Scleractinian Corals Research Articles

Effect of coral‐giant clam artificial reef on coral recruitment: insights for restoration and conservation efforts

Coral recruitment is a vital process for the maintenance and recovery of coral reefs, particularly due to their decline from global change. While it is well established that larval settlement cues significantly influence coral recruitment, the investigation of recruitment success associated with the surrounding community mainly focuses on algae. To investigate other factors controlling this process, we examined the impact of benthic invertebrate assemblages on coral recruitment using artificial reefs. Three types of artificial reefs (mono‐, bi‐, and tri‐species) with different assemblages of three common species, Pocillopora acuta, Acropora cytherea, and Tridacna maxima, were studied over 8 months. This study revealed that benthic assemblages play a significant role in coral recruitment and survival. High biodiversity was found to enhance coral recruitment and inhibit potential negative cues from A. cytherea. Our findings underscore the importance of preserving high biodiversity using not only hard coral but a wide range of phyla, including bivalves, in coral restoration efforts. Maintaining sustainable populations is an important goal to reach in the face of the multiple threats that impact coral reefs.

On some tropical hydroids (Cnidaria: Hydrozoa), with descriptions of four new species

The present study provides a morphological account of six tropical hydroids, of which four are described as new. Halecium turbinariae sp. nov. grows exclusively on brown algae of the genus Turbinaria (Phaeophyceae: Fucales), and contains numerous zooxanthellae in its coenosarc. Nemalecium caeruleus sp. nov. occurs in a peculiar ecological niche, viz. the crevices of scleractinian corals, and is distinguished from its congeners by its sympodial mode of branching and an original, bluish-fluorescent sheen of its polyps. Antennella flava sp. nov. belongs to the A. secundaria (Gmelin, 1791) species group, but its tissues are abundantly filled with zooxanthellae, conferring it a striking yellow coloration. Macrorhynchia fallax sp. nov. imitates the fine morphology of M. philippina Kirchenpauer, 1872, although live specimens lack the characteristic irisation of the cladia met with in the latter. The peculiar, decapod crab-associated Corymorpha balssi Stechow, 1932, so far only known from the original account, is rediscovered and redescribed based on its hydroid stage and the ready-to-detach medusae. According to the morphological features of the latter, C. bitungensis (Xu, Huang & Guo, 2013), and possibly C. juliephillipsi (Gershwin et al., 2010), are considered the mature medusa stages of the same species, and are regarded as potential junior synonyms. The controversial synonymy of Tridentata borneensis (Billard, 1925) is addressed based on the examination of new material and its comparison with part of the type series, supplemented by the reinspection of the types of several nominal species subjectively assigned earlier to its synonymy. The distinctive sculpture of the hydrothecal wall leaves little doubt that it has a recent junior synonym, viz. Sertularia vervoorti Migotto & Calder, 1998, syn. nov. Conversely, the following taxa are removed from its synonymy upon the reevaluation of their taxonomic statuses: 1) Thuiaria maldivensis Borradaile, 1905 is a valid species that has a junior synonym, namely Pasythea heterodonta Jarvis, 1922 (now Dynamena), syn. nov., the former being henceforth referred to as Dynamena maldivensis (Borradaile, 1905), comb. nov., on the account of its polyps lacking an abcauline caecum; 2) Tridentata westindica Stechow, 1919, syn. nov., is a junior synonym of Tridentata turbinata (Lamouroux, 1816); 3) Sertularia tongensis Stechow, 1919 is a valid species that has a recent junior synonym, viz. Sertularia orthogonalis Gibbons & Ryland (1989), syn. nov.; 4) Sertularia tumida Allman, 1877, whose type is reportedly lost, is removed from the synonymy of Billard’s (1925a) species, on the account on its much longer internodes; 5) Sertularia malayensis var. sorongensis Leloup, 1930 remains a subjective junior synonym; 6) also reexamined was type material of the little-known, not formerly illustrated Tridentata occulta Stechow, 1926, syn. nov. of Amphisbetia distans (Lamouroux, 1816). Additionally, we provide single- (16S rRNA or COI) and multi-locus (16S, 18S and 28S rRNA) phylogenetic analyses for many families of athecate and thecate hydroids, including at least 57 species from Bali, with 25 nominal species characterized genetically for the first time. Halecium halecinum var. minor Pictet, 1893 is raised to species, as H. minor Pictet, 1893, nov. status, on both morphological and molecular grounds. Campanularia spinulosa Bale, 1888 is assigned to the genus Obelia Péron & Lesueur, 1810, as O. spinulosa (Bale, 1888), based on its genetic affinities.

Coral reefs in transition: Temporal photoquadrat analyses and validation of underwater hyperspectral imaging for resource-efficient monitoring in Guam.

The island of Guam in the west Pacific has seen a significant decrease in coral cover since 2013. Lafac Bay, a marine protected area in northeast Guam, served as a reference site for benthic communities typical of forereefs on the windward side of the island. The staghorn coral Acropora abrotanoides is a dominant and characteristic ecosystem engineer of forereef communities on exposed shorelines. Photoquadrat surveys were conducted in 2015, 2017, and 2019, and a diver-operated hyperspectral imager (i.e., DiveRay) was used to survey the same transects in 2019. Machine learning algorithms were used to develop an automated pipeline to assess the benthic cover of 10 biotic and abiotic categories in 2019 based on hyperspectral imagery. The cover of scleractinian corals did not differ between 2015 and 2017 despite being subjected to a series of environmental disturbances in these years. Surveys in 2019 documented the almost complete decline of the habitat-defining staghorn coral Acropora abrotanoides (a practically complete disappearance from about 10% cover), a significant decrease (~75%) in the cover of other scleractinian corals, and a significant increase (~55%) in the combined cover of bare substrate, turf algae, and cyanobacteria. The drastic change in community composition suggests that the reef at Lafac Bay is transitioning to a turf algae-dominated community. However, the capacity of this reef to recover from previous disturbances suggests that this transition could be reversed, making Lafac Bay an excellent candidate for long-term monitoring. Community analyses showed no significant difference between automatically classified benthic cover estimates derived from the hyperspectral scans in 2019 and those derived from photoquadrats. These findings suggest that underwater hyperspectral imagers can be efficient and effective tools for fast, frequent, and accurate monitoring of dynamic reef communities.

Assess the level of damage to the coral reef ecosystem based on substrate coverage on Bira Island, Kepulauan Seribu, Indonesia

Abstract. Komala R, Noer MI, Miarsyah M, Widyartini DS, Handayani. 2024. Assess the level of damage to the coral reef ecosystem based on substrate coverage on Bira Island, Kepulauan Seribu, Indonesia. Biodiversitas 25: 971-977. Coral reefs are coastal ecosystems that have an important ecological and economic role. Environmental pressures cause damage to ecosystems and decrease coral biodiversity. This study aims to analyze the level of damage to coral reef ecosystems based on substrate cover and obtain the latest information on coral reef ecosystem resources. The study employs a descriptive method with a survey design, utilizing Underwater Photo Transect (UPT) sampling at various depths along the coastline. The data is analyzed using Coral Point Count with Excel extension (CPCe) for substrate cover percentage and the Shannon-Wienner index for coral diversity. The findings reveal nine categories of basic substrate cover, with living hard corals constituting 32.51%, indicating a fairly damaged state. Coral resources are identified across 53 genera and 15 families, exhibiting medium diversity across stations and depths. The study highlights the need to monitor environmental threats that could further damage coral reefs and decrease diversity. The coral reef ecosystem in Bira Island is in a relatively damaged condition, with a decline in coral biodiversity, indicating an imbalance in the ecosystem. Several recommended steps include implementing coral restoration programs, monitoring coral growth, establishing critical coral habitat protection zones, and conducting conservation efforts.

Genomics of a novel ecological phase shift: the case of a ‘weedy’ Montipora coral in Ulithi, Micronesia

Local and global ecological stressors are leading to increased documentation of phase shifts in coral reefs from healthy stony corals to macrophytes. In more rare cases, phase shifts result in sponge, zoantharian or other dominant species. In Ulithi Atoll, Federated States of Micronesia, we have documented an unusual phase shift from reefs with a diverse stony coral assemblage to reefs dominated by a single species of stony coral: Montipora sp.—a coral-to-coral phase shift. This monospecific type of reef lowers fish diversity and biomass, impacting both ecological integrity, and livelihoods of reef-dependent human communities. In this study, we used a genomic approach to characterize such a reef. We assembled a de-novo reference genome and used RAD seq data with thousands of SNPs to determine if different reefs result from sexual or asexual reproduction, if weedy Montipora fragments are transported between islands by human activities, and if there is evidence of natural selection on specific genotypes, thus favoring spreading success. We found that sexual reproduction is predominant in the focal species, that there is no evidence of human-mediated spread, and that some genomic regions might be under selection. While such results eliminate a number of spreading hypotheses, more precise dispersal maps will be important to determine the tempo and mode of ‘invasion’ of Montipora in Ulithi Atoll. This study shows that selection and adaptation may be contributing to the success of a stony coral (e.g., Phase shift). While a stony coral may be successful in a disturbed environment, it does not necessarily provide the type of habitat that is conducive to high fish biomass and coral diversity. These results serve as a cautionary tale for restoration efforts that focus on single species coral resilience rather than ecosystem function.

Depth distribution and depth adaptation of microbiomes in juvenile and adult scleractinian corals (Pocillopora verrucosa) in the central South China Sea

Depth distribution and depth adaptation of microbiomes in juvenile and adult scleractinian corals (Pocillopora verrucosa) in the central South China Sea

Symbiosis modulates gene expression of symbionts, but not coral hosts, under thermal challenge.

Increasing ocean temperatures are causing dysbiosis between coral hosts and their symbionts. Previous work suggests that coral host gene expression responds more strongly to environmental stress compared to their intracellular symbionts; however, the causes and consequences of this phenomenon remain untested. We hypothesized that symbionts are less responsive because hosts modulate symbiont environments to buffer stress. To test this hypothesis, we leveraged the facultative symbiosis between the scleractinian coral Oculina arbuscula and its symbiont Breviolum psygmophilum to characterize gene expression responses of both symbiotic partners in and ex hospite under thermal challenges. To characterize host and in hospite symbiont responses, symbiotic and aposymbiotic O. arbuscula were exposed to three treatments: (1) control (18°C), (2) heat (32°C), and (3) cold (6°C). This experiment was replicated with B. psygmophilum cultured from O. arbuscula to characterize ex hospite symbiont responses. Both thermal challenges elicited classic environmental stress responses (ESRs) in O. arbuscula regardless of symbiotic state, with hosts responding more strongly to cold challenge. Hosts also exhibited stronger responses than in hospite symbionts. In and ex hospite B. psygmophilum both down-regulated gene ontology pathways associated with photosynthesis under thermal challenge; however, ex hospite symbionts exhibited greater gene expression plasticity and differential expression of genes associated with ESRs. Taken together, these findings suggest that O. arbuscula hosts may buffer environments of B. psygmophilum symbionts; however, we outline the future work needed to confirm this hypothesis.

Dynamic of coral recruits in the Karimunjawa National Park, Central Java, Indonesia

Abstract. Tarigan SAR, Munasik, Wijayanti DP, Muhidin, Rohman EA, Pardede S. 2024. Dynamic of coral recruits in the Karimunjawa National Park, Central Java, Indonesia. Biodiversitas 25: 869-880. After a disturbance event, coral reefs can recover naturally by recruiting new corals. These can be affected by environmental factors like the substrate's physical and biological structure, predation, and accidental mortality of recruits by grazers, as well as the number and size of parent corals supplying larvae. This study examined the connection between newly recruited corals and biological factors such as sea urchin density, herbivorous fish abundance, and hard coral coverage. The study was monitored changes in coral cover, juvenile coral density, herbivore abundance, and hard coral coverage at 43 locations and two depths (shallow; 2-3 m) and deep (8-10 m) from 2013 to 2022. The locations were distributed across six different zone systems: the core zone, protection zone, tourism zone, traditional fisheries zone, aquaculture zone, and rehabilitation zone. Multiple Linae Regression, ANOVA test, and Principal Component Analysis were employed to assess the relationship between coral recruitment and other variables. Results indicated that the coral recruitment density was not significantly different when comparing different zoning systems (two-way ANOVA test, P-value>0.05). Based on the PCA analysis, we found that in 2013 and 2019, excavator, sea urchin, browser, and hard coral have a positive relationship with coral recruitment, which implies that coral recruitment would increase as sea urchin, browser, and hard coral increase. Meanwhile, in 2019 and 2022, coral recruitment has a negative relationship with scraper, and also with hard coral growth (although only in 2022), implying that coral recruitment would decrease if scraper and hard coral increase. The study recommends restoring the role of herbivorous species in Karimunjawa National Park (KNP) by prioritizing them in conservation efforts and managing their populations.

Cellular adaptations of the scleractinian coral Madracis pharensis to chronic oil pollution in a Mediterranean shipwreck

Chemical pollution in marine ecosystems is a factor of stress interacting in multiple and complex ways with other major causes of deterioration, such as warming seas due to climate change. Here we surveyed epibenthic communities from a shipwreck in the Levantine Basin for temporal and spatial changes in the community in relation to chronic oil pollution, comparing results collected from an area of the wreck characterized by chronic oil leakage with another area not affected by oil. Polycyclic aromatic hydrocarbons (PAHs) bioaccumulation analyses were integrated with characterization of the efficiency of xenobiotics biotransformation processes and antioxidant network of the scleractinian coral Madracis pharensis, chosen as bioindicator species. Results highlighted the two areas hosting different epibenthic communities over a period of 11 years. Significant changes in the percentage cover of M. pharensis could be the result of recent mass mortality associated to Marine Heat Waves. Biological investigation conducted in M. pharensis tissues revealed an increased content of PAHs in specimens collected from the oil-impacted area, coupled with an increased capability of oxyradicals scavenging capacity and a lower functionality of phase II biotransformation mechanisms associated to glutathione S-transferase. Overall, the results suggest that M. pharensis has the capability to develop cellular and physiological adaptations to chemical-mediated stress, with yet unknown possible energy trade-offs to sustain stress response.

Quantifying the δ15N trophic offset in a cold-water scleractinian coral (CWC): implications for the CWC diet and coral δ15N as a marine N cycle proxy

Abstract. The nitrogen (N) isotope composition (δ15N) of cold-water corals is a promising proxy for reconstructing past ocean N cycling, as a strong correlation was found between the δ15N of the organic nitrogen preserved in coral skeletons and the δ15N of particulate organic matter exported from the surface ocean. However, a large offset of 8 ‰–9 ‰ between the δ15N recorded by the coral and that of exported particulate organic matter remains unexplained. The 8 ‰–9 ‰ offset may signal a higher trophic level of coral dietary sources, an unusually large trophic isotope effect or a biosynthetic δ15N offset between the coral's soft tissue and skeletal organic matter, or some combinations of these factors. To understand the origin of the offset and further validate the proxy, we investigated the trophic ecology of the asymbiotic scleractinian cold-water coral Balanophyllia elegans, both in a laboratory setting and in its natural habitat. A long-term incubation experiment of B. elegans fed on an isotopically controlled diet yielded a canonical trophic isotope effect of 3.0 ± 0.1 ‰ between coral soft tissue and the Artemia prey. The trophic isotope effect was not detectably influenced by sustained food limitation. A long N turnover of coral soft tissue, expressed as an e-folding time, of 291 ± 15 d in the well-fed incubations indicates that coral skeleton δ15N is not likely to track subannual (e.g., seasonal) variability in diet δ15N. Specimens of B. elegans from the subtidal zone near San Juan Channel (WA, USA) revealed a modest difference of 1.2 ± 0.6 ‰ between soft tissue and skeletal δ15N. The δ15N of the coral soft tissue was 12.0 ± 0.6 ‰, which was ∼6 ‰ higher than that of suspended organic material that was comprised dominantly of phytoplankton – suggesting that phytoplankton is not the primary component of B. elegans' diet. An analysis of size-fractionated net tow material suggests that B. elegans fed predominantly on a size class of zooplankton ≥500 µm, implicating a two-level trophic transfer between phytoplankton material and coral tissue. These results point to a feeding strategy that may result in an influence of the regional food web structure on the cold-water coral δ15N. This factor should be taken into consideration when applying the proxy to paleo-oceanographic studies of ocean N cycling.

The coral microbiome in sickness, in health and in a changing world.

Stony corals, the engines and engineers of reef ecosystems, face unprecedented threats from anthropogenic environmental change. Corals are holobionts that comprise the cnidarian animal host and a diverse community of bacteria, archaea, viruses and eukaryotic microorganisms. Recent research shows that the bacterial microbiome has a pivotal role in coral biology. A healthy bacterial assemblage contributes to nutrient cycling and stress resilience, but pollution, overfishing and climate change can break down these symbiotic relationships, which results in disease, bleaching and, ultimately, coral death. Although progress has been made in characterizing the spatial-temporal diversity of bacteria, we are only beginning to appreciate their functional contribution. In this Review, we summarize the ecological and metabolic interactions between bacteria and other holobiont members, highlight the biotic and abiotic factors influencing the structure of bacterial communities and discuss the impact of climate change on these communities and their coral hosts. We emphasize how microbiome-based interventions can help to decipher key mechanisms underpinning coral health and promote reef resilience. Finally, we explore how recent technological developments may be harnessed to address some of the most pressing challenges in coral microbiology, providing a road map for future research in this field.

Insights into the molecular mechanisms underlying the different heat tolerance of the scleractinian coral Pavona decussata

Insights into the molecular mechanisms underlying the different heat tolerance of the scleractinian coral Pavona decussata

Depth variation in benthic community response to repeated marine heatwaves on remote Central Indian Ocean reefs.

Coral reefs are increasingly impacted by climate-induced warming events. However, there is limited empirical evidence on the variation in the response of shallow coral reef communities to thermal stress across depths. Here, we assess depth-dependent changes in coral reef benthic communities following successive marine heatwaves from 2015 to 2017 across a 5-25 m depth gradient in the remote Chagos Archipelago, Central Indian Ocean. Our analyses show an overall decline in hard and soft coral cover and an increase in crustose coralline algae, sponge and reef pavement following successive marine heatwaves on the remote reef system. Our findings indicate that the changes in benthic communities in response to elevated seawater temperatures varied across depths. We found greater changes in benthic group cover at shallow depths (5-15 m) compared with deeper zones (15-25 m). The loss of hard coral cover was better predicted by initial thermal stress, while the loss of soft coral was associated with repeated thermal stress following successive warming events. Our study shows that benthic communities extending to 25 m depth were impacted by successive marine heatwaves, supporting concerns about the resilience of shallow coral reef communities to increasingly severe climate-driven warming events.

Response of two temperate scleractinian corals to projected ocean warming and marine heatwaves.

The Mediterranean Sea is a hotspot of global change, particularly exposed to ocean warming and the increasing occurrence of marine heatwaves (MHWs). However, experiments based on long-term temperature data from the field are scarce. Here, we investigate the response of the zooxanthellate coral Cladocora caespitosa and the azooxanthellate coral Astroides calycularis to future warming and MHWs based on 8 years of in situ data. Corals were maintained in the laboratory for five months under four temperature conditions: Warming (3.2°C above the in situ mean from 2012 to 2020), Heatwave (temperatures of 2018 with two heatwaves), Ambient (in situ mean) and Cool (deeper water temperatures). Under the Warming treatment, some C. caespitosa colonies severely bleached and A. calycularis colonies presented necrosis. Cladocora caespitosa symbiosis was impaired by temperature with a decrease in the density of endosymbiotic algae and an increase in per cent whiteness in all the treatments except for the coolest. Recovery for both species was observed through different mechanisms such as regrowth of polyps of A. calycularis and recovery of pigmentation for C. caespitosa. These results suggest that A. calycularis and C. caespitosa may be resilient to heat stress and can recover from physiological stresses caused by heatwaves in the laboratory.

Unidentified fish sounds as indicators of coral reef health and comparison to other acoustic methods

As biodiversity hotspots, coral reefs are rich with sound cues. Monitoring these soundscapes for changes is essential as coral reefs decline around the world rapidly. Despite this, acoustic metrics that reliably represent reef health are still debated, and ground-truthing of methods are limited. We sought to investigate the occurrence and prevalence of fish sounds in relation to reef health, providing a foundation to compare assessment methods. We first quantified fish call rates for three U.S. Virgin Islands reefs exhibiting different community assemblages, by manually annotating fish calls across 8 days per site. Call rates were then compared with traditional visual surveys, and several acoustic methods commonly used in underwater soundscape research. Manually detected fish call rates successfully differentiated between the three reefs, capturing variation in crepuscular activity levels and predicting hard coral cover, fish abundance, and fish species richness. Meanwhile, most acoustic indices failed to parse out fine distinctions among the three sites, although sound pressure level showed the greatest correlation to call rates. Development of methods to improve the utilization of unknown fish sounds, such as automatic detection and classification tools, supports global sound library efforts and is essential to implement large-scale passive acoustic monitoring of coral reefs.

Unidentified fish sounds as indicators of coral reef health and comparison to other acoustic methods

The global decline of coral reefs is a major contributor to the global biodiversity crisis and requires improved monitoring at these critically important habitats. Non-invasive passive acoustic assessments may address this need, leveraging the rich variety and spatiotemporal variability of biological sounds present in coral reef environments and offering near-continuous temporal coverage. Despite this, acoustic metrics that reliably represent coral reef health are still debated, and ground-truthing of methods is limited. Here we investigated how the prevalence of low frequency biotic sounds (without species information) relates to coral reef health, providing a foundation from which one can compare assessment methods. We first quantified call rates of these low frequency sounds for three reefs exhibiting different community assemblages around St. John, U.S. Virgin Islands, by manually annotating presumed fish noises for 1 min every 30 min across 8 days for each site. Annotated days were selected at key points across lunar cycles. These call rates were then compared with traditional visual surveys, and several acoustic methods and indices commonly used in underwater soundscape research. We found that, overall, manually detected fish call rates successfully differentiated between the three reefs, capturing variation in crepuscular activity levels–a pattern consistent with previous work that highlights the importance of diel choruses. Moreover, fish vocal rates were predictors of hard coral cover, fish abundance, and fish species richness, while most acoustic indices failed to parse out fine distinctions among the three sites. Some, such as the Acoustic Complexity Index, failed to reveal any expected differences between sites or times of day, while the Bioacoustic Index could only identify the most acoustically active reef, otherwise having weak correlations to visual metrics. Of the indices tested, root-mean-squared sound pressure level and Acoustic Entropy, both calculated in the low frequency fish band (50–1,200 Hz), showed the strongest association with visual health measures. These findings present an important step toward using soundscape cues for reef health assessments. The limited generalizability of acoustic indices across different locations emphasizes the need for caution in their application. Therefore, it is crucial to improve methods utilizing fish sounds, such as automatic fish call detectors that are able to generalize well to new soundscapes.

Annotated genome and transcriptome of the endangered Caribbean mountainous star coral (Orbicella faveolata) using PacBio long-read sequencing

Long-read sequencing is revolutionizing de-novo genome assemblies, with continued advancements making it more readily available for previously understudied, non-model organisms. Stony corals are one such example, with long-read de-novo genome assemblies now starting to be publicly available, opening the door for a wide array of ‘omics-based research. Here we present a new de-novo genome assembly for the endangered Caribbean star coral, Orbicella faveolata, using PacBio circular consensus reads. Our genome assembly improved the contiguity (51 versus 1,933 contigs) and complete and single copy BUSCO orthologs (93.6% versus 85.3%, database metazoa_odb10), compared to the currently available reference genome generated using short-read methodologies. Our new de-novo assembled genome also showed comparable quality metrics to other coral long-read genomes. Telomeric repeat analysis identified putative chromosomes in our scaffolded assembly, with these repeats at either one, or both ends, of scaffolded contigs. We identified 32,172 protein coding genes in our assembly through use of long-read RNA sequencing (ISO-seq) of additional O. faveolata fragments exposed to a range of abiotic and biotic treatments, and publicly available short-read RNA-seq data. With anthropogenic influences heavily affecting O. faveolata, as well as its increasing incorporation into reef restoration activities, this updated genome resource can be used for population genomics and other ‘omics analyses to aid in the conservation of this species.

Molecular phylogenetic classification of scleractinian corals from Weizhou Island, China

Abstract Scleractinian corals play important roles in the maintenance and restoration of coral systems. However, the evolutionary relationships among species remain unclear, mostly due to the limitations of traditional coral classifications because of their ecophenotypic variation and morphological plasticity. Thus, here we aimed to reconstruct the phylogenetic relationships of corals through single- and multi-gene analyses based on 116 colonies (14 families and 49 species) from Weizhou Island, China, and five molecular markers (CO1, 16S rRNA, 12S rRNA, H3, and ITS). The results reveal four cryptic species (Platygyra pini, Platygyra verweyi, Psammocora nierstraszi, and Coscinaraea columna). In single-gene analyses, mitochondrial genes can classify taxa at the family but not genus level, and vice versa for nuclear genes. Species are divided into complex and robust corals based on multi-gene analysis. Within robust corals, Merulinidae (Group XVII) is classified into eight subclades, and Dipsastraea, Favites, and Goniastrea are polyphyletic. Complex corals comprise the monophyletic Acroporidae (VI), Agariciidae (VII), Euphylliidae (V), Porites (III), and Dendrophylliidae (II). Notably, Turbinaria peltata is highly divergent from its congeners and clusters. Multi-gene analysis proved to be more accurate than single-gene analysis in elucidating phylogenetic relationships among corals. This study enhances our understanding of the diversity, evolution, and conservation of corals from Weizhou Island.

Epizoic yellow sponge (Poecilosclerida, Demospongiae) expansion on living Scleractinian corals in Bintan, Riau Archipelago, Indonesia

AbstractCoral reef ecosystems in Indonesia are under threat due to changes in the environment driven by global climate change, along with local disturbances such as sedimentation and eutrophication. Consequently, comprehensive coral reef monitoring activities have been initiated at numerous locations across Indonesia. In this study, the findings from coral reef health surveys across 14 reef sites (within 40 hectares) in the Bintan area (Riau Archipelago, Indonesia; 100 km southeast of Singapore) revealed a potentially novel epizoic yellow sponge species (Phorbas sp.) that overgrows coral colonies. This species, tentatively classified as a new Phorbas sp. (order Poecilosclerida: family Hymedesmiidae), was identified through a combined approach employing classical taxonomic methods along with DNA barcoding using the cytochrome c oxidase I (COI) gene. At every site, three permanent 20‐m transects were established to annually monitor live coral coverage and species composition between 2014 and 2017. The survey indicated a notable change in the overall coral cover during this period. The abundance of coral diseases was investigated in 2014 and 2017. Additionally, the progress of Phorbas sp., was closely monitored (i.e., every second day for one week) at Bintan Island (site 11) during the dry season in August 2017. This approach aimed to approximate the relative impact of each incident on the coral's condition. The results indicated that the most comprehensive change occurred due to the overgrowth of Phorbas sp., which affected 12 scleractinian coral species across eight genera in almost all sites except one. The abundance of this epizoic sponge infestation was highest at Pulau Beralas Pasir (site 10), constituting 22.9% of all recorded life forms, and lowest at Pulau Pangkil‐Besar (site 13), with only 0.7%. The expansion of the thin yellow sponge tissue was estimated to increase by up to 0.51 ± 0.48 cm2 per day on Porites coral.

Looking for the sponge loop: analyses of detritus on a Caribbean forereef using stable isotope and eDNA metabarcoding techniques.

Coral reefs are biodiverse ecosystems that rely on trophodynamic transfers from primary producers to consumers through the detrital pathway. The sponge loop hypothesis proposes that sponges consume dissolved organic carbon (DOC) and produce large quantities of detritus on coral reefs, with this turn-over approaching the daily gross primary production of the reef ecosystem. In this study, we collected samples of detritus in the epilithic algal matrix (EAM) and samples from potential sources of detritus over two seasons from the forereef at Carrie Bow Cay, Belize. We chose this location to maximize the likelihood of finding support for the sponge loop hypothesis because Caribbean reefs have higher sponge abundances than other tropical reefs worldwide and the Mesoamerican barrier reef is an archetypal coral reef ecosystem. We used stable isotope analyses and eDNA metabarcoding to determine the composition of the detritus. We determined that the EAM detritus was derived from a variety of benthic and pelagic sources, with primary producers (micro- and macroalgae) as major contributors and metazoans (Arthropoda, Porifera, Cnidaria, Mollusca) as minor contributors. None of the sponge species that reportedly produce detritus were present in EAM detritus. The cnidarian signature in EAM detritus was dominated by octocorals, with a scarcity of hard corals. The composition of detritus also varied seasonally. The negligible contribution of sponges to reef detritus contrasts with the detrital pathway originally proposed in the sponge loop hypothesis. The findings indicate a mix of pelagic and benthic sources in the calmer summer and primarily benthic sources in the more turbulent spring.