Proceedings of the Second Mediterranean Symposium on Marine

PROCEEDINGS OF THE SECOND MEDITERRANEAN SYMPOSIUM ON MARINE VEGETATION (ATHENS, 12-13 DECEMBER 2003)
168
MACROALGAL ASSEMBLAGES IN THE GULF OF NAPLES: SPATIAL
VARIABILITY IN RELATION TO ANTHROPOGENIC DISTURBANCE
Ivan GUALA, Antonio ESPOSITO. and Maria Cristina BUIA
Benthic Ecology Laboratory - Stazione Zoologica ‘A. Dohrn’ Punta S. Pietro 80077 Ischia (Naples) - ITALY
Ivan Guala guala@szn.it
ABSTRACT
Subtidal assemblages are affected by biotic and abiotic factors which work at different
spatial scales; moreover human activities can be an important source <strong>of</strong> variation in
community composition.
In order to detect <strong>the</strong> macroalgal assemblages variability in relation to anthropogenic
disturbance, a visual assessment <strong>of</strong> <strong>the</strong> cover <strong>of</strong> algal species was performed on subhorizontal
rocky substrates, at both 5 and 10 m depths, in 12 localities <strong>of</strong> <strong>the</strong> Gulf <strong>of</strong>
Naples (Italy), for a total <strong>of</strong> 216 observations.
Important taxa in differentiating localities were identified. Among <strong>the</strong>se, Caulerpa
racemosa, recently introduced in <strong>the</strong> studied area, was one <strong>of</strong> <strong>the</strong> most important
species in differentiating impacted and relatively undisturbed localities. Deep non
impacted communities seem to be more vulnerable to <strong>the</strong> introduction <strong>of</strong> this alien
seaweed. Its invasiveness, strictly linked to its reproductive modality, may be associated
with summer anchorages <strong>of</strong> many leisure boats ra<strong>the</strong>r than with <strong>the</strong> environmental
conditions <strong>of</strong> recipient localities.
KEY-WORDS: community diversity, anthropogenic disturbance, rocky substrate,
Caulerpa racemosa.
INTRODUCTION
Urban development and anthropogenic activities are <strong>of</strong>ten <strong>the</strong> cause <strong>of</strong> disturbance on
marine communities (GESAMP, 1997; Lindegarth and Hoskin, 2001). Plant assemblages
may be threatened by chemical contaminants, excess nutrients, sewage discharge,
reduced light penetration which can alter species composition and also limit <strong>the</strong> growth
and depth distribution <strong>of</strong> plant species (Boyle, 1984; GESAMP, 1997; Middelboe and
Sand-Jensen, 1998). Industrial centres, mercantile ports, power plants, touristic and
fishing harbours, aquaculture facilities and, generally, densely populated urban zones,
represent <strong>the</strong> most important sources <strong>of</strong> disturbance.
In recent years many authors have also indicated biological invasions as a possible threat
to marine environment. Trade and transports globalisation has favoured a great increase
<strong>of</strong> marine species introductions all over <strong>the</strong> world. In suitable conditions, non-native
species can become invasive, playing a conspicuous role in recipient ecosystems, taking
<strong>the</strong> place <strong>of</strong> native species, affecting <strong>the</strong> biodiversity (Carlton and Geller, 1993;