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International audience; Dams and other man-made barriers impair upstream fish migration and thus threaten fish populations that need access to upper river reaches to complete their life cycle. For many years, fishways have been used to mitigate this impact. Fishways around the globe are typically built based on recommendations made for northern hemisphere species, particularly salmonids. These recommendations do not consider the locomotor characteristics and skills of other species, especially those living in the tropics. Among tropical species, freshwater eels and gobies of the Sicydiinae subfamily are important cultural and economic species that are particularly sensitive to the impact of man-made barriers. Our experimental study aimed to test different substrates and slopes for ramp-like fishways adapted to tropical eels and sicydiines. Among the five substrates tested for 368 eels Anguilla marmorata, elastomer pins appeared to be the most efficient. Elastomer pins also appeared to be more efficient than the fine concrete which is currently used in fishways for sicydiines (Sicyopterus lagocephalus, N = 1797, and Cotylopus acutipinnis, N = 1303). The slope had a lesser effect on the climbing success of sicydiines compared to substrate type, except for gradients greater than 50° that induced a slight decrease in success. Our results indicated that ramp-like fishways fitted with 1.0 cm diameter elastomer pins, positioned in staggered rows with a diagonal spacing of 1.3 cm, wetted with low-flow and angled less than 50°, are well adapted to accommodate the different locomotor characteristics and skills of tropical eels and sicydiines.

In order to provide biological evidence of the real impact of mosquito seine nets in southwestern Madagascar, an efficient procedure for determining the size at maturity of small-sized tropical fishes was developed. The fishes caught by two small-scale fishermen were studied between October 2017 and April 2018. One catch per day was analyzed three days per month during the full-moon period. In the laboratory, fishes were all sorted by morphospecies, photographed and measured. One individual per morphospecies was selected for being identified using CO1 DNA barcoding. A total of 34,051 individual fishes belonging to 144 DNA bacoded species from 48 families was obtained from 42 samples, 467 individuals from 22 morphospecies that had not been successfully barcoded were excluded from the analyses. The macroscopic observations of 8,143 individuals between 0.7 and 10 cm SL indicated the proportion of individuals with clearly observable gonads was 15% only.Among the 144 species identified via DNA barcoding, 83 consisted of individuals that were all without clearly observable gonads, seven of individuals that were all with clearly observable gonads and 54 included of individuals with and without clearly observable gonads. As the determination of L-50 using logistic general linear models failed for most species, the minimum size at maturity was retained to determine the proportion of juveniles and adults for these 54 species. Compared to the data available in FishBase, the minimum size at maturity appears more adequate to discrimine juvenile from adult fish of small-sized tropical species.

Relationships between body shape and escape performance are well established for many species. However, organisms can face multiple selection pressures that might impose competing demands. Many fishes use fast starts for escaping predator attacks, whereas some species of gobiid fishes have evolved the ability to climb waterfalls out of predator-dense habitats. The ancestral ‘powerburst’ climbing mechanism uses lateral body undulations to move up waterfalls, whereas a derived ‘inching’ mechanism uses rectilinear locomotion. We examined whether fast-start performance is impacted by selection imposed from the new functional demands of climbing. We predicted that non-climbing species would show morphology and fast-start performance that facilitate predator evasion, because these fish live consistently with predators and are not constrained by the demands of climbing. We also predicted that, by using lateral undulations, powerburst climbers would show escape performance superior to that of inchers. We compared fast starts and body shape across six goby species. As predicted, non-climbing fish exhibited distinct morphology and responded more frequently to an attack stimulus than climbing species. Contrary to our predictions, we found no differences in escape performance among climbing styles. These results indicate that selection for a competing pressure need not limit the ability of prey to escape predator attacks.

International audience; Die Funktionelle Leistung von Evolutionären Neuheiten: Erkenntnisse durch Kinematische- und Leistungsstudien von Wasserfallklettern an jugendlichen Gobiid-Fischen Zusammenfassung Die Entwicklung neuartiger funktioneller Merkmale kann wesentlich zur Diversifizierung von Abstammungslinien beitragen. Ältere funktionelle Merkmale können aufgrund der im Laufe der Zeit auftretenden evolutionären Veränderungen größere Unterschiede aufweisen als neuere Merkmale. Die funktionale Komplexität und die Eins-zu-Eins-Zuordnung von Struktur-zu-Funktion können solche Erwartungen jedoch erschweren. In diesem Zusammenhang haben wir die Kinematik und Leistung von Jungtieren verschiedener Spezien von Gobiid-Fischen für zwei Arten des Wasserfallkletterns verglichen: das ältere „Powerburst “-Klettern und das in jüngster Zeit entwickelte „Inching“, das nur in einer Gattung von Gobiid- Fischen vorkommt, die in der Gruppe der Powerburst-Kletterer eingeschlossen ist. Ähnliche Netto-Klettergeschwindigkeiten bei “Inching”-Spezien scheinen zunächst darauf hinzudeuten, dass diese neuere Art des Kletterns wenig funktionelle Vielfalt aufweist. Allerdings ist die ähnliche Nettogeschwindigkeit das Resultat von verschiedenen Faktoren: Sicyopterus stimpsoni aus Hawaii bewegt sich langsamer als S. lagocephalus aus La Réunion aber bewegt sich mehr kontinuierlich. Das Ergebnis einer ähnlichen Leistung durch zweierlei Funktionspfade ähnelt dem Phänomen der Eins-zu-Eins Zuordnung von Struktur-zu-Funktion. Eine solche Ähnlichkeit kann die angemessene Interpretation der relativen funktionalen Vielfalt zwischen den Linien erschweren, sofern nicht die der Leistung zugrundeliegenden Mechanismen untersucht werden. Insbesondere zeigt die Ähnlichkeit in der Nettoleistung zwischen “Powerburst” - und “Inching” -Kletterstilen, dass die Entwicklung des neuen Kletterstils wahrscheinlich wenig mit verbesserter Kletterleistung zu tun hat. In diesem Zusammenhang könnten andere Prozesse (z. B. Exaptation) an der Entstehung dieser funktionellen Neuheit beteiligt sein. Translated to German by Heiko Schoenfuss (hschoenfuss@stcloudstate.edu); The evolution of novel functional traits can contribute substantially to the diversification of lineages. Older functional traits might show greater variation than more recently evolved novelties, due to the accrual of evolutionary changes through time. However, functional complexity and many-to-one mapping of structure to function could complicate such expectations. In this context, we compared kinematics and performance across juveniles from multiple species for two styles of waterfall-climbing that are novel to gobiid fishes: ancestral “powerburst” climbing, and more recently evolved “inching”, which has been confirmed only among species of a single genus that is nested within the clade of powerburst climbers. Similar net climbing speeds across inching species seem, at first, to indicate that this more recently evolved mode of climbing exhibits less functional diversity. However, these similar net speeds arise through different pathways: Sicyopterus stimpsoni from Hawai’i move more slowly than S. lagocephalus from La Réunion, but may also spend more time moving. The production of similar performance between multiple functional pathways reflects a situation that resembles the phenomenon of many-to-one mapping of structure to function. Such similarity has the potential to mask appropriate interpretations of relative functional diversity between lineages, unless the mechanisms underlying performance are explored. More specifically, similarity in net performance between “powerburst” and “inching” styles indicates that selection on climbing performance was likely a limited factor in promoting the evolution of inching as a new mode of climbing. In this context, other processes (e.g., exaptation) might be implicated in the origin of this functional novelty.; Diversité fonctionnelle des innovations évolutives: l’exemple de la cinématique et des performances de grimpe des chutes d’eau des juvéniles de gobies Résumé L’évolution de nouveaux traits fonctionnels peut contribuer significativement à la diversification des lignées. Les traits fonctionnels les plus anciens peuvent montrer plus de variabilité que les plus récents du fait de l’accumulation de changements évolutif au cours du temps. Cependant, ces prédictions peuvent être complexifiées par la diversité des fonctions et par l’implication de plusieurs structures dans une même fonction. Dans ce contexte, nous avons étudié la cinématique et les performances de grimpe des chutes d’eau de plusieurs espèces de gobies utilisant deux styles de grimpe originaux au sein de cette famille: le mode « powerburst » plus ancestral et le mode « inching » qui a évolué plus récemment. Le mode inching n’a été confirmé que pour deux espèces du même genre incluses au sein du clade des powerburst. Des vitesses de grimpe similaires entre les espèces utilisant le mode inching paraissent indiquer que ce mode de grimpe, qui a évolué plus récemment, présente une diversité fonctionnelle moins élevée. Toutefois, la similarité des vitesses de grimpe entre les deux espèces s’explique par des processus différents: le Sicyopterus stimpsoni d’Haiwaï se déplace plus lentement que le S. lagocephalus de La Réunion mais passe plus de temps en mouvement. La production de performances similaires, résultant de processus différents, reflète un phénomène semblable à celui de l’implication de plusieurs structures dans une même fonction. Si les mécanismes sous-jacents ne sont pas explorés, ces similarités peuvent perturber l’interprétation des différences relatives de diversité fonctionnelle entre les lignées. Par ailleurs, les performances de grimpe similaires entre certaines espèces utilisant le mode inching et d’autres le mode powerburst paraissent indiquer que la force de sélection sur les performances de grimpe est sans doute un facteur réduisant l’avantage évolutif du mode de grimpe inching. Dans ce contexte, d’autres mécanismes (e.g., exaptation) pourraient être à l’origine de cette innovation fonctionnelle. Translated to French by Raphael Lagarde (raph.lagarde@gmail.com); 進化的ノベルティの機能的多様性：滝登りハゼの稚魚による岩登り時の運動学とパフォーマンスからの洞察 （Abstract: 梗概） 進化的に新しい機能特性は系統の多様化に大きく貢献することが可能である。より古い機能特性は、時間の経過に伴う進化的変化の蓄積により、より新しく発現した特性よりも大きな偏差を示すと考えられるのであるが、機能の複雑さと、構造と機能における多対一の関連性により、この様な予測はより複雑になる可能性がある。これを踏まえて、我々は祖先的岩登りスタイルの“パワーバースト”タイプとその系統群の中から進化的に新しく発現した単一の属が獲得したとされる“インチング”タイプを示す複数種の滝登りハゼの稚魚による岩登り時の運動学とパフォーマンス比較分析した。“インチング”タイプの実質的なクライミング速度はどれも種間の差異が認められなかった、そのためこのもっとも最近進化的に発現した岩登りのスタイルは、機能的多様性をあまり示さないことを示唆しているよう考えられる。しかし、ハワイ島のSicyopterus stimpsoniは、レユニオン島のS. lagocephalusよりも遅いが、クライミング移動により多くの時間を費やす傾向にあることが分かった。したがって、この種間に差異のない実質的速度は異なる経路を介して発生していると考えられ、複数の機能経路間で同様のパフォーマンスが得られたことは、多対一の関連性があると言える。そしてこれはパフォーマンスの基礎となるメカニズムが明確にされない限り、系統間の相対的な機能的多様性の適切な解釈を複雑にするであろう。より具体的に言うなれば、“パワーバースト”タイプと“インチング”タイプの実質的パフォーマンスの類似性は、クライミングパフォーマンスのへ淘汰が進化的に新しい岩登りスタイルとしての“インチング”タイプを確立する上で制限要因になり得る可能性が高いことを示している。さらには、他のプロセス（例えば、外適応）がこの機能的ノベルティの起源に関係している可能性があると考えられる。Translated to Japanese by Takashi Maie (maie.t@lynchburg.edu); Diversidade funcional de novidades evolucionárias: percepções da cinemática da escalada em cascatas e desempenho de peixes juvenis gobiídeos ResumoA evolução de novos traços funcionais pode contribuir substancialmente para a diversificação de linhagens. Os traços funcionais mais antigos podem mostrar maior variação do que as novidades desenvolvidas mais recentemente, devido ao acúmulo de mudanças evolutivas ao longo do tempo. No entanto, a complexidade funcional e os inúmeros mapeamentos de uma estrutura para uma única função podem complicar essas expectativas. Nesse contexto, comparamos a cinemática e a performance em juvenis de várias espécies para dois estilos de escalada em cascata que são novidades em peixes gobiídeos: a ancestral escalada por “explosão” e o evolutivamente mais recente chamado de “avançamento”, que foi confirmado apenas entre espécies de um único gênero que dentro do clado de escaladores por explosão. Velocidades finais de escalada semelhantes entre espécies usando “avançamento” parecem, inicialmente, indicar que esse modo de escalada evolutivamente mais recente exibe menor diversidade funcional. No entanto, essas velocidades finais similares ocorrem por diferentes formas: Sicyopterus stimpsoni do Havaí se move mais devagar que S. lagocephalus das Ilhas Reunião, mas pode gastar mais tempo se movendo. Desempenhos semelhantes entre várias vias funcionais refletem uma situação que se assemelha ao fenômeno de mapeamento de uma estrutura para um única função. Essa semelhança tem o potencial de ocultar interpretações apropriadas sobre relativa diversidade funcional entre linhagens, a menos que os mecanismos que afetam o desempenho sejam explorados. Mais especificamente, a semelhança no desempenho final entre os estilos “explosão” e “avançamento”indica que a seleção na performance em escalada provavelmente foi um fator limitante na promoção da evolução por “avançamento” como um novo modo de escalada. Nesse contexto, outros processos (e.g., exaptação) podem estar relacionados com a origem dessa novidade funcional.Translated to Portuguese by Diego Vaz (dbistonvaz@vims.edu)

Water warming induced by human activities can impact fish larvae survival, notably because it influences larval development and prey abundances. Amphidromous gobies of the subfamily Sicydiinae are particularly sensitive to this threat as the newly hatched free embryos are poorly developed and the first feeding opportunity only occurs after they reach the ocean. Here, we studied how water temperature (21, 23, 25, 29 and 31 degrees C) impacts early development stages of Sicyopterus lagocephalus in both freshwater and marine aquaria (salinity 35). We monitored survival time, larval condition and the occurrence of critical developmental events such as mouth opening, yolk sac and oil globule resorption. In freshwater, the survival exceeded 150 hours at 21 degrees C, while it dropped below 50 hours at 31 degrees C. In seawater, the larval development of unfed larvae was significantly affected by temperature, survival time being greatly reduced in warmer waters. Accounting for the observed duration between mouth opening and the resorption of the oil globule, we estimated that larvae need to find suitable prey in seawater within a short time: around 30 hours during the peak of reproduction in summer. Otherwise, their endogenous reserves become depleted and their condition degrades. This study emphasises the sensitivity of free embryos to stream flow alterations, which contributes to the increase in water temperature and to the slowing down of larvae drift to the ocean. We conclude that once in seawater the temperature and feeding conditions experienced by amphidromous larvae are critical for survival.

International audience; Determining the relative importance of niche‐ and dispersal‐based processes in the structuring of animal communities is central in ecology. Freshwater fish and crustacean communities of small tropical islands can bring new insights for understanding these processes as all their species present a pelagic larval stage which gives them important dispersal capacities. Consequently, we hypothesized that dispersal‐based process may be preponderant for structuring these communities from the regional to the local, that is, survey site, scales. Gradient forest analyses allowed us to model the effect of 12 environmental variables on freshwater taxa abundances in two southwestern Indian Ocean islands: Mayotte (26 taxa) and Reunion (21). A total of 153 surveys in Mayotte and 266 in Reunion were used for building the models. Despite the strong heterogeneity of environmental conditions between the two islands, the main factors structuring freshwater fish and crustacean communities in both islands were the elevation and the slope of the sites. The observed structure appeared more pronounced for predatory species than for primary consumers and omnivores. As predators generally have limited locomotor capacities, it is concluded that dispersal‐based process structures these communities not only at large geographical scales but also at the intra‐watershed scale, by limiting the inland penetration (or dispersion) of species in relation to their locomotor capacities. However, more knowledge concerning ecological traits and taxonomic status of many species is needed to confirm this assumption.; Une des questions centrales en écologie consiste à déterminer l'importance des processus de niche et de dispersion dans la structuration des peuplements faunistiques. L’étude des peuplements de poissons et de crustacés d'eau douce des petites îles tropicales peut apporter de nouveaux éclairages pour comprendre ces processus. En effet, ces espèces présentent toutes une phase de développement larvaire en milieu marin qui augmente fortement leurs capacités de dispersion. Nous avons donc émis l'hypothèse que les processus de dispersion ont un effet majeur sur la structure des peuplements à l’échelle régionale, mais également à l’échelle locale, c'est‐à‐dire celle du site d’étude. Des analyses de type « gradient forest» nous ont permis de modéliser l'influence de 12 variables environnementales sur les fluctuations d'abondance des taxons d'eau douce de deux îles du sud‐ouest de l'océan Indien: Mayotte (26 taxons) et la Réunion (21 taxons). Au total, 153 inventaires à Mayotte et 266 à La Réunion ont été pris en compte dans les modèles. Malgré l'hétérogénéité marquée des conditions environnementales entre les deux îles, les principaux facteurs structurant les peuplements de poissons et de crustacés étaient similaires, à savoir la pente du site d'inventaire et son altitude. De plus, la structuration des peuplements de prédateurs était plus marquée que celle des consommateurs primaires et des omnivores. Comme la plupart des prédateurs ont des capacités locomotrices limitées, nous avons conclu que les processus de dispersion jouent un rôle prépondérant dans la structuration de ces peuplements que ce soit à large échelle ou à l'intérieur des bassins versants. En effet, les faibles performances locomotrices des prédateurs peuvent limiter leur capacité à coloniser (ou se disperser vers) les zones amont des cours d'eau. Cependant, des connaissances plus approfondies concernant le statut taxinomique et l’écologie de plusieurs de ces espèces seraient nécessaires pour confirmer cette hypothèse.

International audience; The life cycle of gobies of the Sicydiinae subfamily depends on climbing waterfalls. Two sympatric sicydiines species from Reunion Island, Sicyopterus lagocephalus (SIL) and Cotylopus acutipinnis (COA), employ different climbing modes. SIL uses a steady “inching” mode interrupted by short rest periods, whereas COA exhibits short “power-burst” undulatory movements punctuated by longer rest periods. Consequently, we explored the relationship between climbing performance and metabolic activity in these two species. We demonstrated that the two climbing modes are supported by different ecophysiological profiles that promote the interspecific variability of locomotor performance. More specifically, SIL performed better than COA during a climbing experiment because of its inching climbing mode, supported by a generally greater metabolic capacity and a higher potential for oxidative metabolism. Interestingly, we did not detect any difference in metabolic fuel storage and lactate production during climbing in either species, suggesting that these species can maintain fuel reserves and limit lactate accumulation through extensive rest times. Overall, this study provides new insights into the ecophysiology of these two emblematic species and suggests that the better climbing capacity of SIL is supported by its muscular metabolic capacity.

International audience; Understanding the interannual effect of various environmental factors on biodiversity distribution is fundamental for developing biological monitoring tools. The interannual variability of environmental factors on presettlement fish assemblages (PFAs) has been so far under investigated, especially in Madagascar. Numerous explanatory variables including local hydro-dynamic conditions recorded during the sampling night, characteristics of the benthic substrate and remotely sensed oceanic conditions (RSOC) were used to explain the spatio-temporal variability of PFAs in southwestern Madagascar. Gradient forest analyses were used to hierarchically classify the effect of these explanatory variables on the PFAs for two sites and during two different recruitment seasons. RSOC variables appeared to better explain the PFAs than the local variable and the characteristics of the benthic substrate. The PFAs caught in water masses with coastal characteristics were better explained than those with open water characteristics. This spatial variability is hypothesised to be linked to differences in feeding conditions among water masses. The gradient forest analyses also highlighted the complexity of predicting PFAs as the species for which abundances were better explained by RSOC variables varied between years. This interannual variability was mainly explained by the interannual variation of chlorophyll a (Chl a) concentration, wind and surface current, with better prediction obtained during the year with high Chl a values associated with high averaged sea surface temperature. These findings suggest the importance of forecasting Chl a concentrations, taking into account the impact of tropical storms and climate variability in order to predict PFAs in the future.

International audience; Fish locomotor performance depends on inter-individual morphological differences and influences the response of populations to anthropogenic impacts. Amphidromous gobies, Sicyopterus lagocephalus and Cotylopus acutipinnis can climb up obstacles several metres high, after their arrival in rivers from the ocean. A previous study demonstrated that juveniles of S. lagocephalus performed better than C. acutipinnis when challenged with an artificial climbing ramp, and that individual morphology explained climbing performance for both species. This present study was focused on the effects of two 10-m high dams on the individual morphological selection of these species. We hypothesized that, compared with C. acutipinnis, (a) S. lagocephalus juveniles will reach the dams faster after they arrive in freshwater and (b) their morphology will play a lesser role in their capacity to climb up the dams. Anatomical traits were measured for 186 and 201 S. lagocephalus and 179 and 221 C. acutipinnis captured downstream and upstream of the dams, respectively. The time they spent in freshwater was estimated by examining the microstructures of their otoliths. As expected, S. lagocephalus individuals reached the dams 10–20 days faster than C. acutipinnis, and their morphology upstream and downstream of the dams did not differ, in contrast to C. acutipinnis. Upstream of the dam, C. acutipinnis had a larger pelvic sucker than downstream, confirming experimental observations. It suggests that juveniles of the cosmopolitan S. lagocephalus have more efficient upstream migration capacities than the endemic C. acutipinnis. Moreover, differences in individual morphologies above and below barriers appear efficient for quantifying their impact on upstream migration of amphidromous species.

This study investigates how age at first maturity of two tropical amphidromous spe‐cies Sicyopterus lagocephalus (Pallas, 1770) and Cotylopus acutipinnis (Guichenot, 1863) varies in relation to their larval and juvenile life history. Reproductive stage was estimated based on histological observation of ovaries of more than 200 females of each species caught monthly over 1 year. The age of fish was estimated by interpret‐ing the daily increments deposited on otoliths during the oceanic larval phase, and the juvenile phase in the river. The age at first maturity was approximately 9 months for S. lagocephalus and 7 months for C. acutipinnis, corresponding to approximately 70–130 and 90–130 days after they returned to freshwater respectively. For both species, the time spent in freshwater before maturity was significantly influenced by the duration of the pelagic larval stage at sea (PLD) and the season of return in freshwater. Individuals with a long PLD, or returning in freshwater during the warmer season, maturated faster once in freshwater. This reproductive advantage may mini‐mise the risk of extirpation due to catastrophic events at each generation and thus probably benefits amphidromous species living in very unpredictable tropical rivers.

Conventional methods for surveying diadromous fish migration from marine coastal waters to freshwater habitats are mainly based on electrofishing, a non-optimal technique for the study of fish migrations in rivers, and fishermen catch data. Underwater video has been recognized for a long time as a good alternative, but those approaches usually require intensive labour for retrieving the information from the video sequences. To overcome these problems, an underwater video system specifically designed for field work (low-weight, low-cost and autonomous) named BichiCAM has been developed for automatically counting, measuring and tracking fish observed in video sequences. The efficiency and precision of the BichiCAM system were tested by filming Sicyopterus lagocephalus juveniles passing through the camera field of vision in the Saint-Etienne River, Reunion Island, Western Indian Ocean. The BichiCAM system accurately measured fish length of the observed individuals when lens distortion of the camera was corrected, and the error percentages on the measurements presented a standard deviation of 5.1% of the total length. The BichiCAM system provides a powerful tool that will not only facilitate research on migrating fishes and invertebrates' communities but also allow studies of the effectiveness of fishways associated to dams or the impacts of fishery activities. Copyright © 2015 John Wiley & Sons, Ltd.

Measuring fish length is useful for exploring size structure of catches and fishing effects on marine resources. However manually measuring large numbers of individuals requires time-consuming manipulations, which are hardly operational in the context of tropical small-scale fisheries. To overcome this limitation, we developed a method to automatically measure total fish length using digital images and an analytical procedure using the ImageJ software. For testing this procedure, a total of 180 fishes (3 to 50 cm TL) from 19 families, presenting two color patterns and two caudal fin types, were obtained from small-scale fishers in southwestern Madagascar in 2018. We took standardized images of the fishes using a locally made, cost-effective camera-equipped device. The accuracy of fish size estimates and the time taken for measurements were compared across the ImageJ automatic procedure, manual measurements made on-screen using ImageJ, and measurements using an ichthyometer, the latter providing the reference fish length. The ImageJ automatic measurement procedure reached 98.4% accuracy while the measurement time was reduced by 57% and 40% compared to the measures using an ichthyometer and ImageJ on-screen tools, respectively. We conclude that the automatic measurement procedure provides very effective results for fish < 50 cm TL. This method is relevant for governmental, non-governmental, and research organizations that investigate size-related fishing and management impacts on fish community structure and dynamics.

International audience; Amphidromous fish species reproduce in rivers, and their larvae immediately drift to the sea after hatching. Most of these larvae survive in freshwater for a few days only, rapidly reaching sea water is thus essential. Being of small size, especially among species of the Sicydiinae subfamily, the larvae possess poor swimming abilities; their drift dynamics is considered to be mainly passive and influenced by flow conditions. The influence of daily fluctuations in flow regime on Sicyopterus lagocephalus (Sicydiinae) larval drift patterns was studied using drift nets at three sites along the dammed Langevin River in Reunion Island. The river flow was stable at the upstream site when frequent anthropogenic river flow fluctuations were observed at the two sites downstream to the dam. Weak diel larval drift dynamics were detected at the upstream site and the first site under anthropogenic river flow conditions. In contrast, larval drift dynamics at the most downstream site was strongly influenced by anthropogenic daily fluctuations of discharge: the abundance of drifting larvae increased with peaks of discharge, regardless of the time. As higher mortality rates of drifting larvae were observed during discharge peaks, the benefit of a more rapid travel to the ocean associated with these peaks should be lower than expected. It is concluded that peaks of discharge increase the number of larvae drifting to the sea probably due to higher physical constraints on the egg clutches, but also decrease the chance of survival for larvae that may be nonfully developed.

International audience; The aim of this study was to demonstrate that fish larvae identified using their COI sequences offer a unique opportunity for improving the knowledge of local fish richness. Fish larvae were sampled at the end of their pelagic phase using light-traps set off the West Coast of La Reunion Island, southwestern Indian Ocean, once per month from October 2014 to March 2015. Among the 5174 larvae caught, 214 morphologically different specimens were selected, 196 successfully barcoded, giving a total of 101 different Barcode Index Numbers (BINs). Among these BINs, 55 had never been recorded in La Reunion exclusive economic zone (EEZ), and 13 were new for the BOLD database. Even if the sampling effort for collecting fish post-larvae during this study was relatively low, it allowed adding at least nine new species to an updated checklist of fishes of La Reunion EEZ.

International audience; Otolith microchemistry can provide crucial information to address gaps of knowledge in spatio-temporal ecology of fish species. However, understanding the seasonal variability of water chemistry and its effect on otolith signatures is needed to interpret fish movements. Otolith multi-elemental signatures were used to examine the diadromous migration and small-scale movements of a tropical goby (Sicyopterus lagocephalus) within a watershed in La Réunion Island, Indian Ocean. The elemental ratios Sr:Ca, Ba:Ca and Sr:Ba recorded monthly in the water of nine sampling sites varied between localities and were correlated with otolith signatures, whereas the Mg:Ca signature was not. The incorporation of some trace elements in otoliths was influenced by the size of fish and site where they were caught, reflecting an effect of endogenous and exogenous factors. Despite these sources of variation, the elemental signatures did not overlap for three river sections distributed along the 26-km-long watershed. The diadromous migration and fish lifetime movements between these river sections were reconstructed using an original process based on random forest analysis. This approach revealed distinct migratory behaviours after fish entered in the river, with some individuals progressing slowly in the watershed whereas other rapidly reached the upper localities. As adults, S. lagocephalus showed a restricted exploratory behaviour and a strong site fidelity to a particular part of the watershed. The detection of adult movement was typically only between adjacent locations and is possibly explained by shifts in local intraspecific hierarchies and/or displacement during extreme discharge caused by cyclones.

The species richness of communities should largely depend on habitat variability and/or on habitat state. We evaluated the ability of habitat variability and habitat state to predict the diversity of juvenile neo-tropical fish communities in creeks of a river floodplain. The young-fish fauna consisted of 73 taxa, and samples were well distributed over a wide range of relevant temporal and spatial habitat variability. We were unable to demonstrate clear patterns of richness in relation to temporal and spatial habitat variability (if habitat state variables were not included), regardless of the temporal variability scale, the grouping of sites (up- and downstream sites differed in temporal variability patterns) taxonomic units or life stages considered. Using stepwise multiple regression, 36% of the variance in species richness was explained for all data, and at best 47% was explained for all taxonomic units at upstream sites using temporal and spatial habitat variability and habitat state (bank length, mean width, mean water level before fishing and/or water turbidity). Using Monte Carlo simulations, we blindly predicted 31% (all data) and at best 37% (all upstream taxa) of the observed variance in species richness from these model types. This limited precision is probably because rare species produced most of the richness patterns in our creeks. The prediction of these rare species is generally difficult for various reasons, and may be a problem in many ecosystem types. (Résumé d'auteur)

The aim of this study was to evaluate the efficiency of geometric morphometrics for describing the body shape of fish larvae and juveniles, and identifying them to species, in comparison with traditional linear measurements. Species of emperor fishes (Perciformes: Lethrinidae, genus Lethrinus) were chosen as the model group, as the late larval and early juvenile stages in this genus are particularly difficult to identify. Forty-five individuals of different species of Lethrinus were collected from the south-western lagoon of New Caledonia between May 2005 and March 2006. The individuals were first identified to species by their partial cytochrome-b gene sequence. They were then morphologically characterized using eight linear measurements and 23 landmarks recorded on digital photographs. Except for a small proportion of individuals, geometric morphometrics gave better results to distinguish the different species than linear measurements. A 'leave one out' approach confirmed the nearly total discrimination of recently settled Lethrinus genivittatus and Lethrinus nebulosus, whereas traditional identification keys failed to distinguish them. Therefore, geometric morphometrics is a promising tool for identifying fish larvae and juveniles to species. An effective approach would require building image databases of voucher specimens associated with their DNA barcodes. These images could be downloaded by the operator and processed with the specimens to be identified.

International audience; Freshwater gobies of tropical islands are amphidromous: adults reproduce in rivers and larvae passively drift down to the sea immediately after hatching. Describing the phenology of this larval drift is essential to understanding the population dynamics of amphidromous gobies and to developing ecologically based recommendations for managing the watersheds. The larval drift patterns of two amphidromous gobies of Réunion Island, Sicyopterus lagocephalus and Cotylopus acutipinnis, were studied on a monthly basis for 1 year using plankton nets at two sites on the Mât River, located 20 km and 7 km from the river mouth. Genetic analyses showed that larval assemblages were dominated at 90% by S. lagocephalus, although the proportion of C. acutipinnis increased during early summer. Our findings highlighted a marked larval drift peak in full austral summer. The diel larval drift dynamic was described using periodic linear models. A diel pattern was only observed downstream, peaking a few hours after sunset. Finally, this study presents a new approach that improves standard methods for sampling and analyzing larval drift of amphidromous species.

Processes occurring at the end of the larval stage are of major importance in shaping spatial structure of fish assemblages in coral reefs. However, because of the difficulty in identifying larvae to species, many studies dealing with these stages are limited to the family level. It remains unknown if variation in the spatial structure of coral-reef fish assemblages across life stages can be detected at such a coarse taxonomic level. Two different surveys conducted in a similar area of New Caledonia, Southwest Pacific, provided the opportunity to compare the structure of coral-reef fish assemblages collected as pre-settlement larvae, juveniles and adults along a coast to barrier reef gradient. Adult and juvenile fish were sampled using underwater visual counts (UVC) during the warm seasons of 2004 and 2005. Pre-settlement larvae were sampled with light-traps during the same seasons. In order to standardize data between sampling methods, analyses were conducted on the relative abundance (for larvae) and density (for juveniles and adults) of 21 families commonly collected with both methods. Relative abundances/densities of families were analysed as a function of life stage (larvae, juveniles or adults), large-scale spatial location (coast, lagoon or barrier) and years (2004, 2005) using non-parametric multidimensional scaling (nMDS) and permutational multivariate analysis of variance (permanova). Kruskal–Wallis tests were then used to examine differences among life stages and locations for individual families. Different levels of spatial and temporal variability characterized fish assemblages from different life stages, and differences among life stages were detected at all locations and years. Differences among life stages were also significant at the level of individual families. Overall results indicate that studies conducted at the family level may efficiently reveal changes in coral-reef fish spatial structure among successive life stages when large spatial scales are considered.

International audience; Species identification is fundamental to address questions about community ecology, biodiversity, conservation and resource management, at any life history stage. Current studies on fish larval ecology of tropical species are hampered by the lack of reliable and effective tools for identifying larvae at the species level. Emperors and large-eye breams comprise fish species from the perciform fish family Lethrinidae. They inhabit coastal and coral-reef habitats of the tropical Indo-Pacific, and they are important fishery resources. Their taxonomy is considered difficult and identification to species is often problematic. Lethrinidae larvae and juveniles can be identified on the basis of meristic counts at the subfamily level, but no further. In this study, we developed a set of polymorphic PCR markers (size polymorphisms at the intron regions from 4/5 nuclear protein-coding genes and single-strand conformation polymorphism of a 205-bp fragment at the mitochondrial 16S rRNA locus), to characterize 341 specimens from 21 Lethrinidae species from New Caledonia (southwestern tropical Pacific). A genetic data-bank was constructed using the genotypes screened from the multiple gene loci of adult or sub-adult specimens used as references for these species. The 16S rRNA gene fragment was able to differentiate species for the genus Lethrinus, but it provided little diagnostic resolution among different species within the genus Gymnocranius. A combination of the 16S rRNA marker and 4 nuclear markers developed herein allowed to sort out species within Gymnocranius spp. from New Caledonia. Using genotype distributions at nuclear loci to test for reproductive isolation, we found that three apparently undescribed large-eye bream species may exist, provisionally referred to as Gymnocranius sp. A, sp. B and sp. C. Subsequent genotyping of 137 Lethrinidae larvae collected from the bays of the Noumea peninsula, New Caledonia, found a total of three species (Lethrinus genivittatus, L. olivaceus and Gymnocranius sp. A).

This study examines the diet of nine taxa from seven families of pre-settlement coral-reef fish larvae collected in the lagoon of New Caledonia, south-west Pacific. Chesson's index of electivity indicated that the major prey groups in the diets, i.e. small copepods, small unidentified crustaceans and eggs, were positively selected by all larvae, provided they were at least 150 microm wide. This result emphasizes the role of larvae's behaviour on their feeding.

Coral reefs are one of the most diverse ecosystems on Earth. They are currently exposed to increasing levels of anthropogenic perturbations. Several recent reviews point to the lack of good indicators for these perturbations especially to monitor their effects on fish populations or fish assemblages. The SW lagoon of New Caledonia is an ideal location to test indicator species in this context as contrasting sites are present within a small geographical range. This study analysed fish from four sites, one with heavy industrial pollution, another dominated by domestic waste, a third with historic mining activities, and the fourth as a control. The butterfly fish, Chaetodon speculum, was chosen to determine C. speculum's potential as an indicator species due to its link to coral, its sedentary behaviour and its wide geographical distribution. The size distribution, growth rate, age distribution and whole otolith composition were analysed at each site. Age and mean growth rate were analysed from daily increments of the otoliths. The concentrations of eight elements (Li, Mg, Co, Ni, Cu, Rb, Sr, and Ba) were measured by ICP-MS in the otoliths of a subset of individuals. The sites under anthropogenic impact were distinct from the control site by fish size frequencies, age distributions, and the chemical content of their otoliths. The chemical elements Mg, Co, Ni, Cu, and Rb showed differences amongst sites. Fish belonging to the sites furthest from Noumea could be discriminated in nearly 80% of samples or 60% of the cases when otolith weight or fish age respectively were taken into account. Ni concentrations of the otoliths were also higher in the bays where water concentrations of this element were known to be higher, but these differences were no longer significant once corrected for otolith weight. These results should be mitigated by the fact that: (1) despite significant differences between sites in age distribution and size frequencies there were no differences in growth rates or body condition; (2) differences in age or size were not correlated to perturbation levels; and (3) discrimination between sites based on chemical levels in the otoliths, even though significant, was not sufficient to identify the origin of the fish at a level useful for screening tests. The hypothesis that environmental differences between sites would be reflected in the otolith chemical composition is therefore not fully supported by our results.

We investigated the diversity of patterns of habitat use by juveniles of coral reef fishes according to seasons and at two spatial scales (10–100 m and 1–10 km). We conducted underwater visual censuses in New Caledonia's Lagoon between 1986 and 2001. Co-inertia analyses highlighted the importance of mid-shelf habitats at large spatial scale (1–10 km) and of sandy and vegetated habitats at small spatial scale (10–100 m) for most juveniles. Among all juvenile species, 53% used different habitats across seasons (e.g. Lutjanus fulviflamma and Siganus argenteus ) and 39% used different habitats as they grow (e.g. Lethrinus atkinsoni and Scarus ghobban ). During their ontogeny, at large and small scales, respectively, 21% and 33% of the species studied showed an increase in the number of habitats used (e.g. L. fulviflamma , L. atkinsoni ), 10% and 3% showed a decrease in the number of habitats used (e.g. Amphiprion melanopus , Siganus fuscescens ), 23% and 3% showed a drastic change of habitat used (e.g. S. ghobban , Scarus sp.) whereas 46% and 61% showed no change of habitat used (e.g. Lethrinus genivittatus , Ctenochaetus striatus ). Changes in habitat use at both small and large spatial scales occurred during the ontogeny of several species (e.g. S. ghobban , Scarus sp.). Results pointed out the different spatial and temporal scales of juvenile habitat use to account for in conservation decisions regarding both assemblage and species-specific levels.

Ten atolls of contrasting morphology and low human pressure were investigated in the Tuamotu Archipelago (French Polynesia) during the research program "Typatoll". This program produced large data sets about species richness of undisturbed fish assemblages and environmental data recorded at three spatial scales. Multivariate analyses defined six groups of transects of similar multi-scale environmental characteristics. Smoothed histograms (spectra) of species richness were plotted for each group of transect according to six size classes, six diet classes and six life-history classes of fish assemblages. The shape of spectra among groups of transects was then modelled through a single equation, determined by goodness-of-fit techniques. The height of each spectrum was then predicted by General Linear Model. Kolmogorov-Smirnov tests showed no significant difference between predicted and observed distributions of species richness. This two-phase model allowed predicting the diversity structure of undisturbed reef fish assemblages from few environmental data for the first time in the Pacific region. The resulting model will provide an efficient tool for detecting anthropogenic effects on the diversity of reef fish assemblages in atolls of the archipelago. This modelling approach could be adapted to provide a tool for the evaluation of variables affecting diversity of coral reef fish assemblages whatever the habitat they live in, and more generally the diversity of any other highly diversified tropical communities. (c) 2006 Elsevier B.V. All rights reserved.

This study aims at describing the diversity and composition of larval and juvenile fish assemblages in coastal areas of New Caledonia, southwest Pacific, and identifying the environmental factors that influence the seasonal and spatial patterns of these assemblages. A total of 97 taxa belonging to 7 orders and 26 familis were captured in three bays near Noumea by light trapping every month between January 2002 and June 2003. The assemblages were dominated by Clupeiform larvae and juveniles (96.4% of total abundance) and followed by Perciform larvae (3%). The number of taxa per sample varied from less than five in July-August to more than ten in October-November and abundances followed the same seasonal pattern. Analyses of similarity showed significant differences in the assemblages caught in the three bays and analyses of contribution to the dissimilarity revealed that these differences were due to the most abundant families. The constant part of the relationship between environmental variables and the composition of assemblages was assessed by the partial triadic analysis STATICO, a statistical approach that takes into account the strong seasonality of the data. Rainfall, wind direction and thermal stratification of the water column were found to play a major role in the structure of the assemblages, although tidal amplitude and wind speed became important when Clupeidae and Engraulididae were excluded from the analyses. The richness, relative abundances and seasonal variations of the assemblages caught in three bays under study are close to what has been observed elsewhere in the tropics. This study shows the efficiency of the STATICO analysis for identifying the environmental factors that have a permanent effect on assemblages and sorting them out from those which act temporally or on specific locations. The high abundances and diversity of coral-reef fish larvae observed in coastal zones of New Caledonia suggest that further studies are needed to fully explore the role of the coastal zones of New Caledonia as nurseries.

The 2D shape of sagittae of Encrasicholina devisi, E. heteroloba, E. cf. punctifer, and Stolephorus indicus, four tropical Engraulididae of New Caledonia, was studied with 1) dimensionless shape descriptors (form factor, roundness, and aspect ratio); 2) elliptic Fourier analysis (EFA) and Fast Fourier Transform (FFT) of 2D outline; and 3) geometric morphometrics (GM) based on four standard landmarks and nine semi-landmarks. The largest sagittae of E. cf. punctifer were lacier, i.e., had a smaller form factor, than the sagittae of the other species. The sagittae of E. devisi and S. indicus were more roundish, and presented a lower aspect ratio, than those of E. heteroloba and E. cf. punctifer. Between-class correspondence analysis (COA) indicated that between-species inertia was the lowest when based on the 96 Fourier coefficients originating from EFA, and the highest when based on the 22 partial warps originating from GM. As otoliths of different sizes from different species presented similar shapes, relative between-species inertia increased markedly when length, width, perimeter, and area were added to the set of variables originating from EFA, FFT, or GM. Despite otoliths having only a few, sparsely located, homologous landmarks, GM appeared slightly more efficient in distinguishing the sagittae of the four species and allowed visualization of the modification of otolith shape as they grow.

The otolith micro-increment technique was applied to assess the growth trajectory of early stages of the neotropical catfish Megalechis thoracata in Kaw Swamp, a coastal swamp in French Guiana, and two contrasting habitats in Suriname: the coastal Lelydorp Swamp with standing water and a rain-forest creek with running water, the Maykaboeka Creek. Daily deposition of increments on the lapilli was validated for the first 35 d after hatching and the innermost increments were deposited from hatching onwards. The natural habitats of M. thoracata in French Guiana and Suriname showed considerable variation in physico-chemical characteristics of the water, density of food organisms and fish fauna. Instantaneous growth rates and size-at-age differed significantly among two vegetation types in Kaw Swamp (3.5% d-1 and 4.1% d-1), Lelydorp Swamp (3.0% d-1) and Maykaboeka Creek (2.5% d-1). Spearman's rank correlation coefficient between instantaneous growth rates and environmental parameters differed significantly from 0 only for water temperature. Hatch date analysis revealed an extended spawning season from January to June in the rain-forest creek.

The growth of most mensural characters of Krobia guianensis and Crenicichla saxatilis during early development was explained by a split regression indicating inflection in allometry at specific standard lengths. Double-centred PCA revealed morphological transformations during ontogeny mostly under the influence of the maximum body depth and the maximum caudal peduncle width, the area of the caudal fin and the horizontal diameter of the eye contributing also, but to a lesser extent. Young K. guianensis switched to larger prey at the end of the period when the growth of most of their studied mensural characters demonstrated an inflection, but young C. saxatilis changed their diet at a much smaller size than that at which an inflection occurred. However, in the lower reservoir sites, most young juveniles of K. guianensis and C. saxatilis did not switch to larger items during their ontogeny and micro-crustaceans occurred more frequently in their diet. It is hypothesized that the low net energy gained when eating such small prey may explain why the young of both species were thinner at these sites than in their undisturbed habitats. If food resources of young cichlids do not improve in the Petit-Saut reservoir, it is hypothesized that these species will develop stunted populations there.

SUMMARY 1. We investigated which environmental parameters control the variation in density, in space and time, of young stages of fish in tributaries of a natural and a flow-regulated section of the Sinnamary River, French Guiana. 2. The density of the progeny in most taxa varied in space and/or time. However, most non-Perciformes responded differently to space and/or time in the two sections. 3. Oxygen, turbidity and habitat structure (i.e. bank length, occurrence of undercut bank, richness in litter, vegetation and substratum) were important, as was the position of the sampling site relatively to the main channel in the downstream tributaries, in explaining the variation of density in space in both sections. Both habitat complexity and distance from the main channel protect young fish against unpredictable flow releases downstream from the Petit Saut dam. 4. Hydrological events played an important role in the temporal variation in densities of many fish taxa. The density of most early life and many juvenile stages (mostly Characiformes) was positively related to hydrological events. 5. Some fish taxa had reproductive habits which were relatively independent of abiotic factors, such as flow variability, and the density of their progeny did not vary with time. 6. The nursery areas of more than 45% of species in the Sinnamary River have been degraded by flow regulation.

A total of 1468 young fish representing 66 taxa from the Sinnamary River, French Guiana was classified by complete cluster analysis of mean relative body width and mean relative body height into four groups. These had anguilliform, disciform, flat or intermediate body shapes and belonged chiefly to Gymnotiformes, Perciformes, Siluriformes and Characiformes, respectively. Several of the taxa shifted from one to another body shape during ontogenesis. Seven diet groups were defined by complete cluster analysis. Among these, six groups were represented by carnivorous fish. The three most frequent groups had diets of (1) mainly insect larvae and small crustaceans, (2) insect larvae, and (3) predominantly terrestrial insects. The majority of the fish taxa showed ontogenetic diet shifts. Carnivorous fish usually switched from small-size prey, such as small crustaceans, to intermediate-size prey, such as insect larvae and/or to large-size prey, such as insects and/or fish. However, taxa differed in their capacities to switch from small prey to intermediate and/or to large prey. Taxa of different body shapes had significantly different diets. Disciform fish fed mainly on aquatic insect larvae and terrestrial insects but also, in small amounts, on small curstaceans. Most anguilliform taxa ate insect larvae. Individuals belonging to the depressiform or intermediate morphotype had varied diets ranging from plant debris and substratum to fish.

We examined fish community structure and habitat use at the start of the dry seasons: (1) in 10 tributaries of the River Sinnamary (French Guiana) before and after the start of dam operation, and (2) in 10 upstream tributaries and at 10 littoral sites in the newly-created reservoir after the start of operation to assess the impact on fish juveniles of a hydroelectric dam built on the river's lower section. After the first year of dam operation, juvenile fish communities downstream of the dam showed an important decrease of the relative abundance of Characiformes, and Perciformes dominated. Principal components analysis revealed a distinct upstream-to-downstream progression in the juvenile fish communities with post-reservoir downstream and reservoir sites representing transitions between the upstream and pre-reservoir downstream sites. Canonical correspondence analysis and electivity indices of fish-habitat associations revealed three relatively distinct groups of sites, corresponding to the downstream, reservoir and upstream taxa. The proportion of juveniles presenting higher-than expected frequencies (Fisher's exact test) towards local environmental variables was higher for taxa more often caught in upstream sites. Inversely, juvenile taxa more frequently observed in downstream and reservoir sites appeared less selective towards local environmental characteristics. In the downstream reaches of the river, hydrodam operation is expected to drive the fish community towards a new biologically accommodated state where tolerant species will dominate and sensitive species will be lacking.

Accumulation of ciguatoxins (CTXs) in tropical reef fish tissues during their life is responsible of the most prevalent human seafood intoxication in the South Pacific called Ciguatera Fish Poisoning (CFP). It has been assumed for a long time that CTXs are transferred and accumulated along the trophic food chain, and consequently that smaller individuals within a given fish species are safer to eat than larger ones. However, the relationship between toxicity and fish size has been studied for a limited number of species only and the conclusions are often contradictory. The toxicity of 856 fishes from 59 different species sampled in six islands in French Polynesia between 2003 and 2011 was assessed by Receptor Binding Assay. Among them, 45 species x island and 32 families x island for which the number of individuals was >= 6 allowed testing the relationship between toxicity and size. Except for six specimens of Lutjanus bohar caught in Fakarava (P < 0.01; R-2 = 0.854), the 44 remaining species x island showed no significant increase of CTXs concentration with fish total length (TL). Moreover, the proportion of toxic individuals decreased significantly for Epinephelus polyphekadion from Fakarava (n = 24; P < 0.05) and Kyphosus cinerascens from Raivavae (n = 29; P < 0.05), while no significant variation was detected for the other 43 species x island. At the family level, only three positive and three negative relationships between size and CTXs concentration were observed among the 32 family x island analyzed. No relationship between the proportion of toxic fish within a family and the relative total length of individuals were observed. The lack of relationship between toxicity and size observed for most of the species and families from the six islands suggests that fish size cannot be used as an efficient predictor of fish toxicity in French Polynesia. These results highlight the need for improving our knowledge about metabolic processes which may play a role in CTXs bio-accumulation and depuration among the different trophic levels of fishes.

Sampling was conducted in the Northwater Polynya (between 70°20' and 77°20'N), on 17 and 19 May 1991. At each of the 14 sampling stations, CTD profiles were recorded from surface to bottom and nutrients and phytoplankton were determined at four depths down to 30 m. The presence, between 220 and 400 m, of water temperatures > 0°C is an indication that, in winter, the West Greenland Current enters the Northwater along the Greenland coast. The worm water is progressively mixed as it moves northward and eastward. It was thus hypothesized that sensible heat is as an important factor in keeping the Northwater open. Measured chemical and biological variables were quite homogeneous on the vertical down to 30 m and they showed longitudinal gradients. From east to west, the average concentrations of nutrients increased (phosphate from 0.5 to 1.4, nitrate from 3.7 to 10.8, and silicate from 6.8 to 34.2 mmol/m3), whereas the areal concentrations of phytoplankton decreased (from 47 to 9 x 10 to the ninth power cells/m2 and from 506 to 50 mg Chla/m2). Nutrient ratios indicated possible silicon deficiency in the easternmost part of the polynya. Diatoms dominated cell numbers (greater or equal to 87% at all stations). Concentrations of the three nutrients were inversely correlated with both Chla and cell numbers. The Y-intercepts of regressions of Chla on nutrients provided an estimate of potential maximum biomass in the upper 30 m, which was ca. 600 mg Chla/m2, or lower if there was silicon limitation. The overall picture was that of a diatom bloom, moving westward and progressively exhausting the nutrients. Initiation of the bloom appeared to have been linked to the absence of sea ice. A source of heat for this would have been the above sensible-heat process. (Résumé d'auteur)

We monitored the feeding success (percent feeding incidence at length and mean feeding ratio at length) of Arctic cod (Boreogadus saida) and sand lance (Ammodytes sp.) larvae in relation to prey density, light, temperature and potential predator density under the ice cover of southeastern Hudson Bay in the spring of 1988, 1989 and 1990. Both prey density and light limited larval fish feeding. The relationship between feeding success and actual food availability (nauplii density X irradiance) was adequately described by an Ivlev function which explained 64 and 76% of the variance in Arctic cod and sand lance feeding success respectively. By affecting both prey density and irradiance, the thickness of the Great Whale River plume (as defined by the depth of the 25 isohaline) was the main determinant of prey availability. Arctic cod and sand lance larvae stopped feeding when the depth of the 25 isohaline exceeded 9 m. Limitation of feeding success attributable to freshwater inputs occurred exclusively in 1988, the only time when the depth of the 25 isohaline exceeded the 9 m threshold. The close dependence of larval fish feeding success on the timing of the freshet and plume dynamics suggests a direct link between climate and survival of Arctic cod and sand lance larvae. The actual impact of climate fluctuations and/or hydro-electric developments on recruitment will depend on the fraction of the larval dispersal area of the two species that is affected by river plumes.

A single autonomous video camera was used to record the abundances of Chromis viridis over a branching Acropora sp. colony eight times per day over a period of 50 days. The poor explanatory power of global radiation suggests the need for recording the light really available to the fish, especially in the UV range. The increasing number of C. viridis observed with increasing wind along shore and water level may correspond to individuals swimming further from their shelter in order to get closer to the food carried by the water currents.

International audience; The objectives of this paper are (1) to present VideoSolo, a new autonomous video system; and (2) to show its relevance through the analysis of temporal variability of fish populations at different temporal scales of years, days and hours. The underwater video system VideoSolo, designed for use in remote places, combines advantages in comparison to older systems necessitating the presence of a ship and whose autonomy is generally limited in time due to biofouling. All these issues have been resolved in VideoSolo, a fully autonomous long-term system, programmable, easy to set up and deploy (the housing weighs only 3 kg). It has sufficient energy storage and an anti-biofouling system in the form of its hydro-wiper, enabling continuous operation for up to one month. The experiment was conducted in a remote place (Glorioso Island, SW Indian Ocean) where the system was installed in front of the same coral colony (1 m2) at a depth of 8 m. Data was recorded in May for two subsequent years and six times per day (between 6 am and 4 pm). The analysis of the video sequences enabled the recording of 6224 individuals of 75 species belonging to 16 families over 41 days of experiment. At a small spatial scale, fish assemblages were variable over time at the three temporal scales studied. The number of individuals and species observed was variable between years whilst the number of individuals observed per day remained relatively stable through time. When occurrences were considered, less variation was observed between years. Analyses of temporal fish variability on the most abundant families revealed that the abundances of Acanthuridae, Labridae, Scaridae and resident Pomacentridae were significantly different between years and inversely so for the non-resident Pomacentridae. When the diurnal variations of fish assemblages were considered, the abundances differed significantly over time for Acanthuridae, higher in the morning (6 am and 9 am), and for Scaridae, higher at sunrise (6 am) and sunset (4 pm). The abundances of Pomacentridae and Labridae were stable from sunrise to sunset. The variability between years could be linked to events such as recruitment whilst daily variations could be more related to the effects of tidal cycles whose effects may have created periodic feeding opportunities. VideoSolo has demonstrated its efficiency and has remarkable potential in the field of aquatic biology in any location, as no human presence is required for it to work.

Invertebrates represent an essential component of coral reef ecosystems; they are ecologically important and a major resource, but their assemblages remain largely unknown, particularly on Pacific islands. Understanding their distribution and building predictive models of community composition as a function of environmental variables therefore constitutes a key issue for resource management. The goal of this study was to define and classify the main environmental factors influencing tropical invertebrate distributions in New Caledonian reef flats and to test the resulting predictive model. Invertebrate assemblages were sampled by visual counting during 2 years and 2 seasons, then coupled to different environmental conditions (habitat composition, hydrodynamics and sediment characteristics) and harvesting status (MPA vs. non-MPA and islets vs. coastal flats). Environmental conditions were described by a principal component analysis (PCA), and contributing variables were selected. Permutational analysis of variance (PERMANOVA) was used to test the effects of different factors (status, flat, year and season) on the invertebrate assemblage composition. Multivariate regression trees (MRT) were then used to hierarchically classify the effects of environmental and harvesting variables. MRT model explained at least 60% of the variation in structure of invertebrate communities. Results highlighted the influence of status (MPA vs. non-MPA) and location (islet vs. coastal flat), followed by habitat composition, organic matter content, hydrodynamics and sampling year. Predicted assemblages defined by indicator families were very different for each environment-exploitation scenario and correctly matched a calibration data matrix. Predictions from MRT including both environmental variables and harvesting pressure can be useful for management of invertebrates in coral reef environments.

With 4 figures and 1 table in the text 0. R.S.T.0.M. F~i~tis 5~~~m~n~~i~~ NQ : 42 344 B Abstract CDk An improved version of the quatrefoil light trap was tested in a tributary of the Sin- namary River, French Guiana, South America, at the beginning of the rainy season. The entire trap was simplified to lower the cost and increase the reliability of the entire system in harsh field work conditions. The major improvement was an inexpensive electronic light-switch that automatically lighted the lamp at dusk and turned it off at down allowing deployment of numerous traps over large distances. Most of the 648 in- dividuals caught in the 76 samples were Characiformes larvae, juveniles, and small adults. Some Clupeiformes, Siluriformes, Cyprinodontiformes, Syngnathiformes and Perciformes were also caught but no Gymnotiformes were represented in the samples. Light traps appear useful to sample in their microhabitat neotropical young and small fishes of several taxonomic groups.

The distribution of zooplanktonic prey of fish larvae was examined in three bays and two lagoonal stations in the Southwest lagoon of New Caledonia. Water column conditions were characterized by increasing chlorophyll a and particulate organic matter (POM) concentrations from the lagoon to the estuarine bay. The mean zooplankton settled volume and total density were significantly higher in the estuarine bay, reaching 35.1 mL m(-3) and 3.5 x 10(5) individuals m(-3), respectively. The total zooplankton density also progressively increased along the sampling period. The composition of assemblages differed between the lagoon and the bays, and was similar in the three bays. Wind speed, surface temperature, chlorophyll a and POM explained these variations, as revealed by a co-inertia analysis (COIA). The prey preferred by fish larvae, i.e. small crustaceans and small copepods, were more abundant in bays. Sheltered bays, most influenced by terrigenous inputs, are likely to provide the best feeding conditions.

In ice-covered southeastern Hudson Bay (northern Quebec, Canada) the production of suitable zooplankton prey for manne fish larvae was simdar withln and outside the area covered by the Great Whale h v e r plume Within the plume however, hght attenuahon by the turbld surface layer reduced the foraging efficiency of first-feeding Arctic cod Boreogadus s a ~ d a nd sand lance Ammodytes sp larvae In daytime, first-feeding larvae accumulated at the pycnocline where food availability (l e light X prey density) was maximum Below the pycnocline, the average number of prey lngested by indiv~dual arvae (foraging gain) decllned with depth At night, fish larvae and their prey redistnbuted more uniformly over the water column, suggesting a similar passive response to the turbulence field In the absence of a light gradient The observed Ideal free distributions (IFDs) were better explained by unequal foraging abilities of the larvae than by density-dependent interactions among the assemblage of planktonic predators

The growth and toxin production in a clonal strain of Gambierdiscus polynesiensis, TB-92, was examined in batch culture conditions. The mean growth rate at exponential phase was (0.13+/-0.03)division day(-1). Regardless of the age of cultures, all mice injected with dichloromethanolic and methanolic extracts showed symptoms specific to ciguatoxin (CTX) and maitotoxin (MTX) bioactivity, respectively. The highest total toxicity assessed in TB-92 cultures was 10.4 x 10(-4) mouse unit cell(-1). The toxin production pattern reveals an enhanced cellular toxin content with the age of the culture. CTX- and MTX-like compounds each accounted for approx. 50% of the total toxicity of TB-92 cultures, except in aged cells where CTXs were dominant. The high ciguatoxic activity of TB-92 was further confirmed in dichloromethanolic extracts by means of the receptor-binding assay. The highest CTX level monitored at late stationary phase was (11.9+/-0.4)pg P-CTX-3C equiv cell(-1). Further HPLC and LC-MS analysis revealed the presence of five CTXs congeners in lipid-soluble extracts, i.e. CTX-3C, -3B, -4A, -4B and M-seco-CTX-3C, and of new CTX congeners. Toxin composition comparison between two G. polynesiensis strains suggests that the toxin profile is a stable characteristic in this species. G. polynesiensis clones also proved inherently more toxic than other Gambierdiscus species isolated from other geographical areas.