Spatial,temporal and structural variations of a Posidonia oceanica seagrass meadow facing human activities |
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Authors: | Agathe Leriche Vanina Pasqualini Charles-François Boudouresque Guillaume Bernard Patrick Bonhomme Philippe Clabaut Jacques Denis |
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Institution: | 1. Centre d’Océanologie de Marseille, UMR CNRS 6540 DIMAR, Campus of Luminy, Case 901, 13288 Marseilles Cedex 9, France;2. Université de Corse, Equipe Ecosystème Littoraux, BP 52, 20250 Corte, France;3. GIS Posidonie, Campus of Luminy, Case 901, 13288 Marseilles Cedex 9, France;4. 14, Rue Paul Doumer, 59110 La Madeleine, France;5. IFREMER, BP 330, 83507 La Seyne sur Mer Cedex, France |
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Abstract: | The Bay of Saint-Cyr (Provence, France, Mediterranean Sea) is the site of two harbours, coastal urban development, trawling, boat anchoring and a sewage outfall. The Posidonia oceanica seagrass distribution was mapped with the help of aerial photographs, side scan sonar and GIS. In addition, the temporal variations of its distribution were studied by aerial photographs and GIS from 1955 to 2000. Finally, coverage and shoot density were measured via scuba-diving. This work reveals (i) the regression of the P. oceanica meadow at sites where harbours have been built, (ii) the occurrence of spaces within the meadow free of live P. oceanica (“intermattes”), which account for 8% of its surface area, (iii) a deep area where P. oceanica coverage and shoot density are low and (iv) evidence of regression, although modest, of the meadow at its lower limit. Nevertheless, the study site also exhibits an extensive and on the whole relatively healthy meadow whose limits have changed little over time. |
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Keywords: | Posidonia oceanica Aerial photography Side scan sonar GIS Human impact |
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