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See detailFood sources of two detritivore amphipods associated with the seagrass Posidonia oceanica leaf litter
Lepoint, Gilles ULg; Cox, Anne-Sophie; Dauby, Patrick ULg et al

in Marine Biology Research (2006), 2(5), 355-365

This study focused on the ingestion and assimilation of Posidonia oceanica (L.) Delile litter by Gammarella fucicola Leach and Gammarus aequicauda Martynov, two dominant detritivore amphipods of the P ... [more ▼]

This study focused on the ingestion and assimilation of Posidonia oceanica (L.) Delile litter by Gammarella fucicola Leach and Gammarus aequicauda Martynov, two dominant detritivore amphipods of the P. oceanica leaf litter. Scanning electron microscope observations indicated that leaf litter is highly colonized by diverse diatoms, bacteria and fungi, which may constitute a potential food source for the litter fauna. Gut content observations demonstrated that these species eat P. oceanica litter, and that this item is an important part of their ingested diet. Stable isotope analyses showed that the species do not experience the same gains from the ingested Posidonia. Gammarella fucicola displayed isotopic values, suggesting a major contribution of algal material (micro- and macro-epiphytes or drift macro-algae). On the other hand, the observed isotopic values of G. aequicauda indicated a more important contribution of P. oceanica carbon. The mixing model used agreed with this view, with a mean contribution of P. oceanica to approximately 50% (range 40-55%) of the assimilated biomass of G. aequicauda. This demonstrated that the two species, suspected to be detritus feeders, display in reality relatively different diets, showing that a certain degree of trophic diversity may exist among the detritivore community of the seagrass litter. [less ▲]

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See detailTrophic diversity and potential role of detritivorous crustaceans in Posidonia oceanica litter
Sturaro, Nicolas ULg; Gobert, Sylvie ULg; Cox, Anne-Sophie et al

Conference (2006, June)

Detrivorous crustaceans are pivotal components of the trophic food webs and are found to be the main constituents of the macrofauna in Posidonia oceanica litter. The coexistence of many of these species ... [more ▼]

Detrivorous crustaceans are pivotal components of the trophic food webs and are found to be the main constituents of the macrofauna in Posidonia oceanica litter. The coexistence of many of these species in the same biotope raises the question of trophic diversity and of its role in litter degradation process. Diet composition of five common species of detrivorous crustaceans in P. oceanica litter (i.e. the gammarid amphipods Gammarella fusicola and Gammarus aequicauda and the isopods Idotea baltica, Idotea hectica and Zenobiana prismatica) were studied using a combination of gut content and stable isotopes analysis. Despite the common food supply (i.e. Posidonia dead leaf, Posidonia epiphytes or drift macroalgae), there were considerable interspecific differences in diet composition. Gut content observations indicate that P. oceanica leaf litter is an important part of the ingested food of all the species. Algae material (macroepiphytes and drift macroalgae) inhabiting the litter is mainly found in G. fusicola, I. hectica and I. baltica. I. baltica displays a high proportion of crustacean fragments. Isotope ratios showed that most of the species do not assimilate much of the ingested Posidonia. Application of a mixing model using isotopic values to estimate the contribution of the potential different food sources confirms this view. On one hand, the tissue of G. aequicauda could be constituted by more than 50 % of P. oceanica carbon. On the other hand, for the other species studied, P. oceanica represented a minor contribution (10 - 30 %), although it is a major component of the gut contents. This could imply that micro-organism (diatoms, bacteria and fungi) living on the Posidonia detritus is a major food source of detrivorous. Moreover, I. baltica, Z. prismatica and G. fusicola have a diversified diet composed mainly of algae. Crustaceans are an important food source for I. baltica. By contrast, I. hectica indicated a major contribution of algae material. Our results demonstrate the trophic diversity existing between the detrivorous crustaceans species in P. oceanica litter. This trophic diversity is probably one of the factors that allows these species to coexist in the same biotope. The results also underline the potential role of these species in the degradation of P. oceanica litter by fragmenting mechanically the Posidonia detritus and by assimilating directly Posidonia carbon and transferring it to higher trophic level (i.e. coastal fishes). Moreover, it allows us to think that micro-organisms (diatoms, bacteria and fungi) colonising leaf litter may constitute an important food source for litter fauna. [less ▲]

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See detailIn situ sampling of pore waters from seagrass meadows
Gobert, Sylvie ULg; Lepoint, Gilles ULg; Biondo, Renzo ULg et al

in Biologia Marina Mediterranea (2006), 13

A routine and low cost method to collect pore water in a seagrass meadow in situ and underwater is here proposed. The method consists of direct-suction filtered sampling allowing the determination of ... [more ▼]

A routine and low cost method to collect pore water in a seagrass meadow in situ and underwater is here proposed. The method consists of direct-suction filtered sampling allowing the determination of nutrient concentrations in the sampled water. Data ranges of nutrient (NO2-+NO3-; HPO4 2- and NH4+) concentrations in a P. oceanica meadow are also discussed [less ▲]

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See detailTrace Metal Concentrations in Posidonia Oceanica of North Corsica (Northwestern Mediterranean Sea): Use as a Biological Monitor?
Gosselin, Marc; Bouquegneau, Jean-Marie ULg; Lefèbvre, Frédéric et al

in BMC Ecology (2006), 6

BACKGROUND: Within semi-closed areas like the Mediterranean Sea, anthropic wastes tend to concentrate in the environment. Metals, in particular, are known to persist in the environment and can affect ... [more ▼]

BACKGROUND: Within semi-closed areas like the Mediterranean Sea, anthropic wastes tend to concentrate in the environment. Metals, in particular, are known to persist in the environment and can affect human health due to accumulation in the food chain. The seagrass Posidonia oceanica, widely found in Mediterranean coastal waters, has been chosen as a "sentinel" to quantify the distribution of such pollutants within the marine environment. Using a technique similar to dendrochronology in trees, it can act as an indicator of pollutant levels over a timeframe of several months to years. In the present study, we measured and compared the levels of eight trace metals (Cr, Ni, Cu, Zn, As, Se, Cd, and Pb) in sheaths dated by lepidochronology and in leaves of shoots sampled from P. oceanica meadows collected from six offshore sites in northern Corsica between 1988 and 2004; in the aim to determine 1) the spatial and 2) temporal variations of these metals in these areas and 3) to compared these two types of tissues. RESULTS: We found low trace metal concentrations with no increase over the last decade, confirming the potential use of Corsican seagrass beds as reference sites for the Mediterranean Sea. Temporal trends of trace metal concentrations in sheaths were not significant for Cr, Ni, Cu, As or Se, but Zn, Cd, and Pb levels decreased, probably due to the reduced anthropic use of these metals. Similar temporal trends between Cu levels in leaves (living tissue) and in sheaths (dead tissue) demonstrated that lepidochronology linked with Cu monitoring is effective for surveying the temporal variability of this metal. CONCLUSION: Leaves of P. oceanica can give an indication of the metal concentration in the environment over a short time period (months) with good accuracy. On the contrary, sheaths, which gave an indication of changes over long time periods (decades), seem to be less sensitive to variations in the metal concentration in the environment. Changes in human consumption of metals (e.g., the reduction of Pb in fuel) are clearly reflected in both organs. These results confirm that P. oceanica is a good bioindicator of metals and a good biomonitor species for assessing Cu in the environment. [less ▲]

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See detailBiology of Posidonia
Gobert, Sylvie ULg; Cambridge, M. L.; Velimirov et al

in Larkum, Anthony WD; Orth, Robert J; Duarte, Carlos M (Eds.) Seagrasses: Biology, Ecology and Conservation (2006)

The aim of this chapter is to place emphasis on the dynamics of Posidonia systems in order to detect key ecosystem processes and to put in evidence the large differences between the Mediterranean and ... [more ▼]

The aim of this chapter is to place emphasis on the dynamics of Posidonia systems in order to detect key ecosystem processes and to put in evidence the large differences between the Mediterranean and Australian systems. These key processes shall be the basis to formulate new working hypothesis in order to verify newly emerging concepts and propose management plans in order to ensure the sustainability of the system. [less ▲]

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See detailDescriptors of Posidonia oceanica meadows: Use and application
Pergent-Martini, Christine; Leoni, Vanina; Pasqualini, Vanina et al

in Ecological Indicators (2005), 5(3), 213-230

The conservation of the coastal marine environment requires the possession of information that enables the global quality of the environment to be evaluated reliably and relatively quickly. The use of ... [more ▼]

The conservation of the coastal marine environment requires the possession of information that enables the global quality of the environment to be evaluated reliably and relatively quickly. The use of biological indicators is often an appropriate method. Seagrasses in general, and Posidonia oceanica meadows in particular, are considered to be appropriate for biomonitoring because of their wide distribution, reasonable size, sedentary habit, easy collection and abundance and sensitivity to modifications of littoral zone. Reasoned management, on the scale of the whole Mediterranean basin, requires standardized methods of study, to be applied by both researchers and administrators, enabling comparable results to be obtained. This paper synthesises the existing methods applied to monitor P. oceanica meadows, identifies the most suitable techniques and suggests future research directions. From the results of a questionnaire, distributed to all the identified laboratories working on this topic, a list of the most commonly used descriptors was drawn up, together with the related research techniques (e.g. standardization, interest and limits, valuation of the results). It seems that the techniques used to study meadows are rather similar, but rarely identical, even though the various teams often refer to previously published works. This paper shows the interest of a practical guide that describes, in a standardized way, the most useful techniques enabling P. oceanica meadows to be used as an environmental descriptor. Indeed, it constitutes the first stage in the process. (c) 2005 Elsevier Ltd. All rights reserved. [less ▲]

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See detailRestoration of Posidonia oceanica meadows : means and limitations.
Gobert, Sylvie ULg; Lepoint, Gilles ULg; Bouquegneau, Jean-Marie ULg et al

in Proceedings of the seventh international conference on the Mediterranean coastal environment. Medcoast 05 (2005)

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See detailTemporal evolution of sediment supply in Lago Puyehue (Southern Chile) during the last 600 yr and its climatic significance
Bertrand, S.; Boes, X.; Castiaux, J. et al

in Quaternary Research (2005), 64(2), 163-175

Short-term climate changes in Southern Chile are investigated by a multi-proxy analysis of a 53-cm-long sedimentary sequence selected among eight short cores retrieved in Lago Puyehue (Chile, 40 degrees S ... [more ▼]

Short-term climate changes in Southern Chile are investigated by a multi-proxy analysis of a 53-cm-long sedimentary sequence selected among eight short cores retrieved in Lago Puyehue (Chile, 40 degrees S). This core contains a 600-yr-long undisturbed record of paleo-precipitation changes. Two measurement methods for sediment density, organic matter and biogenic silica contents are compared and the most appropriate techniques are selected. Together with aluminium and titanium concentrations, grain size and geochemical properties of the organic matter, these proxies are used to demonstrate paleo-precipitation changes around 40 degrees S. Increase of terrigenous particle supply between A.D. 1490 and A.D. 1700 suggests a humid period. Contemporaneously, delta C-13 data show increasing lake productivity, in response to the high nutrient supply. The A.D. 1700-1900 interval is characterized by a decreasing terrigenous supply and increasing delta C-13 values, interpreted as a drying period. The magnetic susceptibility signal, reflecting the terrigenous/biogenic ratio, demonstrates that similar variations occur in all the undisturbed sedimentary environments of Lago Puyehue. The A.D. 1490-1700 wet period is associated with the onset of the European Little Ice Age (LIA) and interpreted as its local signature. This work supports the fact that the LIA was a global event, not only restricted to the Northern Hemisphere. (c) 2005 University of Washington. All rights reserved. [less ▲]

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See detailC, N, P concentrations and requirements of flowering Posidonia oceanica shoots
Gobert, Sylvie ULg; Lejeune, Pierre; Lepoint, Gilles ULg et al

in Hydrobiologia (2005), 533

The carbon, nitrogen and phosphorus contents in flowering and nonflowering shoots were compared after an important flowering event occurred in the Posidonia meadow of the Bay of Calvi. The flower ... [more ▼]

The carbon, nitrogen and phosphorus contents in flowering and nonflowering shoots were compared after an important flowering event occurred in the Posidonia meadow of the Bay of Calvi. The flower formation caused a significant increase of C and a significant decrease of N concentrations in intermediate and adult leaves. Minimum daily requirements in mg shoot(-1) day(-1) of 3.4 and 4.8 of C, 0.09 and 0.09 N, 0.01 and 0.02 of P respectively for nonflowering and flowering shoots were calculated. It shows that additional quantities of C and P are required for the inflorescence elaboration. The unchanged quantity of N required by the shoot for the inflorescence elaboration and the significant modification of N concentration in intermediate and adult leaves suggests that N is limited in the environment and that an efficient resorption of N occurs from leaves to ensure the inflorescence formation. [less ▲]

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See detailPreliminary insights in the feeding ecology of marine mammals from the Ligurian Sea through stable isotope and mercury measurements
Miglio, C.; Das, Krishna ULg; Lepoint, Gilles ULg et al

Poster (2005)

The Ligurian Sea, part of the Cetacean Sanctuary, is known to be a productive area hosting many marine mammal species of the Mediterranean Sea. Investigations on trophic relationship and pollutant ... [more ▼]

The Ligurian Sea, part of the Cetacean Sanctuary, is known to be a productive area hosting many marine mammal species of the Mediterranean Sea. Investigations on trophic relationship and pollutant monitoring are of primary importance for their conservation. As isotopic composition of an animal is related to that of its prey, ð13C and ð15N were measured by mass spectrometry in muscle of 12 striped dolphins (Stenella coeruleoalba), 1 bottlenose dolphin (Tursiops truncatus), 2 fin whales (Balaenoptera physalus), 3 Risso's dolphins (Grampus griseus), 1 Cuvier's beaked whale (Ziphius cavirostris) and 1 juvenile sperm whale (Physeter macrocephalus) stranded along the Ligurian coasts between 1991 and 2004. Hg concentration was also analysed in marine mammal liver by spectrometric absorption. Through ð13C and ð15N measurements, two marine mammal groups appeared: the first group characterised by high ð13C and ð15N values (mean values: -17.5‰ and 11.0‰ respectively) included the sperm whale, the bottlenose dolphin, the Risso’s dolphin and the beaked whale. The second group including striped dolphin and fin whale displayed lower mean ð13C than the first group (-18,48‰), with the fin whale showing the lowest ð15N value (8,8‰ ± 0,7). Our isotopic data are in good agreement with previously described feeding habits: the first group obviously fed at a higher trophic level and in more coastal waters associated with the continental slope while the second fed offshore, with the fin whale occupying the lowest trophic position. Hg concentrations reflected a similar pattern, with the lowest value observed in the fin whale (mean value: 0.1 µg.g-1 dw) and the highest in both the bottlenose dolphin (3769 µg.g-1 dw) and the Risso’s dolphin (1363 µg.g-1 dw). However, beside trophic position, numerous factors might be involved in Hg accumulation in marine mammals such as the age, body condition and specific metabolism. [less ▲]

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See detailMercury, polychlorobiphenyls and stable isotopes in the blood of harbour seals (Phoca vitulina) from the southern North Sea
Das, Krishna ULg; Lepoint, Gilles ULg; Fonfara, Sonja et al

Poster (2005)

The harbor seal (Phoca vitulina) is one of the most widely distributed seal species and the North Sea contains around 10 % of the world population. The harbour seal population in the North Sea was ... [more ▼]

The harbor seal (Phoca vitulina) is one of the most widely distributed seal species and the North Sea contains around 10 % of the world population. The harbour seal population in the North Sea was estimated at 36 000 individuals between 1994 and 1996). However, recurrent Phocine Distemper Virus (PDV) epizooties have affected the North Sea seal population. Recently, 21 500 harbor seals were killed by PDV in the North Sea and adjacent waters in 2002. Some intriguing questions about the interaction between PDV and immunotoxic contaminants, such as mercury (Hg) and polychlorinated biphenyls (PCBs) remain unanswered. In this framework, circulating levels of Hg and PCBs (PCBs 28, 52, 101, 118, 138, 153, 180) were measured in the blood of 24 harbour seals captured on a sandbank between 2001 and 2004 (Schleswig-Holstein, Germany). As pollutant level may be linked to the trophic position in the food web, carbon and nitrogen isotopic ratios (δ13C and δ15N) were measured in clotted blood cells. The average concentration of mercury in these living seals did not differ significantly from those observed previously in stranded harbour seals (94 ± 41 vs 146 ± 71 µg.l-1 respectively). Mean blood concentrations of total PCBs (∑PCBs) were 11 ng/ml. CB 153 clearly dominated the mix (45%) followed by PCB 138 (31%). The average isotopic composition measured in the blood cells was –15.6 ± 0.3 0/00 and 18.7 ± 0.6 0/00 for δ13C and δ15N respectively, similar to that obtained previously in muscle of stranded individuals, confirming the high position of the harbour seal in the North Sea trophic chain. Further investigations are obviously needed on a larger sampling but our preliminary results suggest that blood is an interesting substrate for both trophic and pollutant long-term monitoring of the harbour seal in the North Sea. [less ▲]

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See detailStable isotopes and mercury in blood of harbour seals (Phoca vitulina) caught on a German sandbank
Di-Poi, C.; Siebert, Ursula; Drouguet, Olivier et al

Poster (2005)

More than 21 500 harbour seals were killed by Phocine Distempter Virus in the North Sea and adjacent waters in 2002. After the second seal die-off had ceased, seals were captured alive (and then released ... [more ▼]

More than 21 500 harbour seals were killed by Phocine Distempter Virus in the North Sea and adjacent waters in 2002. After the second seal die-off had ceased, seals were captured alive (and then released) on a sandbank (Schleswig-Holstein, Germany) for health and ecotoxicological investigations. Stable carbon and nitrogen ratios (δ13C and δ15N) were measured by mass spectrometry in clotted blood cells of 24 harbour seals captured between 2002 and 2003. Total mercury (Hg) concentrations were determined by spectrometric absorption in the whole blood of 8 harbour seals and compared to the Hg level measured in blood from 8 seals found stranded along the southern North Sea coast. The average isotopic composition measured in the blood cells was –15.6 ± 0.3 0/00 and 18.7 ± 0.6 0/00 for δ13C and δ15N respectively, similar to that obtained previously in muscle of stranded individuals, confirming the high position of the harbour seal in the trophic food chain. δ13C and δ15N values did not differ significantly between seals caught in November 2002, April 2003 and September 2003 suggesting similar diet throughout these 3 periods. The average concentration of mercury in whole blood of living and stranded harbour seals did not differ significantly (94 ± 41 vs 146 ± 71 µg.l-1 respectively). No biological parameters (weight, length, age status and stable isotopes ratios) seemed to influence these concentrations. Blood is known to reflect recent exposure to mercury through the diet. These preliminary results suggest that blood is an interesting substrate for both trophic studies and pollutant long-term monitoring of the harbour seal in the North Sea. [less ▲]

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See detailEcological and pathological factors related to trace metal concentrations in harbour seal Phoca vitulina in the North Sea
Drouguet, Olivier; Siebert, Ursula; Jauniaux, Thierry ULg et al

Poster (2005)

During the last decade, recurrent epizootics have affected harbour seal (Phoca vitulina) populations in the North Sea. Recent data on their trophic habits and pollutant levels are of primary importance ... [more ▼]

During the last decade, recurrent epizootics have affected harbour seal (Phoca vitulina) populations in the North Sea. Recent data on their trophic habits and pollutant levels are of primary importance for their conservation. As isotopic composition of an animal is related to that of its prey, δ13C and δ15N were measured by mass spectrometry in the muscles of 66 harbour seals beached along the coasts of France (n = 10), Belgium (n = 30) and Netherlands (n = 26) between 1994 and 2004. Trace metals concentrations (Zn, Cu, Fe, Cd, Hg and Se) were also determined in liver, kidney and muscles by Inducted Plasma Spectrometry. δ13C and δ15N values remained similar between harbour seals from France (-15.7 0/00; 18.7 0/00, respectively), Belgium (-15.7 0/00; 19.0 0/00, respectively) and Netherlands (-14.7 0/00; 18.7 0/00, respectively). These data are in good agreement with their coastal and piscivorous life style. Isotopic value remained similar between males and females and between body conditions. Hg levels were significantly higher in seals from the southern North Sea when compared to previously published data from seals collected in Norway, probably due some geographical differential exposure. Hepatic Hg was positively correlated to hepatic Se, both increasing with the length of the seals. Such a relationship reflected an age accumulation process coupled to a detoxication mechanism involving antagonism between Hg and Se in the liver. No relationship between stable isotopes and Hg and Cd levels was observed. Increasing Zn and Hg hepatic levels were observed with degrading body condition of the harbour seals, which is reflected by decreasing blubber thickness and high hepatic to total body mass ratio. These observations tend to indicate a global redistribution of trace metals from muscle and blubber to liver, as a result of protein and lipid catabolism linked to disease and starvation. [less ▲]

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See detailEffect of transplantation on Posidonia oceanica shoots
Vangeluwe, Denis; Lepoint, Gilles ULg; Bouquegneau, Jean-Marie ULg et al

in Vie et Milieu-Life and Environment (2004), 54(4), 223-230

Posidonia oceanica shoots sampled from the healthy meadow in the bay of Revelatta (Corsica, France) were transplanted on metallic grids at 10 m depth. Transplanted shoots have been regularly monitored by ... [more ▼]

Posidonia oceanica shoots sampled from the healthy meadow in the bay of Revelatta (Corsica, France) were transplanted on metallic grids at 10 m depth. Transplanted shoots have been regularly monitored by the measurement of growth, biomass and C, N and P contents in the leaves and the belowground parts. After six months of experiment, the survival rates varied from 14 to 84 % on the different transplantation sites. Leaf biomass on the transplanted cuttings was lower than biomass in the control shoots but root biomass raised from December 2000 to May 2001 on the transplanted shoots. Transplant growth (8,3 +/- 2,3 mm.d(-1).shoot(-1)) after six months was similar to control growth (8,2 +/- 2,8 mm.d(-1). shoot(-1)). The C, N and P contents in transplants were significatively lower than in control shoots suggesting that transplanted cuttings are unable to meet their nutrient requirements. The modifications of the C, N, P contents in the belowground parts of the transplanted shoots indicate a mobilization of these nutrients in those compartments to produce new roots and restore a normal nutrients absorption. [less ▲]

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See detailApplications of C and N stable isotopes to ecological and environmental studies in seagrass ecosystems
Lepoint, Gilles ULg; Dauby, Patrick ULg; Gobert, Sylvie ULg

in Marine Pollution Bulletin (2004), 49(11-12), 887-891

Stable isotopes of carbon and nitrogen are increasingly used in marine ecosystems, for ecological and environmental studies. Here, we examine some applications of stable isotopes as ecological integrators ... [more ▼]

Stable isotopes of carbon and nitrogen are increasingly used in marine ecosystems, for ecological and environmental studies. Here, we examine some applications of stable isotopes as ecological integrators or tracers in seagrass ecosystem studies. We focus on both the use of natural isotope abundance as food web integrators or environmental tracers and on the use of stable isotopes as experimental tools. As ecosystem integrators, stable isotopes have helped to elucidate the general structure of trophic webs in temperate, Mediterranean and tropical seagrass ecosystems. As environmental tracers, stable isotopes have proven their utility in sewage impact measuring and mapping. However, to make such environmental studies more comprehensible, future works on understanding of basic reasons for variations of N and C stable isotopes in seagrasses should be encouraged. At least, as experimental tracers, stable isotopes allow the study of many aspects of N and C cycles at the scale of a plant or at the scale of the seagrass ecosystem. (C) 2004 Elsevier Ltd. All rights reserved. [less ▲]

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See detailContributions of benthic and planktonic primary producers to nitrate and ammonium uptake fluxes in a nutrient-poor shallow coastal area (Corsica, NW Mediterranean)
Lepoint, Gilles ULg; Gobert, Sylvie ULg; Dauby, Patrick ULg et al

in Journal of Experimental Marine Biology and Ecology (2004), 302(1), 107-122

By using the stable isotope N-15, we have measured in situ the uptake of nitrate and ammonium by the seagrass Posidonia oceanica, its leaf epiphyte community, the brown macroalgae Halopteris scoparia and ... [more ▼]

By using the stable isotope N-15, we have measured in situ the uptake of nitrate and ammonium by the seagrass Posidonia oceanica, its leaf epiphyte community, the brown macroalgae Halopteris scoparia and the suspended particulate organic matter (SPOM). In Revellata Bay (Gulf of Calvi, Westem Corsica), which is a very nutrient-poor region, the specific uptake rates (V) (mug N g N 1 h(- 1)) of SPOM measured at ambient concentrations are 10-1000 higher than those of benthic primary producers. Macroalgae have intermediary v, between the seagrass leaf and leaf epiphytes. V are quite variable and the reasons for this variability remain unclear. Despite the difference of specific uptake rates found between benthic and pelagic primary producers, when integrating the uptake fluxes for a water Column of 10 m depth, the contribution of benthic primary producers to N uptake fluxes (g N m(-) (2) h(-) (1)) is significant, corresponding on average to 40% of total uptake flux. This results from the dominance in terms of N biomass of benthic primary producers in this shallow nutrient-poor area. When reported for the entire volume of the Revellata Bay, the contribution of benthic primary producers is reduced to 5 - 10% of total N uptake flux. Although this contribution could appear relatively low, it results in a significant direct transfer of inorganic nitrogen from the water column to the benthic compartment. By this transfer, the benthic plants act as a biological pump incorporating the pelagic N into the benthic compartment for a time longer than the characteristic time of phytoplankton dynamics (month-years vs. day-week). (C) 2003 Elsevier B.V. Alt rights reserved. [less ▲]

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See detailNitrogen dynamics in Posidonia oceanica cuttings: implications for transplantation experiments
Lepoint, Gilles ULg; Vangeluwe, Denis; Eisinger, Michael et al

in Marine Pollution Bulletin (2004), 48(5-6), 465-470

A N-15 tracer study was performed during an experimental transplantation trial of natural Posidonia oceanica cuttings. The experiment was done in situ at 17 m depth in the Revellata Bay (Calvi, NW Corsica ... [more ▼]

A N-15 tracer study was performed during an experimental transplantation trial of natural Posidonia oceanica cuttings. The experiment was done in situ at 17 m depth in the Revellata Bay (Calvi, NW Corsica, France). Despite high survival rates of transplants (>90%) after one year, the weight and the N content of transplants are significantly lower than those of reference plants. In absence of roots, the transplants are not able to meet their N requirement because, leaf uptake is insufficient to replenish the N lost during the natural leaf decay. This could constitute a major cause of long-term failure for transplantation experiments or natural recolonisation processes. The increase of the N-15 content in the roots shows that the plant re-allocates the nitrogen of one organ (i.e. leaves, rhizomes) to ensure the growth of another (i.e. roots). (C) 2003 Elsevier Ltd. All rights reserved. [less ▲]

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