The Mediterranean Sea is one of the most nutrient-depleted seas and is a characteristic oligotrophic system; however, trace metal concentrations are generally high [1], particulary in its surface waters [2]. The Mediterranean coastline is among the most intensively utilized in the world. The approximately 70,000 km coastline (including all islands) receives over one hundred million visitors per year from all over the world. As a result, the Mediterranean coast and the coastal waters have experienced an increasing impact of tourism in addition to the effects of resident demographic growth. Other anthropogenic impacts include agriculture and mariculture as well as wild fisheries, industry, and navigation [3].
The endemic seagrass Posidonia oceanica (L.) Delile forms meadows that are crucial to the health and function of coastal ecosystems (Figure 1). Over the last 30 years, frequent alterations and regressions of these meadows have been noted (e.g., [4,5]). These alterations are often linked to human activities such as tourism, pollution by urban and industrial centers, and coastal facilities [6-8]. Biological pollution in the Mediterranean Sea [9,10] increases the vulnerability of P. oceanica systems [11,12]. Because of the importance of this keystone macrophyte, P. oceanica is now considered a threatened species requiring protection and is listed in the 'Habitats Directive' of the European Community [13,14].
P. oceanica has been recognized as an effective tool for investigating the coastal environment because it has a widespread distribution around the Mediterranean basin, is fixed on the bottom, and is sensitive to both pollution and human activities. Markert et al. [15] define a "bioindicator" as an organism that contains information about the quality of the environment and a "biomonitor" as an organism that contains quantitative information regarding the quality of the environment. Previous studies suggest that P. oceanica can be used as a bioindicator [6,16-18]. In addition, lepidochronology [19-21], phenology [22], and tissue contents [23-26] can be used to examine historical changes in the environment.
The aim of this work was to 1) verify the efficiency of the magnoliophyta P. oceanica as a bioindicator of the baseline of trace metal pollution at a regional scale. We measured eight trace metal contents (Cr, Ni, Cu, Zn, As, Se, Cd, and Pb) in dated remains of sheaths (lepidochronology) at six sites close to urban zones in northern Corsica (Figure 2). 2) attempt to use P. oceanica as a biomonitor by comparing, over the last 10 years, trace metal contents measured in leaves with results found in sheaths at Calvi.
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