Mercury levels and ¯uxes in Posidonia oceanica meadows G. Pergent*, C. Pergent-Martini Faculty of Sciences, University of Corsica, BP 52, 20250 Corte, France Received 19 October 1998; accepted 24 February 1999 Abstract Mercury levels in the marine phanerogam Posidonia oceanica were evaluated at three sites subjected to dierent environmental conditions (anthropogenic activity). Mercury uptake by primary production varied from 9.9 to 100.6 mgm 2 year 1 . For the entire Mediterranean basin, nearly one ton of mercury is mobilized each year, that is to say approximately 0.5% of the annual input. More than 80% of this ¯ux is incorporated into the food webs, mainly through the action of macro-detritivores and micro-organ- isms, thus facilitating the bioavailability of this metal. The remainder of mercury is stored in the matte (sink), in dead sheaths and rhizomes. These mercury stocks are estimated at several dozen tons. # 1999 Elsevier Science Ltd. All rights reserved. Keywords: Mediterranean; Seagrass; Posidonia oceanica; Mercury; Fluxes 1. Introduction In the Mediterranean, the marine phanerogam Posi- donia oceanica (L.) Delile forms vast meadows from the surface down to depths of 40 m. Like the majority of seagrasses, this plant is able to accumulate a range of pollutants, such as organochlorine compounds, arti®cial radionuclides and trace metals (Chabert et al., 1984; Florou et al., 1985; Maserti et al., 1988; Malea and Haritonidis, 1989; Calmet et al., 1991). As is seen in other primary producers (phytoplankton, benthic mac- rophytes), the accumulation of trace metals in P. ocea- nica appears to depend directly on the levels present in the water and sediments (Augier et al., 1977; Maserti et al., 1988; Pergent-Martini, 1998). Recent studies have revealed that pollutant concentrations are in fact memorized within old foliar tissues (dead sheaths and rhizomes) present in the matte (Romeo et al., 1995; Pergent-Martini, 1998). In light of (1) its high toxicity and, in particular, its capacity to become biomagni®ed in the food web, and its possible transformation into methyl-mercury (Bryan, 1984; Cossa et al., 1990), (2) the high number of natural sources of this metal (Bernhard and Renzoni, 1977; Bacci, 1989) and (3) the multiplicity of anthropogenic sources and atmospheric inputs in a semi-enclosed sea such as the Mediterranean (Migon and Caccia, 1990; Maserti et al., 1991), mercury is particularly important in this environment (Civili and Jeftic, 1987). Indeed, the uptake of mercury by P. oceanica appears to be con- siderable, the concentration factors between the water and living leaves (on a wet w basis) having been esti- mated at 3200 in Marseilles (Pergent-Martini, 1998) and between 2083 and 8242 in Tuscany (Maserti et al., 1989). The aim of this study was thus to estimate mercury levels and ¯uxes in P. oceanica meadows in an attempt to increase our understanding of the role of these mea- dows in the cycle of mercury in the Mediterranean basin. 2. Materials and methods P. oceanica shoots were collected by scuba diving at depths of 10 m, from three sites of the Mediterranean: (1) Calvi Bay (42 35 0 N±8 45 0 E, Corsica, France), in an area virtually free of human activities; (2) Ischia Island (40 44 0 N±13 56 0 E, Bay of Naples, Italy), which is located approximately 20 km from the city of Naples; and (3) Marseilles-Cortiou (43 12 0 N±5 21 0 E, Mar- seilles, France), an area which is subject to the direct impact of a city sewage outfall. For each site, 45 ortho- tropic shoots (vertical growth) were sampled and were randomly separated into three replicates of 15 shoots each. Replicates were subsequently analyzed separately. 0269-7491/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S0269-7491(99)00064-0 Environmental Pollution 106 (1999) 33±37 www.elsevier.com/locate/envpol * Corresponding author. E-mail address: pergent@univ-corse.fr (G. Pergent)