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Auteur Houngnandan, F.; Kéfi, S.; Deter, J.
Titre Identifying key-conservation areas for Posidonia oceanica seagrass beds Type Article scientifique
Année 2020 Publication Revue Abrégée Biological Conservation
Volume 247 Numéro Pages 108546
Mots-Clés Human activities; Landscape indices; Random Forest; Submerged aquatic vegetation (SAV)
Résumé The configuration of a habitat often reflects its conservation status and, to be effective, the conservation actions to be implemented must be adapted to local environmental conditions and human activities. Here, we take advantage of a fine resolution map (1:10000) of marine habitats to study the spatial configuration of Posidonia oceanica seagrass beds, a marine habitat of great ecological and economic importance. Six different composition and landscape descriptors were calculated at different resolutions (grid cells of 400 m × 400 m, 200 m × 200 m and 100 m × 100 m) between 0 and 40 m deep along 1700 km of French Mediterranean coastline (mainland and Corsica). A Random Forest approach was applied to relate these landscape descriptors to anthropogenic and environmental factors and to assess their relative importance. The best predictive power of the Random Forests models was obtained for 100 m × 100 m grid cells with models explaining 87% of the variance of the decline index and 70% of the variance of the cohesion index. The identification of threshold points for all environmental variables allowed to localize seagrass beds in either good or bad environmental conditions. We also identified sites whose spatial configuration is degraded despite good environmental conditions. These are sites with greater influence from human activities that could benefit from proactive conservation measures.
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Langue en Langue du Résumé Titre Original
Éditeur de collection Titre de collection Titre de collection Abrégé
Volume de collection Numéro de collection Edition
ISSN 0006-3207 ISBN Médium
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Numéro d'Appel MARBEC @ isabelle.vidal-ayouba @ collection 2800
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Auteur Le Fur, I.; De Wit, R.; Plus, M.; Oheix, J.; Derolez, V.; Simier, M.; Malet, N.; Ouisse, V.
Titre Re-oligotrophication trajectories of macrophyte assemblages in Mediterranean coastal lagoons based on 17-year time-series Type Article scientifique
Année 2019 Publication Revue Abrégée Marine Ecology Progress Series
Volume 608 Numéro Pages 13-32
Mots-Clés Coastal lagoon; Long-term data series; Nutrient reduction; Recovery; Regime shift; Resilience; Restoration; Submerged aquatic vegetation
Résumé Since the mid-20th century, Mediterranean lagoons have been affected by eutrophication, leading to significant changes in primary producers. In the early 2000s, management actions have been implemented to reduce nutrient inputs with the aim to achieve a good ecological status as requested by the EU water framework directive. As a result of these actions, a sharp decline in nutrient loads has been recorded in several lagoons leading to an oligotrophication of the water column. The analyses of a long-term data set (1998-2015) of 21 polyhaline and euhaline lagoons with contrasting trophic status allowed us to infer a general scheme for the changes in macrophyte assemblages during the oligotrophication process. Placing hypertrophic and oligotrophic conditions end to end, we inferred that the general pattern for the re-oligotrophication trajectory in Mediterranean coastal lagoons is described by the following sequence, with regime shifts between each state: (1) bare non-vegetated sediments, phytoplankton-dominated state; (2) opportunistic macroalgae; (3) seagrass and perennial macroalgae dominated state. However, we did not observe the latter regime shift for the most eutrophicated lagoons, which, so far, remained stuck in the opportunistic macroalgae state. So far, the shift from dominance of opportunistic macroalgae to a system dominated by seagrasses was only observed in a single lagoon where seagrasses had never completely disappeared, which possibly relates to resilience. More generally, the conditions favoring regime shifts from opportunistic macroalgae to seagrasses are still poorly understood. In conclusion, we describe a generic pattern for re-oligotrophication of Mediterranean coastal lagoons, although a full recovery from highly eutrophied to oligotrophic conditions may require more than a decade and may include conditions that remain so far poorly recognized.
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Editeur Lieu de Publication Éditeur
Langue en Langue du Résumé Titre Original
Éditeur de collection Titre de collection Titre de collection Abrégé
Volume de collection Numéro de collection Edition
ISSN 0171-8630, 1616-1599 ISBN Médium
Région Expédition Conférence
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Numéro d'Appel MARBEC @ isabelle.vidal-ayouba @ collection 2469
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Auteur Le Fur, I.; De Wit, R.; Plus, M.; Oheix, J.; Simier, M.; Ouisse, V.
Titre Submerged benthic macrophytes in Mediterranean lagoons: distribution patterns in relation to water chemistry and depth Type Article scientifique
Année 2018 Publication Revue Abrégée Hydrobiologia
Volume 808 Numéro 1 Pages 175-200
Mots-Clés southern france; eutrophication; coastal lagoon; Eutrophication; Depth; Salinity; environmental-factors; seagrass; aquatic vegetation; Canonical correspondence analysis (CCA); canonical correspondence-analysis; French coastal lagoons; potamogeton-pectinatus; spatiotemporal dynamics; Submerged aquatic vegetation (SAV); thau-lagoon
Résumé A large spectrum of coastal lagoon types with a wide range of environmental conditions is observed along the French Mediterranean coast. These comprise wide trophic and salinity gradients, ranging from oligotrophic to hypertrophic status, and from nearly freshwater to slightly above marine Mediterranean Sea water salinities, respectively. The statistical analysis of a long-term dataset, including water column variables and observations of macrophyte genera, showed that salinity, depth, and then trophic status, were important factors explaining the distribution of benthic macrophytes for the soft-bottom sediments in the 34 studied French Mediterranean lagoons. Based on this, we assumed that the vegetation succession along the eutrophication gradient was different according to the lagoon salinity ranges. Euhaline and polyhaline lagoons follow the well-known Schramm schematic model, where aquatic angiosperm such as seagrasses dominate under oligotrophic conditions, and opportunistic macroalgae and phytoplankton dominate under eutrophic and hypertrophic conditions. In oligohaline and mesohaline lagoons, the succession is probably an intermediate scheme between the successions observed in small temperate lakes and in marine coastal ecosystems due to the presence of both brackish and freshwater species. We thus propose a conceptual scheme for the oligohaline and mesohaline lagoons.
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Langue English Langue du Résumé Titre Original
Éditeur de collection Titre de collection Titre de collection Abrégé
Volume de collection Numéro de collection Edition
ISSN 0018-8158 ISBN Médium
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Numéro d'Appel MARBEC @ alain.herve @ collection 2280
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Auteur Marre, G.; Deter, J.; Holon, F.; Boissery, P.; Luque, S.
Titre Fine-scale automatic mapping of living Posidonia oceanica seagrass beds with underwater photogrammetry Type Article scientifique
Année 2020 Publication Revue Abrégée Marine Ecology Progress Series
Volume 643 Numéro Pages 63-74
Mots-Clés Benthic habitat mapping; Monitoring; Posidonia oceanica; Reconstruction uncertainty; Submerged aquatic vegetation; Underwater photogrammetry
Résumé The Mediterranean seagrass Posidonia oceanica, which provides highly valuable ecosystem services, is subject to increasing anthropogenic pressures, causing habitat loss or fragmentation. Whilst airborne images and acoustic data can be used for monitoring seagrass coverage at a macro-scale and over long time periods, monitoring its health in the short term requires precision mapping in order to assess current regression/progression of individual meadows. However, current fine-scale underwater techniques in the field are imprecise and time-demanding. We propose an automatic classification approach based on underwater photogrammetry for an operational, cost- and time-effective fine-scale monitoring method. The method uses a property of the sparse cloud generated during bundle adjustment—the reconstruction uncertainty—to map seagrass patches. The mean precision, recall and F1 score of the method over 21 study sites with different morphologies were 0.79, 0.91 and 0.84, respectively. However, the fragmentation level of the meadows had a significant negative effect on classification performances. The temporal monitoring of 3 sites using this method proved its operability and showed a positive evolution index of the corresponding meadows over a period of 3 yr. This method is generalizable for most encountered configurations and can be integrated in a large monitoring system, as it enables the production of numerous seagrass maps over a short period of time. Moreover, our methodology could be generalized and applied in the study of other submerged aquatic vegetation by adjusting the method’s parameters.
Adresse
Auteur institutionnel Thèse
Editeur Lieu de Publication Éditeur
Langue en Langue du Résumé Titre Original
Éditeur de collection Titre de collection Titre de collection Abrégé
Volume de collection Numéro de collection Edition
ISSN 0171-8630, 1616-1599 ISBN Médium
Région Expédition Conférence
Notes Approuvé pas de
Numéro d'Appel MARBEC @ isabelle.vidal-ayouba @ collection 2801
Lien permanent pour cet enregistrement