Preprint volume - SIBM

Pre-print Volume - Posters
Topic 2: MARINE ORGANISMS AND ECOSYSTEMS AS MODEL SYSTEMS
D. AGNETTA, C. BONAVIRI, P. GIANGUZZA, S. RIGGIO
Department of Ecology, University of Palermo, Via Archirafi, 18 – 90123 Palermo, Italia.
davimaxit@yahoo.it
THE MPA “ISOLA DI USTICA”:
A MODEL OF BENTHIC COMMUNITY NATURAL CHANGES
L’AMP “ISOLA DI USTICA”:
UN MODELLO DI CAMBIAMENTI NATURALI DELLA COMUNITÀ
BENTONICA
Abstract – This study, aimed to evaluate the protection effects on Paracentrotus lividus and Arbacia lixula
populations and benthic assemblage, spanned four years (2006-2009) at the MPA “Isola di Ustica”.
Results showed a decrement of sea urchin abundance and a consequent recovery of erect macroalgae.
Multiple factors like lack of sea urchin recruitment and natural predation have possibly promoted the
observed pattern.
Key-words: benthos, protected resources.
Introduction – Rocky infralittoral benthic communities may be controlled by sea
urchin abundance. At high densities, sea urchins eliminate erect macroalgae
maintaining barrens (areas dominated by encrusting algae). In Mediterranean MPAs,
fishing prohibition generally leads to the recovery of populations of sea urchin
predators, such as seabreams (i.e. Diplodus sargus and D. vulgaris), thus promoting the
growth of an erect macroalgae canopy via sea urchin control. The opposite trend has
occurred at the MPA of Ustica Island (SW Italy) where, after the cessation of
harvesting activities, urchin barrens formed due to a burst of the two co-occurring sea
urchins Paracentrotus lividus and Arbacia lixula populations. The natural scarcity of
the two seabream species has probably favoured this process (Bonaviri et al., 2009).
Ustica MPA is characterized by a particular protection regulation; during the summer
season, recreational fishing of the edible P. lividus is permitted exclusively in the take
zone (zone C). It was demonstrated that recreational P. lividus fishing affects
abundance of the species itself and has no effect on the co-occurring, non-edible
species A. lixula in the fished sites of Ustica MPA (Gianguzza et al., 2006). In order to
evaluate if this pattern maintains, the effect of protection on sea urchins abundance was
monitored along four years. We expected that the potential differences in sea urchins
abundance allow a different development of the benthic assemblages in zones A
(integral protection) and C at Ustica MPA. According to these considerations we
hypothesized: (1) higher abundance of P. lividus in the no-take zone (A), (2) similar
abundance of A. lixula in the zones A and C, (3) a different pattern of benthic
assemblage cover in relation to sea urchins abundance. We excepted that this pattern
maintains along years.
Materials and methods –During summers of the years 2006-2009, sea urchin density
and benthic assemblage cover were estimated on rocky bottoms 2-6 m deep, in two
sites for each A and C zones (Fig. 1). At each site and sampling time, sea urchins
density was measured in ten independent random quadrates (1 m²). Thirty-two pictures
of 400 cm² of the substrate were taken to characterize benthic assemblage cover,
summarized in functional group according to Steneck & Dethier (1994) modified to
41 st S.I.B.M. CONGRESS Rapallo (GE), 7-11 June 2010
126