Nitrogen dynamics in Posidonia oceanica cuttings: implications for transplantation experiments

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 ▲]

A model of the seasonal dynamics of biomass and production of the seagrass Posidonia oceanica in the Bay of Calvi (Northwestern Mediterranean)

in Ecological Modelling (2003), 167(1-2), 1-18

Modelling of seagrasses can be an effective tool to assess factors regulating their growth. Growth and production model of Posidonia oceanica, the dominant submerged aquatic macrophyte occurring in the ... [more ▼]

Modelling of seagrasses can be an effective tool to assess factors regulating their growth. Growth and production model of Posidonia oceanica, the dominant submerged aquatic macrophyte occurring in the Bay of Calvi (Corsica, Ligurian Sea, Northwestern (NW) Mediterranean) was developed. The state variables are the above- and below-ground biomass of P oceanica, the epiphyte biomass, and the internal nitrogen concentration of the whole plant. Light intensity and water temperature are the forcing variables. The model reproduces successfully seasonal growth and production for each variable at various depths (10, 20 and 30 m). The model can simulate also a number of consecutive years. Sensitivity analysis of model's parameters showed that the maximum nitrogen quota n(max) rate is the most sensitive parameter in this model. The results simulations imply that light intensity is one of the most important abiotic factors, the diminution of which can cause an important reduction in seagrass density. (C) 2003 Elsevier B.V. All rights reserved. [less ▲]

Marine mammals from the southern North Sea: feeding ecology data from delta C-13 and delta N-15 measurements

in Marine Ecology. Progress Series (2003), 263

The harbour porpoise Phocoena phocoena, grey seal Halichoerus grypus, harbour seal Phoca vitulina and white-beaked dolphin Lagenorhynchus albirostris are regularly found stranded along southern North Sea ... [more ▼]

The harbour porpoise Phocoena phocoena, grey seal Halichoerus grypus, harbour seal Phoca vitulina and white-beaked dolphin Lagenorhynchus albirostris are regularly found stranded along southern North Sea coasts. Occasionally, offshore species such as the fin whale Balaenoptera physalus, the white-sided dolphin L. acutus and the sperm whale Physeter macrocephalus are also found stranded. In order to trace their diet, we measured delta(13)C and delta(15)N in their muscles as well as in 49 invertebrate and fish species collected from the southern North Sea. The delta(15)N data indicate that the harbour seal, grey seal and white-beaked dolphin occupy the highest trophic position, along with ichtyophageous fishes such as the cod Gadus morhua (mean muscle values of 18.7, 17.9, 18.8 and 19.2parts per thousand respectively). The harbour porpoise occupies a slightly lower trophic position (mean delta(15)N value of 16.2parts per thousand), reflecting a higher amount of zooplanktivorous fishes in its diet (mean delta(15)N of 14.7parts per thousand); 2 suckling harbour porpoises displayed a significant delta(15)N enrichment of 2.2parts per thousand compared to adult females. Adult females are delta(15)N-enriched compared to adult male harbour porpoises. Fin whales, sperm whales and white-sided dolphins are C-13-depleted compared to southern North Sea particulate organic matter and species, suggesting that despite regular sightings, they do not feed within the southern North Sea area. [less ▲]

Variations at different spatial scales of Posidonia oceanica (L.) Delile beds; effects on the physico-chemical parameters of the sediment

in Oceanologica Acta (2003), 26

The biometric parameters (shoot density, length and width of leaves, leaf and epiphyte biomasses, leaf surface) of the P. oceanica meadow present a significant spatial variability at the mesoscale level ... [more ▼]

The biometric parameters (shoot density, length and width of leaves, leaf and epiphyte biomasses, leaf surface) of the P. oceanica meadow present a significant spatial variability at the mesoscale level (100 m2). All the parameters studied, excepting the number of leaves, decrease according to the depth. The horizontal spatial variations (centrifuge and centripetal distributions) reach a maximum in the shallower areas. The analysis of the microstructures (m2) of the meadow has not allowed a relationship to be established between the spatial variations of the biometric parameters and the environmental factors in the sediment (pH, water and organic matter content, red-ox potential, nutrient content). The heterogeneity of the meadow in the Revellata Bay quite probably results from the internal shoot and rhyzome growth dynamics. On the other hand, it appears that the presence of the prairie modifies the physical-chemical characteristics of the sediment. In fact, the sandy patches present different physical-chemical characteristics: lower organic matter, different granulometric and much higher interstitial water nutrient levels, as well as a higher pH and oxydo-reduction potential. [less ▲]

Annual nitrogen budget of the seagrass Posidonia oceanica as determined by in situ uptake experiments

in Marine Ecology. Progress Series (2002), 237

The uptake of nitrate and ammonium by the roots and leaves of Posidonia oceanica were determined between February 1993 and June 1999 by in situ experiments using the isotope 15 of nitrogen (N-15) as a ... [more ▼]

The uptake of nitrate and ammonium by the roots and leaves of Posidonia oceanica were determined between February 1993 and June 1999 by in situ experiments using the isotope 15 of nitrogen (N-15) as a tracer in a nutrient-poor coastal zone of the NW Mediterranean Sea (Revellata Bay, Corsica). Nitrate and ammonium leaf uptakes are recorded at 0.05 and 0.1 muM respectively. The high variability observed cannot be explained solely by the variation of the substrate concentrations in the water column. For leaves, mean specific uptake rates were 43 +/- 45 and 43 +/- 64 mug N g N-1 h(-1). Nitrate and ammonium leaf uptake fluxes (g N m(-2) yr(-1)) seem to have the same importance on an annual basis. :Nitrate uptake occurs mainly in winter and early spring, when nitrate concentrations in the water column are highest. The uptake of N, and mainly of ammonium, is significant throughout the year with maxima at the beginning of spring, but it is insufficient to meet the annual N requirement of the plant. Posidonia root biomass was very high and corresponded to high specific N uptake rates by the roots. Ammonium was incorporated by the roots 6 times faster than nitrate. In the sediment, this uptake capacity is limited by the nutrient diffusion rate, and the root uptake is therefore insufficient to meet the N requirements of the plant. In fact, P. oceanica of Revellata Bay have a complex N budget involving uptake and recycling processes and allowing the plants to meet their N requirements in one of the most nutrient-poor areas of the NW Mediterranean Sea. We calculated that leaf and root would contribute to 40 and 60% of the annual N uptake, respectively, and 60% of the annual N requirement of the plant. [less ▲]

Use of stable isotopes to delineate amphipod trophic status in the High Antarctic

Poster (2001, July)

Anthesis effects on Posidonia oceanica (L.) Delile phenology in the Bay of Calvi (Corsica, Mediterranean Sea)

in Hydrobiologia (2001), 455

In Posidonia oceanica (L.) Delile, anthesis induces a decrease in the number of juvenile leaves resulting in a significant reduction in the number of leaves on the flowering shoots. All the leaves of the ... [more ▼]

In Posidonia oceanica (L.) Delile, anthesis induces a decrease in the number of juvenile leaves resulting in a significant reduction in the number of leaves on the flowering shoots. All the leaves of the flowering shoots are narrower than the leaves of nonflowering shoots. A modification of the leaf growth also appears in flowering shoots: the oldest leaves are longer and the leaves induced during or after anthesis are shorter. At 10 m depth, in the Bay of Calvi, anthesis lasts roughly 3 months and the flowering is induced 7 months before anthesis. [less ▲]

Apport des isotopes stables du carbone et de l’azote dans l’étude des réseaux trophiques

Conference (2000, June 13)

Trois types de producteur primaire prolifèrent dans la zone photique côtière méditerranéenne. En dehors des zones d’upwelling et des apports côtiers naturels ou d’origine anthropique, le bloom ... [more ▼]

Trois types de producteur primaire prolifèrent dans la zone photique côtière méditerranéenne. En dehors des zones d’upwelling et des apports côtiers naturels ou d’origine anthropique, le bloom phytoplantonique est de courte durée et les eaux méditerranéennes sont très claires. Les algues benthiques ont une biomasse relativement faible et le principal producteur primaire est l’herbier à Posidonia oceanica (L.) Delile. Cet herbier constitue un écosystème complexe, d’une importance cruciale pour l’équilibre côtier (maintien des côtes, production d’oxygène, plusieurs milliers d’espèces y sont inféodées…). Son influence se fait également ressentir bien au-delà de sa limite de distribution (exportation vers les zones profondes). Les feuilles et les épiphytes de l’herbier sont à la base de nombreuses chaînes trophiques. Les rapports isotopiques (13C/12C et 15N/14N) mesurés dans les tissus d’un animal reflètent ceux de son alimentation avec un léger enrichissement d’un niveau trophique à un autre. Cet discrimination en faveur des isotopes lourds est de l’ordre 30/00 pour le 15N et de 10/00 pour le 13C. Les rapports 15N/14N permettent donc la détermination de la position trophique d’un organisme. Les rapports 13C/12C sont plutôt de bons indicateurs des sources de production primaire. L’application de cette technique au cas d’un herbier à P. oceanica, a permis sur base des rapports 13C/12C de distinguer trois sources primaires de nourriture: la matière particulaire en suspension, les algues (épiflore de P. oceanica et macroalgues) et P. oceanica. Les rapports isotopiques 13C/12C et 15N/14N de différentes catégories trophiques d’organismes capturés dans l’herbier et dans une communauté épilithe adjacente suggèrent que les sources de nourriture sont semblables dans les deux communautés: la matière particulaire en suspension et les algues. La communauté épiphyte des feuilles de posidonie est une source de nourriture très importante pour les organismes de la canopée de l’herbier. Les posidonies ne représentent qu’une partie mineure du régime alimentaire des organismes étudiés à l’exception des holothuries et du téléostéen herbivore Sarpa salpa. Ce poisson est l’un des consommateurs principaux de posidonie vivantes mais la majorité de sa nourriture provient de matériel algal. Les holothuries psamivores assimilent massivement des détritus issus de P. oceanica et jouent ainsi un rôle clé dans le recyclage in situ de ce matériel. La disponibilité en nutriments, en particulier de l'azote inorganique, est un des facteurs majeurs déterminant la dynamique des écosystèmes à phanérogames marines. Le budget en azote de ces plantes est très complexe car elles ont la capacité d'incorporer les nutriments dissous dans la colonne d'eau et dans l'eau interstitielle du sédiment. De plus, le recyclage interne de l'azote est souvent considéré comme un processus clé pour assurer les besoins de la plante. Des expériences utilisant l'isotope 15 de l'azote comme traceur nous ont permis de mesurer in situ l'incorporation de nitrate et d'ammonium ainsi que le recyclage interne de l'azote par P. oceanica. L'incorporation d'azote exogène par les feuilles ne représenterait que 25% des besoins annuels en azote de la plante et le recyclage 40%. Par différence, nous pouvons estimer que l'incorporation d'azote par les racines représenterait environ 35% des besoins annuels en azote de la plante. Nos études isotopiques se sont également avérées particulièrement intéressantes dans la compréhension des processus de transfert de matières organiques ou de polluants au niveau des échelons trophiques supérieurs (thons et dauphins de l’Atlantique nord et mammifères marins de la Mer du Nord). En effet, au sein d’un même écosystème peuvent coexister différentes espèces de prédateurs nécessitant des ressources similaires. L’analyse simultanée des isotopes stables du carbone et de l’azote a permis une définition plus fine de l’écologie alimentaire de ces espèces. [less ▲]

Use of stable isotopes to delineate amphipod trophic status in Antarctic food webs

Poster (2000, May)

Tuna and dolphin associations in the Northeast Atlantic: Evidence of different ecological niches from stable isotope and heavy metal measurements

in Marine Pollution Bulletin (2000), 40

Associations of tunas and dolphins in the wild are quite frequent events and the question arises how predators requiring similar diet in the same habitat share their environmental resources. As isotopic ... [more ▼]

Associations of tunas and dolphins in the wild are quite frequent events and the question arises how predators requiring similar diet in the same habitat share their environmental resources. As isotopic composition of an animal is related to that of its preys, stable isotopes (13C/12C and 15N/14N) analyses were performed in three predator species from the Northeast Atlantic: the striped dolphin, Stenella coeruleoalba, the common dolphin Delphinus delphis, and the albacore tuna, Thunnus alalunga, and compared to their previously described stomach content. Heavy metals (Cd, Zn, Cu and Fe) are mainly transferred through the diet and so, have been determined in the tissues of the animals. Tunas muscles display higher delta15N than in common and striped dolphins (mean: 11.4 0/00 vs. 10.3 0/00 and 10.4 0/00, respectively) which reflects its higher trophic level nutrition. Higher delta13C are found in common (-18.4 0/00) and striped dolphin (-18.10/00) muscles than in albacore tuna (-19.3 0/00) likely in relation with its migratory pattern. The most striking feature is the presence of two levels of cadmium concentrations in the livers of the tunas (32 mg kg-1 dry weight vs. 5 mg kg-1 dry weight). These two groups also differ by their iron concentrations and their delta15N and delta 13C liver values. These results suggest that in the Biscay Bay, tunas occupy two different ecological niches likely based on different squid input in their diet. [less ▲]