Turnover rates of carbon and nitrogen stable isotopes in the amphipod Gammarus aequicauda: insights for trophic studies of Mediterranean macrophytodetritus accumulation.
Remy, François ; ; Darchambeau, François et al
Conference (2014, August 04)
A quite diverse and abundant macrofauna assemblage is found in the Mediterranean Sea in exported Posidonia oceanica macrophytodétritus accumulations along with meiofauna, microalgae, fungi and bacteria ... [more ▼]
A quite diverse and abundant macrofauna assemblage is found in the Mediterranean Sea in exported Posidonia oceanica macrophytodétritus accumulations along with meiofauna, microalgae, fungi and bacteria. This study focused on a dominant vagile macroinvertebrate species living and feeding in exported dead P.oceanica leaves litter from Calvi Bay (Corsica, France): Gammarus aequicauda. Results of gut content observations and stable isotope analysis (SIAR data) showed clearly that G. aequicauda is the most important dead P. oceanica consumer with up to 50% of dead leaves contribution. An isotopic turnover experiment was conducted with 3 controlled simultaneous treatments: 1. amphipod feeding for 43 days, 2. Green algae feeding for 30 days and 3. Posidonia oceanica litter feeding for 30 days. Individuals (n = 12 to 16) have been sampled every 7 days and whole individual stable isotope analysis have been conducted. An exponential decay regression model and calculations resulted in half-lives for C ranging from 11.72 days (treatment 1) to 51.62 days (treatment 3). Treatment 2 data did not allow us to fit a curve, consequence of a potentially very low turnover rate. For N, no significant increase or decrease of the δ15N values have been observed, and we thus concluded that δ15N was at the equilibrium from the beginning to the end of the experiment. It appears that amphipods feeding on low quality food (high to very high C/N ratio) like algae and Neptune grass dead leaves, show a lower turnover rate for C than amphipods feeding on a high quality animal food (low C/N ratio). Carbon and Nitrogen stable isotope “Trophic Enrichment Factor” (TEF) were calculated for treatments where δ13C or δ15N were at the equilibrium at the end of the experiment. Calculated TEF for nitrogen ranged from 0.53‰ ± 0.439 to 0.96‰ ± 0.424 for treatment 2 and 3 (consistent with detritus-feeder invertebrate values) and was 2.91‰ ± 0.558 for treatment 1 (consistent with predator invertebrate values). For C calculations, a TEF of 0,81‰± 0.39 for treatment 1 and a TEF of 1.19‰ ± 0.824 for treatment 3 were calculated. [less ▲]Detailed reference viewed: 19 (9 ULg)
Feeding ecology of harpacticoid copepod species: Insights from stable isotopes analysis and fatty acid profiling
Mascart, Thibaud ; ; Remy, François 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 ▲]Detailed reference viewed: 19 (3 ULg)
Seasonal variability of meiofauna, especially harpacticoid copepods, in Posidonia oceanica macrophytodetritus accumulations
Mascart, Thibaud ; Lepoint, Gilles ; 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 ▲]Detailed reference viewed: 17 (5 ULg)
Has oxygen depletion an impact on nutrients and macrofauna in a highly dynamic macrophytodetritus accumulation?
Remy, François ; Mascart, Thibaud ; Dauby, Patrick 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 ▲]Detailed reference viewed: 20 (5 ULg)
Hypoxia in macrophytodetritus accumulation: Species specific harpacticoid copepod adaptation?
Mascart, Thibaud ; ; Gobert, Sylvie 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 ▲]Detailed reference viewed: 19 (0 ULg)
Evaluation of the relationships between characteristics of the vertebral column of different cetaceans and their ecology: A preliminary study.
Gillet, Amandine ; Ninane, Catherine ; Remy, François et al
Poster (2014, April)
Ecomorphology is the study of the relationships between functional design and the environment. One of its aims is to understand how the environmental factors can constraint the performance of an organism ... [more ▼]
Ecomorphology is the study of the relationships between functional design and the environment. One of its aims is to understand how the environmental factors can constraint the performance of an organism or act on its phenotype. Different studies have already showed in different cetaceans that the number and shape of vertebrae can reflect the stiffness of the body and consequently can impact their swimming mode. The aim of this preliminary study is to establish relationships between characteristics of the vertebral column of different cetaceans and their ecology. To this purpose, we have studied meristic and morphometric data on the vertebrae (centrum length, height and width, neural and haemal spine height and the transverse process length) of different species of mysticetes and odontocetes coming from the Aquarium-Museum of Liège and Royal Institute of Natural Sciences of Bruxelles. Preliminary results showed the distinction of three morphotypes: firstly, the active, cruising, fast swimmers with rigid body, secondly, the maneuverers, slow swimmers with flexible body and thirdly, the steady swimmers. [less ▲]Detailed reference viewed: 37 (16 ULg)
Corsican seagrass detritus: An opportune shelter or a copepod Eldorado?
Mascart, Thibaud ; Lepoint, Gilles ; Remy, François 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 ▲]Detailed reference viewed: 24 (3 ULg)
Trophic and specific diversity of harpacticoid copepods associated to Posidonia oceanica macrophytodetritus
Mascart, Thibaud ; ; Remy, François 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 ▲]Detailed reference viewed: 33 (2 ULg)
Leaf fall impact on diversity and trophic ecology of vagile macrofauna associated with exported P.oceanica litter
Remy, François ; Mascart, Thibaud ; Dauby, Patrick 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 ▲]Detailed reference viewed: 37 (8 ULg)
A descriptive study of physico-chemical characteristics of Posidonia oceanica litter accumulation
Lepoint, Gilles ; Borges, Alberto ; Darchambeau, François et al
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 ▲]Detailed reference viewed: 50 (9 ULg)
Structure trophique et diversité des macro-organismes associés aux litières de Posidonia oceanica (L.) Delile, dans la baie de Calvi en Corse.
Master's dissertation (2010)
Le but de ce travail était d'évaluer la diversité et la variabilité à petite échelle des macro-invertébrésassociés à la litière de feuilles mortes de Posidonia oceanica, ainsi que de caractériser les ... [more ▼]
Le but de ce travail était d'évaluer la diversité et la variabilité à petite échelle des macro-invertébrésassociés à la litière de feuilles mortes de Posidonia oceanica, ainsi que de caractériser les relations trophiques existant entre ces organismes. Le volet trophique du travail a été étudié en utilisant deux méthodes : l'examen de contenus stomacaux et la mesure des rapports isotopiques du carbone et de l'azote. La campagne de prélèvements a eu lieu en novembre 2009, à deux stations situées dans la Baie de la Revellata à proximité de la station STARESO (Calvi, Corse). Les prélèvements ont été effectués sur deux accumulayions de litière, c'est-à-dire de feuilles mortes de posidonie associées à des macroalgues arrachées et à des pousses vivantes de posidonie. Les crustacés, et plus particulièrement les amphipodes gammaridés dominent largement les prélèvements. L'espèce Gammarella fucicola représente à elle seule 55% des organismes prélevés. Les espèces trouvées dans nos prélèvements sont également souvent présentes au sein de l'herbier de posidonie. Nous pensons que les différences existant entre les deux sites de prélèvements du point de vue de l'abondance, la densité et la diversité des organismes sont principalement dues aux caractéristiques physicochimiques de la litière et à son état de stabilité. En effet, il est probable que l'état de dégradation influence l'assemblage d'espèces présentes dans la litière. La combinaison des contenus stomacaux et des rapports isotopiques nous ont permis de confirmer le régime alimentaire détritivore des amphipodes et Idotea baltica, et donc leur rôle dans la fragmentation de la litière. Nous avons également pu mettre en évidence pour Athanas nitescens et Liocarcinus arcuatus, deux décapodes, un niveau trophique intermédiaire entre consommateur primaire et détritivore. Palaemon adspersus, un autre décapode, semble être le seul consommateur secondaire vrai que nous ayons pu analyser et les données suggèrent qu'il se nourrisse principalement d'Amphipodes. Bien qu'ils ne l'assimilent pas tous de la même façon, la plupart des organismes ingèrent une quantité non-négligeable de litière, ce qui suggère que ces animaux jouent tous un rôle plus ou moins important dans la fragmentation des feuilles, et donc dans le flux de carbone de la litière vers les niveaux supérieurs du réseau trophique. [less ▲]Detailed reference viewed: 58 (7 ULg)
Trophic structure and diversity of macro organisms associated with Posidonia oceanica litter in the bay of Calvi.
Remy, François ; Borges, Alberto ; Darchambeau, François et al
Conference (2010)Detailed reference viewed: 68 (13 ULg)