References of "Mascart, Thibaud"
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See detailFeeding ecology of harpacticoid copepod species: Insights from stable isotopes analysis and fatty acid profiling
Mascart, Thibaud ULg; De Troch, Marleen; Remy, François ULg et al

Conference (2014, August 04)

Understanding how biodiversity influence ecosystem functioning is a major research question in current ecology research. Trophic diversity within communities strongly affects ecosystem functioning through ... [more ▼]

Understanding how biodiversity influence ecosystem functioning is a major research question in current ecology research. Trophic diversity within communities strongly affects ecosystem functioning through trophic interactions between species. Various studies tackled ecosystem functioning via interactions between trophic guilds such as bottom-up and top-down control. However, few studies focussed on interspecific variability in the feeding ecology of organisms with overlapping trophic niche. Here, we in a North-Western Corsican Posidonia oceanica seagrass meadow and its variability over one year. The extensive P. oceanica meadows are occasionally interrupted by bare sand patches which serve as deposition and accumulation area for detritus, mainly derived from senescent macrophytes. These macrophytodetritus accumulation harbour a diverse community of Harpacticoida (Crustacea, Copepoda). The most abundant harpacticoids and their potential food sources (i.e. macrophytodetritus, epiphytic biofilm, macroalgae and particulate matter) were analysed for stable isotope ratios (δ13C, δ15N). Bayesian mixing model (SIAR) showed a minor contribution of macrophytodetritus while the epiphytic biofilm, present on the macrophytodetritus, appeared to be the major food source of harpacticoid copepods. In order to distinguish the several components of the epiphytic biofilm and their contribution, fatty acid profiling was used. The outcome revealed a general harpacticoid diet preference towards diatoms and bacteria, however specialisation for certain components seemed to reduce competition between harpacticoid species. In conclusion, our results underline the importance of multiple biomarker species-specific analysis, especially in complex and dynamic environments where a wide variety of potential trophic niches are present. [less ▲]

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See detailSeasonal variability of meiofauna, especially harpacticoid copepods, in Posidonia oceanica macrophytodetritus accumulations
Mascart, Thibaud ULg; Lepoint, Gilles ULg; Deschoemaeker, Silke et al

in Journal of Sea Research (2014)

The overall aim of this study was (1) to assess the diversity and density of meiofauna taxa, especially harpacticoid copepod species, present within accumulated seagrass macrophytodetritus on unvegetated ... [more ▼]

The overall aim of this study was (1) to assess the diversity and density of meiofauna taxa, especially harpacticoid copepod species, present within accumulated seagrass macrophytodetritus on unvegetated sand patches and (2) to elucidate the community structure of detritus-associated harpacticoid copepods in relation to natural temporal variability of physico-chemical characteristics of accumulations. This was investigated in a Posidonia oceanica (L.) Delile seagrass ecosystem in the northwest Mediterranean Sea (Bay of Calvi, Corsica, 42°35’N, 8°43’E) using a triplicate macrophytodetritus core field sampling in two contrasting sites over the four seasons of 2011. Meiofauna higher taxa consisted of 50% Copepoda, which 87% belonged to the Harpacticoida order. Nematoda was the second most abundant taxa. The copepod community displayed a wide variety of morphologically similar and ecologically different species (i.e. mesopsammic, phytal, phytal-swimmers, planktonic and parasitic). The harpacticoid copepod community followed a strong seasonal pattern with highest abundances and species diversity in May-August, revealing a link with the leaf litter epiphyte primary production cycle. Aside from the important role in sheltering, housing and feeding potential of macrophytodetritus, a harpacticoid community BEST analysis demonstrated a positive correlation with habitat complexity and a negative correlation with water movements and P. oceanica leaf litter accumulation. [less ▲]

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See detailHas oxygen depletion an impact on nutrients and macrofauna in a highly dynamic macrophytodetritus accumulation?
Remy, François ULg; Mascart, Thibaud ULg; Dauby, Patrick ULg et al

Poster (2014, May 06)

Posidonia oceanica is an endemic Mediterranean highly productive seagrass. Depending on the ability of the primary consumers to digest it alive, a generally important part of its foliar primary production ... [more ▼]

Posidonia oceanica is an endemic Mediterranean highly productive seagrass. Depending on the ability of the primary consumers to digest it alive, a generally important part of its foliar primary production falls in autumn, to decay inside the meadow or to be exported to sand patches to form “exported litter accumulations”. These accumulations are highly dynamic depending on hydrodynamics and seafloor geomorphology. Literature says that low O2 conditions might occur inside litter accumulations, but the annual oxygen dynamics or its impact on the litter-associated macrofauna has never been measured. We focused on 2 exported litter accumulations in Calvi Bay (Corsica), during 2 years for a total of 8 seasons. For each season, we collected water samples (n=6) from 3 different strata: Water Column (WC), Water Just Above the litter (WJA) and Water Inside the litter (WI). Oxygen was measured for each replicate using a Winkler-based automated routine for oxygen concentration measurements on micro-volumes. At the same time, nutrients concentrations (PO4, NH4, and NO2+NO3) were measured in WC, WJA and WI, but also in the Interstitial Water (IW) using a spectrophotometric continuous flow analyzer (adapted for low nutrients level in an oligotrophic environment). In parallel, macrofaunal (size >500µm) samples (n=3-6) were also collected, counted and identified to the specific level. Our results show significant differences between O2 concentrations/saturation from WI and the two other strata. Significant differences were detected between seasons, sites and years for WI which is the only stratum where really low O2 conditions can be observed. Significant differences were also detected between seasons for both WC and WJA but no differences between sites and years. On the other hand no significant differences were detected between WC and WJA. A similar observation was made for the nutrients at the annual, seasonal and spatial level. Moreover differences are also observed between the nutrients themselves. Our data shows no correlation between WI O2 concentrations and saturation, and global macrofauna abundance or biodiversity. Results are more contrasting at an individual specific level for the 4 most dominant species. For two amphipod species, Gammarella fucicola (55% of the global abundance) and Gammarus aequicauda, no significant correlations were detected between their abundance and O2. For the leptostracan species, Nebalia strausi, a significant negative correlation with O2 concentration was detected. For the last amphipod species, Melita hergensis, a significant positive correlation was observed. Our analyses also show significant correlations between WI O2 concentration/saturation, and WI / IW nutrients concentration. To conclude, this work shows that WI is a very particular and dynamic environment considering O2 concentration and saturation. Low O2 conditions can be observed in WI but never in WC or WJA showing that internal processes and relations with the sediment determine the O2 dynamics in WI and showing a potential “barrier” effect between WI and WC. Moreover O2 dynamics and its consequences may play a role in the nutrients dynamics and cycles. It is clear that faunal responses to low O2 conditions are not identifiable at a global community level. At a specific level, we show a more complex situation: some species do not seem to be impacted by low O2 conditions, but some present a significant positive, or a significant negative response. This shows the existence and complexity of species-dependent low O2 tolerance/adaptation, and the importance of a specific level data analyses to detect responses of dominant litter associated macro- invertebrates to O2 concentration and saturation variations. [less ▲]

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See detailHypoxia in macrophytodetritus accumulation: Species specific harpacticoid copepod adaptation?
Mascart, Thibaud ULg; De Troch, Marleen; Gobert, Sylvie ULg et al

Poster (2014, May 05)

Mediterranean Posidonia oceanica seagrass meadows generate high primary production and support large biodiversity of associated fauna and flora. The majority of the foliar material falls on the ... [more ▼]

Mediterranean Posidonia oceanica seagrass meadows generate high primary production and support large biodiversity of associated fauna and flora. The majority of the foliar material falls on the unvegetated sea floor during the autumnal leaf senescence, fuelling the detrital food web. Whilst laying on the sea floor the freshly formed macrophytodetritus pile up into accumulations according to the local hydrodynamics and seafloor geomorphology. In these litter accumulations, harpacticoid copepods (Crustacea, Copepoda) are the main meiofaunal players (metazoans in the size range of 38µm – 1mm) and show a high specific diversity. They are primarily grazers, but their high specific diversity suggests that they occupy also a large variety of trophic niches. This large morphological and trophic diversity can partly be promoted by the complexity of the phytodetritus in seagrass accumulations. On the other hand, macrophytodetritus degradation and flux of reduced compounds from the sediments is responsible for oxygen consumption inside the accumulation of seagrass litter. Therefore, concentration of oxygen inside the accumulation is very variable and often under the concentration observed in the water column just above the litter. Frequently, oxygen levels reach very low values. The present study aims to link the oxygen variability inside the accumulation to the densities of the five most dominant harpacticoid copepods found living in the P. oceanica litter. Standardized samples were collected seasonally in two contrasting sites of the Calvi Bay (Corsica) during one year. Our results showed no correlation between the oxygen concentrations and harpacticoid community diversity or their total abundances. The five most dominant species showed divergent results, but none had a clear correlation with the oxygen concentration. This contrasts with observation done for sediment meiofaunal community where most harpacticoid copepods are sensitive to oxygen level and where nematodes often dominate the community. This could be explained by their high mobility and the patchiness and variability of the oxygen concentrations present in the accumulations. Harpacticoid copepods, whilst being sensitive to hypoxia and anoxia developed a strategy to live in this fast oxygen changing environment. To conclude, our results underline the importance of species-specific analysis of correlation data. Especially in complex and dynamic environments where a variety of potential trophic niches are present and species competition is very likely to occur. The overall abundance pattern and diversity of the copepod community showed no relation to the oxygen concentration while the most abundant copepod species did not responded to fluctuating oxygen concentrations. [less ▲]

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See detailCorsican seagrass detritus: An opportune shelter or a copepod Eldorado?
Mascart, Thibaud ULg; Lepoint, Gilles ULg; Remy, François ULg et al

Poster (2014, March 07)

Seagrass ecosystems are extensive beds of marine flowering plants bordering tropical and temperate coastal regions. They play an important role in maintaining biological productivity and bio-geochemical ... [more ▼]

Seagrass ecosystems are extensive beds of marine flowering plants bordering tropical and temperate coastal regions. They play an important role in maintaining biological productivity and bio-geochemical cycles in the sea and support higher diversity and abundance of fauna in comparison to adjacent non-vegetated areas. The seagrass meadow primary production can be directly consumed through herbivory but the majority of the plant material falls on the sea floor during the autumnal leaf senescence. The leaf litter then degrades within the meadow or accumulates with other micro- and macrophytodetritus to form detritus accumulations on the adjacent non-vegetated sand patches. These exported accumulations are quite dynamic in relation to seafloor geomorphology and local hydrodynamics. Thus, the detritus accumulations are an easily disturbed ephemeral environment with one large influx a year. Consequently the physico-chemical characteristics can change very fast and impact the sheltering capacity and food supply present. Nonetheless, fishes, macrofauna and meiofauna are omnipresent throughout the year. In our study site along the shore of N-W Corsica, Posidonia oceanica seagrass meadows are characterised by substantial detritus accumulations. The present study aimed to analyse the biodiversity of the copepod species communities (Crustacea, Copepoda) in those detritus accumulations. The results showed that the copepod detritus community consisted of a mixture of species that are also found in adjacent habitats (seagrass meadow, sediment, epilithic habitats, water column). Each adjacent habitat is characterised by organisms that are morphologically adapted to the specific features of that habitat. The majority of copepods are epiphytic (order Harpacticoida), that occur typically on seagrass leaves and macroalgae. Other species are planktonic (orders Cyclopoida and Calanoida) and some were benthic (order Harpacticoida), known from the nearby sediment. A minority of the copepod community were parasitic on fish or invertebrate (order Siphonostomatoida). In order to clarify their origin, we assume that passive transport by currents plays a significant role next to the active migration from the anoxic sediments under the detritus. For sure they also reproduce within the detritus packages as we found many nauplii, copepodites and gravid females. The above mentioned suggestions cannot explain such high density of copepods by themselves. Other attraction mechanisms are needed to explain the important amount of planktonic and epiphytic species with good swimming ability, such as higher food accessibility. In the detritus no plant-defence mechanisms are present anymore and a lot of micro-organisms and thus potential food sources are present. Furthermore, the dense detritus package provides shelter and protection from potential predators. Subsequently we may consider the detritus accumulations as a copepod species-specific opportune Eldorado for sheltering, nursing and feeding. [less ▲]

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See detailMeiofauna and harpacticoid copepods in different habitats of a Mediterranean seagrass meadow
Mascart, Thibaud ULg; Lepoint, Gilles ULg; De Troch, Marleen

in Journal of the Marine Biological Association of the United Kingdom (2013), 93(06), 1557-1566

This study investigated whether associated meiobenthic communities, especially harpacticoid copepods differed, amongst habitats. Five pre-defined habitats within and next to the Posidonia oceanica ... [more ▼]

This study investigated whether associated meiobenthic communities, especially harpacticoid copepods differed, amongst habitats. Five pre-defined habitats within and next to the Posidonia oceanica seagrass meadow were sampled: living seagrass canopy leaves (LL), small (SMF) and large (LMF) macrophytodetritus fragments accumulations and sand, bare (BS) and covered (CS). The highest meiofauna abundances were recorded in the BS for the core sampled habitats (BS, CS, SMF and LMF) and in the LMF for seagrass material habitats (SMF, LMF and LL). Harpacticoid copepods were the most abundant taxon in all habitats. The assemblage composition at copepod family level showed two distinct habitats clusters: a leaf (LMF and LL) and a sediment cluster (BS, CS and SMF). Subsequently, stable isotope analyses were conducted to analyse the relationship between copepods and their potential food sources in seagrass material habitats. Based on δ13C isotopic analyses and SIAR mixing model, harpacticoid copepods relied for 70% on epiphytes and for 30% on P. oceanica leaf material in the LMF and LL habitats. [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 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 detailThe role of meiofauna in the energy transfer in a Mediterranean seagrass bed (Calvi, Corsica)
Mascart, Thibaud ULg

Master's dissertation (2010)

Meiofaunal communities of five different habitats characterised by different qualities of macrophytodetritus were sampled in a Mediterranean seagrass bed. Two different kinds of meiofauna communities were ... [more ▼]

Meiofaunal communities of five different habitats characterised by different qualities of macrophytodetritus were sampled in a Mediterranean seagrass bed. Two different kinds of meiofauna communities were distinguished amongst the five habitats. A benthic community of meiofauna living on a sediment substrate or in highly fragmented macrophytodetritus and a foliar, epiphytal community associated with seagrass leaves and low fragmented macrophytodetritus leaves. The diversity index amongst these communities was comparable, but the composition in harpacticoid copepods families was different. Trophic biomarkers such as stable isotopes and fatty acids were combined to identify the major sources of organic matter contributing to the diet of these marine invertebrates. Harpacticoid copepods are very likely to feed on the biofilm on the plant material and hence, copepods use the seagrasses and detritus merely as substrate. In addition to the field data, an experimental setup was conducted where detritus biofilm was enriched with 13C stable isotopic carbon. Harpacticoid copepods and Gammarus aquicauda amphipods were inserted in the incubation to observe their interaction and difference in uptake. No interaction between the two invertebrates was observed. The amphipods preferably feed on the detritus. The harpacticoid copepods on the other hand preferred and assimilated more biofilm than the amphipod. [less ▲]

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