Scleractinian Coral Genus Research Articles

Unravelling the relationships among Madrepora Linnaeus, 1758, Oculina Lamark, 1816 and Cladocora Ehrenberg, 1834 (Cnidaria: Anthozoa: Scleractinia).

Despite the widespread use of integrative taxonomic approaches, many scleractinian coral genera and species remain grouped in polyphyletic families, classified as incertae sedis or simply understudied. Oculinidae Gray, 1847 represents a family for which many taxonomic questions remain unresolved, particularly those related to some of the current genera, such as Oculina Lamark, 1816 or recently removed genera, including Cladocora Ehrenberg, 1834 and Madrepora Linnaeus, 1758. Cladocora is currently assigned to the family Cladocoridae Milne Edwards & Haime, 1857 and a new family, Bathyporidae Kitahara, Capel, Zilberberg & Cairns, 2024, was recently raised to accommodate Madrepora . However, the name Bathyporidae is not valid because this was not formed on the basis of a type genus name. To resolve taxonomic questions related to these three genera, the evolutionary relationships are explored through phylogenetic analyses of 18 molecular markers. The results of these analyses support a close relationship between the species Oculina patagonica and Cladocora caespitosa , indicating that these may belong to the same family (and possibly genus), and highlighting the need for detailed revisions of Oculina and Cladocora . By contrast, a distant relationship is found between these two species and Madrepora oculata , with the overall evidence supporting the placement of Madrepora in the resurrected family Madreporidae Ehrenberg, 1834. This study advances our knowledge of coral systematics and highlights the need for a comprehensive review of the genera Oculina , Cladocora and Madrepora .

Molecular Phylogeny and Taxonomy of the Coral Genus Cyphastrea (Cnidaria, Scleractinia, Merulinidae) in Japan, With the First Records of Two Species.

The scleractinian coral genus Cyphastrea is widely distributed in the Indo-Pacific region and is common from the subtropical to the warm-temperate regions in Japan. Three new species in this genus have recently been reported from south-eastern Australia or the Red Sea. However, taxonomic and species diversity have been little studied so far in Japan. In this study, we analyzed 112 specimens of Cyphastrea collected from the subtropical to the warm-temperate regions in Japan to clarify the species diversity in the country. This analysis was based on skeletal morphological and molecular analyses using three genetic markers of the nuclear 28S rDNA, histone H3 gene, and the mitochondrial noncoding intergenic region between COI and tRNAmet. The molecular phylogenetic trees showed that our specimens are separated mainly into four clades. Considering the morphological data with the molecular phylogenetic relationships, we confirmed a total of nine species, including two species, C. magna and C. salae, recorded for the first time in Japan. Although eight out of nine species were genetically included within Cyphastrea, one species, C. agassizi, was genetically distant from all other species and was closely related to the genus Leptastrea, suggesting the return of this species to the genus to which it was originally ascribed. Two newly recorded species were reciprocally monophyletic, while the other six species (excluding C. agassizi) clustered in two clades without forming species-specific lineages, including three polyphyletic species. Thus, the species boundary between species in Cyphastrea remains unclear in most species using these three sequenced loci.

An environmental DNA metabarcoding approach versus a visual survey for reefs of Koh Pha‐ngan in Thailand

AbstractInformation on diversity indices and abundance of individual species is crucial for the assessment of ecosystem health, especially for endangered ecosystems as coral reefs. The application of environmental DNA (eDNA) to monitor coral biodiversity is, however, just beginning to come into focus for marine biologists. In this study, an eDNA metabarcoding approach of seawater samples in three different reefs on Koh Pha‐ngan, Thailand, was compared with simultaneously collected visual census data. In addition, differences in read abundance and number of genera detected between daytime and nighttime eDNA samples were examined, and a local coral barcode reference database (n = 23 genera; COI gene) was constructed to improve assignment of eDNA reads to the genus level. As a technical extension of existing assays, two methods for library construction were compared: a commercial kit and in‐house developed fusion primers. Combining eDNA metabarcoding and visual data, 29 different genera of scleractinian corals from 14 families were detected. In addition, a log‐linear correlation was found between the abundance of eDNA reads and visually determined relative coral cover at the genus level, suggesting a predictive relationship between eDNA reads and coral cover. Results also showed diurnal variation between day and night samples in the number of eDNA reads, purported to relate to the activity phases of corals. The use of uniquely labeled fusion primers, gave comparable results to a commercially available library preparation kit. Especially with frequent use, fusion primers can be very cost‐effective, and therefore a consideration for large‐scale studies. Using a custom reference database of 89 sequences from coral tissue samples of 23 different coral genera produced better results than querying against NCBI GenBank, highlighting the importance of locally optimized databases. We consider these results important for establishing eDNA as a complementary tool to visual surveys to track changes in coral diversity and cover.

Shallow epifaunal sea cucumber densities and their relationship with the benthic community in the Okinawa Islands.

Sea cucumbers are important ecological engineers in marine ecosystems. However, the fishery demand of some species, especially large-epifaunal and commercially used (LEC) sea cucumbers, has risen drastically, resulting in serious depletion of local populations for many species. Despite this problem, basic ecological data on sea cucumbers, such as population densities and preferred habitats, are often still insufficient. Here, we report on the population densities of multiple LEC sea cucumber species, and their ambient benthic communities at eight sites around Okinawa Islands. Further, we discuss the correspondence between sea cucumber densities and the surrounding coral communities. Our results show two sites within national or quasi-national parks, Aka and Manza, where stricter rules have been placed on fisheries and land reclamation compared to other areas, had the highest and third highest sea cucumber population densities among sites, respectively. Holothuria atra was observed at all survey sites and made up the majority of sea cucumber populations at all sites except for Chatan and Sesoko, where Holothuria leucospilota and Stichopus chloronotus were most abundant, respectively. Regarding the relationships between benthic composition and LEC sea cucumber species, S. chloronotus was significantly correlated with dead corals, scleractinian corals, and coralline algae. As well, H. leucospilota had significant correlations with rubble. Although there were no significant correlations between any specific scleractinian coral genus and sea cucumber densities, S. chloronotus was marginally insignificant with Platygyra and Psammocora. Notably, medium- to highly valued species were sparse in our surveys, and most of them appeared at only one site. Additionally, at one site (Odo), only three LEC sea cucumber individuals were observed. Combining these facts with relatively low population densities around the Okinawa Islands compared to densities reported in previous research from the Indo-West Pacific Ocean region, we conclude that Okinawan LEC sea cucumber populations have been and are being impacted by high levels of direct (e.g., overexploitation, as well as coastal development) and indirect anthropogenic pressure (e.g., decreasing water quality). To address the current situation, repeated monitoring and more detailed investigations to reveal the drivers that determine LEC sea cucumber species aggregations and population densities are urgently needed, along with more robust management of remaining LEC sea cucumber populations.

Evolutionary History of DMSP Lyase-Like Genes in Animals and Their Possible Involvement in Evolution of the Scleractinian Coral Genus, Acropora

Dimethlysulfoniopropionate (DMSP) lyase is an enzyme that mediates cleavage of DMSP into dimethyl sulfide (DMS) and acrylate. DMS is an aerosol substance that may affect cloud formation, solar radiation and ocean temperatures. DMSP lyases in marine organisms, such as marine bacteria, release DMS, which might contribute to atmosphere-ocean feedback. Although DMSP lyases were first identified in marine bacteria, eukaryotic DMSP lyases or genes similar to DMSP lyase, DMSP lyase-like (DL-L) genes have been found not only in coccolithophores (Emiliania huxleyi) and symbiotic algae of the Family Symbiodiniaceae, but also in animals, including scleractinian corals (Cnidaria: Anthozoa: Hexacorallia). Comparative genomic analysis showed that gene expansion events of DL-L genes have occurred specifically in the scleractinian genus, Acropora. In the present study, we performed molecular identification of DL-L genes in Acropora digitifera. Thirteen full-length Open Reading Frames were isolated, confirming that these duplicated DL-L genes are likely expressed. A comprehensive survey of available transcriptomic databases revealed that DL-L genes have been identified not only in scleractinians (Hexacorallia), but also Octocorallia (Anthozoa) and even in a jellyfish (Cnidaria: Hydrozoa). Molecular phylogenetic analyses showed that although some sequences from cnidarian transcriptomic databases apparently originated with their symbiotic algae, cnidarian sequences from Anthozoa and Hydrozoa clustered together, indicating that these evolved from a gene in the last common ancestor of Cnidaria, dating to the Precambrian. Interestingly, cnidarian species possessing DL-L genes apparently occur only in coral reefs or shallow, warmer environments, suggesting that these genes may be essential for animals to survive in such environments. Acropora-specific duplicated DL-L genes, which originated during the past warm geological periods, may enable them to adapt to environmental changes.

Phylogenomics of Porites from the Arabian Peninsula

The advent of high throughput sequencing technologies provides an opportunity to resolve phylogenetic relationships among closely related species. By incorporating hundreds to thousands of unlinked loci and single nucleotide polymorphisms (SNPs), phylogenomic analyses have a far greater potential to resolve species boundaries than approaches that rely on only a few markers. Scleractinian taxa have proved challenging to identify using traditional morphological approaches and many groups lack an adequate set of molecular markers to investigate their phylogenies. Here, we examine the potential of Restriction-site Associated DNA sequencing (RADseq) to investigate phylogenetic relationships and species limits within the scleractinian coral genus Porites. A total of 126 colonies were collected from 16 localities in the seas surrounding the Arabian Peninsula and ascribed to 12 nominal and two unknown species based on their morphology. Reference mapping was used to retrieve and compare nearly complete mitochondrial genomes, ribosomal DNA, and histone loci. De novo assembly and reference mapping to the P. lobata coral transcriptome were compared and used to obtain thousands of genome-wide loci and SNPs. A suite of species discovery methods (phylogenetic, ordination, and clustering analyses) and species delimitation approaches (coalescent-based, species tree, and Bayesian Factor delimitation) suggested the presence of eight molecular lineages, one of which included six morphospecies. Our phylogenomic approach provided a fully supported phylogeny of Porites from the Arabian Peninsula, suggesting the power of RADseq data to solve the species delineation problem in this speciose coral genus.

Comparative study of polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs) in corals, sediments and seawater from coral reefs of Hainan, China

This work investigated levels of PAHs and HMs in fourteen species from seven genera of scleractinian corals, adjacent sediments, and surface seawater in Hainan, China. The sources of contaminations were analyzed as well. The results showed that scleractinian corals had a relatively higher bioaccumulation capacity for PAHs from sediments than for HMs. There were inter-species differences for these contaminants enriched in corals. Pavona varians and Porites lutea could accumulate PAHs more readily. While higher concentrations of Cr, Mn and Pb occurred in Favites flexuosa, other metal levels, such as for Ni, Cu, Zn and As, were found to be elevated in Pocillopora damicornis, as well as for Cd in Acropora echinata. It was found that PAHs originated from petrogenic and pyrolytic sources, and were mainly linked to onshore and on-sea activities, such as motorboats. Mn, Ni, As and Cd were from crustal materials or natural weathering, while Cr, Cu, Zn and Pb were non-crustal origin connecting with the use of anti-fouling boat paint and agricultural and/or aquacultural chemicals. This study suggested that corals could serve as good bioindicators for two types of chemical pollution in the reef system, especially for the two species P. varians and P. lutea for PAHs contaminants.

Diversity of cultivable protease-producing bacteria and their extracellular proteases associated to scleractinian corals.

Protease-producing bacteria play a vital role in degrading organic nitrogen in marine environments. However, the diversity of the bacteria and extracellular proteases has seldom been addressed, especially in communities of coral reefs. In this study, 136 extracellular protease-producing bacterial strains were isolated from seven genera of scleractinian corals from Luhuitou fringing reef, and their protease types were characterized. The massive coral had more cultivable protease-producing bacteria than branching or foliose corals. The abundance of cultivable protease-producing bacteria reached 106 CFU g−1 of coral. Phylogenetic analysis of 16S rRNA gene sequences revealed that the isolates were assigned to 24 genera, from which 20 corresponded to the phyla Firmicutes and Proteobacteria. Bacillus and Fictibacillus were retrieved from all coral samples. Moreover, Vibrio and Pseudovibrio were most prevalent in massive or foliose coral Platygyra and Montipora. In contrast, 11 genera were each identified in only one isolate. Nearly all the extracellular proteases from the bacteria were serine proteases or metalloproteases; 45.83% of isolates also released cysteine or aspartic proteases. These proteases had different hydrolytic ability against different substrates. This study represents a novel insight on the diversity of cultivable protease-producing bacteria and their extracellular proteases in scleractinian corals.

Quantifying life history demographics of the scleractinian coral genus Pocillopora at Palmyra Atoll

Characterizations of colony-specific fate are necessary to predict trajectories of coral population change accurately, and a research challenge exists to collect more robust data describing coral demographic rates and the factors that influence them. Colonial, reef-building corals present challenges to the study of demography, given that the size of individual colonies can be decoupled from age, and rates of colony growth and shrinkage can be effectively indeterminate. In this study, we use a large-area imaging approach to quantify demographic rates of the coral genus Pocillopora and test for the influence of colony-specific predictors on net change in live tissue area (labeled growth and shrinkage) and whole-colony mortality. We found that a colony’s fate was linked to its initial size, with larger colonies experiencing far lower probability of mortality, but higher probability of shrinkage, than smaller colonies. Historical effects also significantly affected colony fate, as colonies with a recent history of tissue loss experienced a higher probability of subsequent shrinkage and mortality the following year. Finally, significant variability in growth and mortality rates was linked to intra-island site differences, which we hypothesize may be driven by differences in food availability and heterotrophic feeding rates. Our work highlights the importance of colony-specific characteristics, including size and historical effects, in influencing demographic fates of corals.

Regional persistence of the extant coral genus Stephanocoenia since the Early Cretaceous in the Western Atlantic

The scleractinian coral genus Stephanocoenia was previously only known from the Western Atlantic with two Pliocene and two extant species, of which two are considered synonymous. Systematic sampling and examination of collection material revealed that the genus occurs from the Hauterivian to extant with gaps in the fossil record during the Campanian, Paleocene and Eocene. During this time the genus was restricted to the Western Atlantic and is unknown in other areas with the exception of one specimen from the Maastrichtian of the eastern Pacific. Thirteen species are separated using non-parametric statistical methods. Two species are described as new. One species remained in open nomenclature and two species can only be compared to existing species. The genus reached its highest abundance during the Early Albian with five species and the Pleistocene/extant with four species. Stephanocoenia demonstrates a regional persistence unchanged over the past 135 million years, which is unique among all post-paleozoic scleractinian corals. Stephanocoenia is also the most ancient hermatypic scleractinian coral genus, which still exists today.

New host records of scleractinian-Zanclea symbiosis from Fiji

Scleractinian corals are the host group with the greatest number of species associated with hydroids in the genus Zanclea. There are 34 nominal species and 31 genera of scleractinians reported as Zanclea hosts from a few localities across the Red Sea, Indo-Pacific, and Caribbean. However, little is known about how consistent and cosmopolitan scleractinian-Zanclea relationships are. To test their geographical consistency, we surveyed Fijian corals for Zanclea presence using both field-based surveys and analysis of in situ coral photographs. Surveys targeted 16 species and seven genera of reported Zanclea hosts and five other corals commonly found at the sites. We observed Zanclea hydroids associated with 22 species in seven genera of scleractinian corals with 17 (77%) of the species being newly reported hosts. Our findings suggest that a broad diversity of scleractinian corals hosting Zanclea remains to be documented, and although Zanclea-scleractinian associations are likely cosmopolitan in their distribution across localities, associations with specific coral species may not be.

Spatial Patterns and Environmental Settings of Non-reefal Coral Communities Across the Tropic of Cancer in the Penghu Archipelago (Pescadores), Taiwan.

Hernyi Justin Hsieh, Colin Kou-Chang Wen, Yuan-Chao Huang, Kao-Sung Chen, Chang-Feng Dai, and Chaolun Allen Chen (2016) Non-reefal coral communities occurring at the edges of scleractinian coral distribution ranges normally show a sharp gradient in the composition of coral species. Environmental and biological factors such as sea surface temperature (SST), competition with other benthos, and human disturbances might play roles in shaping the structure of coral communities. The Penghu Archipelago is located on the east side of Taiwan Strait straddling the Tropic of Cancer and hosts non-reefal coral communities. In this study, benthic surveys throughout the Penghu Archipelago were conducted and potential environmental and biological factors that shape coral species distributions were inferred by multivariate analyses. A total of 103 species representing 28 genera of scleractinian corals were recorded. Three major ecological sectors (northeast, south, and inner) were defined based on a canonical analysis of the principal coordinates of scleractinian species composition. Correlation analyses showed that scleractinians in the south and northeast sectors were strongly influenced by SST-related variables. In contrast, the coral communities in inner sector were mainly affect by turbidity or nutrition, which supposed come from human activities. Distance-based redundancy analysis showed that benthos, except soft corals, hardly interacted with scleractinian coral distributions. Our study demonstrated a distinct coral species assemblage among different islands across the Tropic of Cancer in the Penghu Archipelago. Natural and human-derived environmental factors both showed a strong correlation with coral species distribution. It's clear that either natural and human-derived factors influenced coral composition in Penghu archipelago.

Recent origin and semi-permeable species boundaries in the scleractinian coral genus Stylophora from the Red Sea.

Reticulate evolution, introgressive hybridisation, and phenotypic plasticity have been documented in scleractinian corals and have challenged our ability to interpret speciation processes. Stylophora is a key model system in coral biology and physiology, but genetic analyses have revealed that cryptic lineages concealed by morphological stasis exist in the Stylophora pistillata species complex. The Red Sea represents a hotspot for Stylophora biodiversity with six morphospecies described, two of which are regionally endemic. We investigated Stylophora species boundaries from the Red Sea and the associated Symbiodinium by sequencing seven DNA loci. Stylophora morphospecies from the Red Sea were not resolved based on mitochondrial phylogenies and showed nuclear allele sharing. Low genetic differentiation, weak isolation, and strong gene flow were found among morphospecies although no signals of genetic recombination were evident among them. Stylophora mamillata harboured Symbiodinium clade C whereas the other two Stylophora morphospecies hosted either Symbiodinium clade A or C. These evolutionary patterns suggest that either gene exchange occurs through reticulate evolution or that multiple ecomorphs of a phenotypically plastic species occur in the Red Sea. The recent origin of the lineage leading to the Red Sea Stylophora may indicate an ongoing speciation driven by environmental changes and incomplete lineage sorting.

The implementation of rare events logistic regression to predict the distribution of mesophotic hard corals across the main Hawaiian Islands.

Predictive habitat suitability models are powerful tools for cost-effective, statistically robust assessment of the environmental drivers of species distributions. The aim of this study was to develop predictive habitat suitability models for two genera of scleractinian corals (Leptoserisand Montipora) found within the mesophotic zone across the main Hawaiian Islands. The mesophotic zone (30–180 m) is challenging to reach, and therefore historically understudied, because it falls between the maximum limit of SCUBA divers and the minimum typical working depth of submersible vehicles. Here, we implement a logistic regression with rare events corrections to account for the scarcity of presence observations within the dataset. These corrections reduced the coefficient error and improved overall prediction success (73.6% and 74.3%) for both original regression models. The final models included depth, rugosity, slope, mean current velocity, and wave height as the best environmental covariates for predicting the occurrence of the two genera in the mesophotic zone. Using an objectively selected theta (“presence”) threshold, the predicted presence probability values (average of 0.051 for Leptoseris and 0.040 for Montipora) were translated to spatially-explicit habitat suitability maps of the main Hawaiian Islands at 25 m grid cell resolution. Our maps are the first of their kind to use extant presence and absence data to examine the habitat preferences of these two dominant mesophotic coral genera across Hawai‘i.

Species delimitation in the coral genus Goniopora (Scleractinia, Poritidae) from the Saudi Arabian Red Sea

Variable skeletal morphology, genotype induced plasticity, and homoplasy of skeletal structures have presented major challenges for scleractinian coral taxonomy and systematics since the 18th century. Although the recent integration of genetic and micromorphological data is helping to clarify the taxonomic confusion within the order, phylogenetic relationships and species delimitation within most coral genera are still far from settled. In the present study, the species boundaries in the scleractinian coral genus Goniopora were investigated using 199 colonies from the Saudi Arabian Red Sea and sequencing of four molecular markers: the mitochondrial intergenic spacer between CytB and NAD2, the nuclear ribosomal ITS region, and two single-copy nuclear genes (ATPsβ and CalM). DNA sequence data were analyzed using a variety of methods and exploratory species-delimitation tools. The results were broadly congruent in identifying five distinct molecular lineages within the sequenced Goniopora samples: G. somaliensis/G. savignyi, G. djiboutiensis/G. lobata, G. stokesi, G. albiconus/G. tenuidens, and G. minor/G. gracilis. Although the traditional macromorphological characters used to identify these nine morphospecies were not able to discriminate the obtained molecular clades, informative micromorphological and microstructural features (such as the micro-ornamentation and the arrangement of the columella) were recovered among the five lineages. Moreover, unique in vivo morphologies were associated with the genetic-delimited lineages, further supporting the molecular findings. This study represents the first attempt to identify species boundaries within Goniopora using a combined morpho-molecular approach. The obtained data establish a basis for future taxonomic revision of the genus, which should include colonies across its entire geographical distribution in the Indo-Pacific.

Forgotten in the taxonomic literature: resurrection of the scleractinian coral genus Sclerophyllia (Scleractinia, Lobophylliidae) from the Arabian Peninsula and its phylogenetic relationships

The monospecific scleractinian coral genus Sclerophyllia Klunzinger, 1879 was originally described from Al-Qusayr (Egypt) in the Red Sea based on a series of solitary specimens. Thenceforth, it has been considered a junior synonym of Symphyllia and Cynarina based on corallum macromorphology. In this study, several specimens of Sclerophyllia margariticola were collected on the coasts of Saudi Arabia in the northern and central Red Sea. Four molecular markers were sequenced, COI and the intergenic spacer between COI and l-rRNA from mitochondrial DNA and Histone H3 and ribosomal ITS2 from nuclear DNA. Phylogenetic trees and haplotype network analyses show that S. margariticola belongs to the family Lobophylliidae and that it is closely related to Acanthastrea maxima, an uncommon species from waters around the Arabian peninsula (the Gulf of Aden, Arabian Sea, Gulf of Oman and Persian Gulf). Sclerophyllia margariticola and A. maxima share several macro- and micromorphological characters, such as the presence of free septa, high elliptical septal teeth perpendicular to the septal margin, irregular lobate tips, very wide tooth spacing, a very strong granulation with granules scattered all along the septal sides, and a palisade interarea structure, and their micromorphology differs substantially from that of Acanthastrea echinata, the type species of Acanthastrea. Therefore, we formally resurrect Sclerophyllia, provide a revised diagnosis for the genus, and move A. maxima into Sclerophyllia.

Effects of colony size and polyp position on polyp fecundity in the scleractinian coral genus Acropora

This study examined the effects of colony size and polyp position on six variables of polyp fecundity [egg number, egg size, total egg volume, total testis volume, total gonad volume, and gonad ratio (egg volume/testis volume)] in three tabular Acropora corals (Scleractinia), A. hyacinthus, A. japonica, and A. solitaryensis. Samples were collected from various colony sizes (n = 21–30 colonies species−1), just before the predicted spawning at Kochi, Japan, in 2009. Five replicate polyps were sampled at three positions (center, middle, and outer) from the center to the marginal area in each tabular colony. Results indicated effects of colony size and polyp position on both male and female gonads polyp−1. A positive effect of colony size was observed on variables of female gonads polyp−1 (egg number, total egg volume) in A. hyacinthus only, while the positive effect on the variable of male gonads polyp−1 (total testis volume) was common in all Acropora species, with total testis volume polyp−1 increasing 2–4-fold from the small (200–400 cm2) to the large size class (5,000–9,000 cm2). Among the polyp positions, lower values were observed mostly in center polyps in A. hyacinthus, while lower values were observed only in outer polyps in the other Acropora species. The distinct patterns between A. hyacinthus and the other two Acropora species suggest different reproductive strategies at the species level. Further studies are needed to confirm the prevalence of these effects in scleractinian corals, which will broaden our understanding of reproductive life history strategies and improve the estimation of reproductive performance.

Comparison between Colony Morphology and Molecular Phylogeny in the Caribbean Scleractinian Coral Genus Madracis

A major challenge in coral biology is to find the most adequate and phylogenetically informative characters that allow for distinction of closely related coral species. Therefore, data on corallite morphology and genetic data are often combined to increase phylogenetic resolution. In this study, we address the question to which degree genetic data and quantitative information on overall coral colony morphologies identify similar groupings within closely related morphospecies of the Caribbean coral genus Madracis. Such comparison of phylogenies based on colony morphology and genetic data will also provide insight into the degree to which genotype and phenotype overlap. We have measured morphological features of three closely related Caribbean coral species of the genus Madracis (M. formosa, M. decactis and M. carmabi). Morphological differences were then compared with phylogenies of the same species based on two nuclear DNA markers, i.e. ATPSα and SRP54. Our analysis showed that phylogenetic trees based on (macroscopical) morphological properties and phylogenetic trees based on DNA markers ATPSα and SRP54 are partially similar indicating that morphological characteristics at the colony level provide another axis, in addition to commonly used features such as corallite morphology and ecological information, to delineate genetically different coral species. We discuss this new method that allows systematic quantitative comparison between morphological characteristics of entire colonies and genetic data.

Habitat differentiation in the early life stages of simultaneously mass-spawning corals

The settlement process of coral larvae following simultaneous mass-spawning remains poorly understood, particularly in terms of population and community parameters. Here, the larval settlement patterns of Acropora corals, which are the most diverse genera of scleractinian corals at the species (haplotype) level, were investigated within a single subtropical reef. Across a 4-year period (2007–2010), the mitochondrial and nuclear molecular markers of 1,073 larval settlers were analyzed. Of the 11 dominant haplotypes of recruited populations, nine exhibited non-random patterns of settlement distribution. This result suggests that the actual habitat segregation starts during the early swimming larval stages of their life history, rather than by natural selection after random settlement. In addition, the presence of a depth-related settlement pattern supports that species-specific vertical zonation of coral larvae may play a role in the establishment of habitat segregation. Moreover, in some species that showed a preference toward the shoreward area of the bay, the settlement pattern was consistent with that of the adult distribution. This result indicates that the gametes were not mixed between fore and back reefs in the period from fertilization to settlement during the mass-spawning event, even within a single small reef. Another compatible hypothesis of this pattern is that the larvae are able to recognize various types of environmental information, facilitating the selection of optimal micro-habitats. Overall, Acropora coral larvae that are produced from a simultaneous mass-spawning event may have adapted to complex reef topography by means of multi-step habitat selection at settlement, corresponding to different spatial scales.

Coral mucus stable isotope composition and labeling: experimental evidence for mucus uptake by epizoic acoelomorph worms

Mucus released by scleractinian corals can act as an important energy and nutrient carrier in coral reef ecosystems, and a distinct isotopic signature would allow following the fate of this material. This study investigates the natural C and N stable isotopic signatures of mucus released by four scleractinian coral genera (Acropora, Fungia, Pocillopora and Stylophora) in comparison with those of suspended particulate organic matter (POM) in seawater of a Northern Red Sea fringing coral reef near Aqaba, Jordan. The natural δ13C and δ15N signatures of coral mucus differed significantly from seawater POM for the majority of seasonal comparisons, but were inappropriate for explicit tracing of mucus in the coral reef food web. Thus, a labeling technique using stable isotope tracers (13C and 15N) was developed that produced δ13C values of up to 122 ± 5‰ (mean ± SE) and δ15N of up to 2,100 ± 151‰ in mucus exuded by Fungia corals. 13C and 15N-enriched compounds were rapidly (within 3 h) and light-dependently transferred from the endosymbiotic zooxanthellae to the mucus-producing coral host. The traceability of 15N-labeled mucus was examined by evaluating its uptake and potential utilization by epizoic acoelomorph Waminoa worms naturally occurring on a range of scleractinian coral taxa. This tracer experiment resulted in uptake of coral mucus by the coral-associated acoelomorphs and further demonstrated the possibility to trace stable isotope-labeled coral mucus by revealing a new trophic pathway in coral reef ecosystems.