Coral reefs are among the most biologically diverse and productive ecosystems on Earth, supporting an incredible array of marine life (Reaka-Kudla, 1997; Moberg and Rönnbäck, 2003). These vibrant underwater habitats play a crucial role in maintaining biodiversity, sustaining fisheries, protecting coastlines from erosion, driving tourism, and serve as a source for medical discoveries (Bertness et al., 2001; Newman et al., 2015; Brathwaite et al., 2022; Uyarra et al., 2008; Abdelhafez et al., 2019). However, coral reef systems have experienced significant declines over recent decades due to climate change-induced bleaching, ocean acidification, hurricanes, diseases, and several anthropogenic stressors (Høegh-Guldberg et al., 2007; Precht et al., 2016; Graham et al., 2014; Kjerfve et al., 2021; Mallela and Crabbe, 2009; Aronson and Precht, 2001).

The Caribbean Sea, in particular, is regarded as a coral disease ‘hotspot’, with numerous well-documented outbreaks in the last decades (Van Woesik and Randall, 2017; Thurber et al., 2020; Gladfelter, 1982). Coral diseases often arise due to a combination of biological stressors, such as bacteria, fungi, and viruses, as well as non-biological factors like elevated sea surface temperatures, ultraviolet radiation, and pollutants (Rosenberg and Ben-Haim, 2002; Jones et al., 2021). Over the past decade, the incidence of coral diseases has rapidly escalated, leading to significant mortality among reef-building corals (Precht et al., 2016; Costa et al., 2021). This trend is often linked to declining water quality from anthropogenic pollutants and rising sea surface temperatures, which facilitate the growth and spread of pathogenic particles (Merselis et al., 2018; Rosenberg and Ben-Haim, 2002). However, pinpointing definitive causes remains challenging due to the complexity of the interactions between multiple environmental stressors (Jones et al., 2021).

Coral diseases such as black-band, red-band, and yellow-blotch/band typically manifest as discolored bands or lesions on coral tissues, slowly degrading them and exposing the white skeleton underneath (Rosenberg and Ben-Haim, 2002). More virulent diseases like white band, white plague, white pox, and Stony Coral Tissue Loss Disease (SCTLD) cause large patches of coral tissue to deteriorate rapidly, leading to colonization by algae and invertebrates and often resulting in the irreversible decline of entire coral colonies (Aronson and Precht, 2001; Cróquer et al., 2021).

Initially characterized as a form of white-plague disease causing rapid tissue loss (Precht et al., 2016), SCTLD is now recognized by distinct simultaneous lesions that often manifest centrally within coral colonies (Cróquer et al., 2021; Florida Department of Environmental Protection, 2018). While the exact cause of SCTLD remains under investigation, viral-like particles (VLPs) have been associated with the disease in some studies. For instance, Work et al. (2021) identified VLPs associated with endosymbiont pathology in Florida corals affected by SCTLD, but VLPs were also found in unaffected corals, suggesting they may not be specific to this disease. Additionally, microbiome studies have revealed a variety of bacterial groups enriched in SCTLD lesions, pointing to a potential role for bacteria in disease progression (Meyer et al., 2019; Becker et al., 2021; Clark et al., 2021; Rosales et al., 2022, 2023). Further evidence supporting bacterial involvement comes from experiments using antibiotics, which have shown some efficacy in halting lesion progression (Aeby et al., 2019; Neely et al., 2020; Shilling et al., 2021; Walker et al., 2021; Forrester et al., 2022). Together, these findings highlight the complexity of SCTLD’s etiology, with both viral-like particles and bacteria being investigated as contributing factors.

This disease differs from other coral diseases in its extensive impact, affecting at least 20 species of Caribbean corals, including key reef-building species such as Orbicella annularis and Orbicella faveolata (Precht et al., 2016; Muller et al., 2020; Costa et al., 2021; Álvarez-Filip et al. 2019; 2022; Hernández-Delgado and Weil 2019). However, preliminary surveys and observations by STINAPA (Stichting Nationale Parken Nederlandse Antillen), a local NGO responsible for managing Bonaire’s National Parks, as well as training surveys conducted as part of this study, indicate that Orbicella annularis and Orbicella faveolata have not yet shown signs of SCTLD infection in Bonaire, and its colonies remained unaffected during the study period (STINAPA Bonaire National Parks Foundation, 2024). Since its detection in Florida in 2014, SCTLD has spread rapidly across more than 25 countries and territories, causing widespread ecological disruption, as documented by the Atlantic and Gulf Rapid Reef Assessment (AGGRA) SCTLD spread map (Atlantic and Gulf Rapid Reef Assessment (AGGRA), 2024). SCTLD has proven to be a significant threat to coral reefs, sometimes infecting up to 81% of the hard corals present on the reef, with its impact varying among species (Precht et al., 2016). SCTLD spreads swiftly via water currents (Dobbelaere et al., 2020), and research suggests that its dissemination could involve potential vectors such as reef sediments (Studivan et al., 2020), as well as the movement of vessels and ballast water (Studivan et al., 2022; Rosenau et al., 2021).

Bonaire’s coral reefs, often considered some of the most robust and vibrant in the Caribbean, have been highly valued for their biodiversity and as a prime destination for diving tourism, contributing significantly to the island’s economy (Parsons and Thur, 2007; Uyarra et al., 2008). Despite their shown resilience, Bonaire’s reefs have experienced challenges from environmental stressors, including climate-induced bleaching and various disease outbreaks (Lessios, 2016; De Bakker et al., 2017; De Bakker et al., 2019; Aronson and Precht, 2001; Gladfelter, 1982). Coral diseases, such as white band disease, have historically devastated local coral populations, particularly the acroporid species (Bak and Criens, 1981; Gladfelter, 1982). Additionally, a severe decline in the sea urchin Diadema antillarum led to reduced grazing, resulting in algal overgrowth, further stressing the coral ecosystem (Lessios, 2016).

SCTLD is a highly destructive coral disease that spreads rapidly, causing extensive mortality in susceptible species. Highly vulnerable species, such as Meandrina meandrites and Colpophyllia natans, often display early signs of infection, which can escalate to rapid tissue loss and death (Florida Department of Environmental Protection, 2018). Other SCTLD-sensitive species, such as Dendrogyra cylindrus and Dichocoenia stokesi, were not included in the analyses due to their sparse or virtually absent populations in Bonaire. The six SCTLD-sensitive species analyzed in this research—Meandrina meandrites, Eusmilia fastigiata, Montastraea cavernosa, Pseudodiploria strigosa, Diploria labyrinthiformis, and Colpophyllia natans—were selected because they represented nearly all observed SCTLD-like symptoms and recently dead coral. Notably, half of these species are brain corals, which are typically thermally resilient and less affected by bleaching events. This targeted focus allowed us to assess the disease’s effects on the most visibly impacted coral populations in Bonaire’s reef systems.

STINAPA first documented the arrival of SCTLD in Bonaire in March 2023 (STINAPA Bonaire National Parks Foundation, 2024). Since then, the disease has spread rapidly across the island’s reef systems, even reaching remote northern areas within nine months. According to a map created by STINAPA, SCTLD has significantly impacted Bonaire’s coral populations, particularly the six reef-building species analyzed in this study (see Figure 1 ; STINAPA Bonaire National Parks Foundation, 2024).

Among the six SCTLD-sensitive species, the smooth brain coral Pseudodiploria strigosa, once known for its resilience in the Dutch Caribbean. now faces a significant threat. Previously regarded as a ‘winner’ due to its ability to withstand environmental stressors and its expansion over recent decades (De Bakker et al., 2016), P. strigosa is now at risk from SCTLD, marking a potential shift from a resilient survivor to a vulnerable species (Álvarez‐Filip et al., 2022; Florida Department of Environmental Protection, 2018). Additionally, slow-growing, thermally resistant brain corals—despite their inherent resilience—are frequently among the first to be afflicted, with some large colonies succumbing within weeks of infection (Álvarez-Filip et al., 2022; Florida Department of Environmental Protection, 2018). The decline of highly susceptible species, such as these brain corals, could jeopardize their long-term local persistence (Precht et al., 2016). Furthermore, patterns of susceptibility and prevalence vary regionally; species previously considered less vulnerable in one area have shown significant declines in another, suggesting that environmental, physical, and ecological factors play a critical role in SCTLD’s effects (Muller et al., 2020).

Although SCTLD’s presence in Bonaire is recent, its rapid spread underscores an urgent need for research, particularly given the limited documentation of coral disease outbreaks in the Dutch Caribbean. Understanding the disease’s early impact is crucial, as SCTLD progresses swiftly and can cause significant changes in a short period. This study seeks to fill a critical knowledge gap by providing the first systematic assessment of SCTLD’s effects on SCTLD-sensitive coral species in Bonaire, a region with unique reef characteristics compared to other parts of the Caribbean. Specifically, it establishes baseline data on SCTLD within its first year on Bonaire, quantifying its impact and assessing changes in population dynamics, spatial distribution, and overall density of six SCTLD-sensitive species. By analyzing how these species respond to the disease across different subregions and quantifying declines since the 2023 outbreak, this research aims to offer valuable insights into the early phase of SCTLD’s influence. The findings will be crucial in understanding the trajectory of the disease, informing conservation strategies, and contributing to the broader knowledge of SCTLD’s impact on coral reef ecosystems in the Caribbean.

Caribbean coral reefs are facing numerous threats, and SCTLD adds to an already extensive list of coral stressors identified in the region (Gladfelter, 1982; Lessios, 2016). However, SCTLD’s impact is particularly severe, as it affects a broader range of species and exhibits higher prevalence than other diseases, especially in vulnerable coral species. This can lead to rapid ecological shifts and significant degradation of coral reef ecosystems across the Caribbean (Precht et al., 2016). Early detection and monitoring are critical in understanding SCTLD’s spread and impact, as observed in the Virgin Islands and the Bahamas, where its arrival resulted in widespread mortality and severe declines in coral cover (Brandt et al., 2021; Dahlgren et al., 2021).

This study highlights the early impact of SCTLD on Bonaire’s coral reefs, revealing significant species declines and spatial variations that emphasize the complex influence of both disease and environmental stressors. The species analysis shown in Figure 5 suggests that while all examined coral species were likely impacted by SCTLD since its arrival, declines for certain species—such as C. natans, M. cavernosa, and E. fastigiata—may have begun before 2023, indicating that pre-existing stressors, likely made them more vulnerable to the disease (Van Der Geest et al., 2020; Eakin et al., 2019; Meesters et al., 2022; Álvarez-Filip et al., 2022). These historical stressors align with events like the 2014–2017 mass bleaching, which weakened coral populations and likely reduced resilience to subsequent stressors, including SCTLD. Previous studies suggest that corals resistant to bleaching may exhibit compromised immune responses, potentially increasing their susceptibility to subsequent diseases (Merselis et al., 2018). Chronic stressors, including sediment runoff, pollution, and warming sea surface temperatures, further weakened coral vulnerability, particularly for brain corals like C. natans and P. strigosa, which are otherwise thermally resilient (Merselis et al., 2018; Rosenberg and Ben-Haim, 2002). These trends suggest that SCTLD likely added to existing vulnerabilities, accelerating coral declines observed in Bonaire. While bleaching and SCTLD prevalence are not directly linked, the cumulative impact of past stressors likely reduced coral resilience to SCTLD.

The arrival of SCTLD in Bonaire, much like in other regions of the Caribbean, likely exacerbated the decline in coral cover, with all six SCTLD-sensitive species showing consistently low values in 2023, underscoring their susceptibility. This aligns with previous studies that have shown intermediate to high sensitivity among these species to SCTLD, resulting in steep coral cover declines after outbreaks (Williamson et al., 2022; Brandt et al., 2021). The pronounced susceptibility of species like E. fastigiata and M. meandrites, along with the decline of D. labyrinthiformis and P. strigosa at both depths, reflects the widespread impact of SCTLD on coral populations. By 2023, these species reached their lowest recorded cover values within just 6 to 9 months of SCTLD’s arrival in Bonaire’s waters. However, the individual species analysis alone is insufficient to draw definitive conclusions. While SCTLD likely played a significant role in the observed overall low values observed in 2023, attributing these trends solely to the disease is challenging, as many species exhibited declines prior to its documented arrival, likely driven by other stressors.

The spatial analysis reveals that SCTLD’s impact is not uniformly distributed across Bonaire’s coral reefs. Declines in SCTLD-sensitive species were most pronounced in City Limits and Klein Bonaire, which experienced acute drops in coral cover that closely align with SCTLD spread patterns mapped by STINAPA (STINAPA, 2024). In contrast, SCTLD’s impact in the North subregion during the survey period was minimal, suggesting either a lower prevalence of SCTLD or delayed disease progression rather than inherent ecological resistance. Bonaire’s geography, particularly the limited water flow connecting northern reefs with affected areas in the south and central regions, may have slowed SCTLD’s spread.

Declines in total coral cover observed in Klein Bonaire and City Limits also mirror the patterns seen in SCTLD-sensitive species, further underscoring the potential influence of SCTLD. Similar trends have been documented elsewhere in the Caribbean, where SCTLD has caused substantial coral cover losses (Precht et al., 2016; Brandt et al., 2021). However, the lack of widespread declines in total coral cover across other subregions suggests that losses are primarily concentrated among SCTLD-sensitive species, while other coral species have remained relatively stable. While this pattern aligns with the expected impact of SCTLD, further investigation is necessary to rule out additional localized stressors.

Color maps comparing changes in SCTLD-sensitive and total coral cover between 2020 and 2023 ( Figures 12 , 13 ) reveal a gradient of coral cover decline radiating from the Kralendijk area toward outer regions. This pattern likely reflects heightened human activity near the port as well as the spread of SCTLD from its initial detection point, moving progressively along reefs over time. Similar patterns of SCTLD transmission have been reported in Florida and the US Virgin Islands, where waterborne currents played a key role in disease spread (Dobbelaere et al., 2020; Muller et al., 2020; Brandt et al., 2021). These findings emphasize the intersection of disease dynamics, physical factors, and anthropogenic stressors in shaping coral reef health (Brandt et al., 2021; Costa et al., 2021; De Bakker et al., 2016; Van Der Geest et al., 2020).

In summary, the species and spatial analyses indicate that SCTLD is a significant factor in the coral decline observed in Bonaire, though pre-existing stressors likely heightened species vulnerability. The steep declines in City Limits and Klein Bonaire call for urgent conservation actions, such as antibiotic treatments (Forrester et al., 2022). These findings not only shed light on SCTLD’s impact in Bonaire but also contribute to the broader understanding of coral diseases across the Caribbean. Continued monitoring and research are essential to unravel the complex interactions between SCTLD, human activity, and environmental factors affecting SCTLD-sensitive coral species.

While this study provides critical insights into the early impact of SCTLD on Bonaire’s coral reefs, certain limitations must be acknowledged. The use of photographic records to estimate coral cover introduces potential biases, as coral density, human bias and the presence of outliers could affect results. Additionally, high variability in species density across regions and depths, along with the skewed nature of the data (heavily inflated with zeros and low proportions), poses challenges for standard statistical models. Although the analysis strongly indicates changes in coral cover, formal hypothesis testing was not applied due to these constraints. Therefore, the results should be interpreted cautiously but remain indicative of SCTLD’s likely role in driving these declines.

These factors are particularly important when comparing differences across species (see Figure 5 ), where very low densities require careful interpretation. Pre-existing stressors, such as past bleaching events and pollution, complicate efforts to isolate SCTLD’s specific impact during its recent outbreak. The overlap of stressors such as the 2014–2017 bleaching events and other environmental stressors, presents a challenge in disentangling the specific contributions of SCTLD to coral mortality. As previously noted, corals resistant to bleaching may exhibit immune suppression, leaving them more vulnerable to coral diseases like SCTLD (Merselis et al., 2018; Eakin et al., 2019). This overlap between several stressors highlights the difficulty of interpreting disease-related coral cover changes over time and emphasizes the need for further studies to understand SCTLD’s role in the broader context of coral reef degradation.

Furthermore, SCTLD’s selective impact on a subset of coral species complicates correlating disease prevalence with coral cover changes. While the direct causes of coral mortality cannot be fully disentangled due to the absence of colony-level tracking, observations during surveys indicated that corals presenting SCTLD-like lesions or signs of recent mortality belonged to the six SCTLD-sensitive species analyzed. Many of the recently dead colonies exhibited skeletons that were still visible and free from algal overgrowth, indicating very recent mortality. Nearby colonies, or living portions of the same colony, often displayed SCTLD-like lesions, further supporting the likelihood that SCTLD was the primary cause of mortality. The significant declines observed in SCTLD-sensitive species, particularly in Klein Bonaire and City Limits, strongly align with the documented emergence of SCTLD. These patterns suggest that SCTLD acted as a major driver of recent mortality, compounded by pre-existing stressors such as bleaching and anthropogenic impacts.

We leveraged linear trend models and 95% confidence intervals to track changes in coral cover over time. While significant declines were observed in 2023 in several cases ( Figures 5 – 7 , 10 ), more sophisticated analyses could be required to fully interpret these trends and reduce p-values given by the linear models, offering a more comprehensive understanding of the data (See P. strigosa in Figure 5 ; additional examples in Supplementary Figures 6–13 ). For example, in the five less-impacted subregions, changes in total coral cover were often not significant. This may be due to the relatively small contribution of SCTLD-sensitive species to overall coral cover, as even notable declines in these species may not be reflected on broader metrics. Incorporating more advanced models in future analyses could help detect statistical differences and changes that may go unnoticed, providing a deeper understanding of SCTLD’s impact across all subregions.

The full extent of SCTLD’s impact has yet to be determined, as it only reached the northern part of Bonaire several months after its first sighting in the Kralendijk area (STINAPA Bonaire National Parks Foundation, 2024). Currently, it affects fewer coral species than anticipated (Precht et al., 2016; Brandt et al., 2021; Costa et al., 2021), with some species that have been severely impacted in other regions showing resistance in Bonaire. Regional differences in SCTLD’s progression and species resilience, as observed in other studies, warrant further investigation, particularly for key reef-building species such as O. faveolata and O. annularis, which have seemingly not yet shown signs of infection by SCTLD in Bonaire (Brandt et al., 2021; Costa et al., 2021; Eaton et al., 2021; STINAPA Bonaire National Parks Foundation, 2024). Additionally, species like Dendrogyra cylindrus, Dichocoenia stokesi, and Porites spp., while highly susceptible to SCTLD elsewhere, are found in very low densities in Bonaire and were therefore almost absent from our dataset. This highlights the importance of focusing on locally dominant species to better understand SCTLD’s ecological impact in Bonaire.

Ongoing monitoring is essential to track SCTLD’s progression among the six highly SCTLD-sensitive coral species and to detect any emerging symptoms in other species. Additionally, future research should explore other stressors impacting these species, such as thermal stress, pollution, and runoff (Eakin et al., 2019; Meesters et al., 2022; Van Der Geest et al., 2020). While slow-growing brain corals are typically thermally resistant, they are not immune to SCTLD, which has reduced their populations and weakened their resilience to climate change (Álvarez-Filip et al., 2022).

For example, P. strigosa, once showing signs of recovery (De Bakker et al., 2016), has suffered significant declines in 2023, likely due to SCTLD, highlighting a concerning shift in reef diversity. The population dynamics of P. strigosa and other SCTLD-sensitive species will require close attention and monitoring to assess their long-term viability.

Our findings, which detail the immediate and mid-term effects of SCTLD on key coral species, contribute to the broader understanding of stressors affecting Bonaire’s reefs and inform targeted restoration efforts. Future research could expand on these results by correlating coral mortality with water quality parameters, offering deeper insights into SCTLD’s spread and the influence of human activity.

This study provides the first systematic assessment of the impact of Stony Coral Tissue Loss Disease (SCTLD) on Bonaire’s SCTLD-sensitive coral species, capturing the disease’s early effects on local reefs. The research revealed a significant decline in coral cover across multiple species, particularly in 2023, marking SCTLD’s detrimental influence on Bonaire’s reefs. Importantly, the decline was not uniformly distributed, with certain subregions like City Limits and Klein Bonaire experiencing the most severe reductions, while others, such as the North, exhibited a degree of resilience.

The findings emphasize the vulnerability of key reef-building species, M. meandrites, E. fastigiata, M. cavernosa, P. strigosa, C. natans, and D. labyrinthiformis, which have shown significant susceptibility to SCTLD. This highlights the broader ecological concern of the disease, particularly for species previously recognized for their resilience to other stressors like thermal stress. The spatial variability observed underscores the potential need for targeted conservation efforts that take into account regional differences in coral health and disease prevalence.

Moving forward, long-term monitoring is essential to track the continued progression of SCTLD and to identify potential resilience mechanisms within certain coral species. Additionally, further research should explore the role of environmental and anthropogenic factors, such as water quality and human activity, in exacerbating or mitigating the disease’s spread. This understanding will be critical for developing effective management strategies aimed at preserving Bonaire’s coral reefs.

Ultimately, the health of these ecosystems is not only an ecological priority but also crucial for the island’s economy and community well-being. This research contributes to the broader global effort to protect coral reefs in the face of emerging diseases, offering valuable insights for both scientific understanding and conservation practices.