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Habitat degradation is a key factor leading to the global loss of biodiversity. This problem is particularly acute in coral reef ecosystems. We investigated whether recognition of predator odours by damselfish was influenced by coral degradation and whether these changes altered survival in the wild. We taught whitespot damselfish to recognize the odour of a predator in the presence of live/healthy coral or dead/degraded coral. Fish were tested for a response to predator odours in environments that matched their conditioning environment or in environments that were mismatched. Next, we taught blue damselfish to recognize the odour of three common reef predators in live and degraded coral environments and then stocked them onto live or degraded patch reefs, where we monitored their subsequent response to predator odour along with their survival. Damselfish learned to recognize predator odours in both coral environments, but the intensity of their antipredator response was much greater when the conditioning and test environments matched. Fish released on degraded coral had about 50% higher survival if they had been trained in the presence of degraded coral rather than live coral. Altering the intensity of antipredator responses could have rather profound consequences on population growth.

Disturbance can result in the fragmentation and/or loss of suitable habitat, both of which can have important consequences for survival, species interactions, and resulting patterns of local diversity. However, effects of habitat loss and fragmentation are typically confounded during disturbance events, and previous attempts to determine their relative significance have proved ineffective. Here we experimentally manipulated live coral habitats to examine the potential independent and interactive effects of habitat loss and fragmentation on survival, abundance, and species richness of recruitment-stage, coral-associated reef fishes. Loss of 75%% of live coral from experimental reefs resulted in low survival of a coral-associated damselfish and low abundance and richness of other recruits 16 weeks after habitat manipulations. In contrast, fragmentation had positive effects on damselfish survival and resulted in greater abundance and species richness of other recruits. We hypothesize that spacing of habitat through fragmentation weakens competition within and among species. Comparison of effect sizes over the course of the study period revealed that, in the first six weeks following habitat manipulations, the positive effects of fragmentation were at least four times stronger than the effects of habitat loss. This initial positive effect of fragmentation attenuated considerably after 16 weeks, whereas the negative effects of habitat loss increased in strength over time. There was little indication that the amount of habitat influenced the magnitude of the habitat fragmentation effect. Numerous studies have reported dramatic declines in coral reef fish abundance and diversity in response to disturbances that cause the loss and fragmentation of coral habitats. Our results suggest that these declines occur as a result of habitat loss, not habitat fragmentation. Positive fragmentation effects may actually buffer against the negative effects of habitat loss and contribute to the resistance of reef fish populations to declines in coral cover.

Coral bleaching events constitute compound disturbances often resulting in coral death as well as successive degradation of the reef framework. The 1997/1998 El Niño Southern Oscillation (ENSO) was the most severe on record and affected coral reefs worldwide. The present study examined the response of fish assemblages in plots of transplanted coral before and after the 1998 bleaching. Multidimensional scaling ordinations (MDS) demonstrate significant changes in assemblage composition related to habitat alteration. Within-site variability increased with disturbance, the increase being most apparent following substrate erosion. The differences in long-term responses as opposed to short-term responses were striking. Six mo after coral death, total abundance as well as taxonomic richness had increased at one of the sites, but not the other, whereas 6 yr later, both measures had decreased significantly at both sites. Functional groups, with documented affiliations with coral, were significantly influenced by the habitat alteration. Herbivore abundance increased as an immediate response to bleaching, but was subsequently decimated in eroded habitat. The loss of structural complexity had major detrimental effects on the entire fish community. In conclusion, we present evidence of severe and long-lasting secondary impacts of a catastrophic bleaching event, with no apparent recovery. The discrepancies between short-term and long-term responses underline the importance of long-term monitoring of fish assemblages following habitat alteration.

Coral reef ecosystems have rapidly degraded under the combined pressures of climate change and human activities, with diseases further eroding ecosystem function and habitat resilience. Over the past few decades, different coral diseases have been prevalent in all coral reef regions of the world. However, there are few reports on the prevalence of coral diseases in the South China Sea (SCS). Therefore, this study conducted a systematic survey of coral disease diversity and prevalence in the nearshore regions of the northern SCS, covering seven survey sites along the coastlines of Guangdong Province and Hainan Island. Six common coral diseases were identified: Pink-Line Syndrome, Trematodiasis Inflammation, White Syndrome, Skeletal Eroding Band, Ulcerative White Spot, and Growth Anomalies. The results revealed the prevalence and regional distribution patterns of coral diseases in the nearshore regions of the SCS and further assessed the susceptibility of coral species and host specificity of the common diseases. Additionally, environmental parameters and stress-related phenomena affecting corals were recorded, and generalized linear mixed models (GLMMs) were applied to identify variables significantly correlated with coral disease prevalence. The findings further emphasize the critical role of regional environmental heterogeneity in shaping the prevalence patterns of coral diseases, providing important scientific insights to support coral disease management and coral reef ecosystem conservation in the SCS.

Elevated water temperatures, a decrease in ocean pH, and an increasing prevalence of severe storms have lead to bleaching and death of the hard corals that underpin coral reef ecosystems. As coral cover declines, fish diversity and abundance declines. How degradation of coral reefs affects behavior of reef inhabitants is unknown. Here, we demonstrate that risk assessment behaviors of prey are severely affected by coral degradation. Juvenile damselfish were exposed to visual and olfactory indicators of predation risk in healthy live, thermally bleached, and dead coral in a series of laboratory and field experiments. While fish still responded to visual cues in all habitats, they did not respond to olfactory indicators of risk in dead coral habitats, likely as a result of alteration or degradation of chemical cues. These cues are critical for learning and avoiding predators, and a failure to respond can have dramatic repercussions for survival and recruitment. Elevated water temperatures, a decrease in ocean pH, and an increasing prevalence of severe storms have lead to bleaching and death of the hard corals that underpin coral reef ecosystems. As coral cover declines, fish diversity and abundance declines. How degradation of coral reefs affects behavior of reef inhabitants is unknown. Here, we demonstrate that risk assessment behaviors of prey are severely affected by coral degradation.

There is strong evidence that global climate change over the last several decades has caused shifts in species distributions, species extinctions, and alterations in the functioning of ecosystems. However, because of high variability on short (i.e., diurnal, seasonal, and annual) timescales as well as the recency of a comprehensive instrumental record, it is difficult to detect or provide evidence for long-term, site-specific trends in ocean temperature. Here we analyze five in situ datasets from Florida Keys coral reef habitats, including historic measurements taken by lighthouse keepers, to provide three independent lines of evidence supporting approximately 0.8 °C of warming in sea surface temperature (SST) over the last century. Results indicate that the warming observed in the records between 1878 and 2012 can be fully accounted for by the warming observed in recent decades (from 1975 to 2007), documented using in situ thermographs on a mid-shore patch reef. The magnitude of warming revealed here is similar to that found in other SST datasets from the region and to that observed in global mean surface temperature. The geologic context and significance of recent ocean warming to coral growth and population dynamics are discussed, as is the future prognosis for the Florida reef tract.

The numerous socioeconomic and ecological challenges that coral reef degradation poses in the Greater Caribbean have led to a surge in restoration efforts. In this context, outplanting nursery-reared coral colonies has emerged as one of the most common strategies used to rejuvenate degraded reefs and reinstate critical ecosystem processes such as coral recruitment. However, the extent to which coral outplanting promotes the recruitment of coral species remains a subject of ongoing debate. This study tested the hypothesis that reintroducing the threatened coral Acropora cervicornis to a degraded coral reef promotes coral recruitment. To test our hypothesis, a series of recruitment quadrats were established in an area populated with A. cervicornis outplants and in a reference location devoid of the coral. To further investigate the relationship between A. cervicornis and coral recruitment, an experiment was implemented in which half of the quadrats in the restored area received a coral outplant, while the other half were left undisturbed. After one year, all coral recruits located within the quadrats were counted and identified. It was found that in the restored area the mean recruit density exceeded that of the reference location by a factor of 2.15. Results also unveiled a positive association between coral recruitment and the presence of A. cervicornis. Specifically, the mean recruit density in quadrats that received an A. cervicornis colony was 2.21 to 4.65-times higher than in the quadrats without coral outplants. This intriguing observation underscores the pivotal role of A. cervicornis in shaping the recruitment dynamics of corals within degraded reef areas, highlighting the potential of active coral outplanting to enhance the resilience of deteriorating coral reef ecosystems.

The continued degradation of coral reefs in the East African Marine Ecoregion (EAME) has been on the increase, negatively impacting on dive operators and the dive tourism industry. The EAME includes the coastlines of South Africa, Mozambique, Tanzania and Kenya, which are frequented by dive tourists who explore its coral reefs. Through surveys, this research aimed to determine the scale of coral reef degradation in the EAME due to direct environmental risks from the perspective of dive operators in the region-both overall and then per country. Results indicate the prominent direct environmental risks to be overfishing, marine pollution, and destructive fishing, followed by tourism overuse on the coast and negative impacts caused by divers. The greatest regional impact of these risks is on Tanzania, followed by Mozambique, Kenya, and then South Africa, but the extent thereof differs from country to country. Since dive operators are in regular direct contact with coral reefs, their perceptions are important measures of the actual state of coral reefs. Understanding the risks that they identify is crucial due to the correlation between the healthy state of coral reefs and their attractiveness to scuba divers seeking pristine marine environments. While some risks are harder to mitigate, as stakeholders navigate declining coral reef ecosystems, the research points to the importance of marine protected areas, buffer zones, and no-take zones and the strict governance thereof. Multistakeholder engagement is also crucial in securing the sustainability of the dive tourism industry. Educating marine tourism operators, tourists, coastal communities, and the public is a further requirement if marine resources are to be enjoyed and utilized sustainably.

The 2023-24 El Niño event caused extreme marine heat stress and widespread coral bleaching. Coral reefs at the Reserva Biológica Isla del Caño and the northern coast of the Osa Peninsula, Costa Rica, underpin critical ecosystem services, including biodiversity conservation and marine tourism, and have previously withstood similar events with minimal coral loss. Evaluating the ecological impacts of the 2023-24 El Niño is essential to assess coral reef resilience and guide future management. Coral Reef Watch sea surface temperature (SST) data (1985-2025; CoralTemp V3.1) were used to calculate long-term SST trends and degree heating weeks (DHW). Reef surveys were conducted at nine sites between 2019 and 2025, with primary benthic composition and coral health data collected in 2024-25. Benthic cover was assessed using point-intercept, line-intercept, and quadrat methods, while coral diversity, abundance, and health were measured belt transects. Beta regression was used to assess the effect of temperature on coral cover, and multivariate analyses, including principal component analysis (PCA) and similarity percentage analysis (SIMPER), evaluated benthic community changes and bleaching patterns. An Ecological Recovery Feasibility Index (ERFI) was developed using PCA loadings and benthic indicators to rank sites by recovery potential. SST increased significantly over the past 40 years (∼0.23 °C/decade), with the 2023-24 El Niño recording peak SST (31.2 °C). Bleaching threshold exceedance days increased, while cool days declined. Twelve coral taxa were recorded; spp. and were present at all sites. Coral diversity varied, with Cueva and Ancla highest, and San Josecito lowest. Estimated baseline bleaching prevalence was ∼23%, highest in spp. (33.9%). SIMPER and PCA revealed a shift from coral to algal dominance: turf algae increased by 70.62%, dead coral declined 80.71%, and coral cover fell 40.44%. Major coral declines were statistically significant at Ancla, Esquina, and Tina. Bayesian regression confirmed coral decline at Chorro, Cueva, Tina, and Ancla, alongside turf algae increases. Coral cover was higher at warmer sites, though non-temperature site-specific factors were also influential. Chorro and Esquina had the highest recovery potential; Ancla, San Josecito, and Barco Profundo the lowest. There is an urgent need to develop and implement a coral reef restoration strategy for Isla del Caño that addresses site-specific conditions, integrates tourism management, and promotes long-term resilience. Under continued climate change, localized, targeted restoration will be essential to maintain the ecological function of these historically resilient but increasingly vulnerable reefs in Costa Rica's Eastern Tropical Pacific.

Coral reefs provide natural coastal protection through depth-induced wave breaking and frictional dissipation on the fore reef, the reef crest, and the back reef. The coral reef roughness is a significant factor in wave attenuation through frictional dissipation and is directly linked to the reef’s health. The influence of reef roughness on frictional dissipation under representative conditions, and the extent to which coral reef degradation and Sea Level Rise (SLR) reduces this coastal protection service remains underexplored, especially at coastal sites in Caribbean Small Island Developing States. A numerical modelling approach using a coupled depth-averaged (2DH) hydrodynamic and spectral wave model in Delft3D was used to evaluate the coastal protection effectiveness of a fringing reef under varying scenarios of coral reef degradation and SLR at The Buccoo Reef, Tobago. Using near present day conditions as the baseline scenario, assessed wave conditions showed 100% and 96.45% reductions at low and high tides respectively. Under modelled degraded reef conditions on the reef flat, wave heights increased by an average of 21.74% compared to baseline conditions, while for modelled healthier reefs, there was an 18.9% decrease in wave heights from the baseline scenario. Using various SLR scenarios, wave heights showed increases over baseline conditions between 160.5% and 388.4% for increases in sea level from 0.25 m to 1.00 m. The results highlight the importance of the frictional dissipation provided by healthy coral reefs, with degraded corals and rising sea levels leading to substantial increases in nearshore wave heights which could exacerbate issues such as coastal erosion and flooding. Management strategies such as Integrated Coastal Zone Management (ICZM) and innovative approaches such as the deployment of artificial reefs which are specifically designed to replicate the complex structure and roughness of natural reefs can contribute to wave attenuation by frictional dissipation.