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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It is a matter <strong>of</strong> identifying rare and threatened vegetation types, <strong>the</strong>n localising <strong>the</strong>m,
with <strong>the</strong> aim <strong>of</strong> protecting <strong>the</strong>m. In addition, maps constitute a valuable tool for <strong>the</strong>
management <strong>of</strong> coastal areas: to know <strong>the</strong> location <strong>of</strong> rare and threatened vegetation
types constitutes a basis for setting up new port facilities, sewage outfalls, submarine
cables, sealines, etc… well away from <strong>the</strong> areas where <strong>the</strong>y grow (Charbonnel et al.,
1995; Pasqualini et al., 1999, 2000; Bernard et al., 2003a). Thirdly, to monitor <strong>the</strong>
possible changes over time <strong>of</strong> <strong>the</strong> range <strong>of</strong> climax communities, as biological indicators
<strong>of</strong> human impact and <strong>of</strong> climate shift, under ei<strong>the</strong>r anthropogenic or natural forcing
(Pasqualini and Pergent-Martini, 1996; Boudouresque et al., 2000).
SCALE AND METHODS
Two types <strong>of</strong> method need to be considered: those leading to discrete data and those
leading to continuous data (Meinesz et al., 1981; Colantoni et al., 1982; Cinelli et al.,
1992; Bianchi and Peirano, 1995; Denis et al., 2003; among o<strong>the</strong>rs).
Examples <strong>of</strong> <strong>the</strong> first type <strong>of</strong> method are sounding leads (a method no longer used),
dredges, grabs, submarines, scuba diving, snorkelling, boating (observation <strong>of</strong> <strong>the</strong>
intertidal zone and <strong>the</strong> subtidal fringe from small boats) and towed underwater cameras
(Table I). The accuracy depends upon <strong>the</strong> mesh size <strong>of</strong> <strong>the</strong> grid, whatever <strong>the</strong> depth (e.g.
Marion, 1883; Pruvot, 1897; Bellan-Santini, 1964; Picard, 1965; Augier and
Boudouresque, 1976; Meinesz and Laurent, 1980, 1982; Clarisse, 1984; Meinesz and
Lefèvre, 1984; Bianconi et al., 1987; Meinesz et al., 1987; Bellone and Meinesz, 1995;
Loquès et al., 1995; Piazzi et al., 1996; Meinesz et al., 1998, 1999, 2001). As far as
identification <strong>of</strong> <strong>the</strong> type <strong>of</strong> bottom (or vegetation) is concerned, it is generally unequivocal.
However, this is less certain with sounding leads, dredges and grabs due to <strong>the</strong>
fact that misinterpretation can result from <strong>the</strong> presence <strong>of</strong> drift material on <strong>the</strong> bottom.
Methods leading to <strong>the</strong> acquisition <strong>of</strong> continuous data are satellite imagery, aerial photography,
Casi (digital spectroradiometer) and side scan sonar (Table I) (e.g. Cuvelier,
1976; Cristiani, 1980; Calvo and Fradà Orestano, 1984; Gloux, 1984; Fredj et al., 1990;
Paillard et al., 1993; Pasqualini, 1997; Jaubert et al., 1999; Belsher and Houlgatte, 2000;
Pérez-Blaya et al., 2000; Bonhomme et al., 2003). The contours are usually obvious, but
<strong>the</strong> identification <strong>of</strong> <strong>the</strong> type <strong>of</strong> bottom within <strong>the</strong> contours <strong>of</strong>ten proves doubtful. In
addition, depth is important for satellite imagery and aerial photography (Cristiani, 1980;
Colantoni et al., 1982; Ramos Esplá, 1984; Pasqualini et al., 1998). In <strong>the</strong> north-western
<strong>Mediterranean</strong>, satellite imagery and aerial photography are disappointing below 5 m and
15 m respectively (Meinesz et al., 1981; Belsher et al., 1985, 1988; Hoareau, 1988;
Meinesz et al., 1988, 1991; Paillard et al., 1993; Bianchi and Peirano, 1995; Pasqualini
et al., 1999; but see Fredj et al., 1990 and G. Pergent, pers. comm.). In contrast, side
scan sonar is generally ineffective in shallow waters (Meinesz et al., 1981; but see
Bernard et al., 2003b). For all continuous methods, accuracy is greatly improved when
ground truth is performed (e.g. Colantoni et al., 1982; Augier et al., 1984; Ramos Esplá,