Chemical signals in gametogenesis, spawning, and larval settlement and defense of the soft coral Sinularia polydactyla

 Mass spawning strategies of hard and soft corals on the Great Barrier Reef, Australia have been described in recent years. Nonetheless, the applicability of those studies to corals on other reef systems has not been well documented. Here we describe the mass spawning behavior of the soft coral Sinularia polydactyla on coral reefs surrounding Guam; specifically we describe the events in an annual gametogenic cycle including steroidogenesis, spawning, settlement and early life history defense. The gametogenic cycle of female colonies lasted 12 months while male colonies produced viable sperm within 9 months. Sinularia polydactyla exhibited a split spawn between March and June that correlated with a significant reduction in tissue concentrations of progesterone and testosterone. Estradiol was released into the water column, apparently by female colonies, just prior to spawning. There was a trend for preferential larval settlement in the presence of the crustose coralline algae Hydrolithon reinboldii rather than coral rubble, a natural biofilm, or filtered seawater. The defensive compounds pukalide and 11β-acetoxypukalide were found in eggs and larvae at adult level and three-fold lower than adult-level concentrations, respectively. These compounds provided some predator deterrent and antimicrobial protection against an ecologically relevant omnivorous fish Canthigaster solandri and a sympatric microbe Vibrio sp. Accepted: 10 September 1998     

Sinularia leptoclados (Ehrenberg, 1834) (Cnidaria,?Octocorallia) re-examined

Sinularia leptoclados (Ehrenberg, 1834) is re-described. Sinularia leptoclados var. gonatodes Kolonko, 1926 is synonymized with Sinularia maxima Verseveldt, 1977. Two new species of Sinularia with digitiform lobules, leptoclados-type surface clubs and unbranched interior spindles, are described. An updated maximum likelihood tree of Sinularia species with leptoclados-type clubs (clade 5C) based on two mitochondrial genes (mtMutS, COI) and a nuclear gene (28S rDNA) is presented.     

A comparison of culture-dependent and culture-independent techniques used to characterize bacterial communities on healthy and white plague-diseased corals of the Montastraea annularis species complex

Diseases of hermatypic corals pose a global threat to coral reefs, and investigations of bacterial communities associated with healthy corals and those exhibiting signs of disease are necessary for proper diagnosis. One disease, commonly called white plague (WP), is characterized by acute tissue loss. This investigation compared the bacterial communities associated with healthy coral tissue (N = 15), apparently healthy tissue on WP-diseased colonies (N = 15), and WP-diseased tissues (N = 15) from Montastraea annularis (species complex) colonies inhabiting a Bahamian reef. Aliquots of sediment (N = 15) and water (N = 15) were also obtained from the proximity of each coral colony sampled. Samples for culture-dependent analyses were inoculated onto one-half strength Marine Agar (½ MA) and Thiosulfate Citrate Bile Salts Sucrose Agar to quantify the culturable communities. Length heterogeneity PCR (LH-PCR) of the 16S rRNA gene characterized the bacterial operational taxonomic units (OTU) associated with lesions on corals exhibiting signs of a white plague-like disease as well as apparently healthy tissue from diseased and non-diseased conspecifics. Analysis of Similarity was conducted on the LH-PCR fingerprints, which indicated no significant difference in the composition of bacterial communities associated with apparently healthy and diseased corals. Comparisons of the 16S rRNA gene amplicons from cultured bacterial colonies (½ MA; N = 21) with all amplicons obtained from the whole coral-associated bacterial community indicated ≥39 % of coral-associated bacterial taxa could be cultured. Amplicons from these bacterial cultures matched amplicons from the whole coral-associated bacterial community that, when combined, accounted for >70 % total bacterial abundance. An OTU with the same amplicon length as Aurantimonas coralicida (313.1 bp), the reported etiological agent of WPII, was detected in relatively low abundance (<0.1 %) on all tissue types. These findings suggest a coral disease resembling WP may result from multiple etiologies.     

Identification of Candidate Coral Pathogens on White Band Disease-Infected Staghorn Coral

Bacterial diseases affecting scleractinian corals pose an enormous threat to the health of coral reefs, yet we still have a limited understanding of the bacteria associated with coral diseases. White band disease is a bacterial disease that affects the two Caribbean acroporid corals, the staghorn coral Acropora cervicornis and the elkhorn coral A. palmate. Species of Vibrio and Rickettsia have both been identified as putative WBD pathogens. Here we used Illumina 16S rRNA gene sequencing to profile the bacterial communities associated with healthy and diseased A. cervicornis collected from four field sites during two different years. We also exposed corals in tanks to diseased and healthy (control) homogenates to reduce some of the natural variation of field-collected coral bacterial communities. Using a combination of multivariate analyses, we identified community-level changes between diseased and healthy corals in both the field-collected and tank-exposed datasets. We then identified changes in the abundances of individual operational taxonomic units (OTUs) between diseased and healthy corals. By comparing the diseased and healthy-associated bacteria in field-collected and tank-exposed corals, we were able to identify 16 healthy-associated OTUs and 106 consistently disease-associated OTUs, which are good candidates for putative WBD pathogens. A large percentage of these disease-associated OTUs belonged to the order Flavobacteriales. In addition, two of the putative pathogens identified here belong to orders previously suggested as WBD pathogens: Vibronales and Rickettsiales.     

Phage therapy of the white plague-like disease of Favia favus in the Red Sea

Coral disease is a major factor in the global decline of coral reefs. At present, there are no known procedures for preventing or treating infectious diseases of corals. Immunization is not possible because corals have a restricted adaptive immune system and antibiotics are neither ecologically safe nor practical in an open system. Thus, we tested phage therapy as an alternative therapeutic method for treating diseased corals. Phage BA3, specific to the coral pathogen Thalassomonas loyana, inhibited the progression of the white plague-like disease and transmission to healthy corals in the Gulf of Aqaba, Red Sea. Only one out of 19 (5?%) of the healthy corals became infected when placed near phage-treated diseased corals, whereas 11 out of 18 (61?%) healthy corals were infected in the no-phage control. This is the first successful treatment for a coral disease in the sea. We posit that phage therapy of certain coral diseases is achievable in situ.     

Species composition and structure of coral community of a platform reef at Bach Long Vi Island in the South China Sea

A platform reef at Bach Long Vi Island (Gulf of Tonkin in the South China Sea) was investigated for the first time. In all, 264 species of corals and their accompanying species of macrobenthos were found. Among the scleractinian corals, acroporids, poritids, and mussids dominated. Monospecific aggregations of alcyonarians Sinularia and Lobophytum and the hydroid Millepora were rather numerous. Based on its geomorphological characteristics, coral species diversity and zonal distribution, the investigated reef is comparable with ribbon and platform reefs on the Great Barrier Reef in Australia and in the Indian Ocean.     

Cymo melanodactylus crabs slow progression of white syndrome lesions on corals

Predation on coral tissue by the crab Cymo melanodactylus has been hypothesized to contribute to tissue loss caused by white syndromes (WS) in acroporid corals. Here, we demonstrate that transplanting C. melanodactylus crabs from WS-infected Acropora colonies onto healthy coral fragments in controlled aquarium experiments does not result in WS transmission over a 21-day experimental period. Furthermore, progression of WS lesions was three times more rapid on corals with all C. melanodactylus crabs removed than on those with crabs (2.28 ± 0.21 vs. 0.74 ± 0.22 cm/day, respectively); thus, crabs slow WS disease progression under experimental conditions. In choice experiments, C. melanodactylus crabs were strongly attracted to corals with WS lesions, with 87 % of crabs migrating to WS fragments versus 3 % to healthy fragments. The strong attraction of C. melanodactylus to WS-infected corals and their ability to significantly reduce lesion progression rates suggest a mechanism whereby these coral-dwelling crabs could mitigate the effects of WS diseases on reefs.     

Isolation of potential fungal pathogens in gorgonian corals at the Tropical Eastern Pacific

A major environmental problem in the ocean is the alarming increase in diseases affecting diverse marine organisms including corals. Environmental factors such as the rising seawater temperatures and terrestrial microbial input to the ocean have contributed to the increase in diseased organisms. We isolated and identified the fungal agents that may be leading to a disease in the Pacific sea fan Pacifigorgia eximia (Gorgoniidae, Octocorallia) in the Tropical Eastern Pacific. We isolated thirteen fungal genera in healthy and diseased colonies including Aspergillus sydowii. Aspergillus has been previously identified as responsible for the mortality of gorgonian corals in the Caribbean. This disease was observed in the Eastern Pacific affecting a completely different set of species nearly 30 years after the Caribbean outbreak, which concur with rising seawater temperatures and thermal anomalies that have been observed in the last 4 years.     

Bacterial profiling of White Plague Disease in a comparative coral species framework

Coral reefs are threatened throughout the world. A major factor contributing to their decline is outbreaks and propagation of coral diseases. Due to the complexity of coral-associated microbe communities, little is understood in terms of disease agents, hosts and vectors. It is known that compromised health in corals is correlated with shifts in bacterial assemblages colonizing coral mucus and tissue. However, general disease patterns remain, to a large extent, ambiguous as comparative studies over species, regions, or diseases are scarce. Here, we compare bacterial assemblages of samples from healthy (HH) colonies and such displaying signs of White Plague Disease (WPD) of two different coral species (Pavona duerdeni and Porites lutea) from the same reef in Koh Tao, Thailand, using 16S rRNA gene microarrays. In line with other studies, we found an increase of bacterial diversity in diseased (DD) corals, and a higher abundance of taxa from the families that include known coral pathogens (Alteromonadaceae, Rhodobacteraceae, Vibrionaceae). In our comparative framework analysis, we found differences in microbial assemblages between coral species and coral health states. Notably, patterns of bacterial community structures from HH and DD corals were maintained over species boundaries. Moreover, microbes that differentiated the two coral species did not overlap with microbes that were indicative of HH and DD corals. This suggests that while corals harbor distinct species-specific microbial assemblages, disease-specific bacterial abundance patterns exist that are maintained over coral species boundaries.     

Natural Disease Resistance in Threatened Staghorn Corals

Disease epidemics have caused extensive damage to tropical coral reefs and to the reef-building corals themselves, yet nothing is known about the abilities of the coral host to resist disease infection. Understanding the potential for natural disease resistance in corals is critically important, especially in the Caribbean where the two ecologically dominant shallow-water corals, Acropora cervicornis and A. palmata, have suffered an unprecedented mass die-off due to White Band Disease (WBD), and are now listed as threatened under the US Threatened Species Act and as critically endangered under the IUCN Red List criteria. Here we examine the potential for natural resistance to WBD in the staghorn coral Acropora cervicornis by combining microsatellite genotype information with in situ transmission assays and field monitoring of WBD on tagged genotypes. We show that six percent of staghorn coral genotypes (3 out of 49) are resistant to WBD. This natural resistance to WBD in staghorn corals represents the first evidence of host disease resistance in scleractinian corals and demonstrates that staghorn corals have an innate ability to resist WBD infection. These resistant staghorn coral genotypes may explain why pockets of Acropora have been able to survive the WBD epidemic. Understanding disease resistance in these corals may be the critical link to restoring populations of these once dominant corals throughout their range.     

Long-term dynamics of a high-latitude coral reef community at Sodwana Bay,South Africa

Dynamics in reef cover, mortality and recruitment success of a high-latitude coral community in South Africa were studied over 20 yr with the aim to detect the effects of climate change. Coral communities at this locality are the southernmost on the African continent, non-accretive, attain high biodiversity and are dominated by soft corals. Long-term monitoring within fixed transects on representative reef was initiated in 1993 and has entailed annual photo-quadrat surveys and hourly temperature logging. Although sea temperatures rose by 0.15 °C p.a. at the site up to 2000, they have subsequently been decreasing, and the overall trend based on monthly means has been a significant decrease of 0.03 °C p.a. Despite this, minor bleaching was encountered in the region during the 1998 El Niño–Southern Oscillation event, again in the summer of 2000/2001 and in 2005. A significant decreasing trend of 0.95% p.a. in soft coral cover has been evident throughout the monitoring period, attributable to significant decreases in Sinularia and Lobophytum spp. cover. In contrast, hard coral cover gradually and significantly increased up to 2005, this being largely attributable to increases in cover by Acropora spp. Recruitment success and mortality of both soft and hard corals has displayed high inter-annual variability with increasing but non-significant trends in the last 5 yr. The reduction in soft coral cover has been more consistent and greater than that of hard corals, but it is difficult at this stage to attribute this to changes in water quality, acidification-linked accretion or temperature.     

Potential role of viruses in white plague coral disease

White plague (WP)-like diseases of tropical corals are implicated in reef decline worldwide, although their etiological cause is generally unknown. Studies thus far have focused on bacterial or eukaryotic pathogens as the source of these diseases; no studies have examined the role of viruses. Using a combination of transmission electron microscopy (TEM) and 454 pyrosequencing, we compared 24 viral metagenomes generated from Montastraea annularis corals showing signs of WP-like disease and/or bleaching, control conspecific corals, and adjacent seawater. TEM was used for visual inspection of diseased coral tissue. No bacteria were visually identified within diseased coral tissues, but viral particles and sequence similarities to eukaryotic circular Rep-encoding single-stranded DNA viruses and their associated satellites (SCSDVs) were abundant in WP diseased tissues. In contrast, sequence similarities to SCSDVs were not found in any healthy coral tissues, suggesting SCSDVs might have a role in WP disease. Furthermore, Herpesviridae gene signatures dominated healthy tissues, corroborating reports that herpes-like viruses infect all corals. Nucleocytoplasmic large DNA virus (NCLDV) sequences, similar to those recently identified in cultures of Symbiodinium (the algal symbionts of corals), were most common in bleached corals. This finding further implicates that these NCLDV viruses may have a role in bleaching, as suggested in previous studies. This study determined that a specific group of viruses is associated with diseased Caribbean corals and highlights the potential for viral disease in regional coral reef decline.     

PHYLLODESMIUM GUAMENSIS (NUDIBRANCHIA: AEOLIDOIDEA), A NEW SPECIES FROM GUAM(MICRONESIA)

A new species of Phyllodesmium (Aeolidoidea) from Guam (Micronesia)is described. Phyllodesmium guamensis n.sp. is characterizedby having two rows of denticles in the radular teeth, this beingdifferent from the previously described species of the genus.The shape of the teeth, however, is identical in all the speciesof the genus, and unique among aeolids. Furthermore, P. guamensispossesses a double row of cerata in the precardiac cluster andup to 10 post-cardiac ceratal rows. Also, P. guamensis showsa very dense accumulation of zooxanthellae in the ceratal digestivegland, which is ramified inside the cerata. This species feedson at least three species of the soft coral Sinularia: S. polydactyla,S. maxima and a third, undescribed species. The aeolid matchesthe colour of its prey and is cryptic on the soft coral surface. (Received 3 October 1996; accepted 28 April 1997)     

Vibrio owensii Induces the Tissue Loss Disease Montipora White Syndrome in the Hawaiian Reef Coral Montipora capitata

Incidences of coral disease in the Indo-Pacific are increasing at an alarming rate. In particular, Montipora white syndrome, a tissue-loss disease found on corals throughout the Hawaiian archipelago, has the potential to degrade Hawaii’s reefs. To identify the etiologic agent of Montipora white syndrome, bacteria were isolated from a diseased fragment of Montipora capitata and used in a screen for virulent strains. A single isolate, designated strain OCN002, recreated disease signs in 53% of coral fragments in laboratory infection trials when added to a final concentration of 10⁷ cells/ml of seawater. In addition to displaying similar signs of disease, diseased coral fragments from the field and those from infection trials both had a dramatic increase in the abundance of associated culturable bacteria, with those of the genus Vibiro well represented. Bacteria isolated from diseased fragments used in infection trails were shown to be descendants of the original OCN002 inocula based on both the presence of a plasmid introduced to genetically tag the strain and the sequence of a region of the OCN002 genome. In contrast, OCN002 was not re-isolated from fragments that were exposed to the strain but did not develop tissue loss. Sequencing of the rrsH gene, metabolic characterization, as well as multilocus sequence analysis indicated that OCN002 is a strain of the recently described species Vibrio owensii. This investigation of Montipora white syndrome recognizes V. owensii OCN002 as the first bacterial coral pathogen identified from Hawaii’s reefs and expands the range of bacteria known to cause disease in corals.     

Microbial bioindicators of Stony Coral Tissue Loss Disease identified in corals and overlying waters using a rapid field-based sequencing approach

Stony Coral Tissue Loss Disease (SCTLD) is a devastating disease. Since 2014, it has spread along the entire Florida Reef Tract and into the greater Caribbean. It was first detected in the United States Virgin Islands in January 2019. To more quickly identify microbial bioindicators of disease, we developed a rapid pipeline for microbiome sequencing. Over a span of 10 days we collected, processed and sequenced coral and near-coral seawater microbiomes from diseased and apparently healthy Colpophyllia natans, Montastraea cavernosa, Meandrina meandrites and Orbicella franksi. Analysis of bacterial and archaeal 16S ribosomal RNA gene sequences revealed 25 bioindicator amplicon sequence variants (ASVs) enriched in diseased corals. These bioindicator ASVs were additionally recovered in near-coral seawater (<5 cm of coral surface), a potential reservoir for pathogens. Phylogenetic analysis of microbial bioindicators with sequences from the Coral Microbiome Database revealed that Vibrio, Arcobacter, Rhizobiaceae and Rhodobacteraceae sequences were related to disease-associated coral bacteria and lineages novel to corals. Additionally, four ASVs (Algicola, Cohaesibacter, Thalassobius and Vibrio) were matches to microbes previously associated with SCTLD that should be targets for future research. Overall, this work suggests that a rapid sequencing framework paired with specialized databases facilitates identification of microbial disease bioindicators.     

Heavy metals distribution in the coral reef ecosystems of the Northern Red Sea

Concentrations of seven heavy metals (Cu, Zn, Pb, Cd, Ni, Co and Fe) were measured in the seawater, sediments, common scleractinian reef-building corals and soft corals (Octocorallia : Alcyonacea) at seven reef sites in the Northern Red Sea: I (Hurghada), II (Ras Za’farana), III (El-Ain Al-Sukhna), IV (El-Tur), V (Sha’b Rashdan), VI (Sharm El-Sheikh) and VII (Dahab). Levels of heavy metals were considerably elevated in seawater, sediments and corals collected from reef sites exposed to increased environmental contamination, as a result of diversified natural and anthropogenic inputs. Soft corals of genera Lithophyton, Sarcophyton and Sinularia showed higher concentrations of Zn, Pb, Cd and Ni than hard coral genera Acropora and Stylophora. Soft coral Sarcophyton trocheliophorum collected from El Ain Al-Suhkna (Gulf of Suez) had greater concentration of Cu, followed by hard corals Acropora pharaonis and Acropora hemprichi. The elevated levels of Zn, Cd and Ni were reported in the dry tissue of soft coral Sinularia spp. On the other hand, the soft coral Lithophyton arboreum displayed the highest concentration of Pb at Sha’b Rashdan (Gulf of Suez) and elevated concentration of Zn at Sharm El-Sheikh. Sediments showed significantly higher concentration of Fe than corals. The higher levels of Fe in hard corals than soft corals reflected the incorporation of Fe into the aragonite and the chelation with the organic matrix of the skeleton. The greater abundance of soft corals in metal-contaminated reef sites and the elevated levels of metals in their tissue suggesting that the soft corals could develop a tolerance mechanism to relatively high concentrations of metals. Although the effects of heavy metals on reef corals were not isolated from the possible effects of other stresses, the percentage cover of dead corals were significantly higher as the concentrations of heavy metals increased.     

Studies on Two Closely Related Species of Octocorallians: Biochemical and Molecular Characteristics of the Organic Matrices of Endoskeletal Sclerites

Two species of alcyonarian corals, Lobophytum crassum and Sinularia polydactyla, are closely related to each other. It is reported that the calcified organic substances in the skeletons of both contain a protein–polysaccharide complex playing a key role in the regulation of biocalcification. However, information on the matrix proteins of endoskeletal sclerite has been lacking. Hence we studied the proteinaceous organic matrices of sclerites for both species, to analyze the sequences and the functional properties of the proteins present. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis of the preparations showed four bands of proteins with apparent molecular masses of 102, 67, 48, and 37 kDa for L. crassum and seven bands of 109, 83, 70, 63, 41, 30, and 22 kDa for S. polydactyla. A major protein band of about 67 kDa in L. crassum and two bands of proteins of about 70 and 63 kDa in S. polydactyla yielded N-terminal amino acid sequences. Periodic acid-Schiff staining indicated that the 67-kDa protein in L. crassum, and 83- and 63-kDa proteins in S. polydactyla were glycosylated. For detection of calcium binding proteins, a Ca²⁺ overlay analysis was conducted in the extract via ⁴⁵Ca autoradiography. The 102- and 67-kDa calcium binding proteins in L. crassum, and the 109- and 63-kDa Ca²⁺ binding proteins in S. polydactyla were found to be radioactive. An assay for carbonic anhydrase (CA), which is thought to play an important role in the process of calcification, revealed specific activities. Newly derived protein sequences were subjected to standard sequence analysis involving identification of similarities to other proteins in databases. The significantly different protein expressions and compositional analysis of sequences between two species were demonstrated.     

Long-term dynamics of the brown macroalga <Emphasis Type="Italic">Lobophora variegata</Emphasis> on deep reefs in Curaçao

Lobophora variegata occurs in the eulittoral zone and in deep water on coral reefs in Curaçao. An analysis of the long-term (1979–2006) changes in the vertical distribution of the macroalga in permanent quadrats indicated a significant increase in cover of the deepwater community. In 1998, Lobophora covered 1 and 5% of the quadrats at 20 and 30 m, respectively. By 2006, these values had risen to 25 and 18%, precipitating a shift in abundance of corals and macroalgae at both depths. This increase coincided with losses in coral cover, possibly linked to bleaching, disease and storm-related mortality in deep water plating Agaricia corals. In contrast, macroalgae remained relatively rare (<6% cover) on shallower (10 m) and deeper (40 m) reefs despite declines in coral cover also occurring at these depths, illustrating the depth-dependent dynamics of coral reefs. Several hypotheses are suggested to explain these changes.