From mechanical to chemical impact of anchoring in seagrasses: the premises of anthropogenic patch generation in Posidonia oceanica meadows

Intensive anchoring of leisure boats in seagrass meadows leads to mechanical damages. This anthropogenic impact creates bare mat patches that are not easily recolonized by the plant. Several tools are used to study human impacts on the structure of seagrass meadows but they are not able to assess the indirect and long term implication of mechanical destruction. We chose to investigate the possible changes in the substrate chemistry given contrasted boat impacts. Our observations show that hydrogen sulfide concentrations remain high at 15 and 20 m depth (42.6 µM and 18.8 µM) several months after the highest period of anchoring during the summer. Moreover, our multidisciplinary study reveals that anchoring impacts of large boats at 15 and 20 m depth can potentially change the seascape structure. By taking into account both structural and chemical assessments, different managing strategies must be applied for coastal areas under anthropogenic pressures.STARE-CAPME

Courants et vents

peer reviewedConnaissances, prévisions, stratégie, lacun

Source X par agrégats : contrôle et optimisation des paramètres gouvernant línteraction laser de puissance - agrégats de gaz rare

National audienceLes expériences que nous avons réalisées sur le Laser Ultra Court Accordable du CEA Saclay permettent dóbserver l\'émission de photons X dans la gamme 1-5 keV lors de lírradiation dágrégats de gaz rare (Ar, Kr et Xe comprenant entre 10^3 et 10^6 atomes par agrégat) avec un laser femtoseconde de puissance (Ipic jusqu\'à 10^17 W/cm²). En plus de la distribution des états de charge des ions responsables de l\'émission X, la technique de spectroscopie X que nous utilisons permet de mesurer les taux absolus de photons émis dans 4π par impulsion laser en fonction des paramètres gouvernant línteraction dans des conditions contrôlées. Nous avons déterminé la sensibilité des paramètres physiques régissant la production du rayonnement X pendant línteraction, ce qui permet dáccéder à lóptimisation de cette source. Cet article est plus particulièrement dédié aux résultas relatifs à l\'évolution du taux d\'X avec l\'éclairement laser, dúne part, et avec la durée de límpulsion laser, dáutre part

Émission X(L) du xénon par interaction laser -agrégats

National audienceNous avons étudié le rayonnement X provenant d'ions fortement multichargés (" 24+) présentant des lacunes en couche L produits lors de l'irradiation d'agrégats de xénon par des impulsions lumineuses issues d'un laser femtoseconde de puissance. Les résultats obtenus lors de la toute dernière campagne d'expériences réalisée auprès du serveur LUCA du SPAM/DRECAM au CEA/Saclay mettent en cause certains travaux antérieurs. Des divergences marquées apparaissent tant au niveau de l'interprétation des spectres X que sur la variation du taux d'émission en fonction de l'éclairement et de la longueur d'onde

Exploring a Mediterranean mesozooplankton 13 year time-series.

Zooplankton plays diverse crucial roles within the marine ecosystem and can also be used as bio- indicator of climate changes since it is very sensitive to environmental changes. Therefore it is essential to consider long-term plankton series. Given the analysis of plankton samples is time- consuming, it requires an effective and rapid analytical method. We have used in this work a supervised learning approach adapted for the semi-automatic classification of digital images of the mesozooplankton of the Bay of Calvi (Corsica, France) by using the Zoo/PhytoImage software. Together with a 11-years long zooplankton time-series, a set of nine environmental variables were monitored in order to identify controlling factors and determine whether the communities were sensitive to global environmental changes. The main components of the mesozooplankton community were characterized by both seasonal and inter-annual variability. Additionally, variation of holoplankton and meroplankton differentiated one from each other. The holoplanktonic community could be split into two subgroups according to its variation in function of the environment: cladocerans and appendicularians, and to a lesser extent, copepods on one hand, and cnidarians, chaetognathes and thaliaceans, on the other hand. Regarding inter-annual variation, one year (2007) showed particularly low production of total zooplankton which was also the case for all the different holoplanktonic taxa. Accounting for that phenomenon were identified some potentially underlying environmental factors. Finally, although water temperature increased significantly over the last years along with the frequency of marine heat wave events, no evident change in the global zooplankton composition was observed yet.STARECAPME

Utilisation d'indicateurs biologiques pour évaluer l'état des stocks d’espèces d’intérêt halieutique

Moonfish : Outils de modélisation pour la gestion durable des ressources halieutiques en Cors

Structural Changes of Seagrass Seascapes Driven by Natural and Anthropogenic Factors: A Multidisciplinary Approach

Seascape ecology has been widely applied to marine habitats, including seagrass meadows, through various approaches all over the world for the past 30 years. However, these methods mainly study seagrass meadows on a single spatial scale and monitor a single driver of heterogeneity. Additionally, few assess the seascape's structural evolution. This creates gaps between the scientific data provided and those required by environmental managers and stakeholders in charge of seagrass meadow conservation. To meet their expectations, in this paper we developed a new multidisciplinary approach based on the coupling of mapping techniques, particle flux, and biometric investigations in a Mediterranean Bay, the Calvi Bay (Corsica, France), to assess the structural changes of Posidonia oceanica (L.) Delile meadows subject to disturbances. We focused our investigations on the structural characteristics, the spatial dynamics, and the particle fluxes of natural sand areas generated by bottom currents and dead matte patches which ensued from anchoring damages at 10, 15, and 20 m depth. Natural sand patches and anchoring patches differed in size, the first the largest. They also displayed different erosion-colonization dynamics. Natural sand patches were eroded at a mean speed of 12 cm.a−1 and colonized at a rate of 7 cm.a−1. Anchoring patches showed a mean erosion speed of 3.5 cm.a−1 and a colonization rate of 6.5 cm.a−1. Regarding particle fluxes, continuous meadow, and natural patch sedimentation and resuspension rates were 3.7 gDW.m−2.d−1 and 4.1 gDW.m−2.d−1 in average, respectively. In contrast, anchoring patches at 20 m depth acted as sediment traps (112.60 gDW.m−2.d−1 in winter) and showed a higher particle resuspension rate. Our results highlighted the dichotomous dynamics of seagrass seascapes influenced by natural and anthropogenic factors. Thus, the smallest anchoring patch will take about 27 years to be recolonized while the biggest requires 60 years to be covered by the plant. With an upscaling approach, together with the newest mapping tools of marine habitats, we suggest a new method to study the evolution of seagrass meadows at a large spatial scale

Dynamique sub-picoseconde de l'interaction laser de puissance – agrégats de gaz rare : émission intense de rayons X et production d'ions multichargés.

National audienceLors de campagnes d'expériences réalisées sur le Laser Ultra Court Accordable du CEA/Saclay, nous avons étudié le rayonnement X, tant qualitativement (spectroscopie et énergie moyenne des photons) que quantitativement (taux absolus et lois d'évolution), émis lors de l'interaction d'un jet effusif d'agrégats de gaz rare (Ar, Kr, Xe comprenant entre 10^4 et 10^6 atomes/agrégat) avec un laser femtoseconde de puissance (éclairement jusqu'à quelques 10^17 W/cm2). Les résultats présentés dans ce manuscrit sont uniquement dédiés aux agrégats d'Ar pour lesquels nous avons observé un rayonnement X issu d'ions fortement multichargés (jusqu'à l'Ar16+) présentant des lacunes en couches K. La technique de spectroscopie X utilisée a permis de déterminer pour la première fois des taux absolus ainsi que les lois d'évolution de l'émission X en fonction de l'ensemble des paramètres gouvernant l'interaction (intensité, polarisation, longueur d'onde et durée du pulse laser aussi bien que taille, densité et numéro atomique des agrégats)

Projet REPAIR: Restauration des patchs anthropiques dans l’herbier de Posidonie

REPAIR14. Life below water13. Climate actio