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See detailInter-annual variations over a decade of primary production of the seagrass Posidonia oceanica
Champenois, Willy ULiege; Borges, Alberto ULiege

in Limnology and Oceanography (2019), 64(1), 32-45

We acquired quasi-continuous measurements of community gross primary production (GPP) by mass balanceof O2 measured on a mooring, from August 2006 to October 2016 over a Posidonia oceanica meadow (10 m ... [more ▼]

We acquired quasi-continuous measurements of community gross primary production (GPP) by mass balanceof O2 measured on a mooring, from August 2006 to October 2016 over a Posidonia oceanica meadow (10 m depth) in the Bay of Revelleta (Corsica). Over the 2006–2016 period, annual GPP averaged 88 molO2 m−2 yr−1 and ranged from 61 to 108 molO2 m−2 yr−1 . The 2 yr with the lowest annual GPP (2007 and 2015) were characterized by a low occurrence of fall–winter storms, probably leading to the accumulation of leaf litter in fall and early winter; we hypothesize this might have led to occultation of benthic macro-algae. Among the other years, the inter-annual variability of GPP was related to changes during the February–August period, as GPP was repeatable among years during the September–January period. For the February–August period, inter-annual variations of GPP were correlated to chlorophyll a (Chl a), solar radiation and water temperature. Computed phytoplankton GPP corresponded to a small fraction of community GPP, so the relation between GPP and Chl a probably reflected inter-annual variations of a common driver that we hypothesize to be nutrient inputs. The correlation of GPP with solar radiation shows that light availability contributed to inter-annual variations of the development of P. oceanica. The positive relation between GPP and temperature was consistent with the fact that the observed temperatures in the Bay of Revelleta were during the study period within the comfort range for the growth of P. oceanica. [less ▲]

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See detailDetermination of dimethylsulfoniopropionate and dimethylsulfoxide in Posidonia oceanica leaf tissue
Champenois, Willy ULiege; Borges, Alberto ULiege

in MethodsX (2019), 6

In order to investigate the possible use of the dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO) ratio as a stress indicator of Posidonia oceanica a method for the determination of these ... [more ▼]

In order to investigate the possible use of the dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO) ratio as a stress indicator of Posidonia oceanica a method for the determination of these quantities was developed for this type of material. The method relies on gas chromatography with headspace technique, instead of the purge-and-trap technique commonly used. The method allows the determination of both DMSP and DMSO on the same sample. This method allows to quantify DMSP, DMSO and DMSP:DMSO ratio for calibration curves with a coefficient of variation around 2% and a relative error around 2% and within the ranges natural variability of DMSP and DMSO in P. oceanica leaf tissue. Preliminary tests showed that DMSP in P. oceanica leaf tissue ranged from 20 to 200 mmol g 1 of fresh weight (FW) and 2 to 5 mmol gfw 1 for DMSO. The DMSP:DMSO ratio ranged from 2 to 40. The quantifications were conducted with different mixtures of DMSP and DMSO by measurements of DMSP and DMSO in the same sample of P. oceanica leaf tissue. [less ▲]

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See detailAntarctic landfast sea ice: autotrophy vs heterotrophy, sink vs source of CO2
Van der Linden, Fanny ULiege; Moreau, Sébastien; Champenois, Willy ULiege et al

Conference (2018, June 20)

Sea ice is a biome actively participating in the regional cycling of CO2 as both a source and a sink at different times of the year depending on its trophic status (autotrophic vs heterotrophic). In the ... [more ▼]

Sea ice is a biome actively participating in the regional cycling of CO2 as both a source and a sink at different times of the year depending on its trophic status (autotrophic vs heterotrophic). In the frame of the YROSIAE project (Year-Round survey of Ocean-Sea-Ice-Atmosphere Exchanges), carried out at Cape Evans in McMurdo Sound (Antarctica) from Nov. 2011 to Dec. 2012, ice cores, seawater, and brines were collected at regular time intervals. We used dissolved inorganic carbon (DIC) and chlorophyll-a (chl-a) as proxies of net community production and autotrophic biomass, respectively. From spring, very high chl-a concentrations (>2400𝜇𝑔.𝐿!!) were observed at the bottom of the ice. This suggests high primary production. Strikingly, at the same time, nutrients increased significantly indicating strong remineralization at the bottom. In the ice interior, evolution of DIC was marked by a succession of autotrophic and heterotrophic phases. The overall increase of DIC suggests that the ice interior was rather heterotroph. Such sea ice system should expel CO2. Yet, strong under-saturation in CO2 and DIC depletion appeared at the ice surface, suggesting that sea ice should take up CO2 from the atmosphere. On the whole, land fast sea ice in McMurdo Sound appears as a puzzling ecosystem. High primary production and remineralization develop simultaneously at the bottom while the top of the ice is rather heterotrophic but still able to pump CO2 from the atmosphere. [less ▲]

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See detailPAM fluorometry research in Posidonia oceanica
Richir, Jonathan ULiege; Abadie, Arnaud ULiege; Borges, Alberto ULiege et al

Scientific conference (2018, April 26)

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See detailEtude de la photosynthèse de Posidonia oceanica par fluorimétrie modulée
Richir, Jonathan ULiege; Abadie, Arnaud; Borges, Alberto ULiege et al

Conference (2018, April 10)

Numerous methods for measuring seagrass productivity and growth exist: evolution of O2 or CO2 (incubation chambers, optodes), biomass, shoot leaf elongation, determination of elementary contents … Another ... [more ▼]

Numerous methods for measuring seagrass productivity and growth exist: evolution of O2 or CO2 (incubation chambers, optodes), biomass, shoot leaf elongation, determination of elementary contents … Another possible method relies on pulse amplitude modulation fluorometry (PAM). This technique allows the determination of the photosynthetic quantum yield (Yield) from fluorescence re-emitted by chlorophyll a before and after the application of a saturating light pulse. The Yield determined along a gradient of irradiance draws a light curve (RLC, Rapid Light Curve) similar to photosynthesis-irradiance curves. Since spring 2015 several measurements of Posidonia oceanica photosynthetic activity have been performed at STARESO using diving-PAM fluorometers, for multiple related purposes. The results of these works show that: (i) the absorbance of light by P. oceanica leaves is lower than the average value of terrestrial plants, (ii) the Yield remains constant, being influenced neither by season nor by depth and only the strong light intensities at shallow depths cause its decrease (photoinhibition), (iii) RLCs highlight the high photochemical plasticity of the plant to environmental conditions, (iv) the maximum electron transfer rate modelled from RLCs seems to be a good indicator of the average elongation of shoot leaves and hence of shoot growth and (v) photosynthesis as a biomarker responds to short-term Cu exposures at environmentally relevant levels. Posidonia oceanica photosynthetic activity, which will further be monitored during an in situ shading experiment, is studied in parallel with the development of a new generic biomarker of stress, the ratio of concentrations of organosulfured coumpounds in the plant (dimethylsulfonioproprionate, DMSP and dimethylsulfoxide, DMSO). In conclusion, whether the scientific issue is ecophysiological, environmental, ecotoxicological, PAM fluorometry is a technical approach to consider. [less ▲]

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See detailEtude des séries temporelles : exemple de la température de l’eau
Richir, Jonathan ULiege; Borges, Alberto ULiege; Champenois, Willy ULiege et al

Conference (2018, April 10)

De nombreux paramètres biologiques, environnementaux, climatologiques sont mesurés à et par STARESO depuis des décennies. Les données récoltées sont accessibles via la base de données partagée RACE de ... [more ▼]

De nombreux paramètres biologiques, environnementaux, climatologiques sont mesurés à et par STARESO depuis des décennies. Les données récoltées sont accessibles via la base de données partagée RACE de l’Université de Liège. Dans le cas de séries temporelles, les paramètres suivis sont mesurés de manière séquentielle au cours du temps. La plus représentative est sans aucun doute la série des données de température de l’eau acquise depuis près de 40 ans. La température est un paramètre important qui permet de mettre en évidence sur le long-terme des changements notamment liés au réchauffement climatique, changements qui affectent le fonctionnement des océans tant dans la physique que dans la biologie. L’analyse des séries temporelles de données nécessitent souvent un important travail préparatoire de standardisation (intervalles de mesure irréguliers, trous dans la série, évolution des méthodes d’acquisition des données …). Une fois standardisées, les séries de données peuvent être analysées avec les outils et approches statistiques propres aux séries temporelles : décomposition de la série pour en extraire la tendance générale, statistiques glissantes, calcul des anomalies, analyse des quantiles, mise en évidence d’évènements extrêmes tels les vagues de chaleurs … Tout ce travail, conséquent, doit pouvoir être partagé, vérifié, validé et permettre la mise à jour ultérieure de l’analyse. C’est le concept même de science reproductible. Cette reproductibilité est rendue notamment possible par l’utilisation du langage de programmation R. Cette communication illustre, à travers l’exemple clef de l’évolution de la température de l’eau, l’analyse des séries temporelles de données dans le cadre de STARECAPMED. [less ▲]

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See detailAnnual cycle of dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO) related to phytoplankton succession in the Southern North Sea
Speeckaert, Gaëlle ULiege; Borges, Alberto ULiege; Champenois, Willy ULiege et al

in Science of the Total Environment (2018), 10.1016/j.scitotenv.2017.11.359

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See detailPreservation protocol for dimethylsulfoniopropionate and dimethylsulfoxide analysis in plant material of the Mediterranean seagrass Posidonia oceanica, and re-evaluation of dimethylsulfoniopropionate leaf content
Borges, Alberto ULiege; Champenois, Willy ULiege

in Aquatic Botany (2017), 143C

We tested three treatments to preserve Posidonia oceanica leaves for the analysis of dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO): oven dried at 60 °C for 24 h, frozen at −20 °C, and ... [more ▼]

We tested three treatments to preserve Posidonia oceanica leaves for the analysis of dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO): oven dried at 60 °C for 24 h, frozen at −20 °C, and frozen-in-ice and kept at −20 °C. The DMSP content was analyzed by proxy as dimethylsulfide (DMS) by gas chromatography after alkaline cleavage at room-temperature. The DMSP leaf content of P. oceanica in samples that were oven dried at 60 °C for 24 h, then stored at room temperature decreased by 87% over 80 days of storage and then remained stable for about 88 additional days compared to the control. The DMSO leaf content of P. oceanica in samples that were oven dried increased nine-fold after 198 days of storage following drying compared to the control. Both the DMSP and DMSO leaf content of P. oceanica remained stable for 198 days compared to the control with frozen and frozen-in-ice treatments, which we both recommend as adequate protocols to preserve P. oceanica tissues for DMS(P,O) analysis. The annual average DMSP leaf content of P. oceanica at 10 m in the Bay of Calvi (Corsica, France) was 205 ± 58 μmol g−1 (fresh weight) based on samples preserved frozen, two orders of magnitude higher than the value we previously reported based on samples that were oven dried. The newly determined DMSP leaf content allows ranking P. oceanica as the highest DMSP producer reported to date among marine and inter-tidal autotrophs. [less ▲]

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See detailNatural patches in Posidonia oceanica meadows: the seasonal biogeochemical pore water characteristics of two edge types
Abadie, Arnaud ULiege; Borges, Alberto ULiege; Champenois, Willy ULiege et al

in Marine Biology (2017), 164:166

Seagrass meadows can be assimilated to seascape matrixes encompassing a mosaic of natural and anthropogenic patches. Natural patches within the Mediterranean Posidonia oceanica meadows show a structural ... [more ▼]

Seagrass meadows can be assimilated to seascape matrixes encompassing a mosaic of natural and anthropogenic patches. Natural patches within the Mediterranean Posidonia oceanica meadows show a structural particularity which consist in a duality of their edge types. One edge is eroded by bottom currents, while the adjacent meadow colonizes the bare sediments. This study aims to study the dynamics of these two edges through the investigation of the biogeochemistry (pH, total alkalinity, dissolved inorganic carbon, CO2, CH4, N2O, H2S, dissolved inorganic nitrogen, PO4 3−) within vegetated and unvegetated sediments. These observations are compared with the adjacent meadow to have a better understanding of the colonization processes. Our results reveal that the P. oceanica matrix shows differences from the vegetated edges of sand patches, especially with regard to nutrient availability, which is generally more important at the colonized edge (dissolved inorganic nitrogen up to 65.39 μM in June). A clear disparity also occurs between the eroded and colonized edge with both a seasonal and bathymetrical variation of leaf biomass with higher disparities at 10 m in June (colonized edge 1415 gDW m−2; eroded edge 1133 gDW m−2). Themost important contrasts during this study were assessed in June, suggesting that the warm period of the year is more suitable for sampling to highlight disparate characteristics in temperate seagrass meadows. These findings put into light the potential importance of biogeochemical processes in the dynamics of natural patch edges. We hypothesize that they may influence the structural dynamics of P. oceanica seascapes. [less ▲]

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See detailAntarctic sea ice trophic status
Van der Linden, Fanny ULiege; Moreau, Sébastien; Champenois, Willy ULiege et al

Poster (2017, July)

The sea ice ecosystem is characterized by steep gradients in temperature, salinity, light and nutrient availability. Despite these challenging environmental conditions, sea ice provides a dynamic habitat ... [more ▼]

The sea ice ecosystem is characterized by steep gradients in temperature, salinity, light and nutrient availability. Despite these challenging environmental conditions, sea ice provides a dynamic habitat for diverse communities of microorganisms. These communities include a wide variety of organisms from different taxonomic groups such as algae, bacteria, heterotrophic protists, fungi as well as viruses [Horner et al., 1992; Deming, 2010; Thomas and Dieckmann, 2010; Poulin et al., 2011]. In the frame of the YROSIAE project (Year-Round survey of Ocean-Sea-Ice-Atmosphere Exchanges), carried out at Cape Evans in McMurdo Sound (Antarctica) from Nov. 2011 to Dec. 2012, ice cores, seawater, and brine material were collected at regular time intervals. Physical properties (salinity, temperature, texture) and biogeochemical parameters (pCO2, dissolved inorganic carbon, total alkalinity, chlorophyll-a, macro-nutrients) were analysed. We will here particularly consider changes inused dissolved inorganic carbon (DIC) and chlorophyll-a (chl-a) , used as a proxiesy of net community production and autotrophic biomass, respectively. A high spatial and temporal variability in ice algal biomass and DIC evolution were observed. From spring, very high chl-a concentrations (>2400μg.L^(-1)) were observed at the bottom of the ice, a common feature of land fast ice in the McMurdo Sound. This suggests high primary production. However Strikingly, , at the same time, nutrients at the bottom of the ice increased significantly suggesting high heterotrophyremineralisation. In the middle of the ice column, evolution of DIC is was marked by a succession of autotrophic and heterotrophic phases. The overall increase of DIC suggests that the ice interior was rather heterotroph. Such sea ice system should expel CO2. Yet, strong under-saturation in CO2 and DIC depletion appeared at the ice surface, suggesting that sea ice was taking up CO2 from the atmosphere. On the whole, land fast sea ice in McMurdo Sound appears as a puzzling ecosystem. It is able to support elevated growth of autotrophic organisms at the bottom, but still appears to be heterotrophicin parallel to high remineralization, while the top of the ice appears to be rather heterotrophic but stilland able to pump CO2 from the atmosphere. [less ▲]

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See detailProductivity and temperature as drivers of seasonal and spatial variations of dissolved methane in the Southern Bight of the North Sea
Borges, Alberto ULiege; Speeckaert, Gaëlle ULiege; Champenois, Willy ULiege et al

in Ecosystems (2017), doi:10.1007/s10021-017-0171-7

Dissolved CH4 concentrations in the Belgian coastal zone (North Sea) ranged between 670 nmol L-1 near-shore and 4 nmol L-1 off-shore. Spatial variations of CH4 were related to sediment organic matter (OM ... [more ▼]

Dissolved CH4 concentrations in the Belgian coastal zone (North Sea) ranged between 670 nmol L-1 near-shore and 4 nmol L-1 off-shore. Spatial variations of CH4 were related to sediment organic matter (OM) content and gassy sediments. In near-shore stations with fine sand or muddy sediments, the CH4 seasonal cycle followed water temperature, suggesting methanogenesis control by temperature in these OM rich sediments. In off-shore stations with permeable sediments, the CH4 seasonal cycle showed a yearly peak following the Chlorophyll-a spring peak, suggesting that in these OM poor sediments, methanogenesis depended on freshly produced OM delivery. This does not exclude the possibility that some CH4 might originate from dimethylsulfide (DMS) or dimethylsulfoniopropionate (DMSP) or methylphosphonate transformations in the most off-shore stations. Yet, the average seasonal CH4 cycle was unrelated to those of DMS(P), very abundant during the Phaeocystis bloom. The annual average CH4 emission was 126 mmol m-2 yr-1 in the most near-shore stations (~4 km from the coast) and 28 mmol m-2 yr-1 in the most off-shore stations (~23 km from the coast), 1,260 to 280 times higher than the open ocean average value (0.1 mmol m-2 yr-1). The strong control of CH4 by sediment OM content and by temperature suggests that marine coastal CH4 emissions, in particular in shallow areas, should respond to future eutrophication and warming of climate. This is supported by the comparison of CH4 concentrations at five stations obtained in March 1990 and 2016, showing a decreasing trend consistent with alleviation of eutrophication in the area. [less ▲]

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See detailCopper toxicity on coral holobiont photosynthetic processes
Georges, Nadège; Richir, Jonathan ULiege; Batigny, Antoine et al

Poster (2016, December 16)

Copper (Cu), an essential micronutrient to organisms, may become toxic when present at too high environmental concentrations. This metal remains an aquatic contaminant of concern, notably because of its ... [more ▼]

Copper (Cu), an essential micronutrient to organisms, may become toxic when present at too high environmental concentrations. This metal remains an aquatic contaminant of concern, notably because of its recent re-use as biocide in metal-based antifouling paints. The aim of this study was to monitor the physiological alterations in a zooxanthellate coral species and its endosymbionts (i.e. the coral holobiont) exposed to increasing Cu concentrations. Nubbins of Seriatopora hystrix were exposed for 8 days in 1 L intermittent respirometers to 5 nominal Cu concentrations: 0-2-5-15-50 ppb. Respirometers were maintained at 25.0±0.2°C with successive open/close cycles of 30 min. A 12/12 hours day-night light regime was applied with constant daylight intensity of 200 μmol photons m-2 s-1. Water renewal rate during the 30 min open cycles was 15 mL.min-1. The photosynthetic performances of coral endosymbionts were assessed daily with a fluorescence imaging system (imaging-PAM). At the end of the 8-days experiment, the maximal photochemical quantum yield (FV/FM) of coral nubbins had decreased by 12% and 38%, respectively, in the 15 ppb and 50 ppb treatments. This decrease was even greater for the effective photochemical quantum yield (ɸPSII) with values dropping by 41% and 54%, respectively. Cu exposure also affected the symbiosis between the coral host and its endosymbionts. Nubbins of the 15 ppb treatment slightly lightened from day 6, whilst nubbins exposed to the 50 ppb treatment lightened from day 3, and started to bleach from day 6. The analysis of nubbins’ primary productivity did not coincide with the above observations, the oxygen production within each respirometer remaining relatively constant during the overall experiment for all treatments. This unexpected observation may be the sign of a compensation mechanism. In conclusion, Cu affected the photosynthetic processes of S. histrix within 8 days from relevant environmental concentrations of 15 ppb. The exposure of corals to toxic chemicals thus has to be considered as an additional stressor to, e.g., ocean acidification or elevated temperature, which may disturb their ecophysiology and lead to bleaching. [less ▲]

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See detailEcoNum, a research unit devoted to marine environment monitoring
Richir, Jonathan ULiege; Batigny, Antoine; Georges, Nadège et al

Conference (2016, October 27)

The monitoring of coastal environments remains a research domain of great interest and concern. Coastal ecosystems are threatened by natural and human-induced stressors and are, as transitional ... [more ▼]

The monitoring of coastal environments remains a research domain of great interest and concern. Coastal ecosystems are threatened by natural and human-induced stressors and are, as transitional environments, particularly sensitive to disturbances. EcoNum first research thematic revolves around hermatypic corals, calcifying organisms, and their adaptation potentials to environmental changes including by using original and patented chemostats. The studied organisms are grown and maintained in artificial mesocosms that simulate environmental conditions of a natural system. This infrastructure allows to perform long-term experiments, giving time to organisms to adapt to the tested conditions (e.g., increased temperature or lowered pH). Longer-term studies have demonstrated that many organisms are more resistant to environmental stressors than previously observed on the short-term. EcoNum also studies coastal plankton abundance and diversity. Plankton is particularly sensitive to physicochemical changes of water bodies. The classification and the enumeration of planktonic organisms require specialized tools in order to analyse time series of multiple samples. EcoNum has developed a software for the semi-automatic classification of planktonic organisms called Zoo/PhytoImage. This software has been used to study a 10-year time series of coastal Mediterranean zooplankton samples. The concomitant analysis of environmental parameters registered at high frequency with specific statistical tools such as the R package pastecs allows to understand the processes governing the changes observed in plankton assemblages. The use and the development of statistical tools in R (e.g., Zoo/Phytoimage, pastecs) is a priority of EcoNum to favour open access knowledge and reproductive sciences. EcoNum research topics also focus on coastal ecotoxicology. Chemicals, including trace elements, remain contaminants of concern, mainly in coastal environments that are the final sink of inland pollution sources. The chemical integrity of coastal ecosystems thus has to be accurately monitored. The partitioning of chemicals between their dissolved, particulate and sedimentary phases does not provide information on their bioavailability. EcoNum thus monitors coastal waters using bioindicator species such as seagrasses, mussels or sand worms. A global map of the contamination of the Mediterranean by trace elements has been drawn using seagrasses has bioindicator species. EcoNum also studies trace element ecology and toxicology. For instance, it has demonstrated the toxicity of copper on the coral Seriatopora hystrix and it's symbiont's photosynthetic processes, or its bioaccumulation and basipetal translocation towards rhizomes in the seagrass Posidonia oceanica as reserve nutrient for subsequent leaf growth. Finally, coastal vegetated systems are potential carbon thinks (or sources) in the global carbon cycle. Therefore, EcoNum studies the primary productivity of seagrass meadows, from the individual to the community, with measuring techniques as diverse as PAM-fluorometry or biomass production determination. To conclude, EcoNum is a research unit devoted to marine environment monitoring. It develops research thematics on major coastal communities such as coral reefs, seagrass beds or plankton assemblages and studies their natural dynamics and the effects of stressors on their global functioning. [less ▲]

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See detailHighly productive, yet heterotrophic, and still pumping CO2 from the atmosphere: A land fast ice paradigm?
Delille, Bruno ULiege; Van der Linden, Fanny ULiege; Conte, L et al

Conference (2016, October 21)

The YROSIAE (Year Round survey of Ocean-Sea Ice-Air Exchanges) survey aimed to carry out a year-round survey of land-fast sea ice focusing on the study of sea ice physics and biogeochemistry. Ice cores ... [more ▼]

The YROSIAE (Year Round survey of Ocean-Sea Ice-Air Exchanges) survey aimed to carry out a year-round survey of land-fast sea ice focusing on the study of sea ice physics and biogeochemistry. Ice cores, sea water, brines material were collected at regular intervals about 1 km off cape Evans in McMurdo Sound, Antarctica, from November 2011 to December 2011 and from September 2012 to December 2012. Samples were processed to characterize both the vertical distribution and temporal changes of climate gases (CO2, DMS, CH4, N2O), CO2-related parameters (ice-air CO2 fluxes, dissolved inorganic carbon, total alkalinity and CaCO3 amount), physical parameters (salinity, temperature, and ice texture), biogeochemical parameters (macro-nutrients, particulate and dissolved organic carbon, δ13C, δ30Si and δ15N) and biological parameters (chlorophyll a, primary production within sea ice derived from O2:Ar and O2:N ratios…). Very high chlorophyll a abundance was observed at the bottom of the ice, a common feature of land fast ice in McMurdo Sound. During spring, chlorophyll a exhibited a significant increase suggesting high primary production. . However, at the same time, nutrients at the bottom of the ice increased significantly suggesting high remineralization and heterotrophy. In the middle of the ice column, evolution of dissolved inorganic carbon shown a succession of autotrophic and heterotrophic phases. However, the overall increase of DIC suggests that the ice interior was rather heterotroph. This was consistent with the increase in nutrients observed at the bottom of the ice. Such sea ice system should expel CO2. Yet, strong under saturation in CO2 in surface ice, and negative air-ice CO2 fluxes suggested that sea ice was taking up CO2 from the atmosphere. Meanwhile, measurements of N2O within the sea ice suggest that the ice was releasing N2O to the atmosphere as a result of high nitrification. On the whole land fast sea ice in McMurdo Sound appears as a puzzling ecosystem. It is able to support elevated growth of autotrophic organisms, but appears to be heterotrophic, yet pumping CO2 to the atmosphere but releasing other greenhouse gases. [less ▲]

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See detailDiversity, dynamics and trophic ecology of animal communities associated to Posidonia oceanica (L.) Delile macrophytodetrital accumulation: synthesis of a ten year study
Lepoint, Gilles ULiege; Borges, Alberto ULiege; Champenois, Willy ULiege et al

Poster (2016, October 17)

In the Mediterranean, Neptune grass Posidonia oceanica, produces a huge quantity of detrital biomass. These macrophytodetritus may accumulate in shallow waters, forming litter accumulations colonised by ... [more ▼]

In the Mediterranean, Neptune grass Posidonia oceanica, produces a huge quantity of detrital biomass. These macrophytodetritus may accumulate in shallow waters, forming litter accumulations colonised by abundant, yet understudied, animal communities. These accumulations are especially foraged by juvenile and adult fishes. Here, we aim to synthesize results obtained over the last ten years regarding diversity, dynamics and trophic ecology of associated meio- and macrofauna. Accumulations are found throughout the year but important seasonal and short-term variability in composition, quantity and physico-chemical parameters inside the accumulation is observed. Accumulations are dominated by respiration (litter degradation), however, primary production occurs at exposed surfaces (epiphytic production). Meio- and macrofauna have distinct traits in comparison to adjacent habitats (seagrass meadows or epilithic algae communities). A physico-chemical gradient occurs inside accumulations which partially defines assemblage composition and distribution. Meiofauna, in particular harpacticoid copepods, is diverse, abundant and composed of species from seagrass meadows, water column and sediment. In contrast, macrofaunal assemblages are simplified compared to the ones occurring in the seagrass meadows and are dominated by amphipods. Litter accumulations display a lower macrofaunal diversity than do seagrass meadows, but a higher abundance and animal biomass. Meio- and macrofauna show a high trophic diversity, dominated by ingestion and assimilation of epiphytes (macroalgae and, probably, detrivorous microbiota). Moreover, direct or indirect assimilation of carbon originating from seagrass detritus is demonstrated for many species. Although diverse trophic niches were observed, the assemblage showed a simplified trophic web structure compared to the seagrass meadows. Detritivorous organisms dominate this assemblage and are more abundant in the litter than in the living meadows. Consequently, according to its abundance and the fact it consumes directly and indirectly seagrass material, fauna associated to litter accumulation may play a significant role in the degradation and transfer to higher trophic level of detrital seagrass carbon. [less ▲]

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