Applications of C and N stable isotopes to ecological and environmental studies in seagrass ecosystems

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 ▲]

Contributions of benthic and planktonic primary producers to nitrate and ammonium uptake fluxes in a nutrient-poor shallow coastal area (Corsica, NW Mediterranean)

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 ▲]

Study of the structure, distribution and dynamics of Codium elisabethae populations in the Azorian reef ecosystem, use of submarine image analysis

Poster (2004, March)

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

in Oceanologica Acta (2003), 26(2), 199-207

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 (100m(2)). 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 (m(2)) 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. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All fights reserved. [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 ▲]

Variations spatiale et temporelle de l'herbier à Posidonia oceanica (L.) Delile (Baie de La Revellata-Calvi-Corse)

Doctoral thesis (2002)

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 ▲]

Relative impact of a seagrass bed and its adjacent epilithic algal community in consumer diets

in Marine Biology (2000), 136

The aim of this work was to identify and compare, using nitrogen and carbon stable isotope data, the food sources supporting consumer communities in a Mediterranean seagrass bed (Gulf of Calvi, Corsica ... [more ▼]

The aim of this work was to identify and compare, using nitrogen and carbon stable isotope data, the food sources supporting consumer communities in a Mediterranean seagrass bed (Gulf of Calvi, Corsica) with those in an adjacent epilithic algal dominated community. Isotopic data for consumers are not significantly different in the two communities. Particulate matter and algal material (seagrass epiflora and dominant epilithic macroalgae) appear to be the main food sources in both communities. Generally, the 13C of animals suggests that the seagrass Posidonia oceanica (L.) Delile represents only a minor component of their diet or of the diet of their prey, but the occurrence of a mixed diet is not excluded. P.oceanica dominates the diet of only of few species, among which holothurians appear as key components in the cycling of seagrass material. [less ▲]

Heavy metals, organochlorines and polycyclic aromatic hydrocarbons in sperm whales stranded in Southern North sea during the 1994/1995 winter,

in Marine Pollution Bulletin (1999), 38