Quorum Sensing Signal Production and Microbial Interactions in a Polymicrobial Disease of Corals and the Coral Surface Mucopolysaccharide Layer

Black band disease (BBD) of corals is a complex polymicrobial disease considered to be a threat to coral reef health, as it can lead to mortality of massive reef-building corals. The BBD community is dominated by gliding, filamentous cyanobacteria with a highly diverse population of heterotrophic bacteria. Microbial interactions such as quorum sensing (QS) and antimicrobial production may be involved in BBD disease pathogenesis. In this study, BBD (whole community) samples, as well as 199 bacterial isolates from BBD, the surface mucopolysaccharide layer (SML) of apparently healthy corals, and SML of apparently healthy areas of BBD-infected corals were screened for the production of acyl homoserine lactones (AHLs) and for autoinducer-2 (AI-2) activity using three bacterial reporter strains. AHLs were detected in all BBD (intact community) samples tested and in cultures of 5.5% of BBD bacterial isolates. Over half of a subset (153) of the isolates were positive for AI-2 activity. AHL-producing isolates were further analyzed using LC-MS/MS to determine AHL chemical structure and the concentration of (S)-4,5-dihydroxy-2,3-pentanedione (DPD), the biosynthetic precursor of AI-2. C6-HSL was the most common AHL variant detected, followed by 3OC4-HSL. In addition to QS assays, 342 growth challenges were conducted among a subset of the isolates, with 27% of isolates eliciting growth inhibition and 2% growth stimulation. 24% of BBD isolates elicited growth inhibition as compared to 26% and 32% of the bacteria from the two SML sources. With one exception, only isolates that exhibited AI-2 activity or produced DPD inhibited growth of test strains. These findings demonstrate for the first time that AHLs are present in an active coral disease. It is possible that AI-2 production among BBD and coral SML bacteria may structure the microbial communities of both a polymicrobial infection and the healthy coral microbiome.     

Metagenomic Analysis of Healthy and White Plague-Affected Mussismilia braziliensis Corals

Coral health is under threat throughout the world due to regional and global stressors. White plague disease (WP) is one of the most important threats affecting the major reef builder of the Abrolhos Bank in Brazil, the endemic coral Mussismilia braziliensis. We performed a metagenomic analysis of healthy and WP-affected M. braziliensis in order to determine the types of microbes associated with this coral species. We also optimized a protocol for DNA extraction from coral tissues. Our taxonomic analysis revealed Proteobacteria, Bacteroidetes, Firmicutes, Cyanobacteria, and Actinomycetes as the main groups in all healthy and WP-affected corals. Vibrionales, members of the Cytophaga–Flavobacterium–Bacteroides complex, Rickettsiales, and Neisseriales were more abundant in the WP-affected corals. Diseased corals also had more eukaryotic metagenomic sequences identified as Alveolata and Apicomplexa. Our results suggest that WP disease in M. braziliensis is caused by a polymicrobial consortium.     

Cyanobacteria Associated with Coral Black Band Disease in Caribbean and Indo-Pacific Reefs

For 30 years it has been assumed that a single species of cyanobacteria, Phormidium corallyticum, is the volumetrically dominant component of all cases of black band disease (BBD) in coral. Cyanobacterium-specific 16S rRNA gene primers and terminal restriction fragment length polymorphism analyses were used to determine the phylogenetic diversity of these BBD cyanobacteria on coral reefs in the Caribbean and Indo-Pacific Seas. These analyses indicate that the cyanobacteria that inhabit BBD bacterial mats collected from the Caribbean and Indo-Pacific Seas belong to at least three different taxa, despite the fact that the corals in each case exhibit similar signs and patterns of BBD mat development.     

Cyanotoxins from Black Band Disease of Corals and from Other Coral Reef Environments

Many cyanobacteria produce cyanotoxins, which has been well documented from freshwater environments but not investigated to the same extent in marine environments. Cyanobacteria are an obligate component of the polymicrobial disease of corals known as black band disease (BBD). Cyanotoxins were previously shown to be present in field samples of BBD and in a limited number of BBD cyanobacterial cultures. These toxins were suggested as one of the mechanisms contributing to BBD-associated coral tissue lysis and death. In this work, we tested nine cyanobacterial isolates from BBD and additionally nine isolated from non-BBD marine sources for their ability to produce toxins. The presence of toxins was determined using cell extracts of laboratory grown cyanobacterial cultures using ELISA and the PP2A assay. Based on these tests, it was shown that cyanobacterial toxins belonging to the microcystin/nodularin group were produced by cyanobacteria originating from both BBD and non-BBD sources. Several environmental factors that can be encountered in the highly dynamic microenvironment of BBD were tested for their effect on both cyanobacterial growth yield and rate of toxin production using two of the BBD isolates of the genera Leptolyngbya and Geitlerinema. While toxin production was the highest under mixotrophic conditions (light and glucose) for the Leptolyngbya isolate, it was highest under photoautotrophic conditions for the Geitlerinema isolate. Our results show that toxin production among marine cyanobacteria is more widespread than previously documented, and we present data showing three marine cyanobacterial genera (Phormidium, Pseudanabaena, and Spirulina) are newly identified as cyanotoxin producers. We also show that cyanotoxin production by BBD cyanobacteria can be affected by environmental factors that are present in the microenvironment associated with this coral disease.     

Bacterial community associated with black band disease in corals

Black band disease (BBD) is a virulent polymicrobial disease primarily affecting massive-framework-building species of scleractinian corals. While it has been well established that the BBD bacterial mat is dominated by a cyanobacterium, the quantitative composition of the BBD bacterial mat community has not described previously. Terminal-restriction fragment length polymorphism (T-RFLP) analysis was used to characterize the infectious bacterial community of the bacterial mat causing BBD. These analyses revealed that the bacterial composition of the BBD mat does not vary between different coral species but does vary when different species of cyanobacteria are dominant within the mat. On the basis of the results of a new method developed to identify organisms detected by T-RFLP analysis, our data show that besides the cyanobacterium, five species of the division Firmicutes, two species of the Cytophaga-Flexibacter-Bacteroides (CFB) group, and one species of delta-proteobacteria are also consistently abundant within the infectious mat. Of these dominant taxa, six were consistently detected in healthy corals. However, four of the six were found in much higher numbers in BBD mats than in healthy corals. One species of the CFB group and one species of Firmicutes were not always associated with the bacterial communities present in healthy corals. Of the eight dominant bacteria identified, two species were previously found in clone libraries obtained from BBD samples; however, these were not previously recognized as important. Furthermore, despite having been described as an important component of the pathogenetic mat, a Beggiatoa species was not detected in any of the samples analyzed. These results will permit the dominant BBD bacteria to be targeted for isolation and culturing experiments aimed at deciphering the disease etiology.     

The cellular stress response of the scleractinian coral <Emphasis Type="Italic">Goniopora columna</Emphasis> during the progression of the black band disease

Black band disease (BBD) is a widespread coral pathology caused by a microbial consortium dominated by cyanobacteria, which is significantly contributing to the loss of coral cover and diversity worldwide. Since the effects of the BBD pathogens on the physiology and cellular stress response of coral polyps appear almost unknown, the expression of some molecular biomarkers, such as Hsp70, Hsp60, HO-1, and MnSOD, was analyzed in the apparently healthy tissues of Goniopora columna located at different distances from the infection and during two disease development stages. All the biomarkers displayed different levels of expression between healthy and diseased colonies. In the healthy corals, low basal levels were found stable over time in different parts of the same colony. On the contrary, in the diseased colonies, a strong up-regulation of all the biomarkers was observed in all the tissues surrounding the infection, which suffered an oxidative stress probably generated by the alternation, at the progression front of the disease, of conditions of oxygen supersaturation and hypoxia/anoxia, and by the production of the cyanotoxin microcystin by the BBD cyanobacteria. Furthermore, in the infected colonies, the expression of all the biomarkers appeared significantly affected by the development stage of the disease. In conclusion, our approach may constitute a useful diagnostic tool, since the cellular stress response of corals is activated before the pathogens colonize the tissues, and expands the current knowledge of the mechanisms controlling the host responses to infection in corals.     

Allelochemicals produced by Caribbean macroalgae and cyanobacteria have species-specific effects on reef coral microorganisms

Coral populations have precipitously declined on Caribbean reefs while algal abundance has increased, leading to enhanced competitive damage to corals, which likely is mediated by the potent allelochemicals produced by both macroalgae and benthic cyanobacteria. Allelochemicals may affect the composition and abundance of coral-associated microorganisms that control host responses and adaptations to environmental change, including susceptibility to bacterial diseases. Here, we demonstrate that extracts of six Caribbean macroalgae and two benthic cyanobacteria have both inhibitory and stimulatory effects on bacterial taxa cultured from the surfaces of Caribbean corals, macroalgae, and corals exposed to macroalgal extracts. The growth of 54 bacterial isolates was monitored in the presence of lipophilic and hydrophilic crude extracts derived from Caribbean macroalgae and cyanobacteria using 96-well plate bioassays. All 54 bacterial cultures were identified by ribotyping. Lipophilic extracts from two species of Dictyota brown algae inhibited >50% of the reef coral bacteria assayed, and hydrophilic compounds from Dictyota menstrualis particularly inhibited Vibrio bacteria, a genus associated with several coral diseases. In contrast, both lipo- and hydrophilic extracts from 2 species of Lyngbya cyanobacteria strongly stimulated bacterial growth. The brown alga Lobophora variegata produced hydrophilic compounds with broad-spectrum antibacterial effects, which inhibited 93% of the bacterial cultures. Furthermore, bacteria cultured from different locations (corals vs. macroalgae vs. coral surfaces exposed to macroalgal extracts) responded differently to algal extracts. These results reveal that extracts from macroalgae and cyanobacteria have species-specific effects on the composition of coral-microbial assemblages, which in turn may increase coral host susceptibility to disease and result in coral mortality.     

Bacterial Community Associated with Black Band Disease in Corals

Black band disease (BBD) is a virulent polymicrobial disease primarily affecting massive-framework-building species of scleractinian corals. While it has been well established that the BBD bacterial mat is dominated by a cyanobacterium, the quantitative composition of the BBD bacterial mat community has not described previously. Terminal-restriction fragment length polymorphism (T-RFLP) analysis was used to characterize the infectious bacterial community of the bacterial mat causing BBD. These analyses revealed that the bacterial composition of the BBD mat does not vary between different coral species but does vary when different species of cyanobacteria are dominant within the mat. On the basis of the results of a new method developed to identify organisms detected by T-RFLP analysis, our data show that besides the cyanobacterium, five species of the division Firmicutes, two species of the Cytophaga-Flexibacter-Bacteroides (CFB) group, and one species of δ-proteobacteria are also consistently abundant within the infectious mat. Of these dominant taxa, six were consistently detected in healthy corals. However, four of the six were found in much higher numbers in BBD mats than in healthy corals. One species of the CFB group and one species of Firmicutes were not always associated with the bacterial communities present in healthy corals. Of the eight dominant bacteria identified, two species were previously found in clone libraries obtained from BBD samples; however, these were not previously recognized as important. Furthermore, despite having been described as an important component of the pathogenetic mat, a Beggiatoa species was not detected in any of the samples analyzed. These results will permit the dominant BBD bacteria to be targeted for isolation and culturing experiments aimed at deciphering the disease etiology.     

Long‐term salinity tolerance is accompanied by major restructuring of the coral bacterial microbiome

Scleractinian corals are assumed to be stenohaline osmoconformers, although they are frequently subjected to variations in seawater salinity due to precipitation, freshwater run‐off and other processes. Observed responses to altered salinity levels include differences in photosynthetic performance, respiration and increased bleaching and mortality of the coral host and its algal symbiont, but a study looking at bacterial community changes is lacking. Here, we exposed the coral Fungia granulosa to strongly increased salinity levels in short‐ and long‐term experiments to disentangle temporal and compartment effects of the coral holobiont (i.e. coral host, symbiotic algae and associated bacteria). Our results show a significant reduction in calcification and photosynthesis, but a stable microbiome after short‐term exposure to high‐salinity levels. By comparison, long‐term exposure yielded unchanged photosynthesis levels and visually healthy coral colonies indicating long‐term acclimation to high‐salinity levels that were accompanied by a major coral microbiome restructuring. Importantly, a bacterium in the family Rhodobacteraceae was succeeded by Pseudomonas veronii as the numerically most abundant taxon. Further, taxonomy‐based functional profiling indicates a shift in the bacterial community towards increased osmolyte production, sulphur oxidation and nitrogen fixation. Our study highlights that bacterial community composition in corals can change within days to weeks under altered environmental conditions, where shifts in the microbiome may enable adjustment of the coral to a more advantageous holobiont composition.     

Cyanobacteria associated with coral black band disease in Caribbean and Indo-Pacific Reefs

For 30 years it has been assumed that a single species of cyanobacteria, Phormidium corallyticum, is the volumetrically dominant component of all cases of black band disease (BBD) in coral. Cyanobacterium-specific 16S rRNA gene primers and terminal restriction fragment length polymorphism analyses were used to determine the phylogenetic diversity of these BBD cyanobacteria on coral reefs in the Caribbean and Indo-Pacific Seas. These analyses indicate that the cyanobacteria that inhabit BBD bacterial mats collected from the Caribbean and Indo-Pacific Seas belong to at least three different taxa, despite the fact that the corals in each case exhibit similar signs and patterns of BBD mat development.     

Diversity and stability of coral endolithic microbial communities at a naturally high pCO2 reef

The health and functioning of reef‐building corals is dependent on a balanced association with prokaryotic and eukaryotic microbes. The coral skeleton harbours numerous endolithic microbes, but their diversity, ecological roles and responses to environmental stress, including ocean acidification (OA), are not well characterized. This study tests whether pH affects the diversity and structure of prokaryotic and eukaryotic algal communities associated with skeletons of Porites spp. using targeted amplicon (16S rRNA gene, UPA and tufA) sequencing. We found that the composition of endolithic communities in the massive coral Porites spp. inhabiting a naturally high pCO₂ reef (avg. pCO₂ 811 μatm) is not significantly different from corals inhabiting reference sites (avg. pCO₂ 357 μatm), suggesting that these microbiomes are less disturbed by OA than previously thought. Possible explanations may be that the endolithic microhabitat is highly homeostatic or that the endolithic micro‐organisms are well adapted to a wide pH range. Some of the microbial taxa identified include nitrogen‐fixing bacteria (Rhizobiales and cyanobacteria), algicidal bacteria in the phylum Bacteroidetes, symbiotic bacteria in the family Endozoicomoniaceae, and endolithic green algae, considered the major microbial agent of reef bioerosion. Additionally, we test whether host species has an effect on the endolithic community structure. We show that the endolithic community of massive Porites spp. is substantially different and more diverse than that found in skeletons of the branching species Seriatopora hystrix and Pocillopora damicornis. This study reveals highly diverse and structured microbial communities in Porites spp. skeletons that are possibly resilient to OA.     

Microbial Communities in the Surface Mucopolysaccharide Layer and the Black Band Microbial Mat of Black Band-Diseased Siderastrea siderea

Microbial community profiles and species composition associated with two black band-diseased colonies of the coral Siderastrea siderea were studied by 16S rRNA-targeted gene cloning, sequencing, and amplicon-length heterogeneity PCR (LH-PCR). Bacterial communities associated with the surface mucopolysaccharide layer (SML) of apparently healthy tissues of the infected colonies, together with samples of the black band disease (BBD) infections, were analyzed using the same techniques for comparison. Gene sequences, ranging from 424 to 1,537 bp, were retrieved from all positive clones (n = 43 to 48) in each of the four clone libraries generated and used for comparative sequence analysis. In addition to LH-PCR community profiling, all of the clone sequences were aligned with LH-PCR primer sequences, and the theoretical lengths of the amplicons were determined. Results revealed that the community profiles were significantly different between BBD and SML samples. The SML samples were dominated by γ-proteobacteria (53 to 64%), followed by β-proteobacteria (18 to 21%) and α-proteobacteria (5 to 11%). In contrast, both BBD clone libraries were dominated by α-proteobacteria (58 to 87%), followed by verrucomicrobia (2 to 10%) and 0 to 6% each of δ-proteobacteria, bacteroidetes, firmicutes, and cyanobacteria. Alphaproteobacterial sequence types related to the bacteria associated with toxin-producing dinoflagellates were observed in BBD clone libraries but were not found in the SML libraries. Similarly, sequences affiliated with the family Desulfobacteraceae and toxin-producing cyanobacteria, both believed to be involved in BBD pathogenesis, were found only in BBD libraries. These data provide evidence for an association of numerous toxin-producing heterotrophic microorganisms with BBD of corals.     

Adaptation of cyanobacteria to the sulfide-rich microenvironment of black band disease of coral

Black band disease (BBD) is a cyanobacteria-dominated microbial mat that migrates across living coral colonies lysing coral tissue and leaving behind exposed coral skeleton. The mat is sulfide-rich due to the presence of sulfate-reducing bacteria, integral members of the BBD microbial community, and the sulfide they produce is lethal to corals. The effect of sulfide, normally toxic to cyanobacteria, on the photosynthetic capabilities of five BBD cyanobacterial isolates of the genera Geitlerinema (3), Leptolyngbya (1), and Oscillatoria (1) and six non-BBD cyanobacteria of the genera Leptolyngbya (3), Pseudanabaena (2), and Phormidium (1) was examined. Photosynthetic experiments were performed by measuring the photoincorporation of [¹⁴C] NaHCO₃ under the following conditions: (1) aerobic (no sulfide), (2) anaerobic with 0.5 mM sulfide, and (3) anaerobic with 0.5 mM sulfide and 10 μM 3-(3',4'-dichlorophenyl)-1,1-dimethylurea (DCMU). All five BBD cyanobacterial isolates tolerated sulfide by conducting sulfide-resistant oxygenic photosynthesis. Five of the non-BBD cyanobacterial isolates did not tolerate sulfide, although one Pseudanabaena isolate continued to photosynthesize in the presence of sulfide at a considerably reduced rate. None of the isolates conducted anoxygenic photosynthesis with sulfide as an electron donor. This is the first report on the physiology of a culture of Oscillatoria sp. found globally in BBD.     

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.     

Onset and establishment of diazotrophs and other bacterial associates in the early life history stages of the coral Acropora millepora

Early establishment of coral–microbial symbioses is fundamental to the fitness of corals, but comparatively little is known about the onset and succession of bacterial communities in their early life history stages. In this study, bacterial associates of the coral Acropora millepora were characterized throughout the first year of life, from larvae and 1‐week‐old juveniles reared in laboratory conditions in the absence of the dinoflagellate endosymbiont Symbiodinium to field‐outplanted juveniles with established Symbiodinium symbioses, and sampled at 2 weeks and at 3, 6 and 12 months. Using an amplicon pyrosequencing approach, the diversity of both nitrogen‐fixing bacteria and of bacterial communities overall was assessed through analysis of nifH and 16S rRNA genes, respectively. The consistent presence of sequences affiliated with diazotrophs of the order Rhizobiales (23–58% of retrieved nifH sequences; 2–12% of 16S rRNA sequences), across all samples from larvae to 12‐month‐old coral juveniles, highlights the likely functional importance of this nitrogen‐fixing order to the coral holobiont. Dominance of Roseobacter‐affiliated sequences (>55% of retrieved 16S rRNA sequences) in larvae and 1‐week‐old juveniles, and the consistent presence of sequences related to Oceanospirillales and Altermonadales throughout all early life history stages, signifies their potential importance as coral associates. Increased diversity of bacterial communities once juveniles were transferred to the field, particularly of Cyanobacteria and Deltaproteobacteria, demonstrates horizontal (environmental) uptake of coral‐associated bacterial communities. Although overall bacterial communities were dynamic, bacteria with likely important functional roles remain stable throughout early life stages of Acropora millepora.     

Black-band disease dynamics: Prevalence, incidence, and acclimatization to light

Black-band disease (BBD) is a temperature- and light-dependent syndrome typically found on shallow-dwelling corals. The bacterial consortium that creates BBD contains a photosynthetic cyanobacterium, which is particularly sensitive to light. High light causes the BBD cyanobacteria to self-shade, which encourages the formation of the anoxic microenvironment essential for the BBD consortium. From May to September 2009, a shallow-reef area was monitored to quantify the epizootiology of BBD on the brain coral Diploria strigosa. The prevalence and incidence of BBD were recorded approximately every two weeks. To test the hypothesis that reduced light would increase the rate of disease progression by reducing photoinhibition in the BBD cyanobacteria, shade structures, made out of plastic sheeting on a polyvinyl chloride (PVC) frame, were installed above D. strigosa colonies with BBD. The shade material reduced photosynthetically available radiation (PAR) by > 80%. The progression of BBD on shaded colonies was compared with cage control and control colonies. A pulse-amplitude-modulation fluorometer was used to measure the amount of PAR and maximum excitation pressure (Q_m) on each colony after two weeks of treatment. Linear progression rates and the band width of BBD were measured weekly and treatments were compared through time. During the summer months, the prevalence of BBD showed a positive, exponential relationship with water temperature, whereas the incidence of BBD displayed a positive linear relationship with the rate of change of water temperature. PAR on, and the Q_m of, shaded corals was significantly lower than the two control treatments; however, Q_m values did not indicate excessive photochemical pressure on the coral host. The progression rates of BBD and the black-band width on shaded colonies significantly increased after one week of shading, whereas the control treatments did not change. During the second week of manipulation, however, black-band width and progression rates were similar to values prior to manipulation. These results suggest that, even under low-light conditions, a compact and dense ‘black’ band is essential for the persistence of the BBD consortium.     

Fine structure analysis of black band disease (BBD) infected coral and coral exposed to the BBD toxins microcystin and sulfide

Black band disease (BBD) of corals is a complex pathogenic polymicrobial mat community that lyses coral tissue as it migrates over an infected colony. Two known toxins are produced by BBD microorganisms - sulfide, produced by sulfate-reducing bacteria, and microcystin, produced by cyanobacteria. Experiments were carried out to determine the effects of exposing healthy coral fragments to variable concentrations of purified microcystin, sulfide at a concentration known to exist in BBD, and a combination of the two. Healthy fragments of the coral Montastraea annularis were placed into experimental chambers with known toxin/s for 18-22.5 h. Fine structural analysis using scanning electron microscopy (SEM) showed that toxin exposure resulted in thinning or removal of the coral epidermal layer coupled with degradation of the gastrodermis. These effects were exacerbated when both toxins were used in combination. Exposure to sulfide and the highest concentration of microcystin caused zooxanthellae to dissociate from the coral tissue and to form clusters on the coral surface. Examination of coral fragments infected with BBD was carried out for comparison. It was determined that the effects of exposure to sulfide and microcystin on coral fine structure were consistent, both quantitatively and qualitatively, with the effects of artificially induced and naturally occurring BBD on M. annularis.     

Recruitment of scleractinians onto the skeletons of corals killed by black band disease

To determine what happens to scleractinian corals that have been killed by black band disease (BBD), massive corals with BBD were monitored for 11 years on a shallow reef (<10 m depth) in St. John, US Virgin Islands. Small quadrats (0.039 m²) were used to compare the rates of scleractinian recruitment to the skeletons of corals killed by either BBD or physical disturbance (Hurricane Hugo 1989). Coral recruitment was also quantified on the adjacent fringing reef using larger quadrats (0.25 m²) to detect possible biases associated with using small, permanent quadrats to assess recruitment to BBD-killed corals. Of 28 tagged colonies with BBD in 1988, 43% were lost to Hurricane Hugo in 1989, 7% were lost to unknown causes between 1991 and 1992, and 14 were monitored annually for 11 years; of these, 71% were dead and still in their original growth position in 1998. Between 1988 and 1997, corals recruited to the BBD-killed surfaces at a rate of 1.1 ± 0.3 recruits · 0.039 m⁻² · decade⁻¹ (mean ± SE, n = 14), although mortality reduced the density to 0.3 ± 0.2 recruits · 0.039 m⁻² by 1997. The rate of recruitment and the taxonomic composition of the coral recruits to BBD-killed corals were indistinguishable statistically from those to corals killed by Hurricane Hugo. This demonstrates that BBD creates space that is functionally the same as other dead coral surfaces in providing a substratum for coral recruitment. However, because coral recruits are dispersed widely, clumped in distribution and temporally variable in density on the fringing reef as a whole, it is unlikely that they will be found on monitored coral colonies that have been killed by BBD. While this hypothesis is consistent with the higher density of recruits on the fringing reef compared with BBD-killed corals, further studies are required to investigate alternative explanations such as the role of substratum age in favoring recruitment to surfaces other than those killed recently by BBD. Accepted: 26 August 1999     

Overgrowth and killing of corals by the brown alga Lobophora hederacea (Dictyotales,Phaeophyceae) on healthy reefs in New Caledonia: A new case of the epizoism syndrome

Coral reef degradation is often associated with regime shifts from coral‐ to macroalgal‐dominated reefs. These shifts demonstrate that under certain conditions (e.g. coral mortality, decrease in herbivory, increased nutrients supply) some macroalgae may overgrow corals. The outcome of the competition is dependent on algal aggressiveness and the coral susceptibility. In undisturbed reefs, herbivore grazing is regulating macroalgal cover, thus preventing the latter from overgrowing corals. However, some macroalgae have evolved strategies not only to outcompete corals but also to escape herbivory to some extent, allowing overgrowth of some coral species in undisturbed reefs. Epizoism represents one of those successful strategies, and has been previously documented with red algae, cyanobacteria and Lobophora variegata (Dictyotales, Phaeophyceae). Here we report a new case of epizoism leading to coral mortality, involving a recently described species of Lobophora, L. hederacea, overgrowing the coral Seriatopora caliendrum (Pocilloporidae) in undisturbed reefs in New Caledonia.