Approche quantitative de la fonction de nourricerie jouée par les ...

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Chapitre 4 : Impact of vegetation structure dynamics and usage on the nursery function of West European tidal salt-marshes. Two other salt marsh colonisation behaviours can also be identified. These differ in terms of the timing of colonisation. Some species such as the European anchovy, Seabass and Common sole only occur during their first year (young-of-the-year), or accidentally during their second year. The nursery function sensu stricto as defined by Beck et al. (2001) applies to these species. The salt marshes only actively support the young-of-the-year, so that these species are called Young-of-the-year salt marsh setters. Another less restrictive strategy is that adopted by the Golden grey mullet and European sprat. These species occur during the first few years of their life cycle. This is therefore an extended form of the nursery function since several cohorts are maintained by the production produced in situ. Access to the salt marshes is temporary, because of the tides. At another temporal scale (that of the year), the regularity and/or fidelity of frequenting these productive ecosystems enables various populations of fish to survive. They have developed various colonising strategies enabling them to use the food resources of salt marshes and improve their growth performance and their survival. The trophic role of coastal salt marshes is therefore fundamental for supporting coastal stocks and in the production of the breeding stock. 6. Conclusion. Since European salt marshes are declining in area and number the remaining ones play a crucial role in the survival of coastal fish populations. This study of the colonisation of the salt marshes of the Aiguillon bay showed that there has been a change in the distribution of the young stages of some species of high fisheries value such as the Seabass. Salt marshes are often managed to maintain populations of breeding, passage or wintering birds (Meunier et Joyeux 2003), or for traditional activities such as elver fishing, but these seem to have endangered the initial nursery function of these areas (Laffaille et al. 2000b). The invasion of the initial vegetation structure by couch grass (Elytrigia atherica) also alters this function, obliging the fish to turn to prey of marine origin instead of terrestrial origin such as Orchestia gammarellus (Parlier 2002). If these imbalances persist, the whole of the trophic networks in coastal zones are going to be altered because of adverse changes in recruitment. The whole outwelling process (Odum 1968b) is also going to be affected, with the fish no longer being able to play their role of biotic vector. The understanding of colonisation phenomenon of coastal areas subjected to strong human pressures or biological disturbances through the fish 142
Chapitre 4 : Impact of vegetation structure dynamics and usage on the nursery function of West European tidal salt-marshes. communities and the study of the use of food resources of interface ecosystems must be continued. It will then be possible to draw lessons from activities relating to the conservation and sustainable management of these estuarine ecosystem complexes – European salt marshes. 7. Acknowledgements : This study was funded by the CNRS Programme Environnement Vie et Société (PEVS). It was made possible by the help of many students from the university of La Rochelle (S. Millot, A. Ride, J. Dubreuil, C. Bertin, P. Rhodes and A. Charpentron), whom we thank, plus J.-C. Auguet and O. Herlory for their invaluable help. 143
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UNIVERSITE DE LA ROCHELLE UFR SCIEN
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Remerciements : Je tiens tout d’a
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(Ciboulette), Aurélien RIDE (Lapin
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Sapere aude (N’aie pas peur de sa
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6. REMERCIEMENTS. .................
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3. RESULTATS. .....................
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Introduction générale et contexte
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dorsal Face ventral Introduction g
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Otolithe d’un juvénile de l’an
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TOME 1 : Première partie. TOME 1 :
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TOME 1 : Première partie. Chapitre
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Chapitre 1 : Structuration du peupl
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Chapitre 2 : Evolution des assembla
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Chapitre 1 : Variations régionales
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Chapitre 2 : Les marais salés cont
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15N depleted δ15N‰ 15N enriched
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TOME 2 : Chapitre 3 Chapitre 3 : Di
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Chapitre 3 : Discrimination de quat
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TOME 2 : Chapitre 4 44 : Concentrat
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Chapitre 4 : Reconstitution de l’
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Conclusion générale et perspectiv
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Littérature citée. Bibliographie.
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Bibliographie. Charnov, E. L. et J.
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Bibliographie. Fritsch, M. et Y. Mo
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Bibliographie. Kneib, R. T. (1995).
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Bibliographie. Maitland, P. S. (197
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Bibliographie. Ecobio 6553, Muséum
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Bibliographie. Secor, D. H. (2002).
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Annexes : Annexe 1 : Description de
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Annexe 2 : Curriculum vitae. Emmanu
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Annexes. 2001 Stagiaire: Universit
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Annexes. Parlier E., Duhamel S., Fe
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Résumé Approche quantitative de l
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