References of "Ladrière, Ophélie"
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See detailNatural spatial variability of algal endosymbiont density in the coral Acropora globiceps: a small-scale approach along environmental gradients around Moorea (French Polynesia)
Ladrière, Ophélie ULg; Penin, Lucie; Van Lierde, Elodie et al

in Journal of the Marine Biological Association of the United Kingdom (2013)

This study provides a baseline describing natural small scale variability of Symbiodinium density in the sentinel coral Acropora globiceps during the summer, under non-bleaching conditions. Spatial scales ... [more ▼]

This study provides a baseline describing natural small scale variability of Symbiodinium density in the sentinel coral Acropora globiceps during the summer, under non-bleaching conditions. Spatial scales investigated range from the colony scale (1–10 cm, i.e. among branches of the same colony) to the reef scale (1–10 km, i.e. among stations distributed over several locations and depths), at Moorea Island, French Polynesia. The coral–Symbiodinium symbiosis is a key process in scleractinian coral physiology, and Symbiodinium density provides an easy-to-measure and inexpensive biomarker of this symbiosis health. Spatial variability of three major environmental factors: light intensity, sedimentation and water motion was also assessed to evaluate their potential link with Symbiodinium density. Density of Symbiodinium did not significantly differ within colonies or among colonies within a station. However, a marked depth gradient was observed, showing increasing density with increasing depth and decreasing light intensity. These observations provide an interesting reference for forthcoming comparisons with disturbed conditions, such as bleaching events. [less ▲]

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See detailEtude pluridisciplinaire de l'implication bactérienne du phénomène de blanchissement des coraux Scléractiniaires (Indo-Pacifique)
Ladrière, Ophélie ULg

Doctoral thesis (2012)

Given the increasing number of coral diseases linked to the growing impact of global warming and human activities, the present research focused on the phenomenon of coral bleaching. The Scleractinian ... [more ▼]

Given the increasing number of coral diseases linked to the growing impact of global warming and human activities, the present research focused on the phenomenon of coral bleaching. The Scleractinian Cnidaria are the essential building blocks of the coral reef ecosystem, whose ecological, economic and societal interests are demonstrated. The symptom of bleaching has multiple and complex causes that are still unclear. It corresponds to the rupture of the mutualistic symbiosis between the coral and microalgae, called zooxanthellae, and can causes death of many corals. An assumption underlying this phenomenon suggests that corals are bleaching by the action of pathogenic bacteria, penetrating inside the coral tissues. However, this hypothesis seems quite controversial and the present work attempts to elucidate a set of issues surrounding this controversy. To do this, a multidisciplinary approach combining ecology (general and microbial) and molecular biology has been established through field and experimental studies. Using electron microscopy, morphological criteria were established to characterize the status of coral bleaching. Furthermore, this technique was also used to identify different types of bacteria within coral tissues. Their presence and their role within the coral holobiont were discussed. Several molecular biology techniques (DGGE, sequencing) have provided evidences on the non-specificity of bacterial communities associated with corals species, sampling sites and different status of bleaching. This non-specificity shows that the functions performed by bacteria in the coral holobiont could be the result of opportunistic bacteria from various taxonomic groups. The presence of Cyanobacteria in some corals, detected by microscopy and confirmed by molecular techniques, raises the question about their role within the holobiont and the alternative pathway that they offer for the symbiotic host compared with zooxanthellae. The issues of potential competition between these different symbionts or the benefit of this symbiotic diversity, in case of bleaching event, remain open. Transcriptomic genetics was used to study the response of coral facing a bacterial stress in different experimental conditions of temperature determining the expression of bacterial virulence. Studying the expression profile of genes involved in immunity of the coral allowed to understand the sequence of reactions and changes in resource allocation in response to different stages of bacterial infection. On this experiment, the first antimicrobial peptide of Scleractinia, the damicornin, has been identified and characterized. All these results suggest that the context of changes in environmental parameters is more important than the presence of pathogens itself. The bacteria would then act as an aggravating factor in a situation where the coral, already weakened and stressed, cannot defend itself adequately. Finally, the observation of an increase in cnidocytes in a coral species that has undergone bleaching, suggests that some coral species are able to shift to a more heterotrophic nutritional regime adapting to the lack of inputs caused by the significant loss of zooxanthellae. This would favor the resilience of coral. [less ▲]

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See detailPhysiological responses of the scleractinian coral Pocillopora damicornis to bacterial stress from vibrio coralliilyticus
Vidal-Dupiol, Jérémie; Ladrière, Ophélie ULg; Meistertzheim, Anne-Leila et al

in Journal of Experimental Biology (2011), 214

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See detailInnate immune responses of a scleractinian coral to vibriosis
Vidal-Dupiol, Jérémie; Ladrière, Ophélie ULg; Destoumieux-Garzon, Delphine et al

in Journal of Biological Chemistry (2011)

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See detailSYMBIODINIUM SP. CAN STAY ALIVE THROUGH THE GUT AND IN THE FAECES OF CNIDARIA. PREDATORS. THE CASE OF CORALLIOPHILLA MEYENDORFFI AND ANEMONIA VIRIDIS.
Poulicek, Mathieu ULg; Roberty, Stéphane ULg; Plaza, Sylvain et al

Poster (2010)

The gastropod Coralliophilla meyendorffi is a common predator of the zooxanthellate anemone Anemonia viridis. Zooxanthella from the anemones are an important constitutent of the mollusc faeces. Cell ... [more ▼]

The gastropod Coralliophilla meyendorffi is a common predator of the zooxanthellate anemone Anemonia viridis. Zooxanthella from the anemones are an important constitutent of the mollusc faeces. Cell integrity, occurence of flagellated forms, live/dead proportions and mitotic index of Symbiodinium collected from the faeces and cultivated in vitro were examined and compared to that of algae in hospite. The results show that most algae withstand digestive processes of the predator, staying alive and dividing actively in the faeces. Motile (lagellated) algae arise from dividing cells and escape the fecal pellets. Impact on coral bleaching recovery is discussed. [less ▲]

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See detailPhotoacclimation responses of a symbiotic sea anemone reveal an important host cellular plasticity
Roberty, Stéphane ULg; Fransolet, David ULg; Ladrière, Ophélie ULg et al

Poster (2010)

The high productivity of coral reef ecosystems is largely attributed to the mutualistic symbiosis between reef-building corals and their intracellular dinoflagellate in the genus Symbiodinium commonly ... [more ▼]

The high productivity of coral reef ecosystems is largely attributed to the mutualistic symbiosis between reef-building corals and their intracellular dinoflagellate in the genus Symbiodinium commonly referred to as zooxanthellae. These photosynthetic algae translocate a majority of their photosynthetically fixed carbon to the host and contribute to their metabolic needs and the calcification process. <i>Symbiodinium</i> must maintain a balance between the energy derived from the light reactions in the chloroplast and the amount of energy used during dark reactions and other metabolic processes. Nevertheless, in the natural environment the holobiont have to cope with daily and seasonal changes in light intensity, upsetting that balance and creating a stress that induces a physiological response (photoacclimation) to optimize growth rates. After a ten day exposition to high and very low light intensity, morphological and photophysiological analysis conducted on the symbiotic sea anemone, Anemonia manjano, reveal significant modifications of the host tissues ultrastructure and the Symbiodinium metabolic processes (photosynthesis, respiration). Those results highlight particularly important gastrodermal and ectodermal plasticity in which symbiotic cnidarians acclimate to the Symbiodinium physiological status (mainly photosynthesis) by varying the density of particular cellular types (e.g.: cnidocytes, gastrodermal cells) contained in their tissues. [less ▲]

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See detailFunctional diversity of microbial communities associated to the mucus of scleractinians around Moorea (French Polynesia)
Ladrière, Ophélie ULg; Theunis, Laetitia; Wilmotte, Annick et al

Poster (2008, July 07)

Mucus production by scleractinians appears as an antifouling mechanism which prevents settlement of other organisms and accumulation of sediments on their surface. This Surface Muccopolysaccharide Layer ... [more ▼]

Mucus production by scleractinians appears as an antifouling mechanism which prevents settlement of other organisms and accumulation of sediments on their surface. This Surface Muccopolysaccharide Layer (SML) harbours dense populations of bacteria which play a paramount role in scleractinians nutrition, metabolism and good health maintenance. However, environmental disturbances can alter these microbiocenoses. Characterization of bacterial communities was carried out using a set of simple techniques that enable us to describe the state and functions of whole microbial communities associated with different hard coral species. Multi-comparisons have been performed on bacterial communities from open water, interstitial water, sedimentary interface and macro algae as well as between healthy and bleached colonies, and patches associated or not with Pomacentridae fishes. The functional study included measurements of bacterial biomass, respiration, oxydative and hydrolytic metabolisms. Non-Fungiidae corals and sedimentary interface have a quite similar bacterial biomass but open water, interstitial water and macro-algae are characterized by higher bacterial biomass. Bacterial respiration potential is similar on corals and at the sedimentary interface, but it is higher in interstitial water and lower in open water and for bacterial community associated with macro-algae. Hydrolytic activities are highest in SML. Bleached corals and patches associated with Pomacentridae fishes show more abundant bacteria, with higher respiration rate and higher hydrolytic activity than corals without fishes and healthy ones. In addition, bacteria of bleached corals display a higher division percentage, a higher growth rate and a lower turn-over time We confirmed that bleaching events or the presence of sedentary fishes modify the bacterial communities structure and affect relationships between coral, endosymbiotic algae, SML-associated microbial community and associated organisms. Such results highlight that SML-bacterial communities are modified by bleaching and raise the question of a potential protection of fishes against pathogens. [less ▲]

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See detailHETEROGENEITY OF ZOOXANTHELLAE DENSITY IN THE CORAL ACROPORA GLOBICEPS AROUND MOOREA (FRENCH POLYNESIA)
Ladrière, Ophélie ULg; van Lierde, Elodie; Penin, Lucie et al

Poster (2008)

Understanding the natural heterogeneity of coral zooxanthellae density appears as very important to understand variations in coral survival due to bleaching (the loss of these micro-algal symbionts ... [more ▼]

Understanding the natural heterogeneity of coral zooxanthellae density appears as very important to understand variations in coral survival due to bleaching (the loss of these micro-algal symbionts). Heterogeneity of coral bleaching at different observation scales (within a colony, among neighbouring colonies of the same species or on a wider scale) remains largely misunderstood. The present work explores intracolonial, spatial and temporal variations of zooxanthellae density in the coral Acropora globiceps Dana 1846, over a period of three months on the forereef of Moorea, French Polynesia. In our study, intracolonial zooxanthellae densities did not vary significantly. However, zooxanthellae densities differed slightly between inner and outer branches but this trend was not significant at 6, 12 and 18 meters depth. On a wider scale, zooxanthellae densities also vary spatially : a positive correlation was observed between depth and symbiont density (density increases when light intensity decreases, so according to depth). Moreover, the location of colonies exposed to different hydrodynamical conditions was not a parameter controling the concentration of zooxanthellae. Finally, the temporal variation of zooxanthellae densities did not show significant variations even if it decreased slightly over the study period. The results of this study highlight the importance of accounting for variations within and among colonies to determine zooxanthellae densities and to assess the evolution of zooxanthellae populations. [less ▲]

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See detailHeterogeneity of zooxanthellae density in the coral Acropora globiceps around Moorea (French Polynesia)
Ladrière, Ophélie ULg; van Lierde, Elodie; Penin, Lucie et al

Poster (2008)

Understanding the natural heterogeneity of coral zooxanthellae density appears as very important to understand variations in coral survival due to bleaching (the loss of these micro-algal symbionts ... [more ▼]

Understanding the natural heterogeneity of coral zooxanthellae density appears as very important to understand variations in coral survival due to bleaching (the loss of these micro-algal symbionts). Heterogeneity of coral bleaching at different observation scales (within a colony, among neighbouring colonies of the same species or on a wider scale) remains largely misunderstood. The present work explores intracolonial, spatial and temporal variations of zooxanthellae density in the coral Acropora globiceps Dana 1846, over a period of three months on the forereef of Moorea, French Polynesia. In our study, intracolonial zooxanthellae densities did not vary significantly. However, zooxanthellae densities differed slightly between inner and outer branches but this trend was not significant at 6, 12 and 18 meters depth. On a wider scale, zooxanthellae densities also vary spatially : a positive correlation was observed between depth and symbiont density (density increases when light intensity decreases, so according to depth). Moreover, the location of colonies exposed to different hydrodynamical conditions was not a parameter controling the concentration of zooxanthellae. Finally, the temporal variation of zooxanthellae densities did not show significant variations even if it decreased slightly over the study period. The results of this study highlight the importance of accounting for variations within and among colonies to determine zooxanthellae densities and to assess the evolution of zooxanthellae populations. [less ▲]

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See detailPotential implication of host/symbiont recognition mechanisms in coral bleaching
Vidal-Dupiol, Jérémie; Mitta, Guillaume; Roger, Emmanuel et al

Poster (2008)

Bleaching in corals can be attributed to loss of endosymbiotic zooxanthellae and/or loss of photosynthetic pigments within zooxanthellae. This major disturbance of the reef ecosystem is principally ... [more ▼]

Bleaching in corals can be attributed to loss of endosymbiotic zooxanthellae and/or loss of photosynthetic pigments within zooxanthellae. This major disturbance of the reef ecosystem is principally induced by increases in water temperature. Since the beginning of the 80ís and the onset of global climate change, this phenomenon has been occurring at increasing rates and scales, and with increasing severity. In this study, we focused on finding early regulated genes involved in bleaching. In aquaria, one set of Pocillopora damicornis nubbins was subjected to a gradual seawater temperature increase from 28°C to 32°C over 15 days, and a second control set remained at constant temperature (28°C). Bleaching was monitored by measuring zooxanthellae density. The mRNA differentially expressed between the stressed state (sampled just before the onset of bleaching) and the non stressed state (control) were isolated from the nubbins by Suppression Subtractive Hybridization. The corresponding cDNA were sequenced and confronted to sequence databases to obtain gene similarities. Finally, transcription rates of the most interesting genes were conducted by Q-PCR. Two particularly interesting candidate genes showed an important decrease in their transcription rates following thermal stress and before zooxanthellae loss. These two genes show similarities with genes involved in host/symbiont and host/parasite models. The implication of these molecular actors suggests a possible role of recognition mechanisms between the host and its symbiont, in the breakdown of the symbiosis during the bleaching phenomenon. Experiments such as RACE-PCR, in situ hybridization and immunohistochemistry are currently underway to confirm our hypotheses. [less ▲]

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See detailMorphological alterations of zooxanthellae in bleached cnidarian hosts
Ladrière, Ophélie ULg; Compère, Philippe ULg; Decloux, Nicole ULg et al

in Cahiers de Biologie Marine (2008), 49(3), 215-227

Studying the morphological changes of zooxanthellae in the host gastroderm is essential to understand the mechanisms of bleaching. Transmission electron microscopy was used to observe samples from four ... [more ▼]

Studying the morphological changes of zooxanthellae in the host gastroderm is essential to understand the mechanisms of bleaching. Transmission electron microscopy was used to observe samples from four coral species-three collected from a barrier reef in Madagascar (Acropora digitifera (Dana, 1846), Echinopora hirsutissima Milne-Edwards & Haime, 1849 and Porites (Synaraea) rus Forskal, 1775)) and one cut from an aquarium-grown coral (Pocillopora damicornis (Linnaeus, 1758)-and from the hermatypic (zooxanthellae-containing) sea anemone Aiptasia pulchella (Carlgren, 1943). Zooxanthellae from bleached animals showed different stages of degradation or disorganization. Some were free, detached from the host gastroderm, associated or not with host-cell remains. Others were vacuolated, with abundant reserve material globules and angular holes probably created by the loss of crystalline material during cutting. Experimentally heat-shocked P. damicornis harboured, moreover, a greater number of dividing algae. Bleached individuals were found to vary as regards their response to stress, and zooxanthellae expelled from heat-shocked anemones showed a greater mitotic index and a higher survival rate than algae extracted or naturally externalized from healthy individuals. We propose a combination of morphological criteria for use in diagnosing the health state of algae-cnidarian symbiosis, so vulnerable in the case of bleaching. [less ▲]

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See detailThe tropical sea anemone Aiptasia pallida as a lab model for the study of coral bleaching
Ladrière, Ophélie ULg; Roberty, Stéphane ULg; Baudesson, Charlotte et al

Poster (2008)

Bleaching is still among major events threatening coral reefs. New tools have to be developped to better understand the mechanisms leading to this pathology : we studied the use of the hermatypic anemone ... [more ▼]

Bleaching is still among major events threatening coral reefs. New tools have to be developped to better understand the mechanisms leading to this pathology : we studied the use of the hermatypic anemone Aiptasia pallida as experimental model for coral bleaching. Aiptasia appears as a good candidate as it is easy to maintain in aquarium and subjected to bleaching like corals. Both morphological and physiological approaches were performed to investigate the ultrastructure of the anemone tissues (TEM) and the zooxanthellae photophysiology (chlorophyll a fluorescence, respiration and pigmentation). Experiments under light and dark stress reveal that anemone tissues ultrastructure can be differently affected. In darkness, the ectoderm activity is reoriented to capture prey by increasing cnidocyte density. In contrast, intense light affects especially the gastroderm : intercellular spaces increase, the expulsion of intact algae in the gastric cavity and the degradation of zooxanthellae inside vacuoles seem to reduce the zooxanthellae density, chloroplast thylakoids lose their parallel arrangement. The analysis of the fluorescence induction curve appears as a powerful tool to analyse the physiological events series previous to bleaching. Although no significant zooxanthellae density reduction was observed, the decrease of pigments concentrations indicates that light or dark stresses induce anemone bleaching. Under strong light intensity, A. pallida zooxanthellae show an increased proportion of PSII QB non reducing, leading to partial photoinhibition. This phenomenon favours the ROS production that damages cellular structures of host and zooxanthellae. In darkness, there is no photosynthesis; anemones have therefore to find other feeding sources, as suggested by the ultrastructural approach. As the present results confirm some of those obtained on scleractinians, A. pallida can be regarded as a good model for coral bleaching studies and has numerous advantages for experimentation. [less ▲]

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See detailInfluence of coral heterogenous susceptibility to warming on reef biodiversity
Ladrière, Ophélie ULg; Penin, Lucie; Adjeroud, Mehdi et al

Poster (2007)

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See detailEchinoderm skeletons record sea temperatures
Ranner, Herwig; Ladrière, Ophélie ULg; Navez, Jacques et al

Poster (2006)

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See detailEchinoderm skeletons record sea temperatures
Ranner, Herwig; Ladrière, Ophélie ULg; Navez, Jacques et al

Poster (2005, December 31)

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See detailDo echinoderms store temperature changes in their skeleton?
Ranner, Herwig; Ladrière, Ophélie ULg; Navez, Jacques et al

Poster (2005, April 24)

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