Contents lists available at ScienceDirect Ecological Indicators journal homepage: www.elsevier.com/locate/ecolind Evaluating the coastal ecosystem status of two Western and Eastern Mediterranean islands using the seagrass Posidonia oceanica A. Güreşen a, ⁎ , G. Pergent b , S.O. Güreşen a , Y. Aktan a a University of Istanbul, Faculty of Aquatic Sciences, Turkey b University of Corsica, Faculty of Sciences, France ARTICLE INFO Keywords: Posidonia oceanica Biological quality element Biotic index Ecological status Monitoring ABSTRACT Mediterranean seagrass Posidonia oceanica is used as a ‘biological quality element’ in the long-term monitoring programmes of the Water Framework Directive (WFD 2000/60/EC) for the evaluation of ecological status of coastal waters. Due to its low resilience to anthropogenic pressures, P. oceanica meadows have disappeared irreversibly along some of the Mediterranean coasts. The main objective of this survey, is therefore to compare the ecological status of coastal waters and P. oceanica meadows in two islands from Eastern (Gökçeada, Turkey) and Western (Corsica, France) Mediterranean Sea based on the Posidonia Biotic Index (BiPo) and the Vitality Index besides concentrating on: (i) their consistency in different environmental conditions present in the Mediterranean Sea, (ii) their effectiveness to discriminate the ecological status of coastal waters in relation to different anthropogenic pressures and (iii) their application capacity to initiate long-term data series for mon- itoring the evolution of the meadows in less evaluated regions (i.e. from the Eastern Mediterranean). The measurements of several descriptors of P. oceanica are interpreted based on the BiPo and the Vitality indices for 2 regions; 9 sites from Gökçeada and 15 sites from Corsica exposed to different human pressures. The mean BiPo and Vitality indices are higher in Corsica than in Gökçeada, where the values correspond to a “good” status for Corsica and a “moderate” status in Gökçeada. The application of these biotic indices showed their feasibility and comparability to assess the ecological status in different environmental conditions. Significant relationships between the scores of Anthropization index and the EQR values of the BiPo index (r = −0.745, p < 0.01) and the Vitality index (r = −0.702, p < 0.01) highlighted their efficiency to determine the seagrass degradation in the sites subjected to higher pressure levels. It can be assumed that this study initiates the development of long- term data series and also meets the essential data deficiency in less evaluated regions. 1. Introduction Changing climate conditions and recent anthropogenic pressures on coastal regions, cause irreversible regressions and habitat losses of the seagrass meadows (Ruiz et al., 2001; Duarte, 2002; Ruiz and Romero, 2003; Boudouresque et al., 2009; Waycott et al., 2009; Telesca et al., 2015). Apart from these, wastewater discharges, aquacultural, agri- cultural and recreational activities (Manzanera et al., 1995; Boudouresque et al., 2012) cause water quality degradation as eu- trophication, harmful algal blooms, high turbidity and mucilage for- mation (Innamorati et al., 2001; Precali et al., 2005). Therefore, the Water Framework Directive (WFD 2000/60/EC) has been established (EC, 2000) with the aim of conserving and managing of all types of water bodies for a sustainable development. The WFD is also concentrated on the evaluation of the coastal ecosystem status through angiosperm classification practices in a wide spatial extent in order to reach “good” ecological status for all types of waterbodies by 2020 (EC, 2000). As a common representative species of the angiosperms in the Mediterranean Sea in terms of abundance (Med-GIG, 2011), Posidonia oceanica (Linnaeus) Delile is used as a “biological quality element” in the long-term monitoring programmes implemented by the WFD (Pergent et al., 1995; Ruiz and Romero, 2003; Balestri et al., 2004; Pergent-Martini et al., 2005; Boudouresque et al., 2009; Montefalcone, 2009). Various biotic indices using P. oceanica, have been developed to assess the ecological status in general and in a wide spatial extent as much as possible (A Multivariate Index_POMI by Romero et al., 2007; https://doi.org/10.1016/j.ecolind.2019.105734 Received 22 February 2019; Received in revised form 9 September 2019; Accepted 12 September 2019 ⁎ Corresponding author at: Department of Marine and Freshwater Resources and Management, Faculty of Aquatic Sciences, University of Istanbul, 34134 Istanbul, Turkey. E-mail address: aysugumusoglu@gmail.com (A. Güreşen). Ecological Indicators 108 (2020) 105734 1470-160X/ © 2019 Elsevier Ltd. All rights reserved. T