Proceedings of the Second Mediterranean Symposium on Marine

PROCEEDINGS OF THE SECOND MEDITERRANEAN SYMPOSIUM ON MARINE VEGETATION (ATHENS, 12-13 DECEMBER 2003)
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This study aims at appreciating <strong>the</strong> use <strong>of</strong> Posidonia oceanica for <strong>the</strong> evaluation <strong>of</strong> <strong>the</strong>
actual and past environment quality.
MATERIALS AND METHODS
The study is realised in three sites <strong>of</strong> <strong>the</strong> Corsican littoral (Bastia, Lumio, Macinaggio;
Fig. 1), characterized by different quality levels (Ifremer, 1994).
10 orthotropic shoots <strong>of</strong> Posidonia oceanica are sampled, by scuba diving, at -10 meters,
in 2002, in each site. A lepidochronological analysis is realised. This technique, related to
<strong>the</strong> dendrochronology, allows to date <strong>the</strong> scales (or old foliar petioles) which persist
along <strong>the</strong> rhizomes (Pergent, 1990). Scales and rhizomes constitute <strong>the</strong> belowground
part <strong>of</strong> <strong>the</strong> plant.
Fig. 1: Localization <strong>of</strong> <strong>the</strong> studied sites (SHOM).
At <strong>the</strong> end <strong>of</strong> <strong>the</strong> treatment, a series <strong>of</strong> rhizomes sections and <strong>the</strong> corresponding scales lots are
obtained, each section/lot corresponding to a lepidochronological year (Pergent, 1990). The
samples (scales and rhizomes) are frozen (-20° C), frozen-dry (>72 h) and <strong>the</strong>n reduced in
powder. After microwave digestion in closed vessel (Ferrat et al., 2002), <strong>the</strong> mercury is
measured by flameless atomic absorption spectrometry (FIMS 100, Perkin Elmer®).
RESULTS
The measured mercury concentrations vary in function <strong>of</strong> <strong>the</strong> tissue, <strong>the</strong> year and <strong>the</strong> site.
• Influence <strong>of</strong> <strong>the</strong> tissue
A significant difference <strong>of</strong> <strong>the</strong> mercury concentrations is observed between <strong>the</strong> two
studied tissues, all sites and years mingled, with higher values in <strong>the</strong> rhizomes (Kruskall
Wallis, p = 0.000056; Table 1). This difference is also observed, all sites mingled, for <strong>the</strong>
years 1998 to 2001 (ANOVA; Table 1). The concentrations in <strong>the</strong> rhizomes are here still
higher than in <strong>the</strong> scales, except for 1998.