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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Therefore, <strong>the</strong> <strong>Mediterranean</strong> Sea may be considered as a hot spot <strong>of</strong> marine
macrophyte species diversity. One <strong>of</strong> <strong>the</strong> reasons for its richness is <strong>the</strong> coexistence, in
<strong>the</strong> <strong>Mediterranean</strong>, <strong>of</strong> species from <strong>the</strong> warm and boreal Atlantic, <strong>the</strong> tropical Atlantic and
<strong>the</strong> Indo-Pacific Ocean. Ano<strong>the</strong>r reason is <strong>the</strong> high rate <strong>of</strong> endemism.
RANKING HUMAN IMPACT
Human impact can be ranked according to <strong>the</strong> time necessary for <strong>the</strong> impact to become
reversible after <strong>the</strong> disturbance occurred (e.g. an oil spill) or after <strong>the</strong> suspension <strong>of</strong> <strong>the</strong>
stress (e.g. <strong>the</strong> setting up <strong>of</strong> a wastewater treatment plant) (Table I).
Domestic pollution effects on s<strong>of</strong>t bottom assemblages become barely discernible after
less than a decade (Bellan et al., 1999). In a station impacted by hydrocarbons from <strong>the</strong>
Amoco Cadiz wreck (English Channel, France), recolonization by <strong>the</strong> benthic Amphipoda
Ampelisca was achieved after 12 years; recoloni-zation was retarded due to <strong>the</strong>
combination <strong>of</strong> <strong>the</strong> demographic strategy <strong>of</strong> Ampelisca (e.g. absence <strong>of</strong> pelagic larvae
and low fecundity) and <strong>the</strong> distance from non-impacted population which could supply
recruits (Poggiale and Dauvin, 2001). As far as o<strong>the</strong>r taxa are concerned, <strong>the</strong> impact <strong>of</strong>
oil spills is <strong>of</strong>ten weak and only lasts a few years (Marchand, 1981; Raffin et al., 1991;
but see Peterson et al., 2003). In some cases, <strong>the</strong> impact <strong>of</strong> cleaning processes (e.g.
scrubbing <strong>the</strong> rocks with brushes and high pres-sure water jets; fortunately, surfactant is
no longer used) is greater than that <strong>of</strong> <strong>the</strong> oil spill itself (e.g. Clark, 1986; Cognetti and
Cognetti, 1992).
Table 1. Ranking <strong>of</strong> <strong>the</strong> relative importance <strong>of</strong> human impact, according to <strong>the</strong> time necessary
for <strong>the</strong> impact to become reversible.
Rank Time necessary for reversibility Some examples
1 1 day through 1 month Some local pollution events
2 1 month through 1 year Some local pollution events
3 1 year through 10 years Overfishing (cascade effect), some pollution events, oil spills
4 10 years through 1 century Long-lived species destruction (e.g. Cystoseira spp.)
5 1 century through 1 millennium Long-lived species destruction (e.g. Posidonia oceanica), overfishing
(genetic shift)
6 More than 1 millennium Coastal development, species introduction, species extinction, global
warming
In contrast, long lasting and irreversible impact (e.g. long-lived species destruction, coastal
development, introduced species) are greater cause for concern. Unfortunately, <strong>the</strong>
public, and <strong>the</strong>refore journalists and decision makers, give priority to spectacular events,
or accidents, as opposed to what is lasting, what is chronic, even though <strong>the</strong>
consequences <strong>of</strong> chronic impact are <strong>of</strong>ten more serious than those <strong>of</strong> a one-<strong>of</strong>f event.