October 2015
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Mediterranean Seagrasses are represented by five species, whose most representative are Posidonia oceanica (L.) Delile and Cymodocea nodosa (Ucria) Ascherson. Meadows of these two species have been also considered as priority habitat according Annex I of the EC Directive 92/43/EEC on the Conservation of Natural Habitats and of Wild Fauna and Flora (EEC, 1992). But the importance of these seagrassess is also due to the considerable biomass – especially P. oceanica meadows – that represents an obstacle that hinders and effectively dampens hydrodynamics (waves and currents) of the sea bottom (hydrodynamic forces are reduced from 10% to 75% under the leaves following Gacia et al., 1999). Very severe storms can be the cause of a very important natural issue: the massive sediment progradation of allochthonous and autochthonous sediments tends to bury the leafs of P. oceanica, determining its death. Project SIGIEC ”Integrated Management System for Coastal Erosion” has applied an experimental technique of multiscale mapping to assess the effects (mesoscale and macroscale level) of coastal erosion over the P. oceanica meadows and in this paper we’ll present the preliminary results. The study has been conducted in Alimini, Southern Adriatic Sea (Apulia), in April 2015. The mesoscale level has been analysed with 8 transects (4 perpendicular and 4 parallel to the coastline). A towing vehicle equipped with (HD) high-definition vertical cameras. Images were processed by Structure From Motion (SfM) algorithms that allowed us to generate 3D models for identifying and classifying physiographic and structural features of the meadow. Processing and image analysis has been performed trough unsupervised classification algorithms. The macroscale level has been analysed by processing a WorldView-2 multispectral satellite 8-band scene, with 1.8 meters resolution (dated April 2012). The relevant spectral signatures have been identified for the different physiographic - structural features in the Alimini meadow. Processing and image analysis has been performed trough supervised classification algorithms. Cartographic data acquired at different scales were then integrated in order to assess the effects of coastal erosion over the P. oceanica meadows. EEC. 1992. Council Directive 92/43/EEC on the conservation of natural habitats and of wild fauna and flora. Official Journal of the European Communities. Law 206 of 22 July 1992. Gacia E, Granata T., Duarte C. 1999. An approach to measurement of particle flux and sediment retention within seagrass (Posidonia oceanica) meadows. Aquatic Botany 65: 255–268. This study has been conducted in the SIGIEC Project “Sistema di Gestione Integrata per l’Erosione Costiera”, financed in the Italian Programme PON01 02651/F6 - Programma Operativo Nazionale Ricerca e Competitività 2007-2013, financed by the Italian Ministry for Education, University and research with the ESFR co-financement (Objective Convergence) including regions Calabria and Apulia. http://www.sigiec.sister.it