Monitoring the coral disease, plague type II, on coral reefs in St. John, U.S. Virgin Islands

In July 1997, conspicuous white patches of necrotic tissue and bare skeleton began to appear on scleractinian corals in several bays around St. John, US Virgin Islands. Analysis of diseased coral tissue from five different species confirmed the presence of a Sphingomonas-like bacterium, the pathogen for plague type II. To date, 14 species of hard corals have been affected by plague type II around St. John. This disease was monitored at Haulover and Tektite Reefs at depths of 7-12 meters. The study site at Tektite Reef has > 50% cover by scleractinian corals with 90% of hard corals being composed of Montastraea annularis. Monthly surveys at Tektite Reef from December 1997 to May 2001 documented new incidence of disease (bare white patches of skeleton) every month with associated loss of living coral and 90.5% of all disease patches occurred on M. annularis. The frequency of disease within transects ranged from 3 to 58%, and the area of disease patches ranged from 0.25 to 9000 cm2. The average percent cover by the disease within 1 m2 ranged from 0.01% (+/- 0.04 SD) to 1.74% (+/- 9.08 SD). Photo-monitoring of 28 diseased corals of 9 species begun in September 1997 at Haulover Reef revealed no recovery of diseased portions with all necrotic tissue being overgrown rapidly by turf algae, usually within less than one month. Most coral colonies suffered partial mortality. Very limited recruitment (e.g., of Agaricia spp., Favia spp. and sponges) has been noted on the diseased areas. This coral disease has the potential to cause more loss of live coral on St. John reefs than any other stress to date because it targets the dominant reef building species, M. annularis.     

Coral disease outbreak at Navassa,a remote Caribbean island

In November 2004, a high prevalence of coral disease was observed at several sites around Navassa, an uninhabited Caribbean island between Haiti and Jamaica. At least fifteen mounding and foliaceous scleractinian species were affected with ‘white disease’ signs. Coral disease incidence was observed to be absent in quantitative surveys in 2002, but in 2004 average prevalence (i.e., % of colonies) of active disease ranged up to 15% and an additional 19% prevalence of colonies with patterns of recent mortality consistent with disease. Large and/or Montastraea spp. colonies were disproportionately affected and the anticipated loss of these large, reef-building colonies will impact coral community structure. One or more potential factors may influence the initiation and persistence of disease outbreak conditions at Navassa including recent hurricane disturbance, regional patterns of increasing disease impact in deep or remote Caribbean reefs, or vectoring of disease by the corallivorous worm, Hermodice carunculata.     

Disturbance Driven Colony Fragmentation as a Driver of a Coral Disease Outbreak

In September of 2010, Brewer''s Bay reef, located in St. Thomas (U.S. Virgin Islands), was simultaneously affected by abnormally high temperatures and the passage of a hurricane that resulted in the mass bleaching and fragmentation of its coral community. An outbreak of a rapid tissue loss disease among coral colonies was associated with these two disturbances. Gross lesion signs and lesion progression rates indicated that the disease was most similar to the Caribbean coral disease white plague type 1. Experiments indicated that the disease was transmissible through direct contact between colonies, and five-meter radial transects showed a clustered spatial distribution of disease, with diseased colonies being concentrated within the first meter of other diseased colonies. Disease prevalence and the extent to which colonies were bleached were both significantly higher on unattached colony fragments than on attached colonies, and disease occurred primarily on fragments found in direct contact with sediment. In contrast to other recent studies, disease presence was not related to the extent of bleaching on colonies. The results of this study suggest that colony fragmentation and contact with sediment played primary roles in the initial appearance of disease, but that the disease was capable of spreading among colonies, which suggests secondary transmission is possible through some other, unidentified mechanism.     

Impact of the 2005 coral bleaching event on <Emphasis Type="Italic">Porites porites</Emphasis> and <Emphasis Type="Italic">Colpophyllia natans</Emphasis> at Tektite Reef,US Virgin Islands

A thermal stress anomaly in 2005 caused mass coral bleaching at a number of north-east Caribbean reefs. The impact of the thermal stress event and subsequent White-plague disease type II on Porites porites and Colpophyllia natans was monitored using a time series of photographs from Tektite Reef, Virgin Islands National Park, St. John. Over 92% of the P. porites and 96% of the C. natans experienced extensive bleaching (>30% of colony bleached). During the study, 56% of P. porites and 42% of C. natans experienced whole-colony mortality within the sample plots. While all whole-colony mortality of P. porites was directly attributed to coral bleaching, the majority (82%) of the C. natans colonies that experienced total mortality initially showed signs of recovery from bleaching, before subsequently dying from White-plague disease type II.     

Competitive interactions between corals and Trididemnum solidum on Mexican Caribbean reefs

The ascidian Trididemnum solidum competes for space on Caribbean reefs and is capable of overgrowing live scleractinian corals. From 2006 to 2009, we monitored over 30,000 coral colonies and quantified competitive interactions with this ascidian at four reef sites along the Mexican Caribbean. The total number of competitive interactions increased in time, but the mean percentage of coral colonies involved in interactions remained lower than 1% in all reefs. Bottom cover by T. solidum was also low (mean < 0.5%) in all reef sites in all sampling years. We conclude that during the temporal scope of our study, the overall potential effect of T. solidum on the dynamics of Mexican Caribbean coral populations was minimal.     

Caribbean corals exhibit species-specific differences in competitive abilities with an aggressive encrusting alga,Ramicrusta textilis

Caribbean coral cover has decreased substantially in recent decades, with much of the live coral being replaced by macroalgae. Encrusting red algae in the genus Ramicrusta have become abundant throughout the region and have demonstrated widespread harm to corals by overgrowing living tissue, causing colony mortality, and impairing coral recruitment. In this research, Ramicrusta textilis was identified by morpho-anatomy and DNA sequencing from nine sites around St. Thomas, US Virgin Islands, and 3D photogrammetry was used to measure the rate of algal growth on stony corals. 3D models of individual coral colonies (five species plus controls, N = 72) competing with R. textilis revealed differential competitive abilities among taxa, with Siderastrea siderea being the only species capable of inhibiting overgrowth by the alga (mean linear algal growth − 1.1 mm yr⁻¹). Important reef building coral species such as Orbicella annularis and Orbicella faveolata were poor competitors (mean linear algal growth + 15 mm yr⁻¹ and + 7.7 mm yr⁻¹, respectively), indicating that the emergence of the alga could have significant impacts on Caribbean coral reef species diversity, community composition, and structural complexity.

     

Decadal-scale changes in abundance of non-scleractinian invertebrates on a Caribbean coral reef

The benthic community structure of the shallow reefs of St. John, US Virgin Islands, was studied from 1992 to 2007 to test the hypotheses that the abundances of non-scleractinian invertebrates have changed, and further, that the changes are associated with variation in the percentage cover of scleractinian coral and macroalgae. The study utilized photoquadrats (0.25 m²) from fringing reefs (7-9 m depth) characterized by igneous boulders and low (< 5%) coral cover, and results from six sites were pooled to describe these reefs as a single habitat. Photoquadrats were analyzed biennially for the abundance of invertebrates, particularly those belonging to four well represented classes (Anthozoa, Demospongiae, Echinoidea, and Polychaeta), as well as the cover of scleractinians and macroalgae. Overall, the combined (multivariate) abundance of 30 invertebrate taxa changed over time, the combined (multivariate) abundance of the four invertebrate classes changed over time, and the individual (univariate) abundance of anthozoans, sponges, and echinoids changed over time. Throughout the study, coral cover remained < 5%, and while it varied significantly, it did not display a consistent trajectory of change; in contrast, the cover of macroalgae increased throughout the study. While it is unsurprising that the abundances of invertebrates changed over 15 y, notably they varied even though coral cover remained stable, in only a few cases were they related positively to macroalgal cover, and in most cases it was members of the suspension feeding guild that became more abundant. These outcomes suggest that: (1) benthic invertebrates on the shallow reefs of St. John may be more strongly influenced by regional (e.g., larva supply) than local (e.g., coral cover) conditions, (2) Caribbean reefs have changed more since the early 1990s than can be inferred from variation in cover of coral and macroalgae, and (3) suspension feeding invertebrates have become more common on shallow fringing reefs in at least one location.     

Chronic nutrient enrichment increases prevalence and severity of coral disease and bleaching

Nutrient loading is one of the strongest drivers of marine habitat degradation. Yet, the link between nutrients and disease epizootics in marine organisms is often tenuous and supported only by correlative data. Here, we present experimental evidence that chronic nutrient exposure leads to increases in both disease prevalence and severity and coral bleaching in scleractinian corals, the major habitat‐forming organisms in tropical reefs. Over 3 years, from June 2009 to June 2012, we continuously exposed areas of a coral reef to elevated levels of nitrogen and phosphorus. At the termination of the enrichment, we surveyed over 1200 scleractinian corals for signs of disease or bleaching. Siderastrea siderea corals within enrichment plots had a twofold increase in both the prevalence and severity of disease compared with corals in unenriched control plots. In addition, elevated nutrient loading increased coral bleaching; Agaricia spp. of corals exposed to nutrients suffered a 3.5‐fold increase in bleaching frequency relative to control corals, providing empirical support for a hypothesized link between nutrient loading and bleaching‐induced coral declines. However, 1 year later, after nutrient enrichment had been terminated for 10 months, there were no differences in coral disease or coral bleaching prevalence between the previously enriched and control treatments. Given that our experimental enrichments were well within the ranges of ambient nutrient concentrations found on many degraded reefs worldwide, these data provide strong empirical support to the idea that coastal nutrient loading is one of the major factors contributing to the increasing levels of both coral disease and coral bleaching. Yet, these data also suggest that simple improvements to water quality may be an effective way to mitigate some coral disease epizootics and the corresponding loss of coral cover in the future.     

Bleaching,disease and recovery in the threatened scleractinian coral Acropora palmata in St. John,US Virgin Islands: 2003–2010

Coral Reefs - A long-term study of the scleractinian coral Acropora palmata in the US Virgin Islands (USVI) showed that diseases, particularly white pox, are limiting the recovery of this...     

<Emphasis Type="Italic">Symbiodinium</Emphasis> associations with diseased and healthy scleractinian corals

Despite recent advances in identifying the causative agents of disease in corals and understanding the impact of epizootics on reef communities, little is known regarding the interactions among diseases, corals, and their dinoflagellate endosymbionts (Symbiodinium spp.). Since the genotypes of both corals and their resident Symbiodinium contribute to colony-level phenotypes, such as thermotolerance, symbiont genotypes might also contribute to the resistance or susceptibility of coral colonies to disease. To explore this, Symbiodinium were identified using the internal transcribed spacer-2 region of ribosomal DNA from diseased and healthy tissues within individual coral colonies infected with black band disease (BB), dark spot syndrome (DSS), white plague disease (WP), or yellow blotch disease (YB) in the Florida Keys (USA) and the US Virgin Islands. Most of the diseased colonies sampled contained B1, B5a, or C1 (depending on host species), while apparently healthy colonies of the same coral species frequently hosted these types and/or additional symbiont diversity. No potentially “parasitic” Symbiodinium types, uniquely associated with diseased coral tissue, were detected. Within most individual colonies, the same dominant Symbiodinium type was detected in diseased and visually healthy tissues. These data indicate that specific Symbiodinium types are not correlated with the infected tissues of diseased colonies and that DSS and WP onset do not trigger symbiont shuffling within infected tissues. However, few diseased colonies contained clade D symbionts suggesting a negative correlation between hosting Symbiodinium clade D and disease incidence in scleractinian corals. Understanding the influence of Symbiodinium diversity on colony phenotypes may play a critical role in predicting disease resistance and susceptibility in scleractinian corals.     

Depth-Independent Reproduction in the Reef Coral Porites astreoides from Shallow to Mesophotic Zones

Mesophotic coral ecosystems between 30–150 m may be important refugia habitat for coral reefs and associated benthic communities from climate change and coastal development. However, reduced light at mesophotic depths may present an energetic challenge to the successful reproduction of light-dependent coral organisms, and limit this refugia potential. Here, the relationship of depth and fecundity was investigated in a brooding depth-generalist scleractinian coral, Porites astreoides from 5–37 m in the U.S. Virgin Islands (USVI) using paraffin tissue histology. Despite a trend of increasing planulae production with depth, no significant differences were found in mean peak planulae density between shallow, mid-depth and mesophotic sites. Differential planulae production over depth is thus controlled by P. astreoides coral cover, which peaks at 10 m and ~35 m in the USVI. These results suggest that mesophotic ecosystems are reproductive refuge for P. astreoides in the USVI, and may behave as refugia for P. astreoides metapopulations providing that vertical larval exchanges are viable.     

Ecological Physiology of a Coral Pathogen and the Coral Reef Environment

Laboratory studies on the ecological physiology of a coral pathogen were carried out to investigate growth potential in terms of environmental factors that may control coral diseases on reefs. The disease chosen for this study, white plague type II, is considered to be one of the major diseases of Caribbean scleractinian corals, affecting a wide range of coral hosts and causing rapid and widespread tissue loss. It is caused by a single pathogen, the bacterium Aurantimonas coralicida. A series of laboratory experiments using a pure culture of the pathogen was carried out to examine the roles of temperature, pH, and O₂ concentration on growth rate. Results revealed optimal growth between 30 and 35°C, and between pH values of 6 and 8. There was a distinctive synergistic relationship between pH and temperature. Increasing temperature from 25 to 35°C expanded the range of pH tolerance from a minimum of 6.0 down to 5.0. O₂ concentration directly affected growth rate, which increased with increasing O₂. The combined effects of increasing O₂ and increasing temperature resulted in a synergistic effect of more rapid growth. These laboratory results are discussed in terms of the coral host and the range of the environmental factors that occur on coral reefs. We conclude that changing environmental conditions in the reef environment, in particular observed increases in water temperature, may be promoting coral diseases by allowing coral pathogens to expand their ecological niches. In the case of the white plague type II pathogen, elevated temperature would allow A. coralicida to colonize the low pH environment of the coral surface mucopolysaccharide layer as an initial stage of infection. The synergistic effect between temperature and oxygen concentration appeared to be less environmentally relevant for this coral pathogen.     

Suppressed recovery of functionally important branching Acropora drives coral community composition changes following mass bleaching in Indonesia

Mass coral bleaching events may have disproportionate effects on branching corals, leading to coral community restructuring, reduced biodiversity, and decreased structural complexity. This affects overall reef health and resilience. Functionally important, fast-growing branching Acropora corals were a historically dominant and vital component of Indonesian reefs throughout the twentieth century, yet the genus is also one of the most vulnerable to external stressors. This study used long-term annual reef monitoring data from Indonesia’s Wakatobi Marine National Park (WMNP) to investigate the effects of a mass bleaching event in 2010 on Acropora and other branching corals, evaluate their post-disturbance recovery trajectories, and analyse shifts in coral community composition. Post-bleaching scleractinian coral cover decreased across study sites, with losses in branching corals especially evident. Long-term branching Acropora cover decreased significantly and failed to demonstrate the significant post-disturbance recovery of other branching corals (especially Porites). In areas characterised by relatively high branching Acropora cover (> 15% mean cover) prior to bleaching, long-term coral community composition changes have trended predominately towards branching and massive Porites and branching Montipora. The novelty and key contribution of this study is that results suggest suppressed recovery of Acropora in the WMNP. Contributing factors may include the Allee effect (inhibition of reproduction at low population densities), other forms of inhibited larval recruitment, direct and indirect spatial competition, and changes in the physical reef habitat. These findings have critical implications for this functionally important taxon, future reef conservation efforts, and overall reef health and resilience in the park.

     

Regional‐scale dominance of non‐framework building corals on Caribbean reefs affects carbonate production and future reef growth

Coral cover on Caribbean reefs has declined rapidly since the early 1980's. Diseases have been a major driver, decimating communities of framework building Acropora and Orbicella coral species, and reportedly leading to the emergence of novel coral assemblages often dominated by domed and plating species of the genera Agaricia, Porites and Siderastrea. These corals were not historically important Caribbean framework builders, and typically have much smaller stature and lower calcification rates, fuelling concerns over reef carbonate production and growth potential. Using data from 75 reefs from across the Caribbean we quantify: (i) the magnitude of non‐framework building coral dominance throughout the region and (ii) the contribution of these corals to contemporary carbonate production. Our data show that live coral cover averages 18.2% across our sites and coral carbonate production 4.1 kg CaCO₃ m^?2 yr^?1. However, non‐framework building coral species dominate and are major carbonate producers at a high proportion of sites; they are more abundant than Acropora and Orbicella at 73% of sites; contribute an average 68% of the carbonate produced; and produce more than half the carbonate at 79% of sites. Coral cover and carbonate production rate are strongly correlated but, as relative abundance of non‐framework building corals increases, average carbonate production rates decline. Consequently, the use of coral cover as a predictor of carbonate budget status, without species level production rate data, needs to be treated with caution. Our findings provide compelling evidence for the Caribbean‐wide dominance of non‐framework building coral taxa, and that these species are now major regional carbonate producers. However, because these species typically have lower calcification rates, continued transitions to states dominated by non‐framework building coral species will further reduce carbonate production rates below ‘predecline’ levels, resulting in shifts towards negative carbonate budget states and reducing reef growth potential.     

Effects of frequent fish predation on corals in Hawaii

The abundance of lesions from fish bites on corals was quantified at nine shallow reefs in the main Hawaiian Islands. There were on average 117 bite scars m⁻² on Pocillopora meandrina tissue from the barred filefish Cantherhines dumerilii, 69 bites m⁻² on Porites compressa tissue, and 4 bites m⁻² on Porites lobata tissue from the spotted puffer Arothron meleagris. Across sites, the frequency of A. meleagris bites on P. compressa per unit area of living coral cover declined exponentially with increasing coral cover. P. compressa nubbins in two size classes (1–2 cm and 4–5 cm) were transplanted onto six study reefs. Nubbins in the small size class were entirely removed by bites from A. meleagris, while nubbins ≥4 cm were only partially consumed, leaving them able to recover. At sites with abundant P. compressa, predation had little effect on transplanted nubbins; at sites where P. compressa comprised less than 5% of living cover, all nubbins were preyed upon. A. meleagris bite lesions on P. compressa were monitored through time and fully recovered in 42 ± 4 days. A model of the risk of over-predation (a second predation event before the first is healed) decreased exponentially with increasing coral cover and increased linearly with increasing lesion healing time. The increased risk of over-predation at low coral cover could indicate an Allee effect limiting the recovery of coral populations if coral cover is substantially reduced by natural or anthropogenic disturbances.     

Algal turf negatively affects recruitment of a Caribbean octocoral

Coral Reefs - Algal cover has increased and scleractinian coral cover has steadily declined over the past 40&nbsp;years on Caribbean coral reefs, while octocoral abundance has increased at...     

Coral population dynamics across consecutive mass mortality events

Annual coral mortality events due to increased atmospheric heat may occur regularly from the middle of the century and are considered apocalyptic for coral reefs. In the Arabian/Persian Gulf, this situation has already occurred and population dynamics of four widespread corals (Acropora downingi, Porites harrisoni, Dipsastrea pallida, Cyphastrea micropthalma) were examined across the first‐ever occurrence of four back‐to‐back mass mortality events (2009–2012). Mortality was driven by diseases in 2009, bleaching and subsequent diseases in 2010/2011/2012. 2009 reduced P. harrisoni cover and size, the other events increasingly reduced overall cover (2009: ?10%; 2010: ?20%; 2011: ?20%; 2012: ?15%) and affected all examined species. Regeneration was only observed after the first disturbance. P. harrisoni and A. downingi severely declined from 2010 due to bleaching and subsequent white syndromes, while D. pallida and P. daedalea declined from 2011 due to bleaching and black‐band disease. C. microphthalma cover was not affected. In all species, most large corals were lost while fission due to partial tissue mortality bolstered small size classes. This general shrinkage led to a decrease of coral cover and a dramatic reduction of fecundity. Transition matrices for disturbed and undisturbed conditions were evaluated as Life Table Response Experiment and showed that C. microphthalma changed the least in size‐class dynamics and fecundity, suggesting they were ‘winners’. In an ordered ‘degradation cascade’, impacts decreased from the most common to the least common species, leading to step‐wise removal of previously dominant species. A potentially permanent shift from high‐ to low‐coral cover with different coral community and size structure can be expected due to the demographic dynamics resultant from the disturbances. Similarities to degradation of other Caribbean and Pacific reefs are discussed. As comparable environmental conditions and mortality patterns must be expected worldwide, demographic collapse of many other coral populations may soon be widespread.     

Rapid phase-shift reversal on a Jamaican coral reef

Many Caribbean reefs have experienced a phase-shift in community structure, the principle features being a decline in coral cover and an increase in macroalgal biomass. However, one Jamaican reef—Dairy Bull on the north shore near Discovery Bay—is once again dominated by scleractinian corals and several key species have returned. Living coral cover at 6–8 m depth at Dairy Bull has doubled over the past 9 years and is now ~54%. The absolute cover of Acropora cervicornis was <1% in 1995, but increased to ~11% by January 2004. During this time the cover of macroalgae decreased by 90%, from 45 to 6%. We speculate that long-lived colonies of Montastraea annularis may have facilitated the recovery of this reef by providing structural refugia.     

Coral reef crisis in deep and shallow reefs: 30 years of constancy and change in reefs of Curacao and Bonaire

Coral reefs are thought to be in worldwide decline but available data are practically limited to reefs shallower than 25 m. Zooxanthellate coral communities in deep reefs (30–40 m) are relatively unstudied. Our question is: what is happening in deep reefs in terms of coral cover and coral mortality? We compare changes in species composition, coral mortality, and coral cover at Caribbean (Curacao and Bonaire) deep (30–40 m) and shallow reefs (10–20 m) using long-term (1973–2002) data from permanent photo quadrats. About 20 zooxanthellate coral species are common in the deep-reef communities, dominated by Agaricia sp., with coral cover up to 60%. In contrast with shallow reefs, there is no decrease in coral cover or number of coral colonies in deep reefs over the last 30 years. In deep reefs, non-agaricid species are decreasing but agaricid domination will be interrupted by natural catastrophic mortality such as deep coral bleaching and storms. Temperature is a vastly fluctuating variable in the deep-reef environment with extremely low temperatures possibly related to deep-reef bleaching. An erratum to this article can be found at