Sediment and turbidity associated with offshore dredging increase coral disease prevalence on nearby reefs

Multi-Factor Coral Disease Risk: A new product for early warning and management

Ecological forecasts are becoming increasingly valuable tools for conservation and management. However, there are few examples of near-real-time forecasting systems that account for the wide range of ecological complexities. We developed a new coral disease ecological forecasting system that explores a suite of ecological relationships and their uncertainty and investigates how forecast skill changes with shorter lead times. The Multi-Factor Coral Disease Risk product introduced here uses a combination of ecological and marine environmental conditions to predict the risk of white syndromes and growth anomalies across reefs in the central and western Pacific and along the east coast of Australia and is available through the US National Oceanic and Atmospheric Administration Coral Reef Watch program. This product produces weekly forecasts for a moving window of 6 months at a resolution of ~5 km based on quantile regression forests. The forecasts show superior skill at predicting disease risk on withheld survey data from 2012 to 2020 compared with predecessor forecast systems, with the biggest improvements shown for predicting disease risk at mid- to high-disease levels. Most of the prediction uncertainty arises from model uncertainty, so prediction accuracy and precision do not improve substantially with shorter lead times. This result arises because many predictor variables cannot be accurately forecasted, which is a common challenge across ecosystems. Weekly forecasts and scenarios can be explored through an online decision support tool and data explorer, co-developed with end-user groups to improve use and understanding of ecological forecasts. The models provide near-real-time disease risk assessments and allow users to refine predictions and assess intervention scenarios. This work advances the field of ecological forecasting with real-world complexities and, in doing so, better supports near-term decision making for coral reef ecosystem managers and stakeholders. Secondarily, we identify clear needs and provide recommendations to further enhance our ability to forecast coral disease risk.

Temperature and local anthropogenic pressures limit stony coral assemblage viability in southeast Florida

Climate change is viewed as the primary threat to coral reefs, with local pressures exacerbating coral cover decline. The consensus is that improving water quality may increase resilience, but disentangling water quality and temperature impacts is difficult. We used distance-based linear models and random forests to analyze spatiotemporal variation in benthic community structure and interannual changes in the coral assemblage, in relation to specific environmental metrics in Southeast Florida. Temperature accounted for most of the variation, recruitment doubled and interannual increases in coral abundance tripled when mean annual temperature reached 27 °C, until maximum temperatures exceeded 31 °C. Benefits associated with warmer temperatures were negated by poor water quality, as nutrient enrichment was related to increased macroalgal cover, reduced coral recruitment and higher coral partial mortality. We suggest reducing local pressures will contribute to reduced macroalgae and enhance coral recovery, but that temperature is the predominant influence on coral assemblages.

Removal of detritivore sea cucumbers from reefs increases coral disease

Coral reefs are in global decline with coral diseases playing a significant role. This is especially true for Acroporid corals that represent ~25% of all Pacific coral species and generate much of the topographic complexity supporting reef biodiversity. Coral diseases are commonly sediment-associated and could be exacerbated by overharvest of sea cucumber detritivores that clean reef sediments and may suppress microbial pathogens as they feed. Here we show, via field manipulations in both French Polynesia and Palmyra Atoll, that historically overharvested sea cucumbers strongly suppress disease among corals in contact with benthic sediments. Sea cucumber removal increased tissue mortality of Acropora pulchra by ~370% and colony mortality by ~1500%. Additionally, farmerfish that kill Acropora pulchra bases to culture their algal gardens further suppress disease by separating corals from contact with the disease-causing sediment-functioning as mutualists rather than parasites despite killing coral bases. Historic overharvesting of sea cucumbers increases coral disease and threatens the persistence of tropical reefs. Enhancing sea cucumbers may enhance reef resilience by suppressing disease.

Characterizing transcriptomic responses to sediment stress across location and morphology in reef-building corals

Anthropogenic activities increase sediment suspended in the water column and deposition on reefs can be largely dependent on colony morphology. Massive and plating corals have a high capacity to trap sediments, and active removal mechanisms can be energetically costly. Branching corals trap less sediment but are more susceptible to light limitation caused by suspended sediment. Despite deleterious effects of sediments on corals, few studies have examined the molecular response of corals with different morphological characteristics to sediment stress. To address this knowledge gap, this study assessed the transcriptomic responses of branching and massive corals in Florida and Hawai'i to varying levels of sediment exposure. Gene expression analysis revealed a molecular responsiveness to sediments across species and sites. Differential Gene Expression followed by Gene Ontology (GO) enrichment analysis identified that branching corals had the largest transcriptomic response to sediments, in developmental processes and metabolism, while significantly enriched GO terms were highly variable between massive corals, despite similar morphologies. Comparison of DEGs within orthogroups revealed that while all corals had DEGs in response to sediment, there was not a concerted gene set response by morphology or location. These findings illuminate the species specificity and genetic basis underlying coral susceptibility to sediments.

Current status of coral disease prevalence at Karimunjawa Island: correlation between land zonation and lesion occurrence

Coral diseases have contributed significantly to the decline of coral populations at both local and global scales. The Karimunjawa Archipelago, located off the coast of Java in Indonesia, is a marine national park with a zonation-based approach, designated by the local government due to its rich coral reef biodiversity. Unfortunately, there is a limited amount of research regarding the prevalence of coral diseases in coral reefs located on the islands. We analyzed the coral reef lesion assemblages at 6 sites within 3 designated zones, namely Tourism, Aquaculture, and Core zones. Our investigation aimed to determine (1) the types, prevalence, and patterns of coral lesions, (2) the correlation between coral cover and lesion prevalence, and (3) the susceptibility of coral taxa to lesions. A significant difference of 80.54% in the total number of coral lesions was observed between the tourism zone (24.34%) and the core zone (10.36%). Fourteen different lesion types were identified; among the non-disease lesions, sediment damage was the most prevalent (9.95%), followed by disease lesions caused by white syndrome (3.7%). A correlation was found between the cover of dominant coral taxa and the prevalence of lesions (disease and non-disease) at all sites. Mean lesion prevalence across all zones ranged from moderate to high categories. These findings present current data on the distribution of coral lesions and their patterns across zones around Karimunjawa Island. Research on the etiology and epidemiology of coral lesions should be promoted to identify ways to prevent the spread of coral diseases in Karimunjawa.

Seasonal coral-algae interactions drive White Mat Syndrome coral disease outbreaks

Ocean warming drives not only the increase of known coral disease prevalence but facilitates the emergence of new undescribed ones too. As climate change is restructuring coral ecosystems, novel biological interactions could lead to an increase in coral disease in both tropical and marginal coral communities. White Mat Syndrome (WMS) represents one such emerging coral disease, with outbreaks associated with high algal interactions and seasonal summer temperatures. However, the mechanisms behind its pathogenesis, modes of transmission and causative pathogens remain to be identified. Ex situ infection experiments pairing the coral Porites heronensis together with local potential contributory factors show that the macroalga Gelidium elegans hosts and proliferates the WMS microbial mat. This pathogenic consortium then infects adjacent corals, leading to their mortality. WMS was also observed to transmit following the fragmentation of the microbial mat, which was able to infect healthy corals. Sulfur-cycling bacteria (i.e., Beggiatoa, Desulfobacter sp., Arcobacteraceae species) and the free-living spirochete Oceanospirochaeta sediminicola were found consistently in both WMS and G. elegans consortia, suggesting they are putative pathogens of WMS. The predicted functional roles of these pathogenic consortia showed degradative processes, hinting that tissue lyses could drive mat formation and spread. Coral-algae interactions will rise due to ongoing ocean warming and coral ecosystem degradation, likely promoting the virulence and prevalence of algal-driven coral diseases.

First report of yellow-banded tissue loss disease on coral reefs outside the Arabian/Persian Gulf

Coral disease is a major cause of coral reef degradation, yet many diseases remain understudied. Yellow-banded tissue loss disease (YBTLD) has a distinct gross lesion morphology and to date has only been reported from the Arabian/Persian Gulf; little else is known about the ecology of the disease. We report on the first occurrence of YBTLD outside of the Arabian/Persian Gulf at 2 sites (Laku Point, Narara Reef) within the Gulf of Kachchh (GoK) located on the northwest coast of India. At Narara Reef, YBTLD was observed at 12 out of 24 transects with an average prevalence of 4.7 ± 1.3%. At Laku Point, YBTLD was observed at 19 out of 24 transects with an average prevalence of 5.4 ± 1%. Four out of 15 coral genera within transects had signs of YBTLD and included Goniopora, Dipsastraea, Lobophyllia, and Turbinaria. Lobophyllia and Turbinaria had the highest susceptibility to the disease, with prevalence significantly higher than expected based on their abundance on the reefs. The distribution and prevalence of YBTLD in the GoK was higher than in coral reefs in the Arabian/Persian Gulf. The GoK is an extreme environment for coral reefs with both natural stressors (high salinities, strong, seasonal storm activities, and extreme tides) and anthropogenic pollutants from industrial, mining, agricultural, and domestic activities. These poor environmental conditions may help explain the high occurrence of YBTLD on GoK reefs.

Reef on the edge: resilience failure of marginal patch coral reefs in Eastern Arabian Sea under recurrent coral bleaching, coral diseases, and local stressors

Marked by strong El Niño-Southern Oscillation (ENSO) effects during 2014-2016, global coral reefs underwent mass bleaching. Here, we conducted a comprehensive (2014-2019) study, coinciding with the 2014-16 ENSO, to investigate the response and resilience potential of marginal coral communities to the combined impact of recurrent thermal anomalies and multiple anthropogenic stressors before, during, and after the mass bleaching episodes. Our result unveiled that thermal-stress-driven back-to-back annual coral bleaching episodes caused coral mortality and significantly decimated coral cover, primarily in 2015 and 2016. Subsequent benthic regime shifts toward macroalgal and algal turf colonization, followed by an increase in coral disease prevalence and recruitment failure was observed after the recurrent bleaching episodes. Algal cover increased from 21% in 2014 to 52.90% in 2019, and a subsequent increase in coral disease occurrence was observed from 16% in 2015 to 29% in 2019. The cascading negative effect of multiple stressors magnified coral loss and decreased the coral cover significantly from 45% in 2014 to 20% in 2019. The corals in the intensive recreational diving activity sites showed higher disease prevalence, concurring with high mechanical coral damage. The present study demonstrates that consecutive thermal bleaching episodes combined with local stressors can cause declines in coral cover and promote an undesirable regime shift to algal dominance in marginal coral reef habitats within a short duration. These results are of particular interest given that marginal reefs were traditionally perceived as resilient reef habitats due to their higher survival threshold to environmental changes. The present study indicates that mitigation of local stressors by effective management strategies, in conjunction with globally coordinated efforts to ameliorate climate change, can protect these unique coral reefs.

Diversity and Distribution of Microbial Communities Associated with Reef Corals of the Malay Peninsula

Coral-associated bacteria play critical roles in the regulation of coral health and function. Environmental perturbations that alter the bacterial community structure can render the coral holobiont more susceptible and less resilient to disease. Understanding the natural variation of the coral microbiome across space and host species provides a baseline that can be used to distinguish shifts in community structure. Using a 16S rRNA gene metabarcoding approach, this study examines bacterial community structure across three scleractinian coral hosts. Our results show that corals of three regions-eastern and western Peninsular Malaysia and Singapore-host distinct bacterial communities; despite these differences, we were able to identify a core microbiome shared across all three species. This core microbiome was also present in samples previously collected in Thailand, suggesting that these core microbes play an important role in promoting and maintaining host health. For example, several have been identified as dimethylsulfoniopropionate (DMSP) metabolizers that have roles in sulfur cycling and the suppression of bacterial pathogens. Pachyseris speciosa has the most variable microbiome, followed by Porites lutea, with the composition of the Diploastrea heliopora microbiome the least variable throughout all locations. Microbial taxa associated with each region or site are likely shaped by local environmental conditions. Taken together, host identity is a major driver of differences in microbial community structure, while environmental heterogeneity shapes communities at finer scales.

Untapped policy avenues to protect coral reef ecosystems

Coral reefs are experiencing severe decline, and urgent action is required at local and global scales to curb ecosystem loss. Establishing new regulations to protect corals, however, can be time consuming and costly, and it is therefore necessary to leverage existing legal instruments, such as policies originally designed to address terrestrial rather than marine activities, to prevent coral reef degradation. Focusing on the United States, but drawing on successful examples worldwide, we present actionable pathways to increase coral protections under legislation that was originally designed to advance clean freshwater, safe drinking water, and emergency management. We identify specific legal policies and procedures (e.g., industrial permit limits, nonpoint source management incentives, and floodplain restoration programs) that can curb coral reef pollution and can be extended to other countries with similar regulations in place. Coral reef practitioners should consider a broad array of currently underused, actionable, and intersecting environmental policies that can be applied to mitigate coral stress.

Strategies for managing marine disease

The incidence of emerging infectious diseases (EIDs) has increased in wildlife populations in recent years and is expected to continue to increase with global environmental change. Marine diseases are relatively understudied compared with terrestrial diseases but warrant parallel attention as they can disrupt ecosystems, cause economic loss, and threaten human livelihoods. Although there are many existing tools to combat the direct and indirect consequences of EIDs, these management strategies are often insufficient or ineffective in marine habitats compared with their terrestrial counterparts, often due to fundamental differences between marine and terrestrial systems. Here, we first illustrate how the marine environment and marine organism life histories present challenges and opportunities for wildlife disease management. We then assess the application of common disease management strategies to marine versus terrestrial systems to identify those that may be most effective for marine disease outbreak prevention, response, and recovery. Finally, we recommend multiple actions that will enable more successful management of marine wildlife disease emergencies in the future. These include prioritizing marine disease research and understanding its links to climate change, improving marine ecosystem health, forming better monitoring and response networks, developing marine veterinary medicine programs, and enacting policy that addresses marine and other wildlife diseases. Overall, we encourage a more proactive rather than reactive approach to marine wildlife disease management and emphasize that multidisciplinary collaborations are crucial to managing marine wildlife health.

Algal turf structure and composition vary with particulate loads on coral reefs

Algal turfs trap and retain particulates, however, little is known about the relationship between particulate accumulation and taxonomic composition of algal turfs. We investigated how particulate mass related to algal turf structure (length and density) and community composition (taxonomic and functional) on two disparate reefs. Particulate mass was positively related to algal turf length. By contrast, the relationship between particulate mass and turf density was more complex and followed a negative parabolic shape; density increased with particulate mass before stabilising and then declining. Community analyses showed taxonomic, but not functional group compositions differed significantly between reefs and with increasing particulate mass. Our results suggest high loads of particulates accumulated in algal turfs are related to a longer, lower density turf structure, typified by filamentous forms such as Cladophora. Changes in algal turf structure and composition could have a variety of bottom-up influences on coral reef ecosystems.

Dredging transforms the seafloor and enhances functional diversity in urban seascapes

Landscape modification alters the condition of ecosystems and the complexity of terrain, with consequences for animal assemblages and ecosystem functioning. In coastal seascapes, dredging is routine practice for extracting sediments and maintaining navigation channels worldwide. Dredging modifies processes and assemblages by favouring species with wide trophic niches, diverse habitat requirements and tolerances to dredge-related eutrophication and sedimentation. Dredging also transforms the three-dimensional features of the seafloor, but the functional consequences of these terrain changes remain unclear. We investigated the effects of terrain modification on the functional diversity of fish assemblages in natural and dredged estuaries to examine whether dredging programs could be optimised to minimise impacts on ecological functioning. Fish assemblages were surveyed with baited remote underwater video stations and variation in functional niche space was described using species traits to calculate metrics that index functional diversity. Terrain variation was quantified with nine complementary surface metrics including depth, aspect, curvature, slope and roughness extracted from sonar-derived bathymetry maps. Functional diversity was, surprisingly, higher in dredged estuaries, which supported more generalist species with wider functional niches, and from lower trophic levels, than natural estuaries. These positive effects of dredging on functional diversity were, however, spatially restricted and were linked to both the area and orientation of terrain modification. Functional diversity was highest in urban estuaries where dredged channels were small (i.e. <1% of the estuary), and where channel slopes were orientated towards the poles (i.e. 171-189°), promoting both terrain variation and light penetration in urban estuaries. Our findings highlight previously unrecognised functional consequences of terrain modification that can easily be incorporated into dredging programs. We demonstrate that restricting the spatial extent of dredging operations and the orientation of dredged channel slopes, wherever this is practical, could help to limit impacts on ecosystem functioning and productivity in urban seascapes.

A community and functional comparison of coral and reef fish assemblages between four decades of coastal urbanisation and thermal stress

Urbanized coral reefs experience anthropogenic disturbances caused by coastal development, pollution, and nutrient runoff, resulting in turbid, marginal conditions in which only certain species can persist. Mortality effects are exacerbated by increasingly regular thermal stress events, leading to shifts towards novel communities dominated by habitat generalists and species with low structural complexity.

There is limited data on the turnover processes that occur due to this convergence of anthropogenic stressors, and how novel urban ecosystems are structured both at the community and functional levels. As such, it is unclear how they will respond to future disturbance events.

Here, we examine the patterns of coral reef community change and determine whether ecosystem functions provided by specialist species are lost post‐disturbance. We present a comparison of community and functional trait‐based changes for scleractinian coral genera and reef fish species assemblages subject to coastal development, coastal modification, and mass bleaching between two time periods, 1975–1976 and 2018, in Nakagusuku Bay, Okinawa, Japan.

We observed an increase in fish habitat generalists, a dominance shift from branching to massive/sub‐massive corals and increasing site‐based coral genera richness between years. Fish and coral communities significantly reassembled, but functional trait‐based multivariate space remained constant, indicating a turnover of species with similar traits. A compression of coral habitat occurred, with shallow (<5 m) and deep (>8 m) coral genera shifting towards the mid‐depths (5–8 m).

We show that although reef species assemblages altered post disturbance, new communities retained similar ecosystem functions. This result could be linked to the stressors experienced by urban reefs, which reflect those that will occur at an increasing frequency globally in the near future. Yet, even after shifts to disturbed communities, these fully functioning reef systems may maintain high conservation value.

A biological condition gradient for Caribbean coral reefs: Part II. Numeric rules using sessile benthic organisms

The Biological Condition Gradient (BCG) is a conceptual model used to describe incremental changes in biological condition along a gradient of increasing anthropogenic stress. As coral reefs collapse globally, scientists and managers are focused on how to sustain the crucial structure and functions, and the benefits that healthy coral reef ecosystems provide for many economies and societies. We developed a numeric (quantitative) BGC model for the coral reefs of Puerto Rico and the US Virgin Islands to transparently facilitate ecologically meaningful management decisions regarding these fragile resources. Here, reef conditions range from natural, undisturbed conditions to severely altered or degraded conditions. Numeric decision rules were developed by an expert panel for scleractinian corals and other benthic assemblages using multiple attributes to apply in shallow-water tropical fore reefs with depths <30 m. The numeric model employed decision rules based on metrics (e.g., % live coral cover, coral species richness, pollution-sensitive coral species, unproductive and sediment substrates, % cover by Orbicella spp.) used to assess coral reef condition. Model confirmation showed the numeric BCG model predicted the panel's median site ratings for 84% of the sites used to calibrate the model and 89% of independent validation sites. The numeric BCG model is suitable for adaptive management applications and supports bioassessment and criteria development. It is a robust assessment tool that could be used to establish ecosystem condition that would aid resource managers in evaluating and communicating current or changing conditions, protect water and habitat quality in areas of high biological integrity, or develop restoration goals with stakeholders and other public beneficiaries.

Histopathology of a threatened surf clam, toheroa (Paphies ventricosa) from Aotearoa New Zealand

The toheroa (Paphies ventricosa) is endemic to Aotearoa (New Zealand). Following decades of overfishing in the 1900 s, commercial and recreational fishing of toheroa is now prohibited. For unknown reasons, protective measures in place for over 40 years have not ensured the recovery of toheroa populations. For the first time, a systematic pathology survey was undertaken to provide a baseline of toheroa health in remaining major populations. Using histopathology, parasites and pathologies in a range of tissues are assessed and quantified spatio-temporally. Particular focus is placed on intracellular microcolonies of bacteria (IMCs). Bayesian ordinal logistic regression is used to model IMC infection and several facets of toheroa health. Model outputs show condition to be the most important predictor of IMC intensity in toheroa tissues. The precarious state of many toheroa populations around Aotearoa should warrant greater attention from scientists, conservationists, and regulators. It is hoped that this study will provide some insight into the current health status of a treasured and iconic constituent of several expansive surf beaches in Aotearoa.

Characterization of the Microbiome of Corals with Stony Coral Tissue Loss Disease along Florida's Coral Reef

Stony coral tissue loss disease (SCTLD) is an emergent and often lethal coral disease that was first reported near Miami, FL (USA) in 2014. Our objective was to determine if coral colonies showing signs of SCTLD possess a specific microbial signature across five susceptible species sampled in Florida’s Coral Reef. Three sample types were collected: lesion tissue and apparently unaffected tissue of diseased colonies, and tissue of apparently healthy colonies. Using 16S rRNA high-throughput gene sequencing, our results show that, for every species, the microbial community composition of lesion tissue was significantly different from healthy colony tissue and from the unaffected tissue of diseased colonies. The lesion tissue of all but one species (Siderastrea siderea) had higher relative abundances of the order Rhodobacterales compared with other types of tissue samples, which may partly explain why S. siderea lesions often differed in appearance compared to other species. The order Clostridiales was also present at relatively high abundances in the lesion tissue of three species compared to healthy and unaffected tissues. Stress often leads to the dysbiosis of coral microbiomes and increases the abundance of opportunistic pathogens. The present study suggests that Rhodobacterales and Clostridiales likely play an important role in SCTLD.

The MPA Guide: A framework to achieve global goals for the ocean

[Figure: see text].

A comparative baseline of coral disease in three regions along the Saudi Arabian coast of the central Red Sea

Coral disease is a growing problem for coral reefs globally and diseases have been linked to thermal stress, excess nutrients, overfishing and other human impacts. The Red Sea is a unique environment for corals with a strong environmental gradient characterized by temperature extremes and high salinities, but minimal terrestrial runoff or riverine input and their associated pollution. Yet, relatively little is known about coral diseases in this region. Disease surveys were conducted at 22 reefs within three regions (Yanbu, Thuwal, Al Lith) in the central Red Sea along the Saudi Arabian coast. Surveys occurred in October 2015, which coincided with a hyperthermal-induced bleaching event. Our objectives were to 1) document types, prevalence, and distribution of coral diseases in a region with minimal terrestrial input, 2) compare regional differences in diseases and bleaching along a latitudinal gradient of environmental conditions, and 3) use histopathology to characterize disease lesions at the cellular level. Coral reefs of the central Red Sea had a widespread but a surprisingly low prevalence of disease (<0.5%), based on the examination of >75,750 colonies. Twenty diseases were recorded affecting 16 coral taxa and included black band disease, white syndromes, endolithic hypermycosis, skeletal eroding band, growth anomalies and focal bleached patches. The three most common diseases were Acropora white syndrome (59.1% of the survey sites), Porites growth anomalies (40.9%), and Porites white syndrome (31.8%). Sixteen out of 30 coral genera within transects had lesions and Acropora, Millepora and Lobophyllia were the most commonly affected. Cell-associated microbial aggregates were found in four coral genera including a first report in Stylophora. Differences in disease prevalence, coral cover, amount of heat stress as measured by degree heating weeks (DHW) and extent of bleaching was evident among sites. Disease prevalence was not explained by coral cover or DHW, and a negative relationship between coral bleaching and disease prevalence was found. The northern-most sites off the coast of Yanbu had the highest average disease prevalence and highest average DHW values but no bleaching. Our study provides a foundation and baseline data for coral disease prevalence in the central Red Sea, which is projected to increase as a consequence of increased frequency and severity of ocean warming.

Turbid Coral Reefs: Past, Present and Future—A Review

Increasing evidence suggests that coral reefs exposed to elevated turbidity may be more resilient to climate change impacts and serve as an important conservation hotspot. However, logistical difficulties in studying turbid environments have led to poor representation of these reef types within the scientific literature, with studies using different methods and definitions to characterize turbid reefs. Here we review the geological origins and growth histories of turbid reefs from the Holocene (past), their current ecological and environmental states (present), and their potential responses and resilience to increasing local and global pressures (future). We classify turbid reefs using new descriptors based on their turbidity regime (persistent, fluctuating, transitional) and sources of sediment input (natural versus anthropogenic). Further, by comparing the composition, function and resilience of two of the most studied turbid reefs, Paluma Shoals Reef Complex, Australia (natural turbidity) and Singapore reefs (anthropogenic turbidity), we found them to be two distinct types of turbid reefs with different conservation status. As the geographic range of turbid reefs is expected to increase due to local and global stressors, improving our understanding of their responses to environmental change will be central to global coral reef conservation efforts.

Microbial dysbiosis reflects disease resistance in diverse coral species

Disease outbreaks have caused significant declines of keystone coral species. While forecasting disease outbreaks based on environmental factors has progressed, we still lack a comparative understanding of susceptibility among coral species that would help predict disease impacts on coral communities. The present study compared the phenotypic and microbial responses of seven Caribbean coral species with diverse life-history strategies after exposure to white plague disease. Disease incidence and lesion progression rates were evaluated over a seven-day exposure. Coral microbiomes were sampled after lesion appearance or at the end of the experiment if no disease signs appeared. A spectrum of disease susceptibility was observed among the coral species that corresponded to microbial dysbiosis. This dysbiosis promotes greater disease susceptiblity in coral perhaps through different tolerant thresholds for change in the microbiome. The different disease susceptibility can affect coral’s ecological function and ultimately shape reef ecosystems.

MacKnight et al. compared the phenotypic and microbial responses of seven Caribbean coral species with diverse life-history strategies after exposure to white plague disease. The different species exhibited a spectrum of disease susceptibility and associated mortality that corresponded with their tolerances to microbial change, indicating that coral disease and microbial dysbiosis may ultimately shape reef ecosystems.

The Conservational State of Coastal Ecosystems on the Mexican Caribbean Coast: Environmental Guidelines for Their Management

The accelerated rate of environmental degradation of the Mexican Caribbean coast is alarming. In this work, spatial analysis procedures were applied to study relationships among wave and wind climates, water quality, and environmental degradation of the principal coastal ecosystems. We found an increasing North-South gradient in the preservation state of the coastal ecosystems, related to the degree of anthropization of the coastline. In the north, all analysed stressors exert high pressure on coral reefs, seagrass meadows, mangroves, and dunes, and cause chronic coastline erosion. The coastal ecosystems of the central and southern regions are more mature and healthier, and the most significant stressor is reduced water quality. The north has been most hit by high-intensity hurricanes, the frequency of which has increased in the Mexican Caribbean over recent decades. The status of conservation of the ecosystems, added to the long-term intensification of environmental pressures, particularly high-intensity hurricanes, will induce further deterioration if a coordinated management scheme is not adopted by decision-makers. To ensure effective coordinated management, plans should be made on a regional scale using shared guidelines. Spatial analysis procedures aid in prioritizing and adapting the shared guidelines depending on the identified major stressors and the preservation state of each region in the Mexican Caribbean.

Extreme storms cause rapid but short-lived shifts in nearshore subtropical bacterial communities

Climate change scenarios predict tropical cyclones will increase in both frequency and intensity, which will escalate the amount of terrestrial run-off and mechanical disruption affecting coastal ecosystems. Bacteria are key contributors to ecosystem functioning, but relatively little is known about how they respond to extreme storm events, particularly in nearshore subtropical regions. In this study, we combine field observations and mesocosm experiments to assess bacterial community dynamics and changes in physicochemical properties during early- and late-season tropical cyclones affecting Okinawa, Japan. Storms caused large and fast influxes of freshwater and terrestrial sediment - locally known as red soil pollution - and caused moderate increases of macronutrients, especially SiO₂ and PO₄ ^3-, with up to 25 and 0.5 μM respectively. We detected shifts in relative abundances of marine and terrestrially derived bacteria, including putative coral and human pathogens, during storm events. Soil input alone did not substantially affect marine bacterial communities in mesocosms, indicating that other components of run-off or other storm effects likely exert a larger influence on bacterial communities. The storm effects were short-lived and bacterial communities quickly recovered following both storm events. The early- and late-season storms caused different physicochemical and bacterial community changes, demonstrating the context-dependency of extreme storm responses in a subtropical coastal ecosystem.

Deciphering Coral Disease Dynamics: Integrating Host, Microbiome, and the Changing Environment

Diseases of tropical reef organisms is an intensive area of study, but despite significant advances in methodology and the global knowledge base, identifying the proximate causes of disease outbreaks remains difficult. The dynamics of infectious wildlife diseases are known to be influenced by shifting interactions among the host, pathogen, and other members of the microbiome, and a collective body of work clearly demonstrates that this is also the case for the main foundation species on reefs, corals. Yet, among wildlife, outbreaks of coral diseases stand out as being driven largely by a changing environment. These outbreaks contributed not only to significant losses of coral species but also to whole ecosystem regime shifts. Here we suggest that to better decipher the disease dynamics of corals, we must integrate more holistic and modern paradigms that consider multiple and variable interactions among the three major players in epizootics: the host, its associated microbiome, and the environment. In this perspective, we discuss how expanding the pathogen component of the classic host-pathogen-environment disease triad to incorporate shifts in the microbiome leading to dysbiosis provides a better model for understanding coral disease dynamics. We outline and discuss issues arising when evaluating each component of this trio and make suggestions for bridging gaps between them. We further suggest that to best tackle these challenges, researchers must adjust standard paradigms, like the classic one pathogen-one disease model, that, to date, have been ineffectual at uncovering many of the emergent properties of coral reef disease dynamics. Lastly, we make recommendations for ways forward in the fields of marine disease ecology and the future of coral reef conservation and restoration given these observations.

Microbiome dynamics in the tissue and mucus of acroporid corals differ in relation to host and environmental parameters

Corals are associated with diverse microbial assemblages; however, the spatial-temporal dynamics of intra-species microbial interactions are poorly understood. The coral-associated microbial community varies substantially between tissue and mucus microhabitats; however, the factors controlling the occurrence, abundance, and distribution of microbial taxa over time have rarely been explored for different coral compartments simultaneously. Here, we test (1) differentiation in microbiome diversity and composition between coral compartments (surface mucus and tissue) of two Acropora hosts (A. tenuis and A. millepora) common along inshore reefs of the Great Barrier Reef, as well as (2) the potential linkage between shifts in individual coral microbiome families and underlying host and environmental parameters. Amplicon based 16S ribosomal RNA gene sequencing of 136 samples collected over 14 months, revealed significant differences in bacterial richness, diversity and community structure among mucus, tissue and the surrounding seawater. Seawater samples were dominated by members of the Synechococcaceae and Pelagibacteraceae bacterial families. The mucus microbiome of Acropora spp. was dominated by members of Flavobacteriaceae, Synechococcaceae and Rhodobacteraceae and the tissue was dominated by Endozoicimonaceae. Mucus microbiome in both Acropora species was primarily correlated with seawater parameters including levels of chlorophyll a, ammonium, particulate organic carbon and the sum of nitrate and nitrite. In contrast, the correlation of the tissue microbiome to the measured environmental (i.e., seawater parameters) and host health physiological factors differed between host species, suggesting host-specific modulation of the tissue-associated microbiome to intrinsic and extrinsic factors. Furthermore, the correlation between individual coral microbiome members and environmental factors provides novel insights into coral microbiome-by-environment dynamics and hence has potential implications for current reef restoration and management efforts (e.g. microbial monitoring and observatory programs).

Effects of polluted and non-polluted suspended sediments on the oxygen consumption rate of olive flounder, Paralichthys olivaceus

The potential ecological impacts of elevated suspended sediments (SS) in coastal areas due to human activities remain unclear. In particular, physiological response of benthic fish to SS exposure in polluted environment has not been documented. We determined sub-lethal toxicity of polluted and non-polluted SS to olive flounder. Test organism was exposed to varying concentrations of SS (0-4000 mg L^-1) and real-time oxygen consumption rate (OCR) was measured for 12 h. The early-juvenile was sensitive to SS, particularly at >500 mg L^-1, but late-juvenile was tolerant up to 4000 mg SS L^-1. Metal polluted SS (HQ_metal > 1) increased OCR in general, particularly at >1000 SS mg L^-1. Combined effect of copper and SS exposure on fish was either synergistic or antagonistic. Overall, potential adverse effect of polluted SS on fish greatly varied at different life stage and/or by metal pollution gradients.

Physiological Characteristics and Environment Adaptability of Reef-Building Corals at the Wuzhizhou Island of South China Sea

The health of coral reef has declined significantly around the world due to the impact of human activities and natural environment changes, and corals have to develop effective resistance mechanisms to survive. In this study, we examined the physiological characteristics and Symbiodiniaceae types of four dominant scleractinian corals in the reefs at the Wuzhizhou Island (WZZ) in South China Sea. The water environmental conditions are complex on the north side of WZZ due to regional geography and tourism development, and all corals had their unique physiological conditions and Symbiodiniaceae types. For all corals of this study, the rETRm ax and protein content were significantly lower and the SOD enzyme activity was significantly higher in the north than in the south. Interestingly, ITS2 genotyping showed that Galaxea fascicularis contained dominant Symbiodiniaceae either genotype C21 or D1a depending on the regional environmental stress, and had stronger heterotrophy than the other three coral species. In addition, the light use efficiency of the dominant Symbiodiniaceae type C1 for Pocillopora verrucosa was significantly lower in the north and the half saturating irradiance was stable. Besides, Montipora truncata and P. verrucosa increased their density of the symbiotic zooxanthella C1 in the north to offset the decline of photosynthetic efficiency and thus supply energy. For Porites lutea and G. fascicularis, their half saturating irradiance declined sharply in the north, where P. lutea resorted to heterotrophic feeding to balance the energy budget when the number of zooxanthellas fell short and G. fascicularis reduced its energy reserve significantly when the energy source was limited. We thus demonstrated the differences in the physiological responses and energy metabolism strategies between the zooxanthella and the host coral of the four reef-building coral species under the stress of complex water environment on the north side of WZZ. The corals were found to cope with natural and anthropogenic stressors by adjusting the nutrient input sources and the energy structure metabolism of coral hosts or adapting to more sustainable relationship with Symbiodiniaceae clades. The corals exhibited their capacity against long-term disturbances by developing their own successful resistance mechanisms at symbiotic relationship and energy metabolism level.

Damselfishes alleviate the impacts of sediments on host corals

Mutualisms play a critical role in ecological communities; however, the importance and prevalence of mutualistic associations can be modified by external stressors. On coral reefs, elevated sediment deposition can be a major stressor reducing the health of corals and reef resilience. Here, we investigated the influence of severe sedimentation on the mutualistic relationship between small damselfishes (Pomacentrus moluccensis and Dascyllus aruanus) and their coral host (Pocillopora damicornis). In an aquarium experiment, corals were exposed to sedimentation rates of approximately 100 mg cm-2 d-1, with and without fishes present, to test whether: (i) fishes influence the accumulation of sediments on coral hosts, and (ii) fishes moderate partial colony mortality and/or coral tissue condition. Colonies with fishes accumulated much less sediment compared with colonies without fishes, and this effect was strongest for colonies with D. aruanus (fivefold less sediment than controls) as opposed to P. moluccensis (twofold less sediment than controls). Colonies with symbiont fishes also had up to 10-fold less sediment-induced partial mortality, as well as higher chlorophyll and protein concentrations. These results demonstrate that fish mutualisms vary in the strength of their benefits, and indicate that some mutualistic or facilitative interactions might become more important for species health and resilience at high-stress levels.

Ecology, histopathology, and microbial ecology of a white-band disease outbreak in the threatened staghorn coral Acropora cervicornis

This study is a multi-pronged description of a temperature-induced outbreak of white-band disease (WBD) that occurred in Acropora cervicornis off northern Miami Beach, Florida (USA), from July to October 2014. We describe the ecology of the disease and examine diseased corals using both histopathology and next-generation bacterial 16S gene sequencing, making it possible to better understand the effect this disease has on the coral holobiont, and to address some of the seeming contradictions among previous studies of WBD that employed either a purely histological or molecular approach. The outbreak began in July 2014, as sea surface temperatures reached 29°C, and peaked in mid-September, a month after the sea surface temperature maximum. The microscopic anatomy of apparently healthy portions of colonies displaying active disease signs appeared normal except for some tissue atrophy and dissociation of mesenterial filaments deep within the branch. Structural changes were more pronounced in visibly diseased fragments, with atrophy, necrosis, and lysing of surface and basal body wall and polyp structures at the tissue-loss margin. The only bacteria evident microscopically in both diseased and apparently healthy tissues with Giemsa staining was a Rickettsiales-like organism (RLO) occupying mucocytes. Sequencing also identified bacteria belonging to the order Rickettsiales in all fragments. When compared to apparently healthy fragments, diseased fragments had more diverse bacterial communities made up of many previously suggested potential primary pathogens and secondary (opportunistic) colonizers. Interactions between elevated seawater temperatures, the coral host, and pathogenic members of the diseased microbiome all contribute to the coral displaying signs of WBD.

Setting priorities for conservation at the interface between ocean circulation, connectivity, and population dynamics

Population persistence in the marine environment is driven by patterns of ocean circulation, larval dispersal, ecological interactions, and demographic rates. For habitat-forming organisms in particular, understanding the relationship between larval connectivity and meta-population dynamics aids in planning for marine spatial management. Here, we estimate networks of connectivity between fringing coral reefs in the northwest shelf of Australia by combining a particle tracking model based on shelf circulation with models of subpopulation dynamics of individual reefs. Coral cover data were used as a proxy for overall habitat quality, which can change as a result of natural processes, human-driven impacts, and management initiatives. We obtain three major results of conservation significance. First, the dynamics of the ecological network result from the interplay between network connectivity and ecological processes on individual reefs. The maximum coral cover a zone can sustain imposes a significant nonlinearity on the role an individual reef plays within the dynamics of the network, and thus on the impact of conservation interventions on specific reefs. Second, the role of an individual reef within these network dynamics changes considerably depending on the overall state of the system: a reef's role in sustaining the system's state can be different from the same reef's role in helping the system recover following major disturbance. Third, patterns of network connectivity change significantly as a function of yearly shelf circulation trends, and nonlinearity in network dynamics make mean connectivity a poor representation of yearly variations. From a management perspective, the priority list of reefs that are targets for management interventions depends crucially on what type of stressors (system-wide vs. localized) need addressing. This choice also depends not only on the ultimate purpose of management, but also on future oceanographic, climate change, and development scenarios that will determine the network connectivity and habitat quality.

Regional coral disease outbreak overwhelms impacts from a local dredge project

A repeated-measures coral monitoring program established as part of the PortMiami expansion program provided an unparalleled opportunity to quantify the levels of coral mortality that resulted from both local dredging stress and as a result of climate-related bleaching stress and the subsequent outbreak of a white-plague-like disease (WPD) epizootic. By comparing measured rates of coral mortality at 30 sites throughout Miami-Dade County to predicted mortality levels from three different coral mortality scenarios, we were able to evaluate the most likely source of coral mortality at both the local and regional levels during the 2014-2016 coral bleaching and WPD event. These include scenarios that assume (1) local dredging increases coral disease mortality, (2) regional climate-related stress is the proximal driver of coral disease mortality, and (3) local and regional stressors are both responsible for coral disease mortality. Our results show that species-specific susceptibility to disease is the determining factor in 93.3% of coral mortality evaluated throughout Miami-Dade County, whereas local dredging stress only accurately predicted coral mortality levels 6.7% of the time. None of the monitoring locations adjacent to the PortMiami expansion had levels of coral mortality that exceeded predictions when coral community composition was taken into account. The novel result of this analysis is that climate-mediated coral disease mortality was more than an order of magnitude (14x) more deadly than even the largest marine construction project performed in the USA, and that until climate change is addressed, it is likely that local attempts to manage coral resilience will continue to fail.

Borneo coral reefs subject to high sediment loads show evidence of resilience to various environmental stressors

For reefs in South East Asia the synergistic effects of rapid land development, insufficient environmental policies and a lack of enforcement has led to poor water quality and compromised coral health from increased sediment and pollution. Those inshore turbid coral reefs, subject to significant sediment inputs, may also inherit some resilience to the effects of thermal stress and coral bleaching. We studied the inshore turbid reefs near Miri, in northwest Borneo through a comprehensive assessment of coral cover and health in addition to quantifying sediment-related parameters. Although Miri’s Reefs had comparatively low coral species diversity, dominated by massive and encrusting forms of Diploastrea, Porites, Montipora, Favites, Dipsastrea and Pachyseris, they were characterized by a healthy cover ranging from 22 to 39%. We found a strong inshore to offshore gradient in hard coral cover, diversity and community composition as a direct result of spatial differences in sediment at distances <10 km. As well as distance to shore, we included other environmental variables like reef depth and sediment trap accumulation and particle size that explained 62.5% of variation in benthic composition among sites. Miri’s reefs showed little evidence of coral disease and relatively low prevalence of compromised health signs including bleaching (6.7%), bioerosion (6.6%), pigmentation response (2.2%), scars (1.1%) and excessive mucus production (0.5%). Tagged colonies of Diploastrea and Pachyseris suffering partial bleaching in 2016 had fully (90–100%) recovered the following year. There were, however, seasonal differences in bioerosion rates, which increased five-fold after the 2017 wet season. Differences in measures of coral physiology, like that of symbiont density and chlorophyll a for Montipora, Pachyseris and Acropora, were not detected among sites. We conclude that Miri’s reefs may be in a temporally stable state given minimal recently dead coral and a limited decline in coral cover over the last two decades. This study provides further evidence that turbid coral reefs exposed to seasonally elevated sediment loads can exhibit relatively high coral cover and be resilient to disease and elevated sea surface temperatures.

Extensive coral mortality and critical habitat loss following dredging and their association with remotely-sensed sediment plumes

Dredging poses a potential threat to coral reefs, yet quantifying impacts is often difficult due to the large spatial footprint of potential effects and co-occurrence of other disturbances. Here we analyzed in situ monitoring data and remotely-sensed sediment plumes to assess impacts of the 2013-2015 Port of Miami dredging on corals and reef habitat. To control for contemporaneous bleaching and disease, we analyzed the spatial distribution of impacts in relation to the dredged channel. Areas closer to dredging experienced higher sediment trap accumulation, benthic sediment cover, coral burial, and coral mortality, and our spatial analyses indicate that >560,000 corals were killed within 0.5 km, with impacts likely extending over 5-10 km. The occurrence of sediment plumes explained ~60% of spatial variability in measured impacts, suggesting that remotely-sensed plumes, when properly calibrated against in situ monitoring data, can reliably estimate the magnitude and extent of dredging impacts.

Reduced diversity and stability of coral-associated bacterial communities and suppressed immune function precedes disease onset in corals

Disease is an emerging threat to coral reef ecosystems worldwide, highlighting the need to understand how environmental conditions interact with coral immune function and associated microbial communities to affect holobiont health. Increased coral disease incidence on reefs adjacent to permanently moored platforms on Australia's Great Barrier Reef provided a unique case study to investigate environment-host-microbe interactions in situ. Here, we evaluate coral-associated bacterial community (16S rRNA amplicon sequencing), immune function (protein-based prophenoloxidase-activating system), and water quality parameters before, during and after a disease event. Over the course of the study, 31% of tagged colonies adjacent to platforms developed signs of white syndrome (WS), while all control colonies on a platform-free reef remained visually healthy. Corals adjacent to platforms experienced significant reductions in coral immune function. Additionally, the corals at platform sites that remained visually healthy throughout the study had reduced bacterial diversity compared to healthy colonies at the platform-free site. Interestingly, prior to the observation of macroscopic disease, corals that would develop WS had reduced bacterial diversity and significantly greater community heterogeneity between colonies compared to healthy corals at the same location. These results suggest that activities associated with offshore marine infrastructure impacts coral immunocompetence and associated bacterial community, which affects the susceptibility of corals to disease.

Contrasting responses of the coral Acropora tenuis to moderate and strong light limitation in coastal waters

Coastal water quality and light attenuation can detrimentally affect coral health. This study investigated the effects of light limitation and reduced water quality on the physiological performance of the coral Acropora tenuis. Branches of individual colonies were collected in 2 m water depth at six inshore reefs at increasing distances from major river sources in the Great Barrier Reef, along a strong water quality gradient in the Burdekin and a weak gradient in the Whitsunday region. Rates of net photosynthesis, dark respiration, and light and dark calcification were determined at daily light integrals (DLI) of moderate (13.86-16.38 mol photons m^-2 d^-1), low (7.92-9.36 mol photons m^-2 d^-1) and no light (0 mol photons m^-2 d^-1), in both the dry season (October 2013, June 2014) and the wet season (February 2014). Along the strong but not the weak water quality gradient, rates of net photosynthesis, dark respiration and light calcification increased towards the river mouth both in the dry and the wet seasons. Additionally, a ∼50% light reduction (from moderate to low light), as often found in shallow turbid waters in the Burdekin region, reduced rates of net photosynthesis and light calcification by up to 70% and 50%. The data show the acclimation potential in A. tenuis to river derived nutrients and sediments at moderate DLI (i.e., in very shallow water). However, prolonged and frequent periods of low DLI (i.e., in deeper water, especially after high river sediment discharges) will affect the corals' energy balance, and may represent a major factor limiting the depth distribution of these corals in turbid coastal reefs.

Quantifying sediment dynamics on an inshore coral reef: Putting algal turfs in perspective

Increased sediment loads within algal turfs, can be highly detrimental to coral reef systems. However, significant knowledge gaps remain in relation to sediment dynamics, especially linking suspended sediments, sedimentation and turf-bound sediments. To examine these links, a series of different methods for quantifying suspended sediments, sedimentation and the accumulation of turf sediments were compared, simultaneously, on an inner-shelf reef. We revealed that the amount and composition of sediment quantified using different methods varied markedly, with commonly employed measures of sedimentation failing to accurately reflect patterns of sediment accumulation in turfs. Our results highlighted the propensity for turfs to trap and retain sediments, with turfs accumulating approximately 2.6 times more sediment than traps, and 6 times more sediment than SedPods, over a seven-day period. This study highlights the major, but often overlooked, role that algal turfs can play in sediment dynamics on coral reefs.

No effect of dredging on the prevalence of coral disease detected during a large dredging program

The frequency of disease within coral communities was evaluated using an 18-month series of coral photographs taken before, during, and after a major dredging program at Barrow Island, off Australia's northwest coast. Up to 60 corals were assessed repeatedly at each of four dredging 'impact' sites (<1 km from dredging), and four 'reference' sites (>20 km from dredging). Contrary to an earlier report, the frequency of occurrence of coral disease (usually <5% of corals) was not significantly altered by dredging. The pattern of occurrence of coral disease does not constitute a suitable early warning bioindicator of dredging impacts on coral. This study suggests that disease is difficult to measure and evaluate, and is not a key indicator in the potential impacts of dredging on coral health. We propose that environmental monitoring during dredging should continue to focus on known impact indicators.

Whale Shark Tourism: Impacts on Coral Reefs in the Philippines

Reef-based tourism has been developing rapidly in recent decades yet its impacts on reef ecosystems are often overlooked. In Tan-awan, Oslob, Philippines, whale sharks are attracted to the shallow reefs where they are provisioned up to 50 tons y^-1 of feed and this phenomenon in turn attracts >300,000 y^-1 visitors. Given the intensive provisioning and concentrating tourism activities, we hypothesized that the whale shark tourism-impacted site (IS) will have greater impacts on reef degradation and higher anthropogenic nitrogen pollution level compared to its reference site (RS). Ecological surveys revealed that relative to the RS, the IS had 36% higher relative abundance of Pocillopora and Porites coral over other genera, >2.5-fold lower coral density, and 20% higher macroalgal cover, which we concluded are signs of reef degradation. Also, we conducted stable nitrogen isotope analysis on gorgonian skeletons to trace nitrogen sources at both sites through time. Although an average 1‰ isotope enrichment found in the IS relative to the RS could indicate anthropogenic nitrogen inputs in the IS, this enrichment was consistent over time and existed before the tourism developed. Despite that, we cautioned against the imminent threat of local eutrophication caused by the continued inputs of nitrogen derived from provisioning and tourism activities. In summary, this study provided the first documentation of the impacts of provisioned whale shark tourism on the local reefs in Tan-awan and established an ecological baseline for future comparisons. Such assessments can offer important information on reef health, coastal development, and tourism management.

Urban coral reefs: Degradation and resilience of hard coral assemblages in coastal cities of East and Southeast Asia

Given predicted increases in urbanization in tropical and subtropical regions, understanding the processes shaping urban coral reefs may be essential for anticipating future conservation challenges. We used a case study approach to identify unifying patterns of urban coral reefs and clarify the effects of urbanization on hard coral assemblages. Data were compiled from 11 cities throughout East and Southeast Asia, with particular focus on Singapore, Jakarta, Hong Kong, and Naha (Okinawa). Our review highlights several key characteristics of urban coral reefs, including "reef compression" (a decline in bathymetric range with increasing turbidity and decreasing water clarity over time and relative to shore), dominance by domed coral growth forms and low reef complexity, variable city-specific inshore-offshore gradients, early declines in coral cover with recent fluctuating periods of acute impacts and rapid recovery, and colonization of urban infrastructure by hard corals. We present hypotheses for urban reef community dynamics and discuss potential of ecological engineering for corals in urban areas.

Photoacclimation to light-limitation in a clionaid sponge; implications for understanding sponge bioerosion on turbid reefs

Watershed-based pollution is a common form of coral reef degradation. Affected reefs are often highly turbid, where light-limitation confines the distribution of photosynthetic benthic taxa and the capacity for photoacclimation is important for survival. We investigated low light photoacclimation in a Symbiodinium-hosting bioeroding sponge using in situ PAM fluorometry. Cliona aff. viridis was artificially shaded (70 & 95% ambient light reduction) on a low turbidity Indonesian reef for 25 days, with a subsequent 14-day recovery period. Significant changes in rETR_max, and qP, and a non-significant but observable decline in E_k, demonstrated that C. aff. viridis is able to photoacclimate to conditions of extreme light reduction and recover within a relatively short period of time. The sponge is therefore unlikely to be light limited on even the most turbid reefs. However, other aspects of watershed-pollution such as sedimentation may still limit their distribution in affected coastal waters.

Ecosystem-based management of coral reefs under climate change

Coral reefs provide food and livelihoods for hundreds of millions of people as well as harbour some of the highest regions of biodiversity in the ocean. However, overexploitation, land-use change and other local anthropogenic threats to coral reefs have left many degraded. Additionally, coral reefs are faced with the dual emerging threats of ocean warming and acidification due to rising CO 2 emissions, with dire predictions that they will not survive the century. This review evaluates the impacts of climate change on coral reef organisms, communities and ecosystems, focusing on the interactions between climate change factors and local anthropogenic stressors. It then explores the shortcomings of existing management and the move towards ecosystem-based management and resilience thinking, before highlighting the need for climate change-ready marine protected areas (MPAs), reduction in local anthropogenic stressors, novel approaches such as human-assisted evolution and the importance of sustainable socialecological systems. It concludes that designation of climate change-ready MPAs, integrated with other management strategies involving stakeholders and participation at multiple scales such as marine spatial planning, will be required to maximise coral reef resilience under climate change. However, efforts to reduce carbon emissions are critical if the long-term efficacy of local management actions is to be maintained and coral reefs are to survive.

Influence of salinity and sedimentation on Vibrio infection of the Hawaiian coral Montipora capitata

Environmental cofactors alter host-pathogen interactions and influence disease dynamics by impairing host resistance and/or increasing pathogen virulence. Terrestrial runoff is recognized as a major threat to coral reef health. However, the direct links between runoff and coral disease are not clear. Montipora white syndrome (MWS) is a coral disease that occurs in the Hawaiian archipelago, can be caused by various bacterial pathogens, including Vibrio species, and is linked to conditions associated with heavy rainfall and runoff. The objective of this study was to determine whether a short-term hyposalinity stress (20 ppt for 24 h) or sedimentation stress (1000 g m-2 d-1) would influence bacterial infection of the coral Montipora capitata. Hyposalinity increased M. capitata susceptibility to infection by 2 MWS pathogens, Vibrio coralliilyticus strain OCN008 and Vibrio owensii strain OCN002. Specifically, hyposalinity allowed OCN008 to infect at lower doses (106 CFU ml-1 compared with 108 CFU ml-1) and reduced the amount of time before onset of OCN002 infection at high doses (108 CFU ml-1). In contrast, short-term sedimentation stress did not affect M. capitata infection by either of these 2 pathogens. Although several studies have found a correlation between runoff and increased coral disease prevalence in field studies, this is the first study to show that one aspect of runoff (reduced salinity) enhances bacterial infection of coral using manipulative experiments.

Unraveling the structure and composition of Varadero Reef, an improbable and imperiled coral reef in the Colombian Caribbean

Coral reefs are commonly associated with oligotrophic, well-illuminated waters. In 2013, a healthy coral reef was discovered in one of the least expected places within the Colombian Caribbean: at the entrance of Cartagena Bay, a highly-polluted system that receives industrial and sewage waste, as well as high sediment and freshwater loads from an outlet of the Magdalena River (the longest and most populated river basin in Colombia). Here we provide the first characterization of Varadero Reef’s geomorphology and biological diversity. We also compare these characteristics with those of a nearby reference reef, Barú Reef, located in an area much less influenced by the described polluted system. Below the murky waters, we found high coral cover of 45.1% (±3.9; up to 80% in some sectors), high species diversity, including 42 species of scleractinian coral, 38 of sponge, three of lobster, and eight of sea urchin; a fish community composed of 61 species belonging to 24 families, and the typical zonation of a Caribbean fringing reef. All attributes found correspond to a reef that, according to current standards should be considered in “good condition”. Current plans to dredge part of Varadero threaten the survival of this reef. There is, therefore, an urgent need to describe the location and characteristics of Varadero as a first step towards gaining acknowledgement of its existence and garnering inherent legal and environmental protections.