Search

International audience; The multidisciplinary programme BioReCIE (Biodiversity, Resources and Conservation of coral reefs at Eparses Is.) inventoried multiple marine animal groups in order to provide information on the coral reef health of the Iles Eparses. All five classes of echinoderms were observed by visual census, photographed and later identified. About 100 species are reported, including a few unidentified ones which require further studies. The Holothuroidea and Ophiuroidea are the most diverse. One new species, the asterinid Aquilonastra chantalae O'Loughlin and McKenzie (2013), was discovered in addition to several new records of echinoderms. The illegal fishery targeting holothurians, which are presently highly valuable resources in this zone, is discussed.

During the past two decades, the emergence and spread of infectious diseases have caused substantial declines in the biodiversity and abundance of reef-building corals. Despite their increased global prevalence and virulence, little is known about coral diseases on Indian Ocean coral reefs. This study aims to fill this gap in knowledge by identifying the main coral diseases and quantify their prevalence at three localities Reunion, South Africa and Mayotte, determining their spatial distribution and seasonal variation. Principal findings of this study demonstrated the presence of six main coral diseases including black band disease (BBD), white syndromes (WS), pink line syndrome (PLS), growth anomalies (GA), skeleton eroding band (SEB) and Porites white patch syndrome (PWPS). The overall disease prevalence was higher in Reunion (7.5 ± 2.2%; mean ± SE) compared to South Africa (3.9 ± 0.8%; mean ± SE) and Mayotte (2.7 ± 0.3%; mean ± SE). Acropora and Porites were the genera most vulnerable to disease. Spatial variability was detected in both Reunion and South Africa with BBD and WS more prevalent on shallow than deep reefs. There was also evidence of seasonality in two diseases: BBD and WS, their prevalence being higher in summer than winter. Corals exhibiting signs of PWPS revealed extensive tissue fragmentation, generally associated with ovoid basophilic bodies resembling bacterial aggregates within the mesoglea of the body wall. Other organisms, including Cyanobacteria, Nematoda, Ciliata and endophytic algae, were also observed on diseased tissues and were generally associated with the dead epidermis and cell debris. Results of 16S rRNA sequence analysis revealed a high variability between bacterial communities associated with PWPS-infected and healthy tissues in Porites lutea. Several bacterial ribotypes affiliated to potential putative pathogens notably Shimia marina and Vibrio hepatarius were consistently found among the 16S rRNA sequences derived from the PWPS lesions, and absent and/or poorly represented in HT. Primary pathogens involved in the PWPS were also investigated in this study using traditional culturing techniques and laboratory infection trials. Of the 14 isolates selected for the inoculation trials, only the bacterial strain P180R mostly phylogenetically closely related8 to Vibrio tubiashii with its closest known sister taxon, V. hepatarius, was shown to cause signs resembling those of PWPS and satisfied the four Henle-Koch’s postulates. P180R displayed focalised and progressive tissue paling 12 h after inoculation and visible lesions of PWPS were observed 12 h thereafter. Signs of PWPS appeared on 90% of the exposed coral fragments (27 of 30) under controlled environmental conditions. Moreover, the virulence of this marine pathogen was tested and seemed to be strongly dependent on seawater temperature, resulting in significantly higher tissue loss at 30°C than 28°C and 26°C. Finally, a multidisciplinary approach involving field surveys, gross lesion monitoring, histopathology and 454-pyrosequencing was investigated to characterize an atypical form of BBD named PBPS. Histology revealed cyanobacterial penetration of the compromised tissue as well as the presence of basophilic bodies resembling bacterial aggregates in the living tissue, adjacent to the bacterial mat. Bacterial 16S rRNA sequences yielded a broader diversity of bacterial taxa in PBPS-infected tissues than in healthy tissue, represented by the genus Vibrio (24.9%), followed by sulfate-reducers or sulfide-oxidizers such as Desulfovibrio (20%), Clostridium (12.9%) and Arcobacter (9.9%). PBPS appears to be a multi-stage disease triggered by cyanobacterial invasion and resulting in secondary infections by environmental bacteria that grow in mucus-like decomposing tissue., Cette étude a pour but d'identifier les principales maladies coralliennes, de quantifier leurs prévalences sur les récifs de la Réunion, d'Afrique du Sud et de Mayotte et de déterminer leurs variations spatiales et saisonnières. Les résultats ont révélé la présence de six grands types de maladies coralliennes. Les prévalences totales moyennes des maladies ont été plus élevées à la Réunion (7.5 ± 2.2%) qu'en Afrique du Sud (3.9 ± 0.8%) et qu'à Mayotte (2.7 ± 0.3%). Les genres coralliens Acropora et Porites ont été les plus vulnérables aux maladies dans les trois régions étudiées. Des variations spatiales et saisonnières ont été détectées pour la maladie de la bande noire (BBD) et les syndromes blancs (WS) à la fois à la Réunion et en Afrique du Sud avec des prévalences plus élevées sur les récifs peu profonds et pendant la saison chaude. Ce travail a également pour but de caractériser deux maladies non décrites à ce jour : le syndrome des patches blancs (PWPS) et le syndrome du patch noir (PBPS) chez Porites. PWPS, observé à fois à la Réunion, en Afrique du Sud et à Mayotte est caractérisé par d'importantes fragmentations tissulaires généralement associées à des corps ovoïdes basophiles ressemblant à des agrégats bactériens. L'analyse bactérienne a révélé une grande variabilité entre les tissus infectés et sains. L'identification des pathogènes responsables de PWPS a également été réalisée en laboratoire. Sur les 14 souches bactériennes sélectionnées et testées, seule la P180R, génétiquement proche de Vibrio tubiashii a généré des signes de PWPS. Pour finir, PBPS, une forme atypique de BBD a été observée sur les récifs de la Réunion. Les suivis réalisés ont montré des variations spatiales et saisonnières avec des prévalences plus élevées sur le platier et pendant l'été. L'histologie a mis en évidence la présence de cyanobactéries et de corps basophiles dans les tissus infectés du corail. L'analyse génétique a révélé la présence d'une plus grande diversité de taxons dans les tissus infectés par PBPS que dans les tissus sains représentés par le genre Vibrio.

Coral reproduction and recruitment in Scleractinia were compared between the subtropical reefs of South Africa and the tropical reefs of Reunion to assess variations between contrasting environments. In addition, coral larvae and juvenile polyps were exposed to elevated temperature in aquarium to simulate global warming. The two targeted species, Acropora austera and Platygyra daedalea, exhibited the same reproductive mode (hermaphroditic broadcast spawner), gamete development (5-6 months) and breeding seasonality (October to February) in South Africa and Reunion. Coral fecundity was nevertheless higher in South Africa than in Reunion. A. austera and P. certaine limite.AbstractCoral reproduction and recruitment in Scleractinia were compared between the subtropical reefs of South Africa and the tropical reefs of Reunion to assess variations between contrasting environments. In addition, coral larvae and juvenile polyps were exposed to elevated temperature in aquarium to simulate global warming. The two targeted species, Acropora austera and Platygyra daedalea, exhibited the same reproductive mode (hermaphroditic broadcast spawner), gamete development (5-6 months) and breeding seasonality (October to February) in South Africa and Reunion. Coral fecundity was nevertheless higher in South Africa than in Reunion. A. austera and P. daedalea produced respectively 43 and 100% more oocytes per polyp than their Reunion counterparts. The recruitment rate was also higher on the subtropical reefs of South Africa (548 recruits m2 year-1) compared to Reunion (305 recruits m2 year-1). Recruitment was dominated by Pocilloporidae at the two localities, followed by Acroporidae in South Africa and Poritidae in Reunion. In South Africa, an increase in sea temperature of 2°C strongly affected the larval development of the sensitive A. austera, while the more robust P. daedalea sustained temperatures up to 4°C (i.e. 30°C) above ambient. In Reunion, diminished fecundity and recruitment rate seemed to be an indicator of reef perturbation. In contrast in South Africa, the high reproductive effort and larval supply in corals associated with the low levels of disturbance on the reefs may favour coral adaptation, to some extent, under global change., Cette étude a pour but de comparer la reproduction et le recrutement des coraux entre les récifs subtropicaux d'Afrique du Sud et les récifs tropicaux de la Réunion représentant des milieux contrastés. D'autres part, afin de simuler le réchauffement climatique, l'effet de l'augmentation de la température de l'eau en aquarium a été testé sur le développement des larves et les juvéniles de coraux. Les deux espèces étudiées, Acropora austera et Platygyra daedalea ont un mode de reproduction (hermaphrodite ‘pondeur’), un développement des gamètes (5-6 mois) et une période de reproduction (d'Octobre à Février) similaires en Afrique du Sud et à la Réunion. La fécondité de ces coraux est néanmoins supérieure en Afrique du Sud par rapport à la Réunion. Les deux espèces produisent 43-100% plus d'ovocytes en Afrique du Sud qu'à la Réunion. Le taux de recrutement des coraux est aussi supérieur sur les récifs subtropicaux d'Afrique du Sud (548 recrues m2 an-1) comparé à ceux de la Réunion (305 recrues m2 an-1). Le recrutement est dominé par les Pocilloporidae dans les deux régions, suivis par les Acroporidae en Afrique du Sud et les Poritidae à la Réunion. En Afrique du Sud, l'augmentation de la température de l'eau de 2°C a une influence négative sur le développement larvaire du sensible A. austera alors que P. daedalea est plus vigoureux et supporte des températures de 4°C supérieures à la normale (30°C). À la Réunion, le faible taux de fécondité et de recrutement semble être un indicateur de perturbation des récifs. Au contraire en Afrique du Sud, l'effort de reproduction des coraux et l'important approvisionnement en larves, associés à la faible anthropisation des récifs, pourraient favoriser l'adaptation des coraux aux changements climatiques dans une certaine limite.

Thirteen discrete air-fall tephra layers were identified in the last 200,000-yr section of the EPICA-Dome C ice record drilled in the East Antarctic plateau (75°06′S, 123°21′E). Quantitative grain size, glass particle morphology, and the grain-discrete major element composition of the glass fraction of these layers were investigated. Through comparison with literature data on the rock composition of Quaternary volcanic centres located within and around Antarctica, five tephra layers were attributed to South Sandwich volcanoes in the South Atlantic Ocean, two to South Shetland volcanoes (northern Antarctic Peninsula), two to Andean volcanoes, and four to Antarctic (Marie Byrd Land and Melbourne) provinces. The abundance of layers originating in the southern part of the Atlantic confirms that westerly atmospheric circulation spiralling towards East Antarctica prevailed over the last 200 ka. Moreover, the record of events from Antarctic centres suggests that atmospheric trajectories from West to East Antarctica can also be significant. A few ash layers are geochemically distinct and appear equivalent to levels from Vostok and Dome Fuji deep ice records, located ca. 600 km and ca. 2000 km, respectively, from Dome C on the Antarctic plateau. These layers provide unambiguous markers for future correlation with other Antarctic ice cores and circumpolar marine climatic records. They also provide reliable constraints to get a common timescale by glaciological modelling, and represent a first step towards absolute ice core dating. © 2005 Published by Elsevier B.V.