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Auteur Ba, K.; Thiaw, M.; Fall, M.; Thiam, N.; Meissa, B.; Jouffre, D.; Thiaw, O.T.; Gascuel, D. doi  openurl
  Titre Long-term fishing impact on the Senegalese coastal demersal resources: diagnosing from stock assessment models Type Article scientifique
  Année 2018 Publication Revue Abrégée Aquat. Living Resour.  
  Volume 31 Numéro Pages 8  
  Mots-Clés west-africa; dynamics; management; West Africa; fisheries; overexploitation; marine ecosystems; populations; mauritania; lessons; Bayesian approach; Coastal demersal species; delta-GLM models; epinephelus-aeneus; experience; surplus production models  
  Résumé For the first time in Senegal, assessments based on both stochastic and deterministic production models were used to draw a global diagnosis of the fishing impact on coastal demersal stocks. Based one national fisheries databases and scientific trawl surveys data: (i) trends in landings since 1971 were examined, (ii) abundance indices of 10 stocks were estimated using linear models fitted to surveys data and commercial catch per unit efforts, and (iii) stock assessments were carried out using pseudo-equilibrium Fox and Pella-Tomlinson models and a Biomass dynamic production model fitted in a Bayesian framework to abundance indices. Most stocks have seen their abundance sharply declining over time. All stocks combined, results of stock assessments suggest a 63% reduction compared to virgin state. Three fifth of demersal stocks are overexploited and excess in fishing effort was estimated until 75% for the worst case. We conclude by suggesting that the fishing of such species must be regulated and an ecosystem approach to fisheries management should be implemented in order to monitor the whole ecosystem.  
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  ISSN 0990-7440 ISBN Médium  
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  Numéro d'Appel MARBEC @ alain.herve @ collection 2278  
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Auteur de Fouw, J.; Govers, L.L.; van de Koppel, J.; van Belzen, J.; Dorigo, W.; Cheikh, M.A.S.; Christianen, M.J.A.; van der Reijden, K.J.; van der Geest, M.; Piersma, T.; Smolders, A.J.P.; Olff, H.; Lamers, L.P.M.; van Gils, J.A.; van der Heide, T. doi  openurl
  Titre Drought, Mutualism Breakdown, and Landscape-Scale Degradation of Seagrass Beds Type Article scientifique
  Année 2016 Publication Revue Abrégée Curr. Biol.  
  Volume 26 Numéro 8 Pages 1051-1056  
  Mots-Clés banc-darguin; bivalvia; climate-change; communities; critical transitions; ecosystems; foundation; mauritania; ocean acidification; perspective  
  Résumé In many marine ecosystems, biodiversity critically depends on foundation species such as corals and seagrasses that engage in mutualistic interactions [1-3]. Concerns grow that environmental disruption of marine mutualisms exacerbates ecosystem degradation, with breakdown of the obligate coral mutualism (“coral bleaching”) being an iconic example [2, 4, 5]. However, as these mutualisms are mostly facultative rather than obligate, it remains unclear whether mutualism breakdown is a common risk in marine ecosystems, and thus a potential accelerator of ecosystem degradation. Here, we provide evidence that. drought triggered landscape-scale seagrass degradation and show the consequent failure of a facultative mutualistic feedback between seagrass and sulfide-consuming lucinid bivalves that in turn appeared to exacerbate the observed collapse. Local climate and remote sensing analyses revealed seagrass collapse after a summer with intense low-tide drought stress. Potential analysis a novel approach to detect feedback-mediated state shifts-revealed two attractors (healthy and degraded states) during the collapse, suggesting that the drought disrupted internal feedbacks to cause abrupt, patch-wise degradation. Field measurements comparing degraded patches that were healthy before the collapse with patches that remained healthy demonstrated that bivalves declined dramatically in degrading patches with associated high sediment sulfide concentrations, confirming the breakdown of the mutualistic seagrass-lucinid feedback. Our findings indicate that drought triggered mutualism breakdown, resulting in toxic sulfide concentrations that aggravated seagrass degradation. We conclude that external disturbances can cause sudden breakdown of facultative marine mutualistic feedbacks. As this may amplify ecosystem degradation, we suggest including mutualisms in marine conservation and restoration approaches.  
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  ISSN 0960-9822 ISBN Médium  
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Auteur van der Geest, M.; van Gils, J.A.; van der Meer, J.; Olff, H.; Piersma, T. url  openurl
  Titre Suitability of calcein as an in situ growth marker in burrowing bivalves Type Article scientifique
  Année 2011 Publication Revue Abrégée Journal of Experimental Marine Biology and Ecology  
  Volume 399 Numéro Pages 1-7  
  Mots-Clés Daily growth rate in situ fluorescent marking Intertidal mudflat Lucinidae Mark-and-recapture Seagrass banc-darguin marking mauritania scallop oxytetracycline abundance shells rates fish age  
  Résumé The fluorochrome calcein has been used in numerous growth studies of molluscs to internally mark calcified structures. Because of interspecific variations in marking success and possible effects on growth performance, methodological assessments of the suitability of calcein as a growth marker, especially in field contexts, remain necessary. Here we report on the effects of different calcein concentrations (100, 200, 400 and 800 mg l(-1) on fluorescent mark deposition, growth rate, density, body condition and size-frequency distribution of an intertidal infaunal bivalve species, Loripes lacteus (Linnaeus, 1758), using an outdoor immersion technique. To avoid stress caused by handling and transportation, in situ enclosures were placed at seagrass-covered patches during low tide, to which calcein solutions were added. After a 1.3- to 2.6-h period of exposure to calcein, the enclosures were removed. Sites were sampled three months later. All calcein concentrations produced live L. lacteus with a clear fluorescent shell mark, but the percentage successfully marked tended to increase with higher calcein concentrations. Furthermore, marking success and growth rate decreased significantly with shell size (i.e., age). Calcein concentration did not measurably affect shell growth rate, body condition and size-frequency distribution, but the numerical densities were lower for sites treated with calcein concentrations >= 400 mg l(-1). Our results suggest that in situ calcein-marking of burrowing lucinid bivalves with low concentrations (100-200 mg l(-1)) is a non-invasive and rapid method to determine growth rate, provided that the lucinids are not too old. (c) 2011 Elsevier B.V. All rights reserved.  
  Adresse [van der Geest, Matthijs; van Gils, Jan A.; van der Meer, Jaap; Piersma, Theunis] NIOZ Royal Netherlands Inst Sea Res, Dept Marine Ecol, NL-1790 AB Den Burg, Texel, Netherlands. [van der Meer, Jaap] Free Univ Amsterdam, Dept Theoret Biol, NL-1081 HV Amsterdam, Netherlands. [Olff, Han] Univ Groningen, Ctr Ecol & Evolutionary Sci CEES, Community & Conservat Ecol Grp, NL-9700 CC Groningen, Netherlands. [Piersma, Theunis] Univ Groningen, Ctr Ecol & Evolutionary Sci CEES, Anim Ecol Grp, NL-9700 CC Groningen, Netherlands. van der Geest, M (reprint author), NIOZ Royal Netherlands Inst Sea Res, Dept Marine Ecol, POB 59, NL-1790 AB Den Burg, Texel, Netherlands Matthijs.van.der.Geest@nioz.nl  
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  ISSN 0022-0981 ISBN Médium  
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  Notes ISI Document Delivery No.: 745QC Times Cited: 0 Cited Reference Count: 33 van der Geest, Matthijs van Gils, Jan A. van der Meer, Jaap Olff, Han Piersma, Theunis Nwo-wotro[w.01.65.221.00] We thank the authorities of the Parc National du Banc d'Arguin (PNBA) for the opportunity to carry out this research on the intertidal flats of PNBA and for the use of facilities at the Iwik field station. Logistical help from Lemhaba Ould Yarba in Nouakchott is much appreciated. We also thank the inhabitants of the Biological Station in Iwik, especially Sidi Ely, Sall Mamdou Alassane and Ahmedou Ould Lameime for their cheerful contribution and co-operation. We are grateful to Tamar Lok and two anonymous referees for constructive comments. We thank Henrike Andresen for help with the development of the calcein-marking method and Amrit Cado van der Lelij who made a large contribution to the work in the laboratory. Joana Cardoso helped with shell preparation. We are grateful to the staff of Laboratoire de Sclerochronologie des Animaux Aquatiques (LASAA) for their assistance with making Fig. 1B and C. Allert Bijleveld, Geert Aarts and all participants of the NIOZ April 2010 Mixed-Effect modeling course of Alain Zuur and Elena N. Ieno are thanked for their constructive comments on statistics. Dick Visser produced the final figures. This study was financed by NWO-WOTRO Integrated Programme grant W.01.65.221.00 to TP. [ST] Elsevier science bv Amsterdam Approuvé pas de  
  Numéro d'Appel MARBEC @ alain.herve @ 712 collection 1380  
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Auteur van Gils, J.A.; van der Geest, M.; Jansen, E.J.; Govers, L.L.; de Fouw, J.; Piersma, T. url  openurl
  Titre Trophic cascade induced by molluscivore predator alters pore-water biogeochemistry via competitive release of prey Type Article scientifique
  Année 2012 Publication Revue Abrégée Ecology  
  Volume 93 Numéro Pages 1143-1152  
  Mots-Clés Banc d'Arguin, Mauritania bivalves (Dosinia isocardia, Loripes lucinalis) facilitation growth rate hydrogen sulfide interspecific competition predation predator-exclosure experiment Red Knot, Calidris canutus canutus seagrass beds top-down effect toxicity knots calidris-canutus food webs ecological consequences habitat communities coexistence depletion bivalvia sulfide diet  
  Résumé Effects of predation may cascade down the food web. By alleviating interspecific competition among prey, predators may promote biodiversity, but the precise mechanisms of how predators alter competition have remained elusive. Here we report on a predator-exclosure experiment carried out in a tropical intertidal ecosystem, providing evidence for a three-level trophic cascade induced by predation by molluscivore Red Knots (Calidris canutus) that affects pore water biogeochemistry. In the exclosures the knots' favorite prey (Dosinia isocardia) became dominant and reduced the individual growth rate in an alternative prey (Loripes lucinalis). Dosinia, a suspension feeder, consumes suspended particulate organic matter (POM), whereas Loripes is a facultative mixotroph, partly living on metabolites produced by sulfur-oxidizing chemoautotrophic bacteria, but also consuming suspended POM. Reduced sulfide concentrations in the exclosures suggest that, without predation on Dosinia, stronger competition for suspended POM forces Loripes to rely on energy produced by endosymbiotic bacteria, thus leading to an enhanced uptake of sulfide from the surrounding pore water. As sulfide is toxic to most organisms, this competition-induced diet shift by Loripes may detoxify the environment, which in turn may facilitate other species. The inference that predators affect the toxicity of their environment via a multi-level trophic cascade is novel, but we believe it may be a general phenomenon in detritus-based ecosystems.  
  Adresse [van Gils, Jan A.; van der Geest, Matthijs; Jansen, Erik J.; de Fouw, Jimmy; Piersma, Theunis] NIOZ Royal Netherlands Inst Sea Res, Dept Marine Ecol, NL-1790 AB Den Burg, Texel, Netherlands. [Govers, Laura L.] Radboud Univ Nijmegen, Fac Sci, Inst Water & Wetland Res, Dept Environm Sci, NL-6500 GL Nijmegen, Netherlands. [Piersma, Theunis] Univ Groningen, CEES, Anim Ecol Grp, NL-9700 CC Groningen, Netherlands. van der Geest, M (reprint author), NIOZ Royal Netherlands Inst Sea Res, Dept Marine Ecol, POB 59, NL-1790 AB Den Burg, Texel, Netherlands matthijs.van.der.geest@nioz.nl  
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  Langue English Langue du Résumé Titre Original  
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  ISSN 0012-9658 ISBN Médium  
  Région Expédition Conférence  
  Notes ISI Document Delivery No.: 946QK Times Cited: 0 Cited Reference Count: 60 van Gils, Jan A. van der Geest, Matthijs Jansen, Erik J. Govers, Laura L. de Fouw, Jimmy Piersma, Theunis Nwo-wotro[w.01.65.221.00] We are grateful to the staff of the Parc National du Banc d'Arguin for allowing us to work and stay in the area under their management. In 2009 we had the pleasant company of Tjisse van der Heide, Han Olff, and Erik Rosendaal, and in 2010 Brecht De Meulenaer joined us. Erik Rosendaal processed fecal samples, and Jeroen Onrust determined shell dry masses. Dick Visser redrew the figures. This work was funded by the NWO-WOTRO Integrated Programme grant W.01.65.221.00 awarded to T. Piersma. Ecological soc amer Washington Approuvé pas de  
  Numéro d'Appel MARBEC @ alain.herve @ 722 collection 1384  
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