Proceedings of the Second Mediterranean Symposium on Marine

Williamson and Fitter, 1996; Piazzi et al. 2001; Boudouresque and Verlaque, 2002;
Carlton, 2002). Human disturbed habitats are <strong>of</strong>ten thought to be more susceptible to
invasions (Ribera and Boudouresque, 1995; Ruiz et al., 1997; Leppäkoski et al., 2002).
With reference to <strong>the</strong> <strong>Mediterranean</strong>, Boudouresque and Verlaque (2002) listed 84
macroalgal species which have probably been introduced, 9 <strong>of</strong> <strong>the</strong>se are considered
invasive. Among <strong>the</strong>m <strong>the</strong> tropical green alga Caulerpa racemosa (Forsskål) J. Agardh
has invaded in <strong>the</strong> last decade <strong>the</strong> western side <strong>of</strong> <strong>the</strong> <strong>Mediterranean</strong>, spreading on
every kind <strong>of</strong> substrate, from <strong>the</strong> surface to 60 m depth, and becoming a severe threat
to algal diversity (Piazzi et al., 2001). Recently, C. racemosa was also observed for <strong>the</strong>
first time in <strong>the</strong> Gulf <strong>of</strong> Naples (Buia et al., 2001).
About 2 000 000 <strong>of</strong> inhabitants live in <strong>the</strong> area <strong>of</strong> <strong>the</strong> Gulf <strong>of</strong> Naples (Italy, Sou<strong>the</strong>rn
Tyrrhenian Sea); a wide urban area and a big commercial port, with a maritime traffic
volume near to 36000 vessels per year (Flagella, pers. comm.), is present in <strong>the</strong> inner
side <strong>of</strong> <strong>the</strong> gulf, and several fishing and touristic harbours, and aquaculture facilities are
spread all around <strong>the</strong> coast. Such high density <strong>of</strong> population and consequent
anthropogenic activities are able to determine strong disturbances on marine ecosystems
with possible changes in macroalgal communities.
In <strong>the</strong> framework <strong>of</strong> <strong>the</strong> ALIENS project, a survey along Neapolitan coasts was performed,
during <strong>the</strong> summer 2002, with <strong>the</strong> aim to detect <strong>the</strong> distribution <strong>of</strong> C. racemosa, also
providing a description <strong>of</strong> <strong>the</strong> recipient communities, comparing habitats with a different
degree <strong>of</strong> human interference. On <strong>the</strong> basis <strong>of</strong> macroalgal composition, differences among
localities placed in human disturbed areas and localities far from possible source <strong>of</strong>
disturbance were descried. The occurrence <strong>of</strong> C. racemosa in many studied localities was
discussed in relation to species richness, total algal coverage and presence <strong>of</strong> main taxa.
MATERIALS AND METHODS
Study area and sampling design
In July 2002 a hierarchical survey in <strong>the</strong> Gulf <strong>of</strong> Naples (Fig. 1) was performed on
subtidal rocky substrate at both 5 and 10 m depth. Sampling localities were selected on
<strong>the</strong> nor<strong>the</strong>rn and sou<strong>the</strong>rn sides <strong>of</strong> <strong>the</strong> Gulf ; <strong>the</strong> inner part was not considered because
<strong>of</strong> its sandy and muddy bottoms. Six “impacted” localities (named from 1 to 6) were a
priori selected in human disturbed areas (close to farming facilities, harbours and urban
zones), six (from 7 to 12) were chosen in relatively undisturbed areas: <strong>the</strong>y were
considered as “controls”. Each locality comprised a stretch <strong>of</strong> shoreline <strong>of</strong> about 0.2 - 1.5
Km and included three sites, 15 m long, randomly selected; at each site three random
quadrats (50 x 50 cm on sub-horizontal substrate at both depths) were examined by
visual estimation <strong>of</strong> <strong>the</strong> coverage <strong>of</strong> conspicuous macroalgal species (more than 2 cm in
size or smaller, but forming patches occupying more than 4 square cm); species not
recognised in field were collected and fixed in formol 4% to be identified in laboratory.
Species richness (number <strong>of</strong> taxa) and total percent coverage were calculated for each
<strong>of</strong> <strong>the</strong> studied quadrats.(Fig.1)
ACTES DU DEUXIEME SYMPOSIUM MEDITERRANEEN SUR LA VEGETATION MARINE (ATHENES, 12-13 DECEMBRE 2003)
169