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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The temporal evolution in <strong>the</strong> scales shows different tendencies for <strong>the</strong> three sites. For
Bastia, a significant decrease <strong>of</strong> <strong>the</strong> mercury concentration is noted (Kruskall Wallis, p <
0.05) from 1997 to 1999, <strong>the</strong>n from 2000 to 2001 (Table 1). For Lumio and
Macinaggio, <strong>the</strong> observed variations are not significant (Kruskall Wallis, p ≥ 0.05; ANOVA,
p ≥ 0.05), never<strong>the</strong>less for Macinaggio an increase <strong>of</strong> <strong>the</strong> concentrations until 1999 and
a decrease since <strong>the</strong>n are observed (Table 1). Conversely, <strong>the</strong> temporal evolution <strong>of</strong>
mercury concentrations in <strong>the</strong> rhizomes is comparable for <strong>the</strong> three sites (ANOVA, p ≥
0.05), with a significant increase from 1998 to 2001 (ANOVA, p = 0.00001; Table 1).
DISCUSSION AND CONCLUSION
The results confirm <strong>the</strong> importance <strong>of</strong> <strong>the</strong> different factors (nature <strong>of</strong> <strong>the</strong> tissue, site and year)
on <strong>the</strong> mercury contents accumulated by <strong>the</strong> marine magnoliophyta Posidonia oceanica.
The tissue factor plays a determinant role, with higher concentrations in <strong>the</strong> rhizomes
than in <strong>the</strong> scales. This preferential accumulation in <strong>the</strong> rhizomes has ever been notified
by several authors (Capiomont, 2000; Maserti et al., 1991). It can be due to <strong>the</strong> fact that
mercurial absorption is mainly made by <strong>the</strong> root system in Posidonia oceanica (Ferrara
and Serriti, 1989; Maserti et al., 1988). It can be also due to <strong>the</strong> fact that rhizomes are
living organs (Francour, 1985) which continue having a functional activity, and so
accumulating trace-metals, during several years, whereas scales (dead organs) have no
active accumulation (Pergent, 1987). A different accumulation (availability <strong>of</strong> <strong>the</strong>
chemical forms) by <strong>the</strong> rhizomes and <strong>the</strong> foliar tissues, especially with regards to <strong>the</strong>
petioles (future scales), can not be excluded, as this difference <strong>of</strong> behaviour is also
observed at <strong>the</strong> level <strong>of</strong> <strong>the</strong> different sites.
So considering only <strong>the</strong> concentrations in <strong>the</strong> rhizomes, Bastia, Lumio and Macinaggio
seem to behave equally. Conversely, <strong>the</strong> contents recorded in <strong>the</strong> scales individualize <strong>the</strong>
site <strong>of</strong> Bastia as more contaminated than <strong>the</strong> two o<strong>the</strong>rs sites. Consequently <strong>the</strong> factor
site seems to be able to overimpose and/or to modify <strong>the</strong> behaviour <strong>of</strong> <strong>the</strong> different
tissues. With regards to <strong>the</strong> literature data (Capiomont, 2000; Pergent-Martini and
Pergent, 2000; Sanchiz et al., 1999), <strong>the</strong> values measured in this study stay relatively
weak, for <strong>the</strong> scales and <strong>the</strong> rhizomes as well as for <strong>the</strong> belowground biomass in its
whole, with concentrations between 50 and 70 ng.g -1 . These values can be considered
as <strong>the</strong> back noise <strong>of</strong> <strong>the</strong> <strong>Mediterranean</strong> Sea.
The mercury concentrations study shows that interannual variations exist at <strong>the</strong> general
level (all sites and tissues mingled), as at <strong>the</strong> level <strong>of</strong> a given tissue (Table 1). So, 2001
appears significantly weaker than <strong>the</strong> o<strong>the</strong>r years, if only mercury concentrations in <strong>the</strong>
scales, all sites mingled, are considered (Table 1). However, it is difficult to know if this
reduction <strong>of</strong> mercury concentrations in <strong>the</strong> scales is correlated to a decrease <strong>of</strong> this metal
in <strong>the</strong> coastal environment or if it only reflects a passive accumulation <strong>of</strong> mercury
(adsorption), during <strong>the</strong> ageing <strong>of</strong> <strong>the</strong> scales or if it illustrates mechanisms <strong>of</strong> biological
dilution. Indeed, Capiomont (2000) shows that during <strong>the</strong> ageing <strong>of</strong> <strong>the</strong> scales, <strong>the</strong>re is a
loss <strong>of</strong> biomass <strong>of</strong> <strong>the</strong>se ones and that this loss is accompanied by an increase <strong>of</strong> <strong>the</strong>
mercury concentrations whereas <strong>the</strong> total quantities <strong>of</strong> mercury decrease weakly.
According to this author, mercury could be consequently associated to a more refractory