Journal of Coastal Research, Special Issue 56, 2009 Journal of Coastal Research SI 56 pg - pg ICS2009 (Proceedings) Portugal ISSN Estimation of available seagrass meadow area in Portugal for transplanting purposes. A. H. Cunha, J. Assis, E. A. Serrão Centro de Ciências do Mar, CIMAR-L.A. Universidade do Algarve, Campus de Gambelas 8005-139 Faro – Portugal acunha@ualg.pt ABSTRACT CUNHA, A. H., ASSIS, J., and SERRÃO, E.A. 2009. Estimation of the available seagrass meadow area in Portugal for transplanting purposes. Journal of Coastal Research, SI 56 (Proceedings of the 10 th International Coastal Symposium), pg – pg. Lisbon, Portugal, ISBN Seagrasses are marine flowering plants found in shallow coastal habitats around the world. These plants create a habitat of substantial importance from an ecological, economic and biodiversity point of view. Unfortunately, there have been considerable losses of seagrass habitat worldwide, leading to increasing interest on the development of seagrass restoration and rehabilitation projects. These projects, often developed as a mitigation tool, deeply benefit from the spatially explicit information included in Geographic Information Systems (GIS). Thus, to have seagrass area estimates for transplanting purposes and, to be able to monitor transplanting impacts, a large-scale GIS map was build for Sado and Mira River Estuaries, Portinho da Arrábida Bay and Ria Formosa regions using: (1) aerial photography analysis, (2) photo-interpretation, (3) on-site groundtruthing surveys and (4) statistical analysis. Habitat boundaries were evaluated through aerial photography, and a complete set of selected sites were visited for groundtruth validation, using 4 types of transect methods (along the shore-line, free-diving, scuba diving and boat transects). Twelve thousand, six hundred and fifty two hectares (12652.17 ha) were assessed, 3944 groundtruth points were recorded and 3 seagrass species were identified and mapped (Zostera marina, Zostera noltii and Cymodocea nodosa). Ria Formosa had the largest distribution area of seagrass species (241.04 ha), followed by Sado Estuary (32.68 ha). Mira Estuary had only one seagrass meadow and in Portinho da Arrábida Bay no seagrass meadows were registered. Zostera noltii was the most abundant species in both regions, followed by Cymodocea nodosa and Zostera marina. The error assessment for species distribution area and diversity, estimated through kappa statistics based on error matrices, gave a perfect agreement value (K=0.912) to the methodology used. ADDITIONAL INDEX WORDS: GIS, Mapping, Seagrass, Restoration INTRODUCTION Seagrass meadows provide a wide array of ecological functions that are important in maintaining healthy estuarine and coastal ecosystems (ORTH et al., 1984, THAYER et al., 1984, HECK et al., 1995). They increase the stability of the seafloor through the growth of extensive rhizome mats (FONSECA and FISHER, 1986), play a critical role in primary production, including the harnessing and cycling of nutrients (HILLMAN et al., 1989), and provide valuable habitat for a diverse array of marine organisms (SHORT and WYLLIE-ECHEVERRIA, 1996, DUARTE, 2002, ORTH et al. 2006). Unfortunately, over the last years, Atlantic seagrass populations have declined due to pollution associated with increased human populations (KEMP et al., 1983, VALIELA et al., 1992) and episodic occurrences of the wasting disease (SHORT et al. 1986, DEN HARTOG, 1994), as well as other human-induced and natural disturbances (SHORT and WYLLIE-ECHEVERRIA, 1996, ORTH et al,. 2006). Major efforts have been developed to implement seagrass restoration and rehabilitation projects (Palling et al., 2009). The approaches that involve the collection of mature seagrass from donor populations for transplanting purposes, to areas of seagrass loss (e.g. SEDDON, 2004), deeply benefit from the spatially explicit information included in benthic habitat maps. With this type of baseline information, planning managers and researchers are allowed to better choose population donor sites and to monitor spatial and temporal changes in species distribution at a landscape level. The use of applications such as Geographic Information System (GIS) and fieldbased measurements using Geographic Positioning System (GPS) have become common place methods to achieve precise habitat mapping and spatial resource management decision-making (BRETZ et al., 1998). The present paper describes the approach used in the Biomares restoration project to build a large-scale benthic habitat map to assess the potential donor seagrass meadows area coverage available in Portugal for transplanting purposes. It is also the first attempt to estimate total seagrass cover in the regions studied. Biomares, a European Union Life project (LIFE06 NAT/P/192), aims to restore and manage the biodiversity of the Marine Park Site Arrábida-Espichel. METHODS A large-scale seagrass habitat map was built during the year 2007, for Sado and Mira Rivers Estuary, Portinho da Arrábida