. daedalea\u003c/em\u003e colonies exhibited visible partial mortality. Whether the mortality was due to a combination of both disease and heat stress or one or the other, the species showed strong evidence of recovery from either bleaching or disease.\u003c/p\u003e \u003cp\u003eThe incidence of benthic competition, as measured by encroachment, substantially changed during this study. At the beginning of the survey (2010), coral-to-coral interaction was about 90% but later declined to \u0026lt;\u0026thinsp;5% (2024, Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). This is primarily attributed to widespread coral loss which demonstrates the influence of disease mortality on competition among the benthos. Also, the disease-mediated loss of branching corals, which were major contributors to the reef framework, and the reduced frequency of massive corals, led to a lack of habitat heterogeneity. The increase of encroachment by other benthic organisms like CCA and turf algae reflects the shifts in the benthic community following coral decline (McCook 1999; Norstr\u0026ouml;m et al. 2009; Riegl Jr. et al. 2024).\u003c/p\u003e \u003cp\u003eThis study provides a continuous long-term assessment of disease prevalence within the southern PAG and demonstrates clear links between temperature stress, coral disease, and shifts in coral assemblages at Ras Ghanada. By combining annual monitoring with species level health assessments, it establishes a baseline of disease prevalence at a region where long term records are not readily available. These findings emphasize the need for continued monitoring of temperature, disease, mortality and benthic community structure to better predict and manage persistence of the now very few corals remaining in the PAG and other thermally challenged systems. More generally, the results show that coral disease is becoming an increasingly important driver of community change in the Persian/ Arabian Gulf \u0026ndash; one of the few regions outside of the Caribbean where long term records now show disease contributing to larger scale coral loss.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eBJR analyzed and wrote manuscript. MSP, JAB, AGB assisted in review of manuscript. Manuel Ploner made map of UAE.\u003c/p\u003e\u003ch2\u003eAcknowledgements:\u003c/h2\u003e \u003cp\u003eThis paper is part of BJR\u0026rsquo;s MPhil thesis at JCU. BJR and AGB were supported by ONR grant N000142512019. BJR analyzed and wrote manuscript. MSP, JAB, AGB assisted in review of manuscript. Manuel Ploner made map of UAE.\u003c/p\u003e \u003cp\u003e \u003cb\u003eDeclarations\u003c/b\u003e: Morgan Pratchett is currently Editor in Chief of Coral Reefs but played no role in review process and final editorial decision regarding this manuscript.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe datasets used and/or analyzed for the current study are available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAeby GS, Howells E, Work TM, Abrego D, Williams GJ, Elliott J, Hobbs JPA (2020) Localized outbreaks of coral disease on Arabian reefs are linked to extreme temperatures and environmental stressors. Coral Reefs 39:829\u0026ndash;846. https://doi.org/10.1007/s00338-020-01928-4\u003c/li\u003e\n\u003cli\u003eAronson RB, Precht WF (2001) White-band disease and the changing face of Caribbean coral reefs. 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Wiley Blackwell.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"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":"","lastPublishedDoi":"10.21203/rs.3.rs-8330824/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8330824/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eCoral reefs in the Persian/ Arabian Gulf (PAG) are subject to extreme heat stress. Moreover, effects of temperature induced bleaching on local coral assemblages are being further compounded by coral disease. This manuscript explores taxonomic and seasonal variation in disease prevalence, at Ras Ghanada, Abu Dhabi, from 2010\u0026ndash;2024. Thirty-two image-based surveys were conducted across winter, spring and summer seasons which looked at active diseases, partial mortality, bleaching, encroachment by neighboring biota and general health from images. Seafloor temperature was also recorded across the monitoring period. Elevated disease prevalence in 2013, 2019, 2021, and 2024 followed marked summer heat stress with significant coral bleaching. Disease was most prevalent in winter after summer thermal stress. \u003cem\u003ePorites harrisoni\u003c/em\u003e showed highest disease prevalence, while species within the genus \u003cem\u003eDipsastraea\u003c/em\u003e spp. were more resilient. \u003cem\u003eAcropora\u003c/em\u003e spp. suffered moderate disease prevalence after bleaching and disappeared from Ras Ghanada after 2015 likely as a result of both stressors. Relative prevalence of diseases increased from 1.42% in 2010 to 5.66% of all corals in 2024. Coral diseases on PAG marginal reefs are chronic stressors that contribute to community shifts and structural loss.\u003c/p\u003e","manuscriptTitle":"Increased disease prevalence in a warming peripheral reef setting (Abu Dhabi, Persian/Arabian Gulf)","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-22 12:42:11","doi":"10.21203/rs.3.rs-8330824/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-04-29T10:02:41+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-20T15:05:31+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"43104188315881221355750381268863865737","date":"2026-04-08T08:10:42+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-03-19T01:06:35+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"156552819826252609333294227770194614474","date":"2026-02-19T22:28:53+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-02-17T08:12:51+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-12-19T13:22:21+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-12-15T01:23:28+00:00","index":"","fulltext":""},{"type":"submitted","content":"Coral Reefs","date":"2025-12-10T20:48:13+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":"03c13914-9c3a-4ce6-b7e0-4e31b2905498","owner":[],"postedDate":"February 22nd, 2026","published":true,"recentEditorialEvents":[{"type":"decision","content":"Revision requested","date":"2026-04-29T10:02:41+00:00","index":"","fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"in-revision","subjectAreas":[],"tags":[],"updatedAt":"2026-04-29T10:10:31+00:00","versionOfRecord":[],"versionCreatedAt":"2026-02-22 12:42:11","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8330824","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8330824","identity":"rs-8330824","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}