Proceedings of the Second Mediterranean Symposium on Marine
Proceedings of the Second Mediterranean Symposium on Marine
Proceedings of the Second Mediterranean Symposium on Marine
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PROCEEDINGS OF THE SECOND MEDITERRANEAN SYMPOSIUM ON MARINE VEGETATION (ATHENS, 12-13 DECEMBER 2003)<br />
26<br />
As a result, <str<strong>on</strong>g>the</str<strong>on</strong>g>re is an urgent need for maps <str<strong>on</strong>g>of</str<strong>on</strong>g> macrophytes o<str<strong>on</strong>g>the</str<strong>on</strong>g>r than seagrasses, such<br />
as Cystoseira zosteroides, C. spinosa, C. brachycarpa, sciaphilous Rhodobi<strong>on</strong>ta, barren<br />
ground (due to sea-urchin overgrazing) with incrusting corallines, etc. In additi<strong>on</strong>, maps<br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> Posid<strong>on</strong>ia oceanica meadows should distinguish landscape types.<br />
QUALITATIVE VERSUS QUANTITATIVE MAPS<br />
Most <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> available maps <strong>on</strong>ly deal with <str<strong>on</strong>g>the</str<strong>on</strong>g> presence or absence <str<strong>on</strong>g>of</str<strong>on</strong>g> a species (or a<br />
community): <str<strong>on</strong>g>the</str<strong>on</strong>g>y are qualitative. A very few maps take into c<strong>on</strong>siderati<strong>on</strong> an<br />
intermediate category, e.g. degraded Posid<strong>on</strong>ia oceanica beds or high versus low<br />
covering or density (e.g. Fredj et al., 1990; Cinelli et al., 1992; Paillard et al., 1993;<br />
Pasqualini, 1997; B<strong>on</strong>homme et al., 2003). As far as shoot density <str<strong>on</strong>g>of</str<strong>on</strong>g> P. oceanica is<br />
c<strong>on</strong>cerned, it has been mapped via kriging (e.g. Francour and Marchadour, 1989).<br />
B<strong>on</strong>homme et al. (2003) did not map <str<strong>on</strong>g>the</str<strong>on</strong>g> actual shoot density, which de-creases<br />
naturally with depth (so that it does not c<strong>on</strong>stitute a pertinent estimate <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> seagrass<br />
health), but c<strong>on</strong>sidered (i) values equal to or above <str<strong>on</strong>g>the</str<strong>on</strong>g> normal density at a given depth<br />
(according to Pergent et al., 1995; Pergent-Martini et al., 1999) and (ii) values below<br />
that normal density. In additi<strong>on</strong>, informati<strong>on</strong> <strong>on</strong> <str<strong>on</strong>g>the</str<strong>on</strong>g> seagrass dynamics (regressi<strong>on</strong> or<br />
expansi<strong>on</strong>) was superimposed <strong>on</strong> <str<strong>on</strong>g>the</str<strong>on</strong>g> map.<br />
For <str<strong>on</strong>g>the</str<strong>on</strong>g> mapping <str<strong>on</strong>g>of</str<strong>on</strong>g> Caulerpa taxifolia, three levels <str<strong>on</strong>g>of</str<strong>on</strong>g> col<strong>on</strong>izati<strong>on</strong> (covering) are<br />
distingui-shed: covered area, affected area and c<strong>on</strong>cerned area (Meinesz et al., 2001,<br />
2003). For <str<strong>on</strong>g>the</str<strong>on</strong>g> mapping <str<strong>on</strong>g>of</str<strong>on</strong>g> Lithophyllum byssoides, isolated individuals versus a rim, and<br />
<str<strong>on</strong>g>the</str<strong>on</strong>g> width <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> rim, were distinguished (Bianc<strong>on</strong>i et al., 1987; Bernard et al., 2003b).<br />
For <str<strong>on</strong>g>the</str<strong>on</strong>g> mapping <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> Cystoseira amentacea belt in <str<strong>on</strong>g>the</str<strong>on</strong>g> subtidal fringe, Ballesteros (in<br />
Soltan, 2001) utilizes 5 categories, from 1 (isolated individuals) to 5 (dense and<br />
c<strong>on</strong>tinuous stand). Finally, for Cystoseira brachycarpa, <str<strong>on</strong>g>the</str<strong>on</strong>g> 6-level Braun-Blanquet scale<br />
(Boudouresque, 1971) was used (Clarisse, 1984).<br />
In order to achieve some <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> purposes <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> cartography, namely <str<strong>on</strong>g>the</str<strong>on</strong>g> management<br />
<str<strong>on</strong>g>of</str<strong>on</strong>g> coastal areas and <str<strong>on</strong>g>the</str<strong>on</strong>g> m<strong>on</strong>itoring <str<strong>on</strong>g>of</str<strong>on</strong>g> change over time, <str<strong>on</strong>g>the</str<strong>on</strong>g> changeover from qualitative<br />
to quantitative maps would be particularly welcome.<br />
CAN WE TRUST EARLY MAPS?<br />
In many regi<strong>on</strong>s, no or very few ancient maps are available. As a result, it is difficult or<br />
impossible to assess <str<strong>on</strong>g>the</str<strong>on</strong>g> dynamics <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> vegetati<strong>on</strong>. In an area near Marseilles<br />
(Provence, France) where <str<strong>on</strong>g>the</str<strong>on</strong>g>re is a series <str<strong>on</strong>g>of</str<strong>on</strong>g> maps <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>the</str<strong>on</strong>g> seagrass Posid<strong>on</strong>ia oceanica<br />
beds spanning more than <strong>on</strong>e century (dating from 1883, 1897, 1958, 1975, 1979,<br />
1991, 2000 and 2003, respectively from Mari<strong>on</strong>, 1883; Pruvot, 1897; Picard, 1965;<br />
Blanc, 1975; Cristiani, 1980; Niéri et al., 1991; Bernard et al., 2000; B<strong>on</strong>homme et al.,<br />
2003), <str<strong>on</strong>g>the</str<strong>on</strong>g> last <strong>on</strong>e very accurate (aerial photographs, side scan s<strong>on</strong>ar and validati<strong>on</strong> by<br />
ground truth), Leriche et al. (2004) pointed out dramatic differences between <str<strong>on</strong>g>the</str<strong>on</strong>g>se<br />
maps (Fig. 1). In c<strong>on</strong>trast with some o<str<strong>on</strong>g>the</str<strong>on</strong>g>r benthic communities, specific biological