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See detailComparing the paleoseismic record obtained by coring a sag-pond and by classical trenching along the eastern segment of the North Anatolian Fault
Hubert, Aurelia ULg; Avsar, Ulas; Fraser, Jeef et al

Conference (2012, October)

Shallow lakes along minor structural bends or discontinuities of strike-slip fault are not usually paleoseismological target sites. In the present talk 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 talk we show that a 2m deep, 700m long lake crosscut by the eastern segment of the North Anatolian Fault contains a reliable paleoseimological record obtained through coring. The North Anatolian Fault, a major strike-slip fault in Turkey, last ruptured across the Aşağıtepecik Lake in 1939 with a slip of about 6 m. Seismic lines still show remains of the fault rupture forming minor scarps across the lake. Collected short cores display a set of sedimentary sequences. Each sequence is composed of similar organic rich sedimentary units. The lower unit is dark and fibrous, and is similar to the present sedimentation at the top of the core. The upper unit is disturbed and has anomalous organic matter content, grain size and mineralogy. It is interpreted as an earthquake induced sedimentary event. The 2.5 m long AT2007LG core comprises four sequences, and four sedimentary events. Radiogenic 210Pb and 137Cs data obtained in Boes et al. (2009) imply that the shallowest event 1 was triggered by the 1939 M=7.9 Erzincan earthquake. Radiocarbon dating suggest that events 2 and 4 were initiated by the 1668 and 1254 historical earthquakes. The event 3 does not correspond to a large historical earthquake on the NAF. The record can be compared to a classical paleoseismological study located about 2.5 km more to the east. The investigation comprised three paleoseismic trenches located along about 2km of the principal fault strand. Trench T1 revealed clear evidence for one earthquake interpreted to be the 1939 Erzincan earthquake. Trench T2 revealed evidence of three earthquakes. Trench T3 revealed a record of colluvial wedges that interfinger with fine-grained inter-fan deposits. We interpreted a sequence of six earthquake event horizons including the 1939 Erzincan earthquake. The first three earthquakes are correlated to historical earthquakes in A.D. 1668, 1254, 499 and two further events were identified at 881 – 673 B.C. and 1406 – 1291 B.C. (2σ age ranges). By comparing all available earthquake timing studies,we conclude that the 1939 earthquake segment does not always rupture in unison. [less ▲]

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See detailTrophic and specific diversity of harpacticoid copepods associated to Posidonia oceanica macrophytodetritus
Mascart, Thibaud ULg; De Troch, Marleen; Remy, François ULg et al

Poster (2012, August 21)

Extended meadows of living Posidonia oceanica plants in the Mediterranean Sea produce large amounts of detritus of dead seagrass plants that are packed at the bottom of the sea. In spite of their large ... [more ▼]

Extended meadows of living Posidonia oceanica plants in the Mediterranean Sea produce large amounts of detritus of dead seagrass plants that are packed at the bottom of the sea. In spite of their large quantities, these phytodetritus are of low nutritional quality (high C:N:P ratio). However, these detritus are massively colonised by bacterial communities, fungi, diatoms, meiofauna and macrofauna. This leads to the assumption that those associated communities enrich the litter and play an important role in the energy transfer to higher trophic levels like macrofauna and juvenile fish that use these accumulations as nursery and feeding grounds. In these litter accumulations harpacticoid copepods (Crustacea) are the main meiofauna players (metazoans in the size range of 38µm – 1mm). Their families are characterised by different specialized morphologies (body form and appendages). Nonetheless their morphological differences they are all grazers and seem to feed on similar sources. Ecological theories state that diversity of trophic niches is an essential parameter to explain specific diversity. Therefore subtle trophic niches may occur among species assemblages, linked to the complexity of the phytodetritus. In order to unravel the ecological function, trophic relations, seasonal fluctuations and habitat interactions in these litter accumulations, a bulk stable isotope analysis (SIA) is conducted. The isotopic composition of C and N of the potential food sources and the most dominant harpacticoid copepod families are measured using an EA-IRMS coupling. The results are run in a SIAR Beyesian mixing model to calculate the approximate contributions of each potential food sources towards the composition of different families of harpacticoid copepods present in the macrophytodetritus. [less ▲]

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See detailLeaf fall impact on diversity and trophic ecology of vagile macrofauna associated with exported P.oceanica litter
Remy, François ULg; Mascart, Thibaud ULg; Dauby, Patrick ULg et al

Poster (2012, August 20)

In the Mediterranean Sea, Posidonia oceanica meadows produce a huge amount of detritus, evaluated up to 300 to 2000 g dry wt m-2 yr-1. This litter is mainly composed of dead leaves but also of uprooted P ... [more ▼]

In the Mediterranean Sea, Posidonia oceanica meadows produce a huge amount of detritus, evaluated up to 300 to 2000 g dry wt m-2 yr-1. This litter is mainly composed of dead leaves but also of uprooted P.oceanica shoots and drift macro-algae from adjacent rocky bottoms. Although rich in refractory materials (lignin) and poor in P and N, these underwater accumulations of leaves are colonised by fungi, micro-algae (like diatoms), bacteria, but also by micro and macrofauna assemblages. These organisms could play an important role in leaf litter degradation and enrichment, but also in energy and carbon transfer from P.oceanica to higher trophic levels in adjacent coastal ecosystems. In this study we focus on the vagile macro-fauna (invertebrates with a size > 500µm) inhabiting the exported litter accumulations of the Calvi Bay (France). We took standardised samples at two different sites (a sheltered one and an exposed one) before and after leaf fall. We emphasised that crustaceans represent 65 – 85% of the biodiversity, followed by annelids and molluscs, representing respectively 10-20% and 10-15% of the diversity. That general pattern differs between sampling sites and we highlighted changes after leaf fall at both sites. In order to assess the impact of the autumn period litter input on the trophic structure of these invertebrates, we conducted gut contents observations and “bulk” stable isotope analysis. The isotopic compositions of C and N stable isotopes of the potential detritic food sources and of the most abundant invertebrate’s species were measured using EA-IRMS. We finally focused on the two most abundant Gammaridean Amphipoda species representing up to about 60% of the vagile macrofauna found in litter accumulations: Gammarella fucicola and Gammarus aequicauda. The results of their isotopic measurements were used in the “SIAR” Bayesian mixing model to calculate the potential contribution of their potential food sources. [less ▲]

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See detailTrophic tracers reveal considerable diversity among diets of dominant amphipods from Posidonia oceanica seagrass meadows
Michel, Loïc ULg; Dauby, Patrick ULg; Gobert, Sylvie ULg et al

Poster (2012, August 20)

Mediterranean Posidonia oceanica meadows shelter a high biomass and an important biodiversity of amphipod crustaceans. In other temperate meadows, the amphipods play an important part in the functioning ... [more ▼]

Mediterranean Posidonia oceanica meadows shelter a high biomass and an important biodiversity of amphipod crustaceans. In other temperate meadows, the amphipods play an important part in the functioning of the ecosystem, notably in organic matter transfers from producers to higher level consumers. However, the situation in Posidonia oceanica meadows remains unclear, and little is known about the trophic ecology of amphipods, which are generally regarded as generalist herbivores/detritivores despite the lack of precise studies. Here, we combined gut content examination and trophic markers (fatty acids, stables isotopes of C and N) to delineate the diet of the dominant species of amphipods from Posidonia oceanica seagrass meadows and to highlight trophic diversity among this community. Our results indicate that contribution of microepiphytic diatoms and of benthic and suspended particulate organic matter to the diet of amphipods were anecdotal. On the other hand, all dominant species heavily relied on macroalgal epiphytes, suggesting a certain extent of overlapping in the diets of the dominant species. Considerable interspecific differences nonetheless existed, notably concerning grazing preferences towards epiphytes from leaves or litter fragments vs. epiphytes from rhizomes. In addition, the use of the SIAR isotopic mixing model showed that most species had a mixed diet, and relied on several food items. None of the examined species seemed to graze on their seagrass host, but Gammarus aequicauda partly relied on seagrass leaf detritus. Overall, our findings demonstrate that amphipods have the potential to be key-items in trophic and functional interactions occurring among Mediterranean Posidonia oceanica meadows. [less ▲]

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See detailAssessment of the ecological status of P. oceanica meadow with a no destructive shoot method
Gobert, Sylvie ULg; Lejeune, Pierre ULg; Chéry, Aurélia et al

in Proceedings of the Mediterranean Seagrass Workshop 2012 (2012, June)

Posidonia oceanica (L.) Delile is a protected species, included in the Red list of marine threatened species of the Mediterranean. Because of its sensitivity to disturbance, P. oceanica is used as a ... [more ▼]

Posidonia oceanica (L.) Delile is a protected species, included in the Red list of marine threatened species of the Mediterranean. Because of its sensitivity to disturbance, P. oceanica is used as a bioindicator to define the health status of coastal waters. Monitoring methods generally require to sample plants, followed by measurements on picked shoots. This implies the total destruction of several tens of shoots. This study presents a method, “The Non Destructive Shoot Methodology”: NDSM, that permits the measurement of (1) the most used seagrass metrics, (2) the determination of C, N, P contents and (3) the measurement of the trace metal levels in P. oceanica leaves. Our technic has been firstly tested by comparison with the results obtained with classic method of biometry. Secondly, differences between levels of C, N, P and trace metals obtained with classic picking and our methodology were tested. Thirdly, the physiological consequences on the shoots were investigated (% of survival, growth, essential element contents (C, N, P, Fe, Cu...). The NDSM gives similar results to classic investigations to assess the ecological status of P. oceanica meadow (i.e. PREI, BiPO...) and avoid the uprooting of the “K-strategist” protected species. This methodology is usable in cases of monitoring and impact studies. [less ▲]

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See detailSeasonal and depth-related distributions of epiphytic Bryozoa in a Mediterranean seagrass meadow
Lepoint, Gilles ULg; Balancier, Boris; Gobert, Sylvie ULg

Poster (2012, May 31)

Although biofouling on Posidonia oceanica (L.) Delile is thought to be driven by the variability of environmental parameters and phenology of the plant, effect of these parameters on sessile animal ... [more ▼]

Although biofouling on Posidonia oceanica (L.) Delile is thought to be driven by the variability of environmental parameters and phenology of the plant, effect of these parameters on sessile animal colonization is still poorly understood. This study aims to document the seasonality and the bathymetric variability of epiphytic Bryozoa diversity and abundance on this seagrass Posidonia shoots were collected in the Revellata bay (Corsica, Mediterranean) in five seasons from 7 to 30 m depth. Colony densities may reach more than 87000 colonies. m-2 at 10 m depth in spring; this probably implies an important contribution of Bryozoa larvae to spring plankton where P. oceanica meadows are present. The Bryozoa specific distribution and abundance appeared to be determined by the seasonality of both the environmental parameters and the plant phenology. However, depth and associated environmental gradients played a structuring role. Based on our data and on the literature, we propose a classification of epiphytic Bryozoa in four categories from hyper-epiphytic specialist to accidental epiphytes and underline the necessity to protect seagrass systems on their full depth range to maximize biodiversity conservation. [less ▲]

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See detailTrace element kinetics in contaminated Posidonia oceanica meadow
Richir, Jonathan ULg; Luy, Nicolas; Lepoint, Gilles ULg et al

in Proceedings of the Mediterranean Seagrass Workshop 2012 (2012, May 29)

The seagrass Posidonia oceanica (L.) Delile is widely used since the mid-70th to biomonitor trace elements (TEs). However, there is a lack of knowledge regarding to pollutant kinetics in that species ... [more ▼]

The seagrass Posidonia oceanica (L.) Delile is widely used since the mid-70th to biomonitor trace elements (TEs). However, there is a lack of knowledge regarding to pollutant kinetics in that species. Posidonia oceanica were in situ contaminated by a mix of 15 TEs (Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Mo, Ag, Cd, Pb and Bi) at experimental levels equivalent to 10 (moderate) and 100 (acute) times seawater average concentrations. TEs concentrations were measured by ICP-MS in P. oceanica leaves and rhizomes sampled at regular time intervals, in epiphytes, in water and in sediment. Posidonia oceanica immediately accumulated pollutants from the beginning of experiments; once contaminations ended, TE concentrations came back to their original levels within two weeks, or at least showed a clear decrease. Leaves exhibited different uptake kinetics for many elements (e.g. Cr, Cu, Ag, Bi etc.): the younger growing leaves forming new tissues incorporated chemicals more rapidly than the older senescent leaves. Rhizomes did not show any clear trend, except for Cu, Zn and Bi. Results demonstrate that P. oceanica is a very sensitive sentinel to immediately delineate punctual pollutions similar to what might be measured in contaminated Mediterranean waters. The good response of P. oceanica leaves to pollutant short-term expositions suggests their routine use in regularly scheduled monitoring programs. Nevertheless, to by-pass P. oceanica leaves deciduous character and their capability to detoxify rapidly, long term accumulation recordings would also necessitate belowground tissues analyses. [less ▲]

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See detailMismatch between shape changes and ecological shifts during the post-settlement growth of the surgeonfish, Acanthurus triostegus
Frederich, Bruno ULg; Colleye, Orphal ULg; Lepoint, Gilles ULg et al

in Frontiers in Zoology (2012), 9

Background: Many coral reef fishes undergo habitat and diet shifts during ontogeny. However, studies focusing on the physiological and morphological adaptations that may prepare them for these transitions ... [more ▼]

Background: Many coral reef fishes undergo habitat and diet shifts during ontogeny. However, studies focusing on the physiological and morphological adaptations that may prepare them for these transitions are relatively scarce. Here, we explored the body shape variation related to ontogenetic shifts in the ecology of the surgeonfish Acanthurus triostegus (Acanthuridae) from new settler to adult stages at Moorea Island (French Polynesia). Specifically, we tested the relationship between diet and habitat shifts and changes in overall body shape during the ontogeny of A. triostegus using a combination of geometric morphometric methods, stomach contents and stable isotope analysis. Results: After reef settlement, stable isotope composition of carbon and nitrogen revealed a change from a zooplanktivorous to a benthic algae diet. The large amount of algae (> 75% of stomach contents) found in the digestive tract of small juveniles (25–30 mm SL) suggested the diet shift is rapid. The post-settlement growth of A. triostegus is highly allometric. The allometric shape changes mainly concern cephalic and pectoral regions. The head becomes shorter and more ventrally oriented during growth. Morphological changes are directly related to the diet shift given that a small mouth ventrally oriented is particularly suited for grazing activities at the adult stage. The pectoral fin is more anteriorely and vertically positioned and its basis is larger in adults than in juveniles. This shape variation had implications for swimming performance, manoeuvrability, turning ability and is related to habitat shift. Acanthurus triostegus achieves its main transformation of body shape to an adult-like form at size of 35–40 mm SL. Conclusion: Most of the shape changes occurred after the reef colonization but before the transition between juvenile habitat (fringing reef) and adult habitat (barrier reef). A large amount of allometric variation was observed after diet shift from zooplankton to benthic algae. Diet shift could act as an environmental factor favouring or inducing morphological changes. On the other hand, the main shape changes have to be achieved before the recruitment to adult populations and start negotiating the biophysical challenges of locomotion and feeding in wave- and current-swept outer reef habitat. [less ▲]

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See detailMercury in blood of free-ranging seals Phoca vitulina from the North Sea: Time-trend and association with environmental factors
Das, Krishna ULg; Brochoire, Charlène ULg; Chambosse, Mélanie et al

Conference (2012, March 27)

The harbour seal (Phoca vitulina) population from the North Sea has experienced various fluctuations these last decades due to habitat loss, prey fluctuation and pollution of the marine environment ... [more ▼]

The harbour seal (Phoca vitulina) population from the North Sea has experienced various 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 allowed blood sampling on a regular basis together with measurements of blubber thickness, body mass, sex and body length. Concentrations of total mercury (T-Hg) and other trace elements (Cd, Pb, Zn, Cu, Fe) as well as ∂13C and ∂15N values were determined by mass spectrometry in blood of 75 wild harbour seals caught in the German Wadden Sea between 1997 and 2011. ∂13C and ∂15N mean values (-17.5‰ and 18.1 ‰ respectively) were strongly similar to that measured previously in the muscle of stranded harbour seals from the Wadden Sea. In contrast, ∂15N mean value was strikingly higher than that recorded in grey seals (Halichoerus grypus) from Scotland (14.1 ‰ respectively; Habran et al. submitted.) while ∂13C values remained similar between the two seal species. These values confirmed the high trophic position of the harbour seal in the North Sea. In contrast to Cd and Pb, T-Hg in blood harbour seals reached concentrations as high as 2.1 μg.g-1 dry weight (10 times higher than the 0.21 μg.g-1 dry weight recorded for grey seals from Scotland) but depended on several factors including ∂15N values, age group and the body mass. T-Hg was detected in juveniles confirming maternal transfer to offspring and time-trend revealed no decrease of T-Hg in blood of harbour seals these last 15 years. [less ▲]

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See detailCharacterization of a population of the Harlequin crab, Lissocarcinus orbicularis Dana, 1852, an obligate symbiont of holothuroids, in Toliara bay (Madagascar)
Caulier, Guillaume; Parmentier, Eric ULg; Lepoint, Gilles ULg et al

in Zoosymposia (2012), 7

Harlequin crabs, Lissocarcinus orbicularis, are commensals found on the integument and in the buccal/cloacal cavity of several species of holothuroids. The population of these crabs was investigated on ... [more ▼]

Harlequin crabs, Lissocarcinus orbicularis, are commensals found on the integument and in the buccal/cloacal cavity of several species of holothuroids. The population of these crabs was investigated on holothuroids of the barrier reef of Toliara (South-West of Madagascar) from 2002 to 2008. Seventeen holothuroid species were observed and eight were crab hosts. There is generally one adult crab or a heterosexual pair per infested holothuroid but up to ten juveniles were recorded on a Thelenota ananas. Carapace length of the observed L. orbicularis was from 0.3 to 1.4 cm from the tip of the rostrum to the end of the cephalothorax, with a mean length of 0.85 cm. L. orbicularis is characterized by a weak sexual dimorphism (females are bigger than males) and the presence of pereiopods morphologically adapted to fixation on the host integument. Gravid females were observed at each month of the survey indicating that the crab reproduces all the year. Considering our results and personal observations, we also discuss the monogamy mating system of the Harlequin crab. [less ▲]

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See detailA descriptive study of physico-chemical characteristics of Posidonia oceanica litter accumulation
Lepoint, Gilles ULg; Borges, Alberto ULg; Darchambeau, François ULg et al

Poster (2012)

The Mediterranean seagrass Posidonia oceanica meadow losses every fall the major part of its leaf biomass after senescing. These phytodetritus may decay within the meadow, be buried or be exported to ... [more ▼]

The Mediterranean seagrass Posidonia oceanica meadow losses every fall the major part of its leaf biomass after senescing. These phytodetritus may decay within the meadow, be buried or be exported to other habitats. They form large litter accumulations, notably on shallow water sand patches. Such accumulation host many organisms which participate to the degradation of this material. In a first step to understand the dynamics of these accumulations and of their associated biota, we have characterised their physico-chemical heterogeneity at different seasons. We measured the dissolved oxygen, nutrients and sulphide concentrations in interstitial waters from litter accumulations varying regarding their phytodetritus composition, fragmentation level and thickness. Results show that oxygen conditions were highly variable depending on litter thickness but also on local hydrodynamics. Anoxic conditions and presence of sulphide were sometimes measured, particularly in very thick litter or in degraded litter at the end of summer. Colonies of sulphur-oxidising bacteria were observed. Litter accumulations were also often enriched in ammonium and, sometimes, in dissolved phosphorus. It is not clear whether this results from the litter degradation within the accumulation or whether this is a consequence of a barrier effect between sediment and water column. Nevertheless, this makes litter accumulations particularly attractive for micro-phytobenthic producers. Litter accumulations appear as key habitats both to understand the dead-face of seagrass dynamics and its consequence for C cycle in coastal areas and to study the consequence of hypoxia on biodiversity in a natural context. [less ▲]

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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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