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See detailVariability of carbon dioxide and methane in the epilimnion of Lake Kivu
Borges, Alberto ULg; Bouillon, S.; Abril, G. et al

in Descy, J.-P.; Darchambeau, François; Schmid, M. (Eds.) Lake Kivu: Limnology and biogeochemistry of a tropical great lake (2012)

We report a dataset of the partial pressure of CO2 (pCO2) and me-thane concentrations (CH4) in the surface waters of Lake Kivu ob-tained during four cruises covering the two main seasons (rainy and dry ... [more ▼]

We report a dataset of the partial pressure of CO2 (pCO2) and me-thane concentrations (CH4) in the surface waters of Lake Kivu ob-tained during four cruises covering the two main seasons (rainy and dry). Spatial gradients of surface pCO2 and CH4 concentrations were modest in the main basin. In Kabuno Bay, pCO2 and CH4 concentra-tions in surface waters were higher, owing to the stronger influence of subaquatic springs from depth. Seasonal variations of pCO2 and CH4 in the main basin of Lake Kivu were strongly driven by deepen-ing of the epilimnion and the resulting entrainment of water charac-terized by higher pCO2 and CH4 concentrations. Physical and chem-ical vertical patterns in Kabuno Bay were seasonally stable, owing to a stronger stratification and smaller surface area inducing fetch limi-tation of wind driven turbulence. A global and regional cross-system comparison of pCO2 and CH4 concentrations in surface waters of lakes highlights the peculiarity of Kabuno Bay in terms of pCO2 values in surface waters. In terms of surface CH4 concentrations, both Kabuno Bay and the main basin of Lake Kivu are at the lower end of values in lakes globally, despite the huge amounts of CH4 and CO2 in the deeper layers of the lake. [less ▲]

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See detailStable isotope composition spatial variability at microhabitat scale of macrofauna inhabiting a tropical freshwater stream (Pérou River, Guadeloupe)
Lepoint, Gilles ULg; Marichal, Nicolas; Troupin, Charles ULg et al

Poster (2012)

The spatial variability of isotopic (C and N) composition of freshwater fauna was assessed in a small and pristine tropical stream (Pérou River, Guadeloupe). In order to assess this variability, a section ... [more ▼]

The spatial variability of isotopic (C and N) composition of freshwater fauna was assessed in a small and pristine tropical stream (Pérou River, Guadeloupe). In order to assess this variability, a section of 80 m was mapped and divided in quadrate (n= 132). Microhabitats (i.e. depth, hydrodynamic facies, presence of litter) were defined for each quadrate. Electric fishing was performed in each quadrate and individual isotopic measurements using EA-IRMS were done using abdominal muscles for crustaceans and lateral muscles for fishes. Isomap was generated for each species. Potential food sources (green ripisylve, macrophytodetritus, epilithic biofilm and deriving organic material) were sampled and analyzed for their isotopic composition. SIAR mixing model was applied to try to delineate isotopic and trophic variability in relation to microhabitat in this river section. Nine species were recorded belonging to four decapod families (n= 8 species) and one fish family (n= 1 species). This fauna, dominated by crustaceans, is typical of high and medium elevations of Caribbean rivers in relatively pristine area. In these turbulent biotopes, species encountered are strongly linked to the hydrological characteristics of their microhabitat and have well defined preferenda. Isotopic compositions of ripisylve material, of deriving matter and of autochtonous biofilm were significantly different for both 13C values and 15N values, allowing to discriminate their respective contributions to consumer diet. Epilithic and epiphytic biofilm appeared to contribute significantly to these diets, but most of the species showed evidence for litter material contribution too. Species repartition and their respective diet were evident at microhabitat scale and strongly related to hydrological regime. [less ▲]

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See detailProcessing samples of benthic marine diatoms from Mediterranean oligotrophic areas
Vermeulen, Simon ULg; Lepoint, Gilles ULg; Gobert, Sylvie ULg

in Journal of Applied Phycology (2012), 24

The processing of benthic diatoms is tedious and involves several potentially damaging steps for cells. Although the preservation of siliceous frustules is of paramount importance in the implementation of ... [more ▼]

The processing of benthic diatoms is tedious and involves several potentially damaging steps for cells. Although the preservation of siliceous frustules is of paramount importance in the implementation of biotic indices, only few studies quantified treatment-induced cell losses. We assumed that commonly used treatments may lead to mechanical (centrifugation, sedimentation, boiling, sonication and mounting in Naphrax) and chemical (cold H2O2 digestion) damages on diatoms. We analysed the potential adverse effects of these treatments and the cleaning efficiency of H2O2 and incineration in order to find out the most suitable technique to process lightly silicified Mediterranean populations. Results showed that successive resuspensions of material after each concentration treatment (sedimentation and centrifugation) and low speed centrifugation did not alter the physical integrity of frustules. In contrast, boiling and sonication exhibited adverse effects especially on the preservation of large frustules and Naphrax mounting proved to be the most damaging step whatever the size of diatoms. For cleaning treatments, incineration provided the most satisfactory results and acted on a non-selective way as opposed to hydrogen peroxide which led to either a large number of non-cleaned frustules or dissolved valves. Our recommendations for processing samples of lightly silicified Mediterranean benthic diatoms include the use of low speed centrifugations, dehydration at room temperature, incineration and dry mounting. [less ▲]

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See detailFeeding ecology of harbour porpoises: stable isotope analysis of carbon and nitrogen in muscle and bone
Jansen, Okka; Geert, Aarts; Das, Krishna ULg et al

in Marine Biology Research (2012), 8(9), 829-841

Harbour porpoises are the most common small cetaceans in the North Sea and Dutch coastal waters. To study their trophic level and feeding location, stable carbon and nitrogen isotope ratios (d13C and d15N ... [more ▼]

Harbour porpoises are the most common small cetaceans in the North Sea and Dutch coastal waters. To study their trophic level and feeding location, stable carbon and nitrogen isotope ratios (d13C and d15N) were analysed in muscle and bone samples collected from 157 porpoises stranded along the Dutch coast (2006􏰄2008). In addition, samples from 30 prey species were analysed. Prey samples showed high d15N values in species of higher trophic level. In addition, geographic differences in isotopic composition were found, with higher d15N and d13C values in prey from more southern, coastal and estuarine areas. Based on muscle d15N values, we found neonatal enrichment and that larger porpoises, in particular males, seem to feed on lower trophic level species, compared to smaller individuals. Also bone d15N values show that larger animals had fed on lower trophic levels in distant times. Porpoises from the Eastern Scheldt reveal distinct d13C values in muscle, but not in bone. This shows that these animals had foraged in the Eastern Scheldt for a longer time period but were not born there. Seasonal variation in bone d15N and d13C values revealed two distinct groups of porpoises along the Dutch coast, a winter group (mainly males) that migrated from neighbouring regions and a Dutch subpopulation in summer. These results furthered our insight about shifts in trophic level and feeding location of harbour porpoises from the southern North Sea over time. [less ▲]

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See detailPaleoseismic record obtained by coring a lacustrine sag-pond along the North Anatolian Fault (Turkey)
Hubert, Aurelia ULg; Avsar, Ulas; El Ouahbi, Meriam et al

in Annals of Geophysics = Annali di Geofisica (2012)

Shallow lakes along minor structural bends or discontinuities of strike-slip fault are not usually paleoseismological target sites. In the present study we show that a 2m deep, 700m long lake crosscut by ... [more ▼]

Shallow lakes along minor structural bends or discontinuities of strike-slip fault are not usually paleoseismological target sites. In the present study we show that a 2m deep, 700m long lake crosscut by the North Anatolian Fault contain a reliable paleoseimological record obtain through coring. The North Anatolian Fault, a major strike-slip fault in Turkey last ruptured across the Asacipetecik Lake in 1939 with a slip of about 6 m. Seismic lines still shows remains of the fault ruptures forming minor 10 cm high scarps across the lake. Collected short cores show a set of sedimentary sequences composed of three different units. The lower unit, dark and fibrous, is similar to the present sedimentation at the top of the core. The strongly disturbed and whitish top unit 1 has anomalous organic matter content, grain size and mineralogy. The unit 2 is intermediate in between unit 1 and 3. The present stratigraphy is related to earthquake shaking inducing (1) sediment resuspension; (2) reworking of sediments coming from co-seismic scarps and lake margins; (3) increase in sedimentary runoff into the lake. The 2.5 m long core comprises 4 sequences, and thus 4 sedimentary events. Cesium and Lead data obtained in Boes et al. (2009) imply that Event 1 was triggered by the 1939 M=7.9 Erzincam Earthquake. Radiocarbon age dating suggest that Events 3 and 4 are initiated by the 1254 and the 1045 historical earthquake. Event 2 may correspond to the 1668 earthquake documented in paleoseimological trenches a few kilometers to the east. [less ▲]

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See detailTrophic relationships and mercury biomagnification in Brazilian tropical coastal food webs
Bisi, Tatiana; Lepoint, Gilles ULg; de Freitas Azevedo et al

in Ecological Indicators (2012), 18(0), 291-302

The present study investigated trophic relationships and mercury flow through food webs of three tropical coastal ecosystems: Guanabara, Sepetiba and Ilha Grande bays. The investigation was carried out ... [more ▼]

The present study investigated trophic relationships and mercury flow through food webs of three tropical coastal ecosystems: Guanabara, Sepetiba and Ilha Grande bays. The investigation was carried out through carbon and nitrogen stable isotopes (δ13C, δ15N) and total mercury (THg) determination in muscle from 35 species, including crustacean, cephalopod, fish and dolphin species. Detritivorous species showed the lowest average δ15N values in all bays. These species were 13C enriched in Sepetiba and Ilha Grande bays, suggesting the presence of 13C enriched macroalgae in their diet. The highest mean δ15N values were found in fish and benthic invertebrate feeders, as well as in species presenting demerso-pelagic feeding habit. The carbon and nitrogen isotopic findings showed different trophic relationship in food webs from Sepetiba, Guanabara and Ilha Grande bays. Guanabara Bay showed to be depleted in δ15N compared to both Sepetiba and Ilha Grande bays. The latter finding suggests substantial contribution of atmospheric nitrogen fixation by cyanobacteria. A positive linear relationship was found between log THg concentrations and δ15N values for Guanabara and Ilha Grande bays, but not for Sepetiba Bay. Our findings showed trophic magnification factors (TMF) above 1, demonstrating that THg is being biomagnified up the food chains in Rio de Janeiro bays. Highlights ► The δ13C and δ15N findings showed different trophic relationship in food webs from Rio de Janeiro bays. ► Guanabara Bay showed depleted δ15N values compared to Sepetiba and Ilha Grande bays. ► Ilha Grande Bay showed significant depleted δ13C values. ► Our findings indicate THg biomagnifications up food webs in Rio de Janeiro bays. ► Ilha Grande Bay food web showed the highest trophic magnification factor. [less ▲]

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See detailSeagrass response to in situ trace element contaminations
Richir, Jonathan ULg; Luy, Nicolas; Lepoint, Gilles ULg et al

Poster (2011, September)

The Mediterranean seagrass Posidonia oceanica (L.) Delile has been widely used since the mid-seventies as bioindicator to monitor trace element (TE) coastal pollution. However, there is a lack of ... [more ▼]

The Mediterranean seagrass Posidonia oceanica (L.) Delile has been widely used since the mid-seventies as bioindicator to monitor trace element (TE) coastal pollution. However, there is a lack of knowledge regarding to that seagrass contamination and decontamination kinetics. For the first time, Posidonia were experimentally in situ contaminated in 2009, at 10m depth in Calvi Bay (Corsica), by a mix of 15 TE (Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Mo, Ag, Cd, Pb and Bi). Trace element concentrations were measured by DRC-ICP-MS in leaves, rhizomes and in overall shoots sampled at regular time intervals. P. oceanica immediately accumulated pollutants from the beginning of experiments; once contaminations ended, TE concentrations came back close to their original levels within 2 weeks, or at least showed a clear decrease. Posidonia leaves exhibited different uptake kinetics for many elements (Cr, Cu, Zn, Ag, Cd, Pb and Bi): the younger growing leaves incorporated chemicals more rapidly than the older ones. Rhizomes did not show any clear trend, except for Cu, Zn and Bi. These results demonstrate that Posidonia is a very sensitive sentinel to immediately delineate punctual pollutions similar to what might be measured in contaminated Mediterranean waters. The very good response of Posidonia leaves to pollutant short term expositions suggests their routine use in regularly scheduled monitoring programs. Nevertheless, to by-pass Posidonia leaves deciduous character and their capability to detoxify rapidly, long term accumulation recordings also necessitate below-ground tissues analyses. [less ▲]

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See detailThe recent introduction of Lamprichthys tanganicanus in Lake Kivu (Eastern Africa): a threat for the pelagic fishery?
Masilya, Pascal M; Isumbisho, Mwapu; Kaningini, M et al

Poster (2011, June 13)

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See detailCombined utilization of DGTs and bioindicators to trace chemical contamination threats on coastal ecosystems
Richir, Jonathan ULg; Luy, Nicolas; Serpe, Pierre et al

Conference (2011, May 03)

Trace metal monitoring in marine organisms and their living habitats permit to trace chronic or acute contaminations of marine ecosystems due to human activities. While dissolved trace metal ... [more ▼]

Trace metal monitoring in marine organisms and their living habitats permit to trace chronic or acute contaminations of marine ecosystems due to human activities. While dissolved trace metal concentrations give us an overall and punctual view over biota contamination status, bioindicator species put their bioavailable and possible toxic fraction in an obvious. However, difficulties mainly inherent to metal measurements in seawater lead field ecotoxicologists to study marine pollution essentially through the use of bioindicators alone. The technique of diffusive gradients in thin films (DGT) for the measurement of trace metals in aqueous solutions was introduced in the mid-ninetieth by Davison and Zhang. This passive probe accumulates labile trace metal species in proportion to their bulk environmental concentrations by maintaining a negative gradient between the environment and an ion-exchange resin (Chelex). DGTs average natural water trace metal concentrations over the deployment period, concentrate them and avoid matrix interferences, notably due to dissolved salts in seawater. Their deployment in passive and experimental monitoring studies permits to reliably measure labile trace metal concentrations and, jointly analysed with bioindicators, to estimate their bioavailability to marine organisms. This combined approach DGT-bioindicator was investigated in Calvi Bay (Corsica) through three monitoring studies. (1) DGTs were deployed in Posidonia oceanica bed, a Mediterranean seagrass forming dense meadows from the surface down to 40 meters depth, to study seasonal, spatial and bathymetrical variations of labile trace metal concentrations within this meadow. These concentrations were analysed jointly with Posidonia trace metal contents in order to quantify their bioaccumulation towards this primary producer, taking into account the seagrass biological cycle. (2) Portions of Posidonia meadow were also in situ experimentally contaminated with a mix of dissolved metals to study seagrass kinetics of pollutant accumulation and decontamination. Thanks to DGTs deployed inside contaminated mesocosms throughout experiments, Posidonia responses to known metal concentrations could be precisely quantified. (3) The blue mussel Mytilus galloprovincialis is widely used in trace metal monitoring programs. Mussels, stored in conchylicultural pouches, were transplanted for 3 months in contrasted stations of Calvi Bay (e.g. aquaculture farm, sewer, etc.) in parallel with DGTs. Such as for Posidonia, the complementary utilization of DGTs and mussels permitted to describe water contamination levels at the scale of the Bay, and their bioaccumulation towards mussels. These 3 studies demonstrate the usefulness of DGTs to monitor labile trace metals in an ecological and ecosystemic approach, in parallel with marine organisms, both indicators furnishing different and complementary informations about ecosystem functioning. [less ▲]

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See detailThe harbor seal and the harbor porpoise from the North Sea: review of their ecotoxicological status based on stranded and free-ranging individuals and potential threaths to the population
Das, Krishna ULg; Weijs, Liesbeth; Habran, Sarah ULg et al

Conference (2011, May)

The harbor seal (Phoca vitulina) and the harbor porpoise (Phocoena phocoena) from the North Sea have experienced major fluctuations these last decades due to habitat loss, prey fluctuation and pollution ... [more ▼]

The harbor seal (Phoca vitulina) and the harbor porpoise (Phocoena phocoena) from the North Sea have experienced major fluctuations these last decades due to habitat loss, prey fluctuation and pollution of the marine environment. Recently, development of monitoring programs and non-invasive sampling techniques, including seal catches in Germany allowed blood sampling together with measurements of blubber thickness, body mass, sex and body length. This approach is complementary to the study of stranded and by-caught individuals sampled during necropsies. Essential (Se, Zn, Cu, Fe) and non-essential elements (T-Hg, MeHg, Cd, Pb), perfluorinated organochemicals (PFCs) polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) were measured in blubber and in blood (for selected compounds) of stranded, by-caught and free-ranging individuals from Belgian and German coasts. In contrast to Cd and Pb, hepatic T-Hg can reach concentrations as high as 2.1 μg.g-1 dry weight but depended on several factors including position in the trophic chain (inferred from δ13C and δ15N values), age group and the body mass. This level has been shown to generate in vitro toxicity on harbor seal lymphocytes. Organic compound analysis (PFCs, PCBs, PBDEs) revealed widespread dispersion of contaminants in the marine environment with higher concentrations in seals compared to porpoises in agreement with the higher trophic position of the harbor seal. However, metabolization of these compounds differed between the two species, as revealed by the higher contribution of the persistent BDE-47 and lower chlorinated and non-persistent congeners (e.g. CB 52, CB95) in tissues of harbor porpoises. T-Hg, PFCs, PCBs and PBDEs were detected in calves confirming maternal transfer to offspring. These pollutants are strongly suspected to affect the immune and endocrine systems as well as vitamin A metabolism and this raises concern about exposure-related health effects, especially in younger individuals. [less ▲]

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See detailYou are what you eat, plus a few per mill: apport des isotopes stables en écologie marine. PARTIM 2- Traçage des polluants chez les mammifères et autres vertébrés marins
Das, Krishna ULg; Lepoint, Gilles ULg

Scientific conference (2011, April 27)

L’utilisation en écologie des isotopes stables d’éléments chimiques légers (H, C, N, O, S) est relativement récente et montre un développement exponentiel ces dernières années. L’évolution rapide des ... [more ▼]

L’utilisation en écologie des isotopes stables d’éléments chimiques légers (H, C, N, O, S) est relativement récente et montre un développement exponentiel ces dernières années. L’évolution rapide des techniques permettant les mesures des abondances relatives naturelles de ces isotopes et leur automatisation est à l’origine de ce développement. D’autre part, la production de molécules marquées (i.e. présentant un rapport isotopique stable non naturel) ouvre de nombreuses perspectives expérimentales. Le premier objectif de ce cours-conférence est de fournir les notions de bases nécessaires à la compréhension des applications des isotopes stables en écologie, et en particulier, en écologie marine. Le second objectif est de donner un large aperçu des utilisations potentielles des abondances isotopiques (naturelles ou expérimentalement modifiées) et de les illustrer par des exemples concrets, tirés de la littérature scientifique récente. La seconde leçon sera focalisée sur des exemples combinant approche isotopique et écotoxicologie appliquée aux vertébrés marins. En effet, l’utilisation combinée du profil en polluants des vertébrés marins et de leur composition isotopique permet d’une part d’appréhender les sources de ces contaminations (i.e. océanique vs terrestre, benthique vs pélagique) et d’autre part d’éclairer la structure de leurs populations et d’éventuelles variations de leurs niches écologiques. [less ▲]

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See detailYou are what you eat, plus a few per mille": apport des isotopes stables en écologie marine PARTIM 1: Introduction et Application générale
Lepoint, Gilles ULg; Das, Krishna ULg

Scientific conference (2011, April 26)

Dans les années 50, les premiers isotopistes découvrirent que les rapports d’abondance des isotopes stables d’éléments légers variaient dans les compartiments de la lithosphère et de l’hydrosphère. Cette ... [more ▼]

Dans les années 50, les premiers isotopistes découvrirent que les rapports d’abondance des isotopes stables d’éléments légers variaient dans les compartiments de la lithosphère et de l’hydrosphère. Cette découverte fut rapidement exploitée dans le domaine des géosciences et de la géophysique. Plus récemment, dans les années 70- 80, il fut démontré que les compositions isotopiques variaient également entre compartiments de la biosphère et que ces variations étaient informatives dans divers champs d’application des sciences biologiques et humaines (y compris archéologie par exemple). Pour cette raison, l’audience pouvant assister à cette leçon est extrêmement large, même si nous proposons de centrer notre propos sur l’application des mesures de rapports isotopiques dans le domaine des sciences de l’environnement. D’autre part, les évolutions technologiques récentes (i.e. automatisation des analyses, mesures en routine des rapports isotopiques du carbone, azote, oxygène et souffre; mesure des rapports isotopiques de composés spécifiques) conduisent à une diversification exponentielle des domaines d’aplication des mesures isotopiques en écologie (par exemple études des réseaux trophiques, flux d’énergie dans les écosystèmes, problème de diversifications trophiques, anthropisation des écosystèmes, biogéographie et phénomène migratoire, etc.). Cette diversification se traduit dans l’élaboration d’outils mathématiques (modèle de mélange, niches isotopiques par exemple) et expérimentaux et par des synergies de plus en plus étroites entre les diverses approches. Pour ces raisons, les techniques isotopiques sont tout-à-fait pertinentes en terme de développement technologique et scientifique actuel, mais également en terme de transdisciplinarité. La leçon-conférence proposée se divise en deux cours de 2 heures chacun : le premier cours introductif permettra d’établir le cadre général de l’utilisation des isotopes stables en écologie (en particulier écologie des réseaux trophiques) , et présentera sommairement quelques cas concrets d’utilisation (et des limites d’utilisation) en écologie terrestre et marine. Le second cours développera les synergies possibles entre études écotoxicologiques et études isotopiques, appliquées à l’études des vertébrés marins. En effet, les concentrations en polluants chez ces espèces dépendent non seulement de la contamination de leur environnement mais également de plusieurs facteurs biotiques, parmi lesquels le régime alimentaire. Des molécules telles que les polychlorobiphényles, les diphényléthers polybromés, les pesticides organochlorés, les composés perfluorinés et les métaux toxiques sont détectés à plus ou moins haute concentration dans les tissus des vertébrés marins. Certains de ces composés sont sujets au phénomène de biomagnification : l’étude des valeurs en δ15N des organismes permet ainsi de situer leur position trophique et d’estimer le potentiel d’accumulation d’une substance dans la chaîne trophique. D’autres types de contaminations, comme certains composés perfluorinés sont liés à la proximité du milieu terrestre et sont associés aux valeurs en δ13C. Les concentrations en polluants combinées aux rapports isotopiques peuvent également fournir des indications tout à fait originales sur la structure des populations des mammifères marins. Partim 1:Le premier cours (Dr. Gilles Lepoint) se divisera comme suit : Qu’est-ce qu’un isotope stable ? Quels sont les isotopes d’intérêt biologique ? Variabilité isotopique dans la biosphère et problématique du fractionnement isotopique. Quelques exemples généraux d’applications (recherche de fraude, migrations animales, …) Intérêt et limites des isotopes stables en tant que traceurs trophiques. Modèles de mélange. Quelques exemples d’application écologiques (réseau trophique associé aux posidonies, diversité et variabilité ontogénique des niches trophiques des poissons coralliens, Complémentarité avec d’autres traceurs trophiques et Rapports isotopiques de composés spécifiques. [less ▲]

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See detailOrganisms as ecosystems engineers: the case of amphipod grazers from Posidonia oceanica meadows
Michel, Loïc ULg; Schnitzler, Joseph ULg; Dupont, Alessandra et al

Poster (2011, February 25)

Posidonia oceanica is a seagrass endemic to the Mediterranean Sea, and is able to form large monospecific areas, called meadows. These meadows shelter high biomasses and biodiversities of amphipod ... [more ▼]

Posidonia oceanica is a seagrass endemic to the Mediterranean Sea, and is able to form large monospecific areas, called meadows. These meadows shelter high biomasses and biodiversities of amphipod crustaceans. Moreover, It is now established that several species of these amphipods feed on the macro-epiphytes present on the leaves of the seagrass. Here, we performed in situ experiments to assess whether this grazing activity could impact the dynamics of the leaves’ epiphytic cover, and thus influence the functioning of the meadow as an ecosystem. We used microcosms containing monospecific populations of 3 amphipods taxa (Apherusa chiereghinii, Dexamine spiniventris and Gammarus spp.), and placed them directly in the meadow, at a depth of 10m. Biomasses of erected macroalgae and erected animals (hydrozoans, bryozoans) were lower in all grazed treatments. However, none of the studied taxa seemed to consume encrusting epiphytes, either vegetal or animal. This selective grazing pressure by amphipods may release encrusting epiphytes from competition for space, light and/or nutriments with the fast-growing erected algae, and could thus play an important role in the structuring of the epiphytic cover from P. oceanica leaves. Moreover, this top-down control might keep erected algae biomass to a normal, sustainable level, therefore also benefiting the seagrass itself. Our results also indicate that amphipod trophic activity caused nitrogen enrichment in both grazed (erected algae) and non-grazed (encrusting algae & seagrass leaves) vegetal tissues. A plausible interpretation could be that sloppy feeding and excretion by the grazers enhanced availability of this nutrient, which is typically limiting for photosynthesis in shallow P. oceanica meadows. This emphasizes the fact that grazing is not a simple negative interaction, but that it can also benefit the primary producers. Our results thus indicate that amphipods from P. oceanica meadows seem to be bound to the epiphytic cover of the leaves by complex and multilateral trophic interactions, and have an indirect influence on the seagrass itself. Amphipods may therefore play an important part in the functioning of the epiphyte/seagrass/grazer system of these meadows, and thus act as ecosystems engineers. This abstract is dedicated to the freshly born Adèle and Côme. [less ▲]

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See detailPotential early indicators of anthropogenically derived nutrients : a multiscale stable isotope analysis
Vermeulen, Simon ULg; Sturaro, Nicolas ULg; Gobert, Sylvie ULg et al

in Marine Ecology. Progress Series (2011), 422

Increasing human pressure along Mediterranean coastlines raises the need to define sensitive bioindicators that provide an early response to nutrient enrichment. We performed multiscale carbon and ... [more ▼]

Increasing human pressure along Mediterranean coastlines raises the need to define sensitive bioindicators that provide an early response to nutrient enrichment. We performed multiscale carbon and nitrogen stable isotope analyses on the limpet Patella caerulea, the snail Monodonta turbinata, epilithic biofilms, and the macroalga Rissoella verruculosa inhabiting the rocky midlittoral zone. Samples were seasonally collected in 2006 from 5 sites exposed to a range of anthropogenic discharges in the Revellata Bay area and in Marseille harbour (France). All bioindicators exhibited strongly elevated δ15N values at impacted sites compared to pristine ones, which revealed the biological availability of anthropogenically derived nutrients. Only epilithic biofilms tended to show both the occurrence of nutrient pulses during the tourist season and a δ13C response at impacted sites. In contrast to macroalgae, which exhibited a somewhat equivocal signal, gastropods and especially M. turbinata provided the best time-integrated picture of the graduated exposure of the 5 sites to anthropogenic impact. Results also showed first evidence of large isotopic variability at a scale of tens of metres, close to that found at the kilometre scale. The intra- and interspecific isotopic variability in gastropods may be explained by the patchiness of resources and specific morphological and behavioural features, but these factors do not greatly hamper their potential as early bioindicators of wastewater disturbances. [less ▲]

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See detailDistribution patterns of Caprella tavolarensis (Crustacea: Amphipoda) in the Tavolara-Punta Coda Cavallo Marine Protected Area.
Sturaro, Nicolas ULg; Gobert, Sylvie ULg; Lepoint, Gilles ULg et al

in Biologia Marina Mediterranea (2011), 18(1), 290-291

Distribution patterns of Caprella tavolarensis was investigated at the tavolara-punta Coda Cavallo Marine protected area. results revealed that C. tavolarensis abundance may exhibit spatial patterns ... [more ▼]

Distribution patterns of Caprella tavolarensis was investigated at the tavolara-punta Coda Cavallo Marine protected area. results revealed that C. tavolarensis abundance may exhibit spatial patterns associated with the protection status of the zones, highlighting the importance of totally protected areas in species conservation and management. [less ▲]

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See detailEpilithic biofilm as a key factor for small-scale river fisheries on Caribbean Islands
Lefrançois, E.; Coat, Sophie; Lepoint, Gilles ULg et al

in Fisheries Management & Ecology (2011)

Numerous freshwater species are consumed or exploited through artisanal fisheries in the rivers of the islands of Guadeloupe, French West Indies. Autochthonous production of organic matter is limited in ... [more ▼]

Numerous freshwater species are consumed or exploited through artisanal fisheries in the rivers of the islands of Guadeloupe, French West Indies. Autochthonous production of organic matter is limited in these flowing rivers and is mainly represented by scarce filamentous green algae and an abundant epilithic biofilm growing on wet stones in the river bed. Stable isotope analysis was used to quantify the relative importance of biofilm and other riverine allochthonous and autochthonous food sources in the diet of tropical shrimps (Palaemonidae, Atyidae and Xiphocarididae) and fishes (Gobiidae and Eleotridae) consumed by the local people. The epilithic biofilm was exploited by most species, constituted an important source of autochthonous carbon and wasan important source of organic matter production at the base of freshwater food webs in Caribbean rivers. Biofilm percentages in the diet reached 32% for molluscs, 85% for atyid shrimps, 29% for xiphocaridid shrimps, 14% for palaemonid shrimps and 13% for fish. Assessment of biofilm in nine rivers showed that blue and red cyanobacteria were quantitatively dominant with a moderately rich diatom flora. These results address the interactions between river biofilm and Caribbean freshwater fauna where trophic links between consumers and their potential resources have poorly been documented. [less ▲]

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