Coral Larvae Research Articles

Environmental constraints on the mode of symbiont transmission in corals

Theory predicts that passing symbionts directly from parent to offspring should benefit the host by reducing conflict between diverse symbionts and benefit the symbiont by guaranteeing transmission. However, in some symbiotic associations, such as those between corals and algae of the family Symbiodiniaceae, vertical transmission is rare, suggesting a substantial cost. Here, we show that coral larvae which contained symbionts had lower survivorship than larvae of the same species that lacked symbionts when exposed to natural sunlight. Higher activity of antioxidant defenses and higher levels of oxidative cellular damage observed in symbiotic larvae suggest that reactive oxygen species, produced by stress on the photosynthetic apparatus of the symbionts, are responsible for these higher rates of mortality under solar radiation. We hypothesize that symbionts are a burden in the early life history of broadcast spawning corals under conditions typically experienced on the ocean surface during dispersal. This is one possible reason why species with an obligate pre-motile period of between 12 and 36 h very rarely have vertical transmission of symbionts, in contrast to species whose larvae are small or swim on release that often have vertical transmission of symbionts.

Supplementation of exogenous lipids via liposomes improves coral larvae settlement post-cryopreservation and nano-laser warming

Coral reefs worldwide are receding because of detrimental human activities, and cryopreservation of coral larvae would ensure that their genetic biodiversity is not irremediably lost. In recent years, the vitrification and laser warming of coral propagules has demonstrated promising results. During cryopreservation, cellular membranes undergo substantial reconfigurations that may affect survival. Fat enrichment may alter the physical proprieties of cell membranes and improve resistance to low temperatures. Therefore, the aim of this study was to determine whether supplementation of exogenous lipids using liposomes would improve cryosurvival and further development of the vitrified and laser-warmed coral larvae of Seriatopora caliendrum and Pocillopora verrucosa. A vitrification solution (VS) composed of 2 M ethylene glycol (EG), 1 M propylene glycol (PG), 40% (w/v) Ficoll, and 10% gold nanoparticles (at a final concentration of 1.2 × 1018 particles/m3 and an optimised emission wavelength of 535 nm) was chosen. Coral larvae were subjected to vitrification with VS incorporating one of four lipid classes: phosphatidylcholine (PC), phosphatidylethanolamine (PE), erucic acid (EA), and linoleic acid (LA). Warming was achieved using a single laser pulse (300 V, 10 ms pulse width, 2 mm laser beam diameter). A significantly higher vitality rate was observed in S. caliendrum larvae subjected to vitrification and laser warming with EA-incorporated VS, and P. verrucosa larvae vitrified and laser warmed using PE-incorporated VS achieved a significantly higher settlement rate. Our study demonstrated that supplementation of exogenous lipids with liposomes enhances coral larvae cryotolerance and improves cryopreservation outcomes. Lipid enrichment may play a key role in cryobanking coral propagules, and in propagule development after thawing.

Modelled larval supply predicts coral population recovery potential following disturbance

It is hypothesized that spatio-temporal variability in larval supply is caused by multiple biophysical drivers which correlate with the occurrence of recruitment pulses, influencing the recovery potential of coral reefs following large-scale disturbances. Here, we used a larval dispersal model to explore coral larvae dispersal patterns under variable oceanographic conditions, densities of parental colonies, and taxon-specific biology of propagules. Model predictions were validated with observed settlement and recruitment data to test the robustness of larval dispersal modelling for forecasting the recovery potential of study reefs. The model was applied to the western Pacific archipelago of Palau for 3 yr before and after major typhoon disturbances, and simulations were run and validated for 2 major broadcast-spawning reef-building taxa:AcroporaandPorites.Investigations into the relative role of physical (currents, wind, waves) and biological (taxa, disturbance impact) parameters on overall larval supply show that low wind speeds and the intermittent occurrence of north and southwest oceanic currents contributed significantly to enhancing larval supply at the scale of the archipelago. Reduced parental colony densities on eastern reefs following disturbances did not have a major impact on predicted larval supply patterns. Relatively low larval supply to most of the disturbed eastern reefs is predicted during the most common oceanographic conditions, forecasting low recovery potential through larval recruitment. Mapping the spatio-temporal dynamics of larval supply and identifying barriers to dispersal from intact to disturbed reefs can help predict recovery patterns across reef communities.

Exploring Traits of Engineered Coral Entities to be Employed in Reef Restoration

Aggregated settlement of coral larvae results in a complex array of compatible (chimerism) and incompatible (rejection) allogenic responses. Each chimeric assemblage is considered as a distinct biological entity, subjected to selection, however, the literature lacks the evolutionary and ecological functions assigned to these units of selection. Here, we examined the effects of creating chimera/rejecting partners in terms of growth and survival under prolonged field conditions. Bi/multichimeras, bi/multi-rejecting entities, and genetically homogenous colonies (GHC) of the coral Stylophora pistillata were monitored under prolonged field conditions in a mid-water floating nursery in the northern Red Sea. Results revealed an increased aerial size and aeroxial ecological volume for rejected and chimeric entities compared to GHCs. At age 18 months, there were no significant differences in these parameters among the entities and traits, and rejecting partners did not differ from GHC. However, survival probabilities were significantly higher for chimeras that further revealed disparate initiation of up-growing branches and high diversity of chimeric phenotypes. These results suggest enhanced fitness for chimerism, augmenting earlier alluded chimeric benefits that trail the increased size at crucial early life-stages. Adding chimerism to the tool-box of reef restoration may enhance coral fitness in mitigating anthropogenic/climate change impacts.

Fecal pellets of giant clams as a route for transporting Symbiodiniaceae to corals.

Because more than 80% of species of gamete-spawning corals, including most Acroporidae species, do not inherit Symbiodiniaceae from their parents, they must acquire symbiont cells from sources in their environment. To determine whether photosynthetically competent Symbiodiniaceae expelled as fecal pellets from giant clams are capable of colonizing corals, we conducted laboratory experiments in which planula larvae of Acropora tenuis were inoculated with the cells in fecal pellets obtained from Tridacna crocea. T. crocea fecal pellets were administered once a day, and three days later, cells of Symbiodiniaceae from the fecal pellets had been taken up by the coral larvae. T. crocea fecal pellets were not supplied from the 4th day until the 8th day, and the cell densities in the larvae increased until the 8th day, which indicated the successful colonization by Symbiodiniaceae. The control group exhibited the highest mean percentage of larvae (100%) that were successfully colonized by culture strains of Symbiodiniaceae, and larvae inoculated with fecal pellets reached a colonization percentage of 66.7 ~ 96.7% on the 8th day. The highest colonization rate was achieved with the fecal pellets containing cells with high photosynthetic competency (Fv/Fm). Interestingly, the genetic composition of Symbiodiniaceae in the larvae retrieved on the 8th day differed from that in the fecal pellets and showed exclusive domination of the genus Symbiodinium. A minor but significant population of the genus Cladocopium in the fecal pellets was not inherited by the larvae. These experiments provided the first demonstration that the Symbiodiniaceae from tridacnine clams provided via fecal pellets can colonize and even proliferate in coral larvae.

An unusual microbiome characterises a spatially-aggressive crustose alga rapidly overgrowing shallow Caribbean reefs

Several species of crustose coralline algae (CCA) and their associated microbial biofilms play important roles in determining the settlement location of scleractinian corals on tropical reefs. In recent decades, peyssonnelid algal crusts (PAC) have become spatial dominants across large areas of shallow Caribbean reefs, where they appear to deter the recruitment of scleractinians. Our genetic investigations of PAC in St. John, US Virgin Islands, amplifying the large-subunit ribosomal RNA and psbA protein D1 marker genes, revealed them to be identical to Ramicrusta textilis previously reported overgrowing corals in Jamaica. Specimens of PAC sampled from the Honduras were likewise identical, confirming that this crustose alga inhabits the easternmost and westernmost regions of the Caribbean. We also analysed 16S rDNA tag amplicon libraries of the biofilms associated with PAC and sympatric CCA, which is favoured for coral settlement. Our results show that the microbial communities on PAC (vs. CCA) are characterized by significantly lower numbers of the epibiotic bacterial genus Pseudoalteromonas, which facilitates the recruitment and settlement of marine invertebrates. From these data, we infer that PAC are therefore unlikely to be attractive as settlement sites for coral larvae. Given the significant ecological change anticipated on these reefs due to increasing cover of PAC, there is an urgent need to further investigate competitive interactions between PAC and scleractinian corals, and elucidate the role of PAC and their associated microbiomes in accentuating phase shifts from coral to algae on tropical reefs.

Potential Acclimatization and Adaptive Responses of Adult and Trans-Generation Coral Larvae From a Naturally Acidified Habitat

Coral reefs are one of the most susceptible ecosystems to ocean acidification (OA) caused by increasing atmospheric carbon dioxide (CO2). OA is suspected to impact the calcification rate of corals as well as multiple early life stages including larval and settlement stages. Meanwhile, there is now a strong interest in evaluating if organisms have the potential for acclimatization or adaptation to OA. Here, by taking advantage of a naturally acidified site in Nikko Bay, Palau where corals are presumably exposed to high CO2 conditions for their entire life history, we tested if adult and the next-generation larvae of the brooder coral Pocillopora acuta originating from the high-CO2 site are more tolerant to high CO2 conditions compared to the individuals from a control site. Larvae released from adults collected from the high-CO2 site within the bay and a control site outside the bay were reciprocally cultivated under experimental control or high-CO2 seawater conditions to evaluate their physiology. Additionally, reciprocal transplantation of adult P. acuta corals were conducted between the high-CO2 and control sites in the field. The larvae originating from the control site showed lower Chlorophyll-a content and lipid percentages when reared under high-CO2 compared to control seawater conditions, while larvae originating from the high-CO2 site did not. Additionally, all 10 individuals of adult P. acuta from control site died when transplanted within the bay, while all P. acuta corals within the bay survived at both control and high-CO2 site. Furthermore, P. acuta within the bay showed higher calcification and net photosynthesis rates when exposed to the condition they originated from. These results are one of the first results that indicate the possibility that the long-living corals could enable to show local adaptation to different environmental conditions including high seawater pCO2.

Enhancing coral recruitment through assisted mass settlement of cultured coral larvae.

The escalating rate at which coral communities are declining globally requires urgent intervention and new approaches to reef management to reduce and halt further coral loss. For reef systems with limited natural larval supply, the introduction of large numbers of competent coral larvae directly to natural reef substrata provides a potentially useful approach to replenish adult coral populations. While few experiments have tested this approach, only one experiment has demonstrated its long-term success to date. Given the differences in life-history traits among corals, and different sensitivities of larvae to abiotic and biotic factors, coupled with the dynamic nature of post-settlement survivorship and recruitment processes, trials of the larval enhancement technique with larvae of different coral species are needed to test the broader applicability and viability of this approach. Accordingly, in this paper we examine the applicability of the larval enhancement technique to restore a population of Acropora loripes in the Bolinao-Anda Reef Complex, Pangasinan, northwestern Philippines. Larvae were cultured ex situ following spawning of collected A. loripes colonies in June 2014. Competent larvae were transported to degraded reef areas and approximately 300,000 larvae were introduced in each of three 6 × 4 m plots directly on the reef. Fine mesh enclosures retained the larvae inside each treatment plot for five days. Three adjacent 6 × 4 m plots that served as controls were also covered with mesh enclosures, but no larvae were introduced. Each plot contained ten 10 × 10 cm conditioned settlement tiles cut from dead tabulate Acropora that were used to quantify initial larval settlement. After allowing larval settlement for five days, mean settlement on tiles from the larval enhancement plots that were monitored under stereomicroscopes was significantly higher (27.8 ± 6.7 spat per tile) than in control plots, in which not a single recruit was recorded. Post-settlement survivorship and growth of spat and coral recruits on tiles and reef substrata inside the experimental plots were monitored periodically for 35 months. After 35 months, the mean size of each of the remaining 47 A. loripes coral colonies surviving on the reef substrata was 438.1 ± 5.4 cm3, with a mean diameter of 7.9 ± 0.6 cm. The average production cost for each of the surviving A. loripes colonies at 35 months was USD 35.20. These colonies are expected to spawn and contribute to the natural larval pool when they become reproductively mature, thereby enhancing natural coral recovery in the area. This study demonstrates that mass coral larval enhancement can be successfully used for restoring populations of coral species with different life-history traits, and the techniques can rapidly increase larval recruitment rates on degraded reef areas, hence catalysing the regeneration of declining coral populations.

Whole-Genome Transcriptome Analyses of Native Symbionts Reveal Host Coral Genomic Novelties for Establishing Coral-Algae Symbioses.

Reef-building corals and photosynthetic, endosymbiotic algae of the family Symbiodiniaceae establish mutualistic relationships that are fundamental to coral biology, enabling coral reefs to support a vast diversity of marine species. Although numerous types of Symbiodiniaceae occur in coral reef environments, Acropora corals select specific types in early life stages. In order to study molecular mechanisms of coral–algal symbioses occurring in nature, we performed whole-genome transcriptomic analyses of Acropora tenuis larvae inoculated with Symbiodinium microadriaticum strains isolated from an Acropora recruit. In order to identify genes specifically involved in symbioses with native symbionts in early life stages, we also investigated transcriptomic responses of Acropora larvae exposed to closely related, nonsymbiotic, and occasionally symbiotic Symbiodinium strains. We found that the number of differentially expressed genes was largest when larvae acquired native symbionts. Repertoires of differentially expressed genes indicated that corals reduced amino acid, sugar, and lipid metabolism, such that metabolic enzymes performing these functions were derived primarily from S. microadriaticum rather than from A. tenuis. Upregulated gene expression of transporters for those metabolites occurred only when coral larvae acquired their natural symbionts, suggesting active utilization of native symbionts by host corals. We also discovered that in Acropora, genes for sugar and amino acid transporters, prosaposin-like, and Notch ligand-like, were upregulated only in response to native symbionts, and included tandemly duplicated genes. Gene duplications in coral genomes may have been essential to establish genomic novelties for coral–algae symbiosis.

Warm temperature alters the chemical cue preference of Acropora tenuis and Heliopora coerulea larvae

Larvae released into the water column rely on chemical cues from the benthos for successful settlement. However, larval preference for substrates may be affected by rising seawater temperature brought about by global climate change. In this study, we examined the effect of elevated temperature on chemical cue preference by larvae of the scleractinian coral, Acropora tenuis, and the octocoral, Heliopora coerulea, collected from northwestern Philippines. At ambient temperature (28 °C), both H. coerulea and A. tenuis larvae showed preference for substrates containing either crustose coralline algae or crude ethanolic extracts from conspecific or congeneric corals. In contrast, at higher temperature (30 °C), greater preference was shown for substrates containing the crude extract from conspecific or congeneric corals. These results demonstrate that elevated temperature can change larval substrate preference, which will have downstream impacts on crucial biological processes, such as larval settlement and recruitment.

Coral larvae avoid substratum exploration and settlement in low-oxygen environments

Oxygen is a critical resource that mediates a multitude of essential processes and interactions at multiple scales on coral reefs. In adult corals, it can directly or indirectly impact physiological processes, such as photosynthesis, respiration, and calcification. Moreover, many corals bleach as a consequence of being exposed to low oxygen. The sessile adult phase of corals makes habitat selection crucial for post-settlement survival and thus their pelagic larvae use a diverse array of cues to determine a suitable spot for settlement. However, the effects of oxygen on the early life stages of corals are still poorly known. This study investigated the importance of oxygen as a potential settlement cue and its effect on swimming and settlement behavior of coral larvae of two Acropora species. Two experiments were performed, one investigating coral larval swimming behavior under different oxygen conditions and the other studying coral larval settlement along an oxygen gradient. Bottom exploration, expressed as the percent of A. cytherea and A. pulchra larvae in the bottom section of experimental cylinders, was reduced by 96% and 100%, respectively, in hypoxic water compared to normoxic water. When offered the choice to settle on an otherwise preferred settlement substrate (Titanoderma prototypum) along an oxygen gradient, larvae of both coral species settled almost exclusively on T. prototypum fragments placed in well-oxygenated environments, with settlement rates increasing nonlinearly with oxygen concentrations. These results suggest that low-oxygen areas can negatively influence the settlement success of coral larvae and that oxygen concentration may be used as a cue for coral larval swimming and settlement behavior.

A step-down photophobic response in coral larvae: implications for the light-dependent distribution of the common reef coral, Acropora tenuis

Behavioral responses to environmental factors at the planktonic larval stage can have a crucial influence on habitat selection and therefore adult distributions in many benthic organisms. Reef-building corals show strong patterns of zonation across depth or underwater topography, with different suites of species aggregating in different light environments. One potential mechanism driving this pattern is the response of free-swimming larvae to light. However, there is little experimental support for this hypothesis; in particular, there are few direct and quantitative observations of larval behavior in response to light. Here, we analyzed the swimming behavior of larvae of the common reef coral Acropora tenuis under various light conditions. Larvae exhibited a step-down photophobic response, i.e. a marked decrease in swimming speed, in response to a rapid attenuation (step-down) of light intensity. Observations of larvae under different wavelengths indicated that only the loss of blue light (wavelengths between 400 and 500 nm) produced a significant response. Mathematical simulations of this step-down photophobic response indicate that larvae will aggregate in the lighter areas of two-dimensional large rectangular fields. These results suggest that the step-down photophobic response of coral larvae may play an important role in determining where larval settle on the reef.

Inventory of Marine Fauna on Reef Balls Structures of Selingan Island, Sandakan, Sabah, Malaysia

Selingan Island is well known as a turtle sanctuary in Sandakan, Sabah. However, beach erosion has affected both infrastructure and turtle nesting grounds on the island. As one of the solutions, stone revetment and reef ball structures were deployed at the southeast part of the island in 2005 and 2007, respectively. The uneven stony surface of reef ball structures creates tiny pockets of space for attachment and colonization of coral larvae and sessile invertebrates. The objectives of this study are to determine the condition of the reef ball structures and to identify the types of marine fauna within these structures. The field surveys were carried out in May and December 2017. The survey area covered the 120 m length of balls structures for inventory of marine fauna using random quadrat sampling and observation of the reef balls condition. The survey areas were divided into Part 1 (1- 40 m), Part II (40-80 m) and Part III (80-120 m) from the shoreline of the island. There was only one reef ball unit damaged and others were intact with encrusting marine invertebrates and other associated marine life. The structures of the reef balls play an important role as an artificial marine habitat. A total of 3,583 individual (298 inv/m-2) of invertebrates (barnacles, bivalves, limpets and gastropods) were identified and 26 marine fauna species comprising of fishes, algae and corals associated with the reef balls structures. The marine fauna was expected to be higher if the survey could be done at the different tidal cycles, weather conditions and increase number of the survey. The findings provide insight of marine fauna at the reef balls structure in Selingan Island and enhance baseline data for marine resources management in the marine protected area of Turtle Island Parks.

Linking large-scale circulation patterns to the distribution of cold water corals along the eastern Rockall Bank (northeast Atlantic)

Cold-water corals (CWC) are known to tolerate a relatively wide range of environmental conditions. However, along the basin margins of the Rockall Trough (NE Atlantic), the habitat of CWC is confined to a narrow range of 525–1200 m water depth, and the reason for that is not fully understood. To investigate the distribution of CWCs in this area, current velocities and water mass distribution in the Logachev Mound Province were measured with two long-term (1 year) moorings equipped with an acoustic doppler current profiler and fluorescence+turbidity sensors. Additional ship-based water column profiles and discrete water samples, covering a full diurnal tidal cycle, were taken for chemical parameters. The results indicate the presence of a boundary current along the eastern flank of the Rockall Bank, that transports a nutrient-rich water mass southwards and governs the direction of particle transport at the depth band of the CWC mounds. Based on literature results, this northern water mass is identified as Wyville Thomson Ridge Overflow Water (WTOW). The density envelope and depth distribution of WTOW match the reported occurrence of CWC mounds in the Rockall Trough. Hence, the presence of WTOW may be a necessary condition for coral growth and therefore mound formation in the Rockall Trough, e.g. by forming a conduit for particles and coral larvae. • A south-westward current is observed at the western slope of the Rockall Trough. • This current transports Wyville Thomson Overflow Water (WTOW) southwards. • The depth band of WTOW matches the occurrence of CWC mounds in the Rockall Trough. • WTOW can impact coral growth by serving as a conduit for coral larvae.

Settlement of larvae from four families of corals in response to a crustose coralline alga and its biochemical morphogens

Healthy benthic substrates that induce coral larvae to settle are necessary for coral recovery. Yet, the biochemical cues required to induce coral settlement have not been identified for many taxa. Here we tested the ability of the crustose coralline alga (CCA) Porolithon onkodes to induce attachment and metamorphosis, collectively termed settlement, of larvae from 15 ecologically important coral species from the families Acroporidae, Merulinidae, Poritidae, and Diploastreidae. Live CCA fragments, ethanol extracts, and hot aqueous extracts of P. onkodes induced settlement (> 10%) for 11, 7, and 6 coral species, respectively. Live CCA fragments were the most effective inducer, achieving over 50% settlement for nine species. The strongest settlement responses were observed in Acropora spp.; the only non-acroporid species that settled over 50% were Diploastrea heliopora, Goniastrea retiformis, and Dipsastraea pallida. Larval settlement was reduced in treatments with chemical extracts compared with live CCA, although high settlement (> 50%) was reported for six acroporid species in response to ethanol extracts of CCA. All experimental treatments failed (< 10%) to induce settlement in Montipora aequituberculata, Mycedium elephantotus, and Porites cylindrica. Individual species responded heterogeneously to all treatments, suggesting that none of the cues represent a universal settlement inducer. These results challenge the commonly-held notion that CCA ubiquitously induces coral settlement, and emphasize the critical need to assess additional cues to identify natural settlement inducers for a broad range of coral taxa.

Larvae of the South Atlantic coral Favia gravida are tolerant to salinity and nutrient concentrations associated with river discharges

Rivers release freshwater, nutrients and pollutants into reefs. This type of environmental stress reduces coral larvae settlement and alter its energy metabolism. We investigated the tolerance of Favia gravida (Scleractinia) larvae to river discharges. We exposed larvae to (i) different salinities (25, 30, 35 and 40 PSU); and (ii) dilutions of river water containing nutrients and metals (0, 20, 40, 60, 80 and 100% river water) under control salinity of 35 PSU. We then examined settlement and larval enzymatic activity. No differences in settlement were detected among salinities. Settlement was also similar to control for larvae under 100% river water. Enzymatic activity for citrate synthase remained unaltered for all treatments. Lactate dehydrogenase activity was slightly altered under different salinities, suggesting a mild stress response. Findings suggest that F. gravida larvae are tolerant to a wide range of salinity and nutrient conditions and that this is a stress-tolerant species.

Rapid counting and spectral sorting of live coral larvae using large-particle flow cytometry

Research with coral embryos and larvae often requires laborious manual counting and sorting of individual specimens, usually via microscopy. Because many coral species spawn only once per year during a narrow temporal window, sample processing is a time-limiting step for research on the early life-history stages of corals. Flow cytometry, an automated technique for measuring and sorting particles, cells, and cell-clusters, is a potential solution to this bottleneck. Yet most flow cytometers do not accommodate live organisms of the size of most coral embryos (> 250 µm), and sample processing is often destructive. Here we tested the ability of a large-particle flow cytometer with a gentle pneumatic sorting mechanism to process and spectrally sort live and preserved Montipora capitata coral embryos and larvae. Average survival rates of mechanically-sorted larvae were over 90% and were comparable to those achieved by careful hand-sorting. Preserved eggs and embryos remained intact throughout the sorting process and were successfully sorted based on real-time size and fluorescence detection. In-line bright-field microscopy images were captured for each sample object as it passed through the flow-cell, enabling the identification of early-stage embryos (2-cell to morula stage). Samples were counted and sorted at an average rate of 4 s larva−1 and as high as 0.2 s larva−1 for high-density samples. Results presented here suggest that large-particle flow cytometry has the potential to significantly increase efficiency and accuracy of data collection and sample processing during time-limited coral spawning events, facilitating larger-scale and higher-replication studies with an expanded number of species.

Shipwrecks help invasive coral to expand range in the Atlantic Ocean

The invasive coral Tubastraea tagusensis (sun coral) is a habitat-forming species currently increasing its geographical range into the Atlantic Ocean, thereby causing negative ecological and socioeconomic impacts. Scuba divers observed this coral in the western equatorial Atlantic in January 2020, growing at high densities on a shipwreck from World War II (sunk in 1943) at a depth of approximately 32 m. Available footage from the beginning of the decade (2012–2018) shows no obvious signs of sun coral on this shipwreck, suggesting recent colonization and range expansion. The recent evidence of expansion was found 200 km east of the last record, which was also found on a WWII shipwreck (sunk in 1942) in 2016. We have identified hundreds of overlooked WWII shipwrecks, as well as new wrecks in shallow and mesophotic waters, that may provide stepping-stone habitats for this coral to expand its distribution in the Atlantic. We discuss the role of shipwrecks as a network of stepping stones for the sun coral spread, creating complementary paths for the invasiveness by overcoming physiological traits and the short lifespan of the coral larvae. Previous research underestimates the importance of these artificial stepping-stone patches in sustaining crucial dispersal events and range expansion of invasive species. These results are a call to action to manage the invasive Tubastraea corals at a national and international scale in the Atlantic basin.

Settlement dynamics and recruitment responses of Mediterranean gorgonians larvae to different crustose coralline algae species

Sessile marine species such as Anthozoans act as ecosystem engineers due to their three-dimensional structure. Gorgonians, in particular, can form dense underwater forests that give shelter to other species increasing local biodiversity. In the last decades, several Mediterranean gorgonian populations have been affected by natural and anthropogenic impacts which drastically reduced their size. However, some species showed unexpected resilience, mainly due to the supply of new individuals. To understand the mechanisms underlying recovery processes, studies on the first life history stages (i.e. larval dispersal, settlement and recruitment) are needed. In tropical coral reefs, crustose coralline algae (CCA) are known to influence coral larvae habitat selection and settlement. This capacity however is not ubiquitous among CCA species and larvae of different coral species may have different preferences. The present work focuses on three Mediterranean gorgonians (Eunicella singularis, Paramuricea clavata and Corallium rubrum) with the objective of quantifying settlement and recruitment in presence of two common CCA species (Litophyllum stictaeforme and Litophyllum incrustans). Results showed that the presence of CCA activates earlier settlement in E. singularis and increases the density of recruits, with different trends for the three species. Our results suggest that CCA should be taken into account in the implementation of conservation strategies. Moreover, a deeper comprehension of settlement mechanisms could help improving restoration techniques based on sexual reproduction.

Factors controlling the development of Fomichevella coral bioconstructions in the Gzhelian-Asselian (Late Pennsylvanian-early Permian) of Houchang, southern Guizhou, South China

Bioconstructions (five biostromes, one patch reef, and one large reef) of the colonial coral Fomichevella are well exposed, if infrequent, in the Upper Pennsylvanian-lower Permian of the Houchang area (southern Guizhou, China). Though they are primarily built by the same species, different growth morphologies and internal constructions are evident, which indicate different factors controlling their formation and development. The coral biostromes alternate with shoal deposits, being attributed to level-bottom communities that were closest to the reef ecosystem. The patch reef consists of a simple coral framework and a low biodiversity community. In contrast, rigid skeletal frameworks of Fomichevella are common and the biodiversity of the community is relatively higher in the large coral reef. Comparing these coral biostromes, the patch reef, and the large coral reef, several factors controlling their formation and development are suggested: stable substrate, water turbulence, sea-level fluctuation, and community structure. Hard substrates can provide stable habitats for the coral larvae during the initial colonisation stage, while the frequently changing sedimentary conditions were not conducive to the healthy development of Fomichevella. The simple community (e.g. the biostromes, patch reef) lacking encrusters and binders was too fragile to tolerate a turbulent environment. In Houchang, though intrinsic and extrinsic factors influenced the development of the Fomichevella bioconstructions, the extrinsic factors seem more important, which may be the key aspects controlling the Carboniferous coral bioconstructions.