Utilisation géochimique des carbonates biogènes marins : exemples des colonies coralliennes, des coquilles de moules et des otolithes de poissons

Cet article présente, à partir d'études et de résultats concrets, les principaux intérêts des analyses isotopiques qu'il est possible de mener sur des archives carbonatées marines. Les mesures des isotopes du plomb et de l'oxygène effectuées par exemple sur des colonies récifales, des coquilles de moules et des pièces calcifiées de l'oreille interne de poissons téléostéens, permettent ainsi d'accéder à une meilleure compréhension des perturbations environnementales

Spatiotemporal structure of narrow-barred Spanish mackerel (Scomberomorus commerson) from the Red Sea and western Indian Ocean based on otolith micro-chemistry

Though the narrow-barred Spanish mackerel (Scomberomorus commerson) is considered to be migratory, the species is nevertheless thought to be locally overexploited in the northwest Indian Ocean. At the regional level, this local depletion is a major concern for food security. As the population structure and connectivity between sub-populations are poorly understood for this species, we examined the spatio-temporal dynamics of narrow-barred Spanish mackerel via elemental concentrations (P, Mg, Sr and Ba) along otolith transects using LA-ICPMS for samples from 6 sites: Egypt, Djibouti North and South, Somalia, Mozambique and South Africa. For homogeneous size class samples (70–90 cm), otolith chemical signatures immediately preceding capture were used to accurately group individuals sharing a spatial proximity and/or season of capture. Notable differences in otolith edge signatures were found among individuals from north and south of the equator and contrasting cluster compositions from nearby sites in the Gulf of Aden of individuals captured in summer versus winter. Otolith core chemistry identified two spawning chemical compositions. The first common composition was characterized by relatively high concentrations of Sr and lower concentrations of P, Ba and Mg. The second less common spawning chemical composition was particularly rich in P, Ba and Mg and corresponded primarily to individuals caught off Mozambique, Somalia and Djibouti. These results are broadly consistent on one hand with patterns of water mass circulation in the Red Sea and western Indian Ocean and on the other hand with the observed spawning seasons. Though further research using, for example, archival tagging is needed to clarify the mechanisms behind these patterns, these results reveal the potential of otolith chemistry to provide insights into the spatio-temporal dynamics of narrow-barred Spanish mackerel

Utilisation géochimique des carbonates biogènes marins : exemples des colonies coralliennes, des coquilles de moules et des otolithes de poissons

Cet article présente, à partir d'études et de résultats concrets, les principaux intérêts des analyses isotopiques qu'il est possible de mener sur des archives carbonatées marines. Les mesures des isotopes du plomb et de l'oxygène effectuées par exemple sur des colonies récifales, des coquilles de moules et des pièces calcifiées de l'oreille interne de poissons téléostéens, permettent ainsi d'accéder à une meilleure compréhension des perturbations environnementales

Exploring fidelity of Sardines (Sardina pilchardus) to feeding grounds in the Atlantic Moroccan waters using stable isotope analyses (C, N) and otolith microchemistry

The Atlantic Moroccan waters (21°-29°N) are part of the Canary Current Large Marine Ecosystem and are enriched by highly productive upwelling systems. Sardine (Sardina pilchardus) is both the most abundant forage fish in this area and the most heavely fish species [1]. It is described as a migratory small pelagic species that feeds on phyto and zooplankton. From population genetics studies (allozyme and micostellite DNA), it is assumed that our area of interest houses a single population [2] with at least two spawning areas [3]. In order to study trophic position and fidelity to feeding grounds, we investigated sardines from two distant sites: 23-24°N and 28-29°N, using stable isotope analysis (d15N and d13C) and otolith microchemistry. Isotopic analyses were performed on delipidated muscle subsamples, and plankton samples (150µm mesh net), using a continuous flow isotope-ratio mass spectrometry. The trophic position of sardine is compared to those of major forage fish of the same area. Otholith microelements concentrations (Li, B, Mg, Mn, Zn, Sr, Ba, Pb and U) were measured by ICP-MS laser on transects from nucleus to the edge of the otoliths of sardines. Chemical analyses were carried out on five individuals per site. Sardine individuals from the different sites showed significantly different trophic position for both C and N isotopes. The northern individuals were depleted in d15N (1‰ difference), suggesting that phytoplankton is more important in their diet. The d13C values showed greater differences (~3‰) for both Sardines and zooplankton between the two sites, pointing high fidelity for sardine individuals towards the feeding grounds. While Anchovy and Horse Mackerel showed a similar pattern with sardine for δ13C, chub mackerel showed no significant differences between the two areas suggesting a higher seasonal migratory behavior for this species. Sardine Microelements profiles reinforced the sedentary behavior hypothesis for sardine. The Barium (Ba) profiles were the most discriminant: the concentration range was 7× higher for the southern area where upwelling intensity is higher [4]

Les isotopes du carbone dans les coquilles de gastéropodes terrestres de la série Loessique de Eustis (Nebraska, USA) : un indicateur de changements rapides de l'environnement entre 20 et 12 KA BP.

Land snails build their shells with carbon extracted pnncipally from their diet and are a good record of the vegetation and climate vanations through time. We have analyzed the carbon isotopic composition of shells of Vertigo modesta sampled in the Eustis Upper Pleistocene loess senes, Nebraska, which deposited between 18, 000 and 12, 000 years. A trend towards andity of the environment is observed from the base to the top of the sequence. Rhythmic and rapid oscillations, of about 1 000 years, of the carbon isotopic composition indicate more humid penods. These results are compared to other indépendant proxies from the same or nearby loess sequences. The validation of the land snails shells as new record of paleochmatic variations in loess sequences is thus demonstrated.Les gastéropodes terrestres tirent principalement le carbone nécessaire à la constitution de leur coquille de leur alimentation, et constituent donc un possible enregistreur des conditions environnementales au cours du temps. Nous avons analysé les compositions isotopiques du carbone de coquilles de Vertigo modesta provenant de la série loessique de Eustis (Nebraska, USA), déposée entre 18 000 et 12 000 ans. Une tendance à l'aridification du milieu, de la base vers le sommet de la série, et une cyclicité d'environ 1000 ans dans l'occurrence de pénodes humides sont observées. Ces résultats sont corroborés par d'autres analyses provenant de la même séquence ou d'autres séries loessiques des grandes plaines américaines. La validation des gastéropodes terrestres en tant que nouvel indicateur paléoclimatique et de la végétation est ainsi démontrée.Labonne Maylis, Rousseau Denis Didier, Metref Slimane. Les isotopes du carbone dans les coquilles de gastéropodes terrestres de la série Loessique de Eustis (Nebraska, USA) : un indicateur de changements rapides de l'environnement entre 20 et 12 KA BP.. In: Quaternaire, vol. 13, n°3-4, 2002. Événements rapides, instabilités, changements culturels au Quaternaire. pp. 193-197

Variabilité spatiale de la signature multi-élémentaire des otolithes de G0 de Solea solea et Pleuronectes platessa au sein d’un habitat côtier : exemple de la baie de Seine

Les zones côtières telles que les baies et les estuaires constituent des nourriceries pour les juvéniles de nombreuses espèces de poissons marins et en particulier les poissons plats. In fine, la fonction de nourricerie d’un habitat repose sur sa capacité à produire des individus qui vont contribuer à la population adulte. La composition élémentaire des otolithes de poissons est devenue un outil important pour étudier la connectivité entre les habitats des juvéniles et des adultes. Cette approche majeure en écologie halieutique repose sur l’identification de signatures multi-élémentaires caractérisant les nourriceries. Il est donc important de considérer les processus spatiaux à plus petite échelle de manière à identifier localement les habitats de nourriceries et d’obtenir une signature multi-élémentaire représentative. L’objectif de cette étude était donc d’analyser la variabilité spatiale de la signature multi-élémentaire des otolithes du groupe d’âge G0 de deux espèces de poissons plats (sole commune, Solea solea et plie commune, Pleuronectes platessa) au sein de la baie de Seine. Les individus (sole : n=77 ; plie : n = 98) ont été capturés au cours d’une même campagne scientifique en septembre-octobre 2008 sur un total de 18 stations dont 8 stations en commun pour les deux espèces. La composition multi-élémentaire des otolithes (sagittae) a été déterminée in toto par ICMP-MS en solution. De plus, l’âge en jours des individus a aussi été estimé à partir d’otolithes (lapilli) entiers polis, la donnée d’âge permettant d’obtenir à la fois la durée d’intégration de la signature chimique et la croissance des individus sur les différentes zones étudiées. Différents patrons spatiaux ont pu être obtenus pour les éléments suivants Li, B, Zn, Rb, Y, Mo, Ag, Ba, Na, Mg, Mn, Cu, Sr et K chez les deux espèces. Les résultats des signatures multi-élémentaires seront présentés de manière à aborder et discuter la zonation spatiale et la représentativité de ces signatures au sein de l’estuaire de Seine ; l’identification de zone(s) de nourriceries potentielles (en lien avec la croissance) et enfin les différences entre ces deux espèces

Changes in environmental salinity during the life of Pangasius krempfi in the Mekong Delta (Vietnam) estimated from otolith Sr : Ca ratios

Pangasius krempfi is a commercially important catfish in the Mekong River and is believed to migrate along the Mekong River basin. To verify this migration, elemental concentrations were measured in the water and in otoliths to infer the salinity of the water through the fish's lifetime. In 2017, eight element concentrations were measured along the Mekong Delta using solution-based inductively coupled plasma mass spectrometry (ICP-MS). Concentrations of Sr, Li and Rb were strongly and positively correlated with salinity. Otoliths were taken from P. krempfi caught in the brackish waters of the lower Mekong Delta and seven element : Ca ratios were measured from the core to the otolith edge using laser ablation ICP-MS. The Sr : Ca, Ba : Ca, P : Ca and Mn : Ca ratios varied through the lifetime of the fish, but only Sr : Ca was suitable for estimating ambient salinity. The Sr : Ca profiles in otoliths were analysed and significantly correlated between individuals, with all fish hatched in water with very low levels of salinity, indicating a single freshwater spawning ground, and then living in waters with higher salinity, with two types of migration behaviour. Some individuals may return to low-salinity waters when older. These conclusions were supported by the Ba : Ca and Mn : Ca ratios. These migration patterns may have implications for fishery management

Otolith chemical signature and growth of Chaetodon speculum in coastal areas of New Caledonia

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

Changes in environmental salinity during the life of Pangasius krempfi in the Mekong Delta (Vietnam) estimated from otolith Sr : Ca ratios

Pangasius krempfi is a commercially important catfish in the Mekong River and is believed to migrate along the Mekong River basin. To verify this migration, elemental concentrations were measured in the water and in otoliths to infer the salinity of the water through the fish's lifetime. In 2017, eight element concentrations were measured along the Mekong Delta using solution-based inductively coupled plasma mass spectrometry (ICP-MS). Concentrations of Sr, Li and Rb were strongly and positively correlated with salinity. Otoliths were taken from P. krempfi caught in the brackish waters of the lower Mekong Delta and seven element : Ca ratios were measured from the core to the otolith edge using laser ablation ICP-MS. The Sr : Ca, Ba : Ca, P : Ca and Mn : Ca ratios varied through the lifetime of the fish, but only Sr : Ca was suitable for estimating ambient salinity. The Sr : Ca profiles in otoliths were analysed and significantly correlated between individuals, with all fish hatched in water with very low levels of salinity, indicating a single freshwater spawning ground, and then living in waters with higher salinity, with two types of migration behaviour. Some individuals may return to low-salinity waters when older. These conclusions were supported by the Ba : Ca and Mn : Ca ratios. These migration patterns may have implications for fishery management

Extent of mangrove nursery habitats determines the geographic distribution of a coral reef fish in a South-Pacific archipelago

Understanding the drivers of species' geographic distribution has fundamental implications for the management of biodiversity. For coral reef fishes, mangroves have long been recognized as important nursery habitats sustaining biodiversity in the Western Atlantic but there is still debate about their role in the Indo-Pacific. Here, we combined LA-ICP-MS otolith microchemistry, underwater visual censuses (UVC) and mangrove cartography to estimate the importance of mangroves for the Indo-Pacific coral reef fish Lutjanus fulviflamma in the archipelago of New Caledonia. Otolith elemental compositions allowed high discrimination of mangroves and reefs with 83.8% and 98.7% correct classification, respectively. Reefs were characterized by higher concentrations of Rb and Sr and mangroves by higher concentrations of Ba, Cr, Mn and Sn. All adult L. fulviflamma collected on reefs presented a mangrove signature during their juvenile stage with 85% inhabiting mangrove for their entire juvenile life (about 1 year). The analysis of 2942 UVC revealed that the species was absent from isolated islands of the New Caledonian archipelago where mangroves were absent. Furthermore, strong positive correlations existed between the abundance of L. fulviflamma and the area of mangrove (r = 0.84 for occurrence, 0.93 for density and 0.89 for biomass). These results indicate that mangrove forest is an obligatory juvenile habitat for L. fulviflamma in New Caledonia and emphasize the potential importance of mangroves for Indo-Pacific coral reef fishes