Polyp Bail-out Research Articles

Advancing the coral propagation toolkit via hypersalinity induced coral micropropagates

In the face of escalating threats posed by human-induced climate change, urgent attention to coral reef restoration is imperative due to ongoing reef degradation. Here, we explored the potential of generating coral micropropagates as a tool to rapidly generate coral tissue for reef restoration and reef engineering. We developed a hypersalinity-induced polyp bailout protocol and a simple attachment device to support the growth of micropropagates on commonly used restoration substrates. We found that hypersalinity induction, at a rate of < 1 ppt hr-1, produced healthy micropropagates of the coral Stylophora pistillata. The highest attachment success (~74%) was achieved in CaCO3 substrate devices, which outperformed PVC (~48%) and Portland cement (~5%). Settled micropropagates displayed rapid growth rates on both CaCO3 (0.037 mm²/day ± 0.002 SE) and PVC (0.057 mm²/day ± 0.008 SE) substrates, while Portland cement induced tissue degradation. Our study provides a detailed methodology for reliably generating, attaching, and growing coral micropropagates and underscores the potential of polyp bailout as a viable technique supporting coral propagation efforts.

Bacterial Community Shifts during Polyp Bail-Out Induction in Pocillopora Corals.

Polyp bail-out constitutes both a stress response and an asexual reproductive strategy that potentially facilitates dispersal of some scleractinian corals, including several dominant reef-building taxa in the family Pocilloporidae. Recent studies have proposed that microorganisms may be involved in onset and progression of polyp bail-out. However, changes in the coral microbiome during polyp bail-out have not been investigated. In this study, we induced polyp bail-out in Pocillopora corals using hypersaline and hyperthermal methods. Bacterial community dynamics during bail-out induction were examined using the V5-V6 region of the 16S-rRNA gene. From 70 16S-rRNA gene libraries constructed from coral tissues, 1,980 OTUs were identified. Gammaproteobacteria and Alphaproteobacteria consistently constituted the dominant bacterial taxa in all coral tissue samples. Onset of polyp bail-out was characterized by increased relative abundance of Alphaproteobacteria and decreased abundance of Gammaproteobacteria in both induction experiments, with the shift being more prominent in response to elevated temperature than to elevated salinity. Four OTUs, affiliated with Thalassospira, Marisediminitalea, Rhodobacteraceae, and Myxococcales, showed concurrent abundance increases at the onset of polyp bail-out in both experiments, suggesting potential microbial causes of this coral stress response. IMPORTANCE Polyp bail-out represents both a stress response and an asexual reproductive strategy with significant implications for reshaping tropical coral reefs in response to global climate change. Although earlier studies have suggested that coral-associated microbiomes likely contribute to initiation of polyp bail-out in scleractinian corals, there have been no studies of coral microbiome shifts during polyp bail-out. In this study, we present the first investigation of changes in bacterial symbionts during two experiments in which polyp bail-out was induced by different environmental stressors. These results provide a background of coral microbiome dynamics during polyp bail-out development. Increases in abundance of Thalassospira, Marisediminitalea, Rhodobacteraceae, and Myxococcales that occurred in both experiments suggest that these bacteria are potential microbial causes of polyp bail-out, shedding light on the proximal triggering mechanism of this coral stress response.

Inducing Polyp Bail-out in Coral Colonies to Obtain Individualized Micropropagates for Laboratory Experimental Use

Corals are colonial animals formed by modular units called polyps. Coral polyps are physiologically linked and connected by tissue. The phenomenon of polyp bail-out is a process induced by acute stress, in which coral polyps digest the tissue connecting them to the rest of the colony and ultimately detach from the skeleton to continue living as separate individuals. Coral biologists have acknowledged the process of polyp bail-out for years, but only recently the micropropagates generated by this process have been recognized as a model system for coral biology studies. The use of polyp bail-out can create a high number of clonal units from a single coral fragment. Another benefit is that single polyps or patches of polyps can be easily visualized under a microscope and maintained in highly standardized low-cost environments such as Petri dishes, flasks, and microfluidic chips. The present protocol demonstrates reproducible methods capable of inducing coral micropropagation and different approaches for maintaining the single polyps alive in the long term. This methodology was capable of successfully cultivating polyps of the coral species Pocillopora verrucosa for up to 8 weeks after bail-out, exhibiting the practicality of using individual coral polyps for coral research.

Inducing Polyp Bail-out in Coral Colonies to Obtain Individualized Micropropagates for Laboratory Experimental Use

Corals are colonial animals formed by modular units called polyps. Coral polyps are physiologically linked and connected by tissue. The phenomenon of polyp bail-out is a process induced by acute stress, in which coral polyps digest the tissue connecting them to the rest of the colony and ultimately detach from the skeleton to continue living as separate individuals. Coral biologists have acknowledged the process of polyp bail-out for years, but only recently the micropropagates generated by this process have been recognized as a model system for coral biology studies. The use of polyp bail-out can create a high number of clonal units from a single coral fragment. Another benefit is that single polyps or patches of polyps can be easily visualized under a microscope and maintained in highly standardized low-cost environments such as Petri dishes, flasks, and microfluidic chips. The present protocol demonstrates reproducible methods capable of inducing coral micropropagation and different approaches for maintaining the single polyps alive in the long term. This methodology was capable of successfully cultivating polyps of the coral species Pocillopora verrucosa for up to 8 weeks after bail-out, exhibiting the practicality of using individual coral polyps for coral research.

Polyp loss and mass occurrence of sea urchins on bamboo corals in the deep sea: an indirect effect of fishing impact?

The ability of corals to detach their polyps (leaving behind a naked skeleton) in times of stress, allows polyps to escape from a local source of hostility (Sammarco 1982). In situ observations of this behavior (referred to as 'polyp bailout') were first documented in tropical reef-building corals. Later it was observed in some cold-water corals of Acanthogorgia (Braga-Henriques 2014), and Acanella arbuscula (Rakka et al. 2019) in aquaria.

Signaling pathways of heat- and hypersalinity-induced polyp bailout in Pocillopora acuta

Polyp bailout is a drastic response to acute stress where coral coloniality breaks down and polyps detach. We induced polyp bailout in Pocillopora acuta with heat stress and tested for differential gene expression using RNAseq and a qPCR assay. Furthermore, we induced polyp bailout with hypersalinity and compared the results to identify stressor-independent signals and pathways active during polyp bailout. Both stressors led to the onset of polyp bailout and the detachment of vital polyps. We observed activation of microbe-associated molecular pattern receptors and downstream signaling pathways of the innate immune system. Further, we detected growth factors and genes active during Wnt-signaling potentially contributing to wound healing, regeneration, and proliferation. Upregulation of several genes encoding for matrix metalloproteinases and the fibroblast growth factor signaling pathway are the most likely involved in the remodeling of the extracellular matrix, as well as in the detachment of polyps from the calcareous skeleton during polyp bailout. Expression of genes of interest in our qPCR assay of vital polyps from our heat-stress experiment, showed a trend for a normalization of gene expression after polyp bailout. Our results provide new insights into the signaling cascades leading to the observed physiological responses during polyp bailout. Comparison between the two stressors showed that certain signaling pathways are independent of the stressor and suggested that polyp bailout is a general response of corals to acute stress. Furthermore, immune system responses during polyp bailout indicate that microbe-associated partners of corals may lead to the polyp bailout response.

Genetic changes involving the coral gastrovascular system support the transition between colonies and bailed-out polyps: evidence from a Pocillopora acuta transcriptome

BackgroundA coral colony is composed of physiologically integrated polyps. In stony corals, coloniality adopts a wide diversity of forms and involves complex ontogenetic dynamics. However, molecular mechanisms underlying coloniality have been little studied. To understand the genetic basis of coloniality and its contribution to coral ecology, we induced polyp bail-out in a colonial coral, Pocillopora acuta, and compared transcription profiles of bailed-out polyps and polyps in normal colonies, and their responses to heat shock and hyposalinity.ResultsConsistent with morphological formation of a gastrovascular system and its neural transmission and molecular transport functions, we found genetic activation of neurogenesis and development of tube-like structures in normal colonies that is absent in bailed-out polyps. Moreover, relative to bailed-out polyps, colonies showed significant overexpression of genes for angiotensin-converting enzymes and endothelin-converting enzymes. In response to hyperthermal and hyposaline treatments, a high proportion of genetic regulation proved specific to either bailed-out polyps or colonies. Elevated temperatures even activated NF-κB signaling in colonies. On the other hand, colonies showed no discernible advantage over bailed-out polyps in regard to hyposalinity.ConclusionsThe present study provides a first look at the genetic basis of coloniality and documents different responses to environmental stimuli in P. acuta colonies versus those in bailed-out polyps. Overexpression of angiotensin-converting enzymes and endothelin-converting enzymes in colonies suggests possible involvement of these genes in development of the gastrovascular system in P. acuta. Functional characterization of these coral genes and further investigation of other forms of the transition to coloniality in stony corals should be fruitful areas for future research.

The history, biological relevance, and potential applications for polyp bailout in corals.

Corals have evolved a variety of stress responses to changing conditions, many of which have been the subject of scientific research. However, polyp bailout has not received widespread scientific attention, despite being described more than 80 years ago. Polyp bailout is a drastic response to acute stress in which coral colonies break down, with individual and patches of polyps detaching from the colony and the calcareous skeleton Polyps retain their symbiotic partners, have dispersal ability, and may undergo secondary settlement and calcification. Polyp bailout has been described worldwide in a variety of anthozoan species, especially in Scleractinia. It can be induced by multiple natural stressors, but also artificially. Little is known about the evolutionary and ecological potential and consequences of breaking down modularity, the dispersal ability, and reattachment of polyps resulting from polyp bailout. It has been shown that polyp bailout can be used as a model system, with promise for implementation in various research topics. To date, there has been no compilation of knowledge on polyp bailout, which prompted us to review this interesting stress response and provide a basis to discuss research topics and priorities for the future.

Microscale tracking of coral-vibrio interactions

To improve our understanding of coral infection and disease, it is important to study host-pathogen interactions at relevant spatio-temporal scales. Here, we provide a dynamic microscopic view of the interaction between a coral pathogen, Vibrio coralliilyticus and its coral host Pocillopora damicornis. This was achieved using a microfluidics-based system facilitating control over flow, light and temperature conditions. Combined with time-resolved biochemical and microbial analyses of the system exudates, this approach provides novel insights into the early phases of a coral infection at unprecedented spatio-temporal resolution. We provide evidence that infection may occur through ingestion of the pathogen by the coral polyps, or following pathogen colonization of small tissue lesions on the coral surface. Pathogen ingestion invariably induced the release of pathogen-laden mucus from the gastrovascular cavity. Despite the high bacterial load used in our experiments, approximately one-third of coral fragments tested did not develop further symptoms. In the remaining two-thirds, mucus spewing was followed by the severing of calicoblastic connective tissues (coenosarc) and subsequently necrosis of most polyps. Despite extensive damage to symptomatic colonies, we frequently observed survival of individual polyps, often accompanied by polyp bail-out. Biochemical and microbial analyses of exudates over the course of symptomatic infections revealed that severing of the coenosarc was followed by an increase in matrix metaloprotease activity, and subsequent increase in both pathogen and total bacterial counts. Combined, these observations provide a detailed description of a coral infection, bringing us a step closer to elucidating the complex interactions underlying coral disease.

Morphological and Genetic Recovery of Coral Polyps After Bail-Out

Contemporary advances in microfluidic and molecular techniques have enabled coral studies to shift from reef and colony scales to polyp- and molecular-level investigations. Polyp bail-out provides an alternative approach to acquire solitary polyps for studies at finer scales. Although induction of polyp bail-out has been reported in several studies, polyp health after bail-out has not been investigated. In this study, we monitored morphological and genetic changes in Pocillopora acuta polyps after bail-out induced by hyperosmosis. In isosmotic conditions, over 80% of bailed-out polyps survived, of which half regenerated normal polyp morphology within 5 days, including a polarized polyp body, extended tentacles, and a distinguishable oral disk. In contrast, the remaining polyps degenerated into tissue ball-like structures that resemble multicellular aggregates reported in earlier studies. In morphologically recovered polyps, transcriptomic analysis showed that ∼87% of genes altered during bail-out induction recovered from stress status, suggesting resumption of metabolism, cell division, and immunity, while in degenerated polyps, only ∼71% of genes recovered. Quantitative polymerase chain reaction data further demonstrated that genetic recovery of energy production, cell proliferation, and immune response was achieved in morphologically recovered polyps within 3 days after bail-out, but was not fully accomplished in degenerated polyps even after 5 days. Our findings indicate that solitary polyps generated by hyperosmosis-induced bail-out can recover rapidly from physiological stress under laboratory conditions, suggesting that bailed-out polyps could be used as new models for coral research.

Polyp bailout and reattachment of the abundant Caribbean octocoral Eunicea flexuosa

Anthozoans exhibit great plasticity in their responses to stressful conditions, including decreasing individual size, detaching from the substratum and relocating, and releasing endosymbiotic microalgae. Another response to stress used by some colonial anthozoans is polyp bailout, in which the coenenchyme breaks down and individual polyps detach from the colony. We observed polyp bailout in the common Caribbean gorgonian Eunicea flexuosa after 8 h of aerial exposure. After 9 days, 28% of bailed-out polyps reattached, although none opened to resume feeding. Polyp bailout is a costly and high-risk escape response, but reattachment indicates that this can be a genet-saving behavior in cases where whole-colony mortality is likely. While it has been described in two octocorals, several species of scleractinians, and one black coral, we still do not know how widespread this behavior is in anthozoans.

Unveiling asexual reproductive traits in black corals: polyp bail-out in Antipathella subpinnata

Cnidarians are known to undergo reverse development as a survival mechanism against adverse environmental conditions. Polyp bail-out consists in the polyps’ detachment from the mother colony due to stressful conditions, followed by a complete tissue and cells rearrangement and in some cases in a regression into a simple, ciliated form. Here we describe a massive polyp bail-out event occurred in the mesophotic black coral Antipathella subpinnata in reared conditions. This is the first report of a bail-out event in this species providing new insights into the life cycle and ecology of black corals.

Signaling pathways in the coral polyp bail-out response

Polyp bail-out is a stress response exhibited by some pocilloporid corals, with mechanisms and consequences distinct from those of bleaching. Although induction of polyp bail-out has been demonstrated in the laboratory, molecular mechanisms underlying this response have rarely been discussed. We conducted genetic analyses of Pocillopora acuta during initiation of hyperosmosis-induced polyp bail-out, using both transcriptomic and qPCR techniques. Beyond upregulation of apoptosis and proteolysis, corals showed significant activation of tumor necrosis factor and fibroblast growth factor (FGF) signaling pathways during induction of polyp bail-out. In our qPCR analysis, a common upregulation profile, peaking at 43.0‰ salinity, was found in the FAS and CASP8 genes, whereas a different profile, showing significant upregulation up to 45.0‰, was displayed by matrix metalloproteinases and genes in the FGF signaling pathway. These results suggest parallel involvement of an extrinsic apoptotic signaling pathway and FGF-mediated extracellular matrix degradation in polyp bail-out. Furthermore, in the XIAP, JNK, and NFKB1 genes, we detected a third expression profile showing linear upregulation that becomes maximal at the endpoint salinity level of the experiment (46.0‰), indicating activation of anti-apoptotic and cell survival signals during polyp bail-out. Our results provide new insights into signaling pathways responsible for polyp bail-out and suggest the feasibility of inducing bail-out by specifically triggering these pathways without exerting lethal stresses on the corals, which in turn will facilitate acquisition of viable polyps for possible use in coral reef restoration.

Long-term Effects of a Cardiovascular Health Supplement on Blood Pressure in Adults with Prehypertension and Stage 1 Hypertension

Marine ecosystems are both stressed and threatened by pesticides that are used on land. Nevertheless, research on the impact of pesticides on coral reefs and the underlying mechanisms is still in its infancy. The insecticide chlordecone is a persistent organic pollutant with carcinogenic effects in rats and mice. Chlordecone has been detected in diverse marine organisms in the Caribbean, but unexpectedly, also in French Polynesia.We combined transcriptomic and morphologic analyses of analyses the response of the coral Pocillopora damicornis to chlordecone stress. We compared chlordecone stress with thermal stress to determine a chlordecone-specific response.We found eight transcripts related to the P450-1A or P450-3A families that were specifically overexpressed in response to chlordecone. There was also sequential overexpression of transcripts involved in apoptosis and degradation of cellular matrix proteins. Finally, we report the first observation of chlordecone-induced P. damicornis polyp bail-out. Altogether, these results strongly suggest that apoptosis and expression of genes belonging to the cathepsin family are sequentially regulated processes leading to coenosarc dissociation and loss.

First description of polyp bailout in cold-water octocorals under aquaria maintenance

Cnidarians, characterized by high levels of plasticity, exhibit remarkable mechanisms to withstand or escape unfavourable conditions including reverse development which describes processes of transformation of adult stages into early developmental stages with higher mobility. Polyp bailout is a stress-escape response common among scleractinian species, consisting of massive detachment of live polyps and subsequent death of the mother colony. Here, we describe two cases of polyp bailout in the cold-water octocoral species Acanthogorgia armata and Acanella arbuscula. During maintenance in aquaria, specimens of both species presented coenosarc withdrawal and loss of sclerites, followed by detachment of intact polyps. This is a strong indication of reverse development which can be a very important strategy under stress conditions and has not been reported before in cold-water octocorals.

First evidence of asexual recruitment of Pocillopora acuta in Okinawa Island using genotypic identification.

Okinawa Island is located near the center of the Nansei Islands (∼24–31°N), at a relatively high latitude for coral reefs. Nevertheless, more than 80 coral genera (over 400 species) are abundant in the Nansei Islands. Since March, 2017, scleractinian corals have been held in an outdoor tank at the OIST Marine Science Station at Seragaki, Onna with natural sea water flow-through in order to be used in molecular biological and physiological studies. In January, 2018, we found small pocilloporid-like colonies suspected to have originated asexually. We collected 25 small colonies and measured their sizes and weights. Also, we validated the classification and clonality of the colonies using a mitochondrial locus and nine microsatellite loci. Almost all of the small colonies collected in the outdoor tank were ≤1 cm in both width and height. The weight of dried skeletons ranged from 0.0287 to 0.1807 g. Genetic analysis determined that they were, in fact, Pocillopora acuta. Only one mitochondrial haplotype was shared and two microsatellite multilocus genotypes were detected (20 colonies of one and four colonies of the other). The mitochondrial haplotype and one microsatellite multilocus genotype for 20 colonies corresponded to those of one P. acuta colony being kept in the tank. One small colony matched both multilocus genotypes. This may have been a chimeric colony resulting from allogenic fusion. These small colonies were not produced sexually, because the only potential parent in the tank was the aforementioned P. acuta colony. Instead, they were more likely derived from asexual planula release or polyp bail-out. Corals as Pocillopora acuta have the capacity to produce clonal offspring rapidly and to adapt readily to local environments. This is the first report of asexual reproduction by planulae or expelled polyps in P. acuta at Okinawa Island.

Exposure to the environmentally-persistent insecticide chlordecone induces detoxification genes and causes polyp bail-out in the coral P. damicornis

Marine ecosystems are both stressed and threatened by pesticides that are used on land. Nevertheless, research on the impact of pesticides on coral reefs and the underlying mechanisms is still in its infancy. The insecticide chlordecone is a persistent organic pollutant with carcinogenic effects in rats and mice. Chlordecone has been detected in diverse marine organisms in the Caribbean, but unexpectedly, also in French Polynesia.We combined transcriptomic and morphologic analyses of analyses the response of the coral Pocillopora damicornis to chlordecone stress. We compared chlordecone stress with thermal stress to determine a chlordecone-specific response.We found eight transcripts related to the P450-1A or P450-3A families that were specifically overexpressed in response to chlordecone. There was also sequential overexpression of transcripts involved in apoptosis and degradation of cellular matrix proteins. Finally, we report the first observation of chlordecone-induced P. damicornis polyp bail-out. Altogether, these results strongly suggest that apoptosis and expression of genes belonging to the cathepsin family are sequentially regulated processes leading to coenosarc dissociation and loss.

Polyp bailout in Pocillopora damicornis following thermal stress.

Polyp bailout is an established but understudied coral stress response that involves the detachment of individual polyps from the colonial form as a means of escaping unfavourable conditions. This may influence both the mortality and asexual recruitment of coral genotypes across a range of species. It has been observed in response to numerous stressors including high salinity and low pH. Polyp expulsion in association with thermal stress has once been described in a geographically restricted, temperate species. We therefore cannot reliably apply this observation to tropical coral reefs around the world, which are increasingly under threat from thermal stress events. We present the first qualitative observation of polyp bailout following acute temperature shock in a near-natural mesocosm experiment. Detached polyps show similar characteristics to those described in previous studies, including the retention of endosymbiotic zooxanthellae and the ability to disperse across short distances. This finding strongly suggests that polyp bailout occurs in tropical coral reef environments and warrants further detailed research into the implication of this response in terms of individual survival, rapid migration into cooler micro-habitats and local recruitment within the reef environment and its coral community.

Polyp bailout in Pocillopora damicornis following thermal stress

Polyp bailout is an established but understudied coral stress response that involves the detachment of individual polyps from the colonial form as a means of escaping unfavourable conditions. This may influence both the mortality and asexual recruitment of coral genotypes across a range of species. It has been observed in response to numerous stressors including high salinity and low pH. Polyp expulsion in association with thermal stress has once been described in a geographically restricted, temperate species. We therefore cannot reliably apply this observation to tropical coral reefs around the world, which are increasingly under threat from thermal stress events. We present the first qualitative observation of polyp bailout following acute temperature shock in a near-natural mesocosm experiment. Detached polyps show similar characteristics to those described in previous studies, including the retention of endosymbiotic zooxanthellae and the ability to disperse across short distances. This finding strongly suggests that polyp bailout occurs in tropical coral reef environments and warrants further detailed research into the implication of this response in terms of individual survival, rapid migration into cooler micro-habitats and local recruitment within the reef environment and its coral community.

Polyp bailout in Pocillopora damicornis following thermal stress

Polyp bailout is an established but understudied coral stress response that involves the detachment of individual polyps from the colonial form as means of escaping unfavourable conditions. This may influence both the mortality and asexual recruitment of coral genotypes across a range of species. It was first described by Goreau & Goreau (1959) and has been observed in response to numerous stressors including high salinity and low pH. However, polyp bailout has not previously been described in association with thermal stress and the coral bleaching response, which is becoming increasingly common around the world. We present the first qualitative observation of polyp bailout following thermal stress in a mesocosm experiment. Detached polyps show similar characteristics to those described in previous studies, including the retention of endosymbiotic zooxanthellae and the ability to disperse across short distances. As the frequency of thermal stress increases globally, we suggest further detailed research into the prevalence of this response in situ and its implications for the survival of individual corals, as well as the potential for migration into cooler micro-habitats within the coral reef environment.