Proceedings of the Second Mediterranean Symposium on Marine

PROCEEDINGS OF THE SECOND MEDITERRANEAN SYMPOSIUM ON MARINE VEGETATION (ATHENS, 12-13 DECEMBER 2003)
34
ANTHROPOGENIC IMPACTS ON MARINE
VEGETATION IN THE MEDITERRANEAN
Charles F. BOUDOURESQUE, Sandrine RUITTON and Marc VERLAQUE
Centre d'Océanologie de Marseille, UMR 6540, Campus <strong>of</strong> Luminy, 13288 Marseilles cedex 9, France
ABSTRACT
The notion <strong>of</strong> plant kingdom, commonly accepted since <strong>the</strong> time <strong>of</strong> Linnaeus (18 th
century) actually encom-passes a highly polyphyletic set <strong>of</strong> taxa belonging to Procaryota
and Eucaryota and, within <strong>the</strong> Eucaryota, to six out <strong>of</strong> <strong>the</strong> eight kingdoms, namely
Opisthokonts, Amaebobionta, Plantae, Stramenopiles, Alveolobionta and
Discicristobionta. Therefore, for at least two decades, plants (and vegetation) have no
longer been scientific concepts but a matter <strong>of</strong> customary usage. Biodiversity means <strong>the</strong>
variety among living organisms including, inter alia, diversity within species, between
species, ecosystems and landscapes and functional diversity. As far as species diversity
is concerned, point diversity, alpha diversity, beta diversity, gamma diversity and epsilon
diversity should be considered separately, since anthropogenic impact can increase alpha
diversity while reducing gamma diversity. The <strong>Mediterranean</strong> Sea may be considered as
a hot spot <strong>of</strong> marine epsilon species diversity. The ranking <strong>of</strong> <strong>the</strong> relative importance <strong>of</strong>
human impact on biodiversity must take into account <strong>the</strong> time necessary for <strong>the</strong> impact
to become reversible: from a few days to millennia. Thus, coastal development, species
introduction, species extinction and global warming are <strong>of</strong> major concern. (i) Coastal
development especially concerns shallow and highly prod-uctive bottoms with seagrass
and o<strong>the</strong>r macrophyte communities. In <strong>the</strong> <strong>Mediterranean</strong>, both tourism (a third <strong>of</strong> total
world tourism) and <strong>the</strong> population explosion are boosting coastal development. (ii) The
<strong>Mediterranean</strong> Sea constitutes a hot spot for species introduction: introduced species
nowadays represent 6,5% <strong>of</strong> its flora, and <strong>the</strong>ir number is doubling every twenty years.
(iii) No "plant" species are known to have become extinct due to human impact, but
many species and communities are vulne-rable, i.e. have experienced a dramatic decline
over <strong>the</strong> last decades (e.g. Lithophyllum byssoides rims, Posidonia oceanica meadows
and Cystoseira forest) (iv) Finally, global warming (partly due to natural climatic shift) can
upset <strong>the</strong> existing equilibrium.
INTRODUCTION
Human impact on biological diversity in <strong>the</strong> <strong>Mediterranean</strong>, in particular on <strong>the</strong> benthic
vege-tation, is generally thought to be high, due to tourism (<strong>the</strong> <strong>Mediterranean</strong> region
accounts for a third <strong>of</strong> <strong>the</strong> total number <strong>of</strong> tourists worldwide), population explosion and
<strong>the</strong> subsequent coastal development.