Contrasting Lesion Dynamics of White Syndrome among the scleractinian corals Porites spp

White syndrome (WS) is currently the most prevalent disease of scleractinian corals in the Indo-Pacific region, with an ability to exist in both epizootic and enzootic states. Here, we present results of an examination of WS lesion dynamics and show that potentially associated traits of host morphology (i.e., branching vs. massive), lesion size, and tissue deposition rate influence disease severity and recovery. Lesion healing rate was positively correlated with initial lesion size in both morphologies, but the rate at which lesions healed differed between morphologies. New lesions in branching Porites cylindrica appeared less frequently, were smaller and healed more quickly, but were more abundant than in closely-related massive Porites sp(p). The positive association between lesion size and healing rate was partly explained by geometry; branching limited lesion maximum size, and larger lesion margins contained more polyps producing new tissue, resulting in faster healing. However, massive colonies deposited tissue more slowly than branching colonies, resulting in slower recovery and more persistent lesions. Corallite size and density did not differ between species and did not, therefore, influence healing rate. We demonstrated multiple modes of pathogen transmission, which may be influenced by the greater potential for pathogen entrainment in branching vs. massive morphologies. We suggest that attributes such as colony morphology and species-specific growth rates require consideration as we expand our understanding of disease dynamics in colonial organisms such as coral.     

Transmission of growth anomalies between Indo-Pacific Porites corals

In this study we provide experimental evidence of transmission of growth anomalies (GAs) between corals. Twenty-four aquaria (16 experimental, 8 containing only apparently healthy corals) were set-up on Negros Island, Philippines, to test for direct-contact and waterborne transmission of GAs. Within seven weeks, two of 16 apparently healthy colonies placed in direct contact with colonies having GAs developed multiple GA lesions whose size and number increased over time. One of 16 apparently healthy colonies in experimental aquaria not touching any diseased colony also developed a GA, exhibiting a single lesion that did not increase in size. Apparently healthy colonies (n=24) in aquaria without a diseased colony remained unchanged.     

Patterns of chemical defense among Caribbean gorgonian corals: a preliminary survey

Ship-board assays employing the common Caribbean wrasse Thalassoma bifasdatum (Bloch) were undertaken to determine the palatability of food pellets coated with freshly-extracted, lipid-soluble metabolites of 37 types of Caribbean gorgonian corals representing at least 19 species from 11 genera. Extracts of 19 types (51%) were highly unpalatable (zero or one of five pellets eaten), four types (11%) were moderately unpalatable (two or three of five pellets eaten) and 14 (38%) were palatable (four or five of five pellets eaten) to fish in feeding assays. Gorgonians of the genera Pterogorgia (three types) and Eunicea (nine types) were consistently highly unpalatable, those of the genus Plexaurella (four types) were palatable and those of the genus Plexaura were most frequently palatable (six of eight types). Further assays of serial dilutions of extracts from seven representative, unpalatable types revealed that extracts inhibited fish feeding at pellet concentrations near or below the concentrations that metabolites occur in the gorgonian soft tissue. Extracts of Erythropodium caribaeorum (Duchassaing and Michelotti) and Pseudopterogorgia rigida (Bielschowsky) deterred fish feeding at pellet concentrations less than an order of magnitude lower than those found in the soft tissues of the corresponding gorgonians. Thin layer chromatographic analyses of extracts revealed the presence of lipid-soluble, secondary metabolites in a majority of the highly unpalatable extracts, although secondary metabolites were also present in a smaller percentage of palatable extracts. These data support the hypothesis that the soft tissues of many gorgonian corals contain lipid-soluble feeding deterrents which act as a defense against predation.     

Reproductive ecology of Caribbean reef corals

The last decade has seen a resurgence of interest in the processes of sexual reproduction by scleractinian reef corals. Earlier investigations had focused fortuitously on brooding (planulating) species, which resulted in the general misconception that brooding was the main form of larval development of reef corals. More recent work on Indo-Pacific species has shown broadcast spawning and short annual reproductive periods to predominate. This report presents the reproductive patterns of eleven Caribbean coral species and attempts to explain the adaptive features and selective pressures that have led to the evolution of the four reproductive patterns described to date: (a) hermaphroditic broadcasters; (b) gonochoric broadcasters; (c) hermaphroditic broadcasters; (b) gonochoric brooders. Both (a) and (b) correlate with large colony size and short annual spawning periods; and (c) and (d) correlate with small colony size, multiple planulating cycles per year, and occupation of unstable habitats. Selection for outcrossing between long-lived individuals is proposed as the reason for gonochorism and for synchronous spawning of hermaphroditic broadcasters, and also for the large amount of sperm produced by hermaphroditic brooders. Selection for high rates of local recruitment is proposed as the force behind the evolution of brooding by species inhabiting unstable habitats and suffering high rates of adult mortality.     

Skeletal records of community-level bleaching in Porites corals from Palau

Tropical Pacific sea surface temperature is projected to rise an additional 2–3 °C by the end of this century, driving an increase in the frequency and intensity of coral bleaching. With significant global coral reef cover already lost due to bleaching-induced mortality, efforts are underway to identify thermally tolerant coral communities that might survive projected warming. Massive, long-lived corals accrete skeletal bands of anomalously high density in response to episodes of thermal stress. These “stress bands” are potentially valuable proxies for thermal tolerance, but to date their application to questions of community bleaching history has been limited. Ecological surveys recorded bleaching of coral communities across the Palau archipelago during the 1998 and 2010 warm events. Between 2011 and 2015, we extracted skeletal cores from living Porites colonies at 10 sites spanning barrier reef and lagoon environments and quantified the proportion of stress bands present in each population during bleaching years. Across Palau, the prevalence of stress bands tracked the severity of thermal stress, with more stress bands occurring in 1998 (degree heating weeks = 13.57 °C-week) than during the less severe 2010 event (degree heating weeks = 4.86 °C-week). Stress band prevalence also varied by reef type, as more corals on the exposed barrier reef formed stress bands than did corals from sheltered lagoon environments. Comparison of Porites stress band prevalence with bleaching survey data revealed a strong correlation between percent community bleaching and the proportion of colonies with stress bands in each year. Conversely, annual calcification rates did not decline consistently during bleaching years nor did annually resolved calcification histories always track interannual variability in temperature. Our data suggest that stress bands in massive corals contain valuable information about spatial and temporal trends in coral reef bleaching and can aid in conservation efforts to identify temperature-tolerant coral reef communities.

     

Post-settlement survivorship in two Caribbean broadcasting corals

The post-settlement phase of broadcast-spawned coral life histories is poorly known due to its almost complete undetectability and, hence, presumed low abundance in the field. We used lab-cultured settled polyps of two important Caribbean reef-building species with negligible larval recruitment to quantify early post-settlement survivorship (6–9 weeks) over multiple years/cohorts and differing orientation on a reef in the Florida Keys. Orbicella faveolata showed significantly and consistently better survivorship in vertical rather than horizontal orientation, but no discernable growth overall. Meanwhile, Acropora palmata showed no significant difference in survivorship between orientations, but significantly greater growth in the horizontal orientation. Both species showed significant variation in mean survivorship between cohorts of different years; 0–47 % for O. faveolata and 12–49 % for A. palmata over the observed duration. These results demonstrate wide variation in success of cohorts and important differences in the larval recruitment capacities of these two important but imperiled reef-building species.     

Fungi in Porites lutea: association with healthy and diseased corals.

Healthy and diseased scleractinian corals have been reported to harbour fungi. However, the species of fungi occurring in them and their prevalence in terms of biomass have not been determined and their role in coral diseases is not clear. We have found fungi to occur regularly in healthy, partially dead, bleached and pink-line syndrome (PLS)-affected scleractinian coral, Porites lutea, in the reefs of Lakshadweep Islands in the Arabian Sea. Mostly terrestrial species of fungi were isolated in culture from these corals. Hyaline and dark, non-sporulating fungi were the most dominant forms. Fungal hyphae extended up to 3 cm within the corals. Immunofluorescence detection using polyclonal immunological probes for a dark, initially non-sporulating isolate (isolate # 98-N28) and for a hyaline, non-sporulating fungus (isolate # 98-N18) revealed high frequencies of these in PLS-affected, dead and healthy colonies of P. lutea. Total fungal biomass accounted for 0.04 to 0.05% of the weight of corals in bleached corals and was higher than in PLS-affected and healthy colonies. Scanning electron microscopy revealed the presence of fungi within the carbonate skeleton and around polyps. Fungi appear to be a regular component of healthy, partially dead and diseased coral skeleton.     

Interspecific interactions among species of the coral genus Porites from Okinawa, Japan

Analysis of field established xenogeneic interactions among five Porites species from Sesoko Island, Okinawa, revealed a transitive type of hierarchy as: P. rus >P. cylindrica >P. lobata >P. australiensis>P. lutea. Out of the 111 interspecific encounters studied, in only 5.4% reciprocal interactions were recorded, and in a single case, the opposite directionality of hierarchy was documented. Allogeneic encounters were also observed. A single major effector mechanism, an overgrowth (together with secondary outcomes such as the formation of small points of rejection, bleaching and pink color formation along a narrow peripheral belt of contacting tissues), was the only response in all 10 xenogeneic and 5 allogeneic combinations. In some massive colonies, a long contacting line of up to 50 cm was established. No sign for allelopathy, stand-off or rejection from a distance (i.e., by sweeper tentacles, sweeper polyps) was observed. Results are discussed with the accumulated data on Porites species from different reefs, worldwide, confirming that this genus is commonly lower in the hierarchy of xenogeneic interactions.     

Shape-shifting corals: Molecular markers show morphology is evolutionarily plastic in Porites

Background  

Corals are notoriously difficult to identify at the species-level due to few diagnostic characters and variable skeletal morphology. This 'coral species problem' is an impediment to understanding the evolution and biodiversity of this important and threatened group of organisms. We examined the evolution of the nuclear ribosomal internal transcribed spacer (ITS) and mitochondrial markers (COI, putative control region) in Porites, one of the most taxonomically challenging and ecologically important genera of reef-building corals.     

Regional decline in growth rates of massive Porites corals in Southeast Asia

This study reports the first well‐replicated analysis of continuous coral growth records from warmer water reefs (mean annual sea surface temperatures (SST) >28.5 °C) around the Thai–Malay Peninsula in Southeast Asia. Based on analyses of 70 colonies sampled from 15 reefs within six locations, region‐wide declines in coral calcification rate (ca. 18.6%), linear extension rate (ca. 15.4%) and skeletal bulk density (ca. 3.9%) were observed over a 31‐year period from 1980 to 2010. Decreases in calcification and linear extension rates were observed at five of the six locations and ranged from ca. 17.2–21.6% and ca. 11.4–19.6%, respectively, whereas decline in skeletal bulk density was a consequence of significant reductions at only two locations (ca. 6.9% and 10.7%). A significant link between region‐wide growth rates and average annual SST was found, and Porites spp. demonstrated a high thermal threshold of ca. 29.4 °C before calcification rates declined. Responses at individual locations within the region were more variable with links between SST and calcification rates being significant at only four locations. Rates of sea temperature warming at locations in the Andaman Sea (Indian Ocean) (ca. 1.3 °C per decade) were almost twice those in the South China Sea (Pacific Ocean) (ca. 0.7 °C per decade), but this was not reflected in the magnitude of calcification declines at corresponding locations. Considering that massive Porites spp. are major reef builders around Southeast Asia, this region‐wide growth decline is a cause for concern for future reef accretion rates and resilience. However, this study suggests that the future rates and patterns of change within the region are unlikely to be uniform or dependent solely on the rates of change in the thermal environment.     

Outplanting of branching Acropora enhances recolonization of a fish species and protects massive corals from predation

Damselfish of the genus Stegastes inhabit territories and cultivate algal gardens on branching corals of the genus Acropora, aggressively protecting their territories from other fish and preventing predation upon corals within the territory. This behaviour has important ecological impacts and could also be useful in reducing predation on outplanted corals during reef restoration efforts. However, the degree of protection from predators may depend on the ability of Stegastes spp. to recolonise outplanted or newly established coral colonies. Protection of bleaching-resilient massive corals within territories may be of particular importance due to the role of these corals in maintaining coral cover following bleaching events. This study examined whether the presence of Stegastes spp. reduces predation on the massive bleaching-resilient coral Porites lutea in the Mauritian lagoon, and whether Stegastes spp. readily colonise outplanted branching coral fragments and provide adjacent massive corals with indirect protection from predation. Predation levels on wild-occurring and outplanted P. lutea within and outside Stegastes spp. territories were measured. In addition, Acropora muricata branches were outplanted adjacent to wild P. lutea colonies outside Stegastes spp. territories, and recolonisation of these outplants by Stegastes spp. and the impacts of recolonisation on predation were monitored. Both wild and outplanted P. lutea colonies within Stegastes spp. territories sustained less predation damage compared to colonies outside territories. Stegastes spp. recolonized outplanted A. muricata colonies within six months of outplanting, and in doing so returned predation protection to adjacent P. lutea colonies. The ability of Stegastes spp. to colonise outplanted corals and provide indirect protection to adjacent massive bleaching-resilient corals may inform coral outplanting efforts in systems where Stegastes spp. are common. Encouraging Stegastes spp. recolonisation may help to reduce predation damage to corals within territories and potentially improve the success of rehabilitation efforts.

     

Species density and associations in Caribbean reef corals

The density of scleractinian corals on portions of two reefs in the Grenadine Islands, W. I. has been investigated by direct observation by SCUBA divers. Grid, transect, and random quadrat methods were compared with total samples to determine the precision and accuracy of these techniques. Transect methods were generally satisfactory provided at least 15% of a 400 m² total grid area was included in the sample. The data strongly indicated clumped distributions of all species, although numerical analysis does not indicate the distinct zones reported by other workers. Species associations based on Jaccard's coefficient and cluster analysis showed possible similarities in physical requirements, although few strong associations were found. Data based on 4 m² quadrats generally provided a more reliable estimate of species associations than did data based on 1 m² quadrats. It is suggested that surveys of these reef types may be better based on a number of parallel transects rather than a single transect, and that well-defined zones are more likely to be the exception than the rule.     

Genetic relatedness among Filobasidiella species

The three accepted species of Filobasidiella, F. neoformans, F. depauperata, and F. lutea, are compared morphologically and by molecular analysis. Sequences of the internally transcribed spacer (ITS) and the small subunit (SSU) gene of the ribosomal RNA (rRNA) gene cluster were obtained, and analysed by Neighbor-joining and Maximum parsimony methods. The three species of Filobsidiella are shown to form a single monophyletic clade, rooted by Tremella mesenterica. F. lutea was recovered as a distinct, but closely related taxon with the Filobasidiella clade. This is the first report of DNA sequences from herbarium specimens of F. lutea.This revised version was published online in October 2005 with corrections to the Cover Date.     

The presence of multiple phenoloxidases in Caribbean reef-building corals

The melanin-synthesis pathways, phenoloxidase (PO) and laccases, are staple components of invertebrate immunity and have been shown to be vital in disease resistance. The importance of this pathway in immunity is a consequence of the release of oxygen radicals with cytotoxic effects and the production of insoluble melanin, which aids in the encapsulation of pathogens and parasites. Recently, melanization has been demonstrated as a critical immune response in several coral systems, although the biochemical components have not been thoroughly investigated. Coral diseases are posing a serious threat to coral reef survival, necessitating a full understanding of resistance mechanisms. In this study, we take a comparative approach to probe potential pathway components of melanin-synthesis in seven species from four different families of healthy Caribbean reef-building corals. Using different quinone substrates, we tested for the activity of the POs catecholase and cresolase, as well as laccase activity in each coral species. Since many invertebrate POs demonstrate some dependence on cations such as copper, calcium and magnesium, we treated the coral extracts with the chelators EDTA and EGTA to test the reliance of coral catecholase on these cations. The activity of the antioxidants peroxidase, superoxide dismutase and catalase was also tested in each coral and correlated to PO activity. All corals had demonstrable catecholase, cresolase and laccase activities, but only catecholase and cresolase activities varied significantly among species. Catecholase activity in each coral species was reduced by treatment with EDTA and EGTA, although some coral species were less affected than the others. Overall, these data show remarkable heterogeneity among the seven coral species of boulder-like reef building Caribbean coral. These differences may originate from the level of investment of each coral species into immunity and may explain disease ecology on the reef.     

Relationship of Vibrio species infection and elevated temperatures to yellow blotch/band disease in Caribbean corals

The bacterial and temperature factors leading to yellow blotch/band disease (YBD), which affects the major reef-building Caribbean corals Montastrea spp., have been investigated. Groups of bacteria isolated from affected corals and inoculated onto healthy corals caused disease signs similar to those of YBD. The 16S rRNA genes from these bacteria were sequenced and found to correspond to four Vibrio spp. Elevating the water temperature notably increased the rate of spread of YBD on inoculated corals and induced greater coral mortality. YBD-infected corals held at elevated water temperatures had 50% lower zooxanthella densities, 80% lower division rates, and a 75% decrease in chlorophyll a and c2 pigments compared with controls. Histological sections indicated that the algal pyrenoid was fragmented into separate segments, along with a reconfiguration and swelling of the zooxanthellae, as well as vacuolization. YBD does not appear to produce the same physiological response formerly observed in corals undergoing temperature-related bleaching. Evidence indicates that YBD affects primarily the symbiotic algae rather than coral tissue.     

Weak prezygotic isolating mechanisms in threatened Caribbean Acropora corals

The Caribbean corals, Acropora palmata and A. cervicornis, recently have undergone drastic declines primarily as a result of disease. Previous molecular studies have demonstrated that these species form a hybrid (A. prolifera) that varies in abundance throughout the range of the parental distribution. There is variable unidirectional introgression across loci and sites of A. palmata genes flowing into A. cervicornis. Here we examine the efficacy of prezygotic reproductive isolating mechanisms within these corals including spawning times and choice and no-choice fertilization crosses. We show that these species have subtly different mean but overlapping spawning times, suggesting that temporal isolation is likely not an effective barrier to hybridization. We found species-specific differences in gametic incompatibilities. Acropora palmata eggs were relatively resistant to hybridization, especially when conspecific sperm are available to outcompete heterospecific sperm. Acropora cervicornis eggs demonstrated no evidence for gametic incompatibility and no evidence of reduced viability after aging four hours. This asymmetry in compatibility matches previous genetic data on unidirectional introgression.     

First report of folliculinid ciliates affecting Caribbean scleractinian corals

This is the first report of a ciliate of the genus Halofolliculina infecting hard coral species of six families (Acroporidae, Agaricidae, Astrocoeniidae, Faviidae, Meandrinidae and Poritidae) and milleporids in the Caribbean. Surveys conducted during 2004–2005 in Venezuela, Panama and México confirmed that this ciliate affects up to 25 scleractinian species. The prevalence of this ciliate at the coral community level was variable across sites, being most commonly found at Los Roques, Venezuela, and at Bocas del Toro, Panama (prevalence 0.2–2.5%), but rarely observed in the Mexican Caribbean. Ciliates were more prevalent within populations of acroporids (Acropora palmata, Acropora cervicornis and Acropora prolifera) in Los Roques. Recent observations also corroborate the presence of these ciliates in Curacao and Puerto Rico. Our observations indicate that ciliates affecting corals have a wider distribution than previously thought, and are no longer exclusively found in the Indo-Pacific and Red Sea.     

Isolation of microsatellite loci from the scleractinian corals,Montastraea cavernosa and Porites astreoides

The ability to assess genetic variation is critical for determining genetic diversity and population structure. In corals, slow evolutionary rates in mitochondrial genomes have left allozymes as the only markers presently available to investigate patterns of intraspecific genetic variation. Characteristics of microsatellites render them more informative than allozymes for such analyses; however, few coral microsatellites are available. This study describes polymorphic microsatellite loci isolated from two scleractinian coral species. Most loci exhibit significant heterozygote deficiencies, likely due to nonrandom mating or Wahlund effects. These markers are being used to investigate gene flow among populations, providing insight into reef connectivity.     

Spongivory on Caribbean reefs releases corals from competition with sponges

Competition for space is an important process on tropical coral reefs. Few studies have examined the role sponges play in community structure despite the fact that many sponges are competitively superior to reef-building corals in space acquisition. Surveys conducted throughout the Florida Keys indicated that Chondrilla nucula was involved in about 30% of all coral-sponge interactions; this sponge has also been observed in 40–50% of coral-sponge interactions on other Caribbean reefs. C. nucula is also the top prey item of the Hawksbill turtle, and among the preferred prey of several spongivorous fish. I examined how predation influenced sponge competitive abilities (particularly those of C. nucula), and whether this type of indirect effect had important consequences for community dynamics in the Florida Keys. Exclusion of sponge predators (primarily angelfish) resulted in increased sponge overgrowth, with a subsequent greater loss of coral cover, compared to uncaged pairwise interactions. When caged, the corals Dichocoenia stokesii and Siderastrea sideraea lost significantly greater surface area and number of polyps to the sponge C. nucula compared to uncaged interactions. For caged interactions involving the sponge Ectyoplasia ferox, there was a trend for greater loss of  S. sideraea surface area and polyps compared to uncaged interactions. Predation had a greater affect on C. nucula than on any of the other sponges examined. Predator exclusion experiments performed with naturally occurring coral-sponge interactions demonstrated a significant decrease in total coral cover compared to uncaged controls. It is proposed that indirect effects arising from spongivory (especially consumption of  C. nucula) may have large community consequences. Species diversity on Caribbean reefs may be maintained, at least in part, by spongivores. Received: 28 January 1998 / Accepted: 22 June 1998