Data from: Bias associated with the detectability of the coral-eating pest crown-of-thorns seastar and implications for reef management

Outbreaks of the predator crown-of-thorns seastar (COTS) Acanthaster planci cause widespread coral mortality across the Indo-Pacific. Like many marine invertebrates, COTS is a nocturnal species whose cryptic behaviour during the day can affect its detectability, particularly in structurally complex reef habitats that provide many refuges for benthic creatures. We performed extensive day and night surveys of COTS populations in coral reef habitats showing differing levels of structural complexity and COTS abundance. We tested whether estimations of COTS density varied between day and night observations, and if the differences were related to changes in COTS abundance, reef structural complexity, and the spatial scale of observation. Estimations of COTS density were on average 27% higher at night than during the day. Differences in COTS detection varied with changing seastar abundance but not reef structural complexity or scale of observation. Underestimation of COTS abundance in daytime was significant for a broad seastar density range, thus potentially affecting most outbreak events. Our study suggests that portions of COTS populations can be undetected during conventional surveys and control campaigns, which are exclusively conducted by day, and significantly affect the trajectory of coral reefs. Accounting for bias in COTS detection can strengthen coral reef management broadly

Bias associated with the detectability of the coral-eating pest crown-of-thorns seastar and implications for reef management

International audienceOutbreaks of the predator crown-of-thorns seastar (COTS) Acanthaster planci cause widespread coral mortality across the Indo-Pacific. Like many marine invertebrates, COTS is a nocturnal species whose cryptic behaviour during the day can affect its detectability, particularly in structurally complex reef habitats that provide many refuges for benthic creatures. We performed extensive day and night surveys of COTS populations in coral reef habitats showing differing levels of structural complexity and COTS abundance. We tested whether estimations of COTS density varied between day and night observations, and if the differences were related to changes in COTS abundance, reef structural complexity and the spatial scale of observation. Estimations of COTS density were on average 27% higher at night than during the day. Differences in COTS detection varied with changing seastar abundance but not reef structural complexity or scale of observation. Underestimation of COTS abundance in daytime was significant for a broad seastar density range, thus potentially affecting most outbreak events. Our study suggests that portions of COTS populations can be undetected during conventional surveys and control campaigns, which are exclusively conducted by day, and significantly affect the trajectory of coral reefs. Accounting for bias in COTS detection can strengthen coral reef management broadly

Data COTS density & reef substrate rugosity

Field surveys of crown-of-thorns seastar (COTS) population densities on 9 reef locations around Moorea, French Polynesia. Paired day and night surveys were performed every 6 months in triplicate 200m2 permanent-transects over a 2 year period. Reef substrate rugosity was also quantified

La diversité des dinoflagellés chez les nudibranches et les éponges de Polynésie française : associations et transfert

International audienceSymbioses with the dinoflagellate Symbiodinium are widespread among marine invertebrates and protists, especially in nutritionally demanding habitats, such as tropical coral reefs, where they play a major role in ecosystem survival. Moreover, apart from corals and sea anemones, many of the Symbiodinium species and clades involved in these partnerships remain to be characterized. This study provides new insights into nudibranch and sponge associations with Symbiodinium by sequencing regions of the Symbiodinium 28S rDNA and the host mitochondrial COI oxidase. Specimens were sampled between 2011 and 2013 from locations around the islands of Moorea and Tahiti, French Polynesia. Our results revealed that some of the sponges and nudibranchs harbored typical Symbiodinium from clade B or C while others harbored new, undescribed Symbiodinium-like dinoflagellates. A detailed analysis of the different life stages of the nudibranch Phestilla lugubris and of its specific coral prey, Porites rus, suggests a prey-predator horizontal transfer of the symbiont and its vertical inheritance from the parent to the eggs.Les symbioses à zooxanthelles, dinoflagellés du genre Symbiodinium, sont largement répandues chez les invertébrés marins et les protozoaires, notamment dans les eaux oligotrophes, où ils jouent un rôle important dans la survie des récifs coralliens. De plus, excepté chez les coraux et les anémones, les différentes espèces et clades de Symbiodinium impliqués dans ces associations restent à être caractérisés. Notre étude, grâce à l’utilisation des marqueurs génétiques 28S ADNr des Symbiodinium et la sous-unité 1 de la cytochrome oxydase mitochondriale (COI) de l’hôte, procure de nouvelles données quant aux associations des éponges et des nudibranches avec les Symbiodinium. L’échantillonnage a eu lieu autour de Moorea et de Tahiti (Polynésie française), entre 2011 et 2013. Nos résultats révèlent que certaines espèces d’éponges et de nudibranches possèdent les clades B et C communément retrouvés, chez les coraux notamment, alors que d’autres présentent de nouveaux dinoflagellés « Symbiodinium-like ». Une analyses détaillée des Symbiodinium à différents stades du cycle de vie du nudibranche corallivore Phestilla lugubris et de son corail hôte Porites rus suggèrent l’existence d’un transfert horizontal de Symbiodinium proie–prédateur et un transfert vertical du parent P. lugubris à ses œufs

Recovery of coral assemblages despite acute and recurrent disturbances on a South Central Pacific reef

International audienc

Predator crown-of-thorns starfish (Acanthaster planci) outbreak, mass mortality of corals, and cascading effects on reef fish and benthic communities

Outbreaks of the coral-killing seastar Acanthaster planci are intense disturbances that can decimate coral reefs. These events consist of the emergence of large swarms of the predatory seastar that feed on reef-building corals, often leading to widespread devastation of coral populations. While cyclic occurrences of such outbreaks are reported from many tropical reefs throughout the Indo-Pacific, their causes are hotly debated, and the spatio-temporal dynamics of the outbreaks and impacts to reef communities remain unclear. Based on observations of a recent event around the island of Moorea, French Polynesia, we show that Acanthaster outbreaks are methodic, slow-paced, and diffusive biological disturbances. Acanthaster outbreaks on insular reef systems like Moorea's appear to originate from restricted areas confined to the ocean-exposed base of reefs. Elevated Acanthaster densities then progressively spread to adjacent and shallower locations by migrations of seastars in aggregative waves that eventually affect the entire reef system. The directional migration across reefs appears to be a search for prey as reef portions affected by dense seastar aggregations are rapidly depleted of living corals and subsequently left behind. Coral decline on impacted reefs occurs by the sequential consumption of species in the order of Acanthaster feeding preferences. Acanthaster outbreaks thus result in predictable alteration of the coral community structure. The outbreak we report here is among the most intense and devastating ever reported. Using a hierarchical, multi-scale approach, we also show how sessile benthic communities and resident coral-feeding fish assemblages were subsequently affected by the decline of corals. By elucidating the processes involved in an Acanthaster outbreak, our study contributes to comprehending this widespread disturbance and should thus benefit targeted management actions for coral reef ecosystems

Réseau de surveillance des polluants anthropiques dans les lagons de Polynésie française. Rapport final - Septembre 2014. Contrat de projet Etat-Pays

La mise en place d’un réseau d’observation de la qualité des eaux lagonaires de Polynésie française, financé par le contrat de projet Etat – Pays, a été initiée mi 2012 pour une durée de deux ans. Durant un à trois semestres la contamination in situ a été suivie sur 6 sites : Vairao et la baie de Phaéton à Tahiti, Moorea (Vaiare), Huahine (Faie), Maupiti et Rangiroa. Le mollusque bioindicateur utilisé est l’huître perlière Pinctada margaritifera. Après transplantation et 4 mois d’immersion sur site, la mesure dans les chairs de la radioactivité gamma n’a pas permis de détecter de radionucléides artificiels, cependant du césium 137 a été mesuré dans les sédiments sur 2 sites. Le plutonium (émetteur alpha) est présent en faibles quantités dans les chairs. L’analyse des métaux lourds a montré que le cadmium est toujours présent dans les chairs des bivalves avec des teneurs qui diminuent parfois, les teneurs en mercure et plomb sont très faibles dans tous les échantillons. Les huîtres perlières sont de bons biointégrateurs du fer et du zinc. L’analyse des composés organochlorés a mis en évidence la présence d’acétochlore sur 2 des suivis, d’autres composés (PCB, isodrine, …) ont été détectés sur plusieurs sites. Les mesures de HAP (Hydrocarbures Aromatiques polycycliques) sont assez variables dans le temps, des composés différents ont été détectés sur les trois suivis, le phénanthrène a été détecté systématiquement. Le suivi du milieu ne laisse apparaître aucun résultat problématique en termes de pollution. Les paramètres hydrologiques sont principalement influencés par les conditions météorologiques et la localisation du site par rapport à l’influence de la côte. Les analyses sédimentologiques ont permis de différencier les sites exposés à une sédimentation d’origine terrigène (Phaéton et Moorea) ou biogène (Vairao, Huahine, Maupiti et Rangiroa) où les peuplements de la faune et la flore marine sont plus importants. Parallèlement, des expériences menées en laboratoire ont permis de mettre en évidence le phénomène d’accumulation des métaux lourds, cadmium et chrome, dans la chair des huîtres perlières. Ces teneurs augmentent rapidement au cours du temps lorsque le milieu est contaminé, notamment pour le cadmium. Les byssus intègrent également ce métal dans une moindre mesure. Ces expérimentations ont également permis d’identifier 3 gènes candidats biomarqueurs d’une contamination par les métaux lourds dans le cadre du projet Biolag. Cette expérience permet d’établir un outil performant de quantification du plutonium pour les expertises que mène l’IRSN dans l’environnement et pour la mesure des autres polluants dans les lagons comme dans le cas du projet INTEGRE

Dynamics of various communities surveyed at the reference reef locations.

<p>These nine locations consist of three sites (Haapiti: H, Tiahura: T, Vaipahu: V) × three water depths (6, 12, 18 m). Y-axes on the left indicate cover values (mean ± SE) of the sessile communities: reef-building corals and other benthic components. Y-axes on the right indicate densities (mean ± SE) of coral-predators: populations of the outbreaking seastar <i>Acanthaster</i> and butterflyfish assemblages. Arrows on the x-axes indicate the occurrence of the tropical cyclone <i>Oli</i>. Refer to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0047363#pone-0047363-g005" target="_blank">Figure 5</a> for correlations between the dynamics of different communities. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0047363#pone-0047363-g002" target="_blank">Figure 2</a> for an illustration of the changes observed on reefs.</p

Distributions and densities of <i>Acanthaster</i> feeding-scars as observed around Moorea through time.

<p>The dimensions of the circles are proportional to the abundance of scars (n scars per 2 min-towing section), and a color code is used to distinguish different abundance classes (refer to the legend). A mean relation of 8.6±1.7 SE scars per individual seastar was estimated during the outbreak (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0047363#pone.0047363.s001" target="_blank">Table S1</a>). The positions of the three reference sites where reef communities were surveyed are also displayed on the graphs: Haapiti (H), Tiahura (T), Vaipahu (V). Original satellite image from © Google Earth.</p

A portion of Moorean outer-reef (6 m-depth on the site Vaipahu) is shown through time.

<p>(<b>A</b>) Corals dominate the healthy reef (coral cover >40%). (<b>B</b>) Algae have colonized dead coral skeletons following severe predation by the seastar <i>Acanthaster</i> (∼10% coral cover). (<b>C</b>) Mostly dead and weakened coral skeletons were swept away by a cyclone occurring at the end of the seastar outbreak (Lison de Loma et al. <i>unpublished data</i>) and colonizing algae once again dominate the devastated reef (∼5% coral cover). © Photos Mohsen Kayal.</p