Preprint volume - SIBM
Preprint volume - SIBM
Preprint volume - SIBM
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Pre-print Volume - Oral presentations<br />
Topic 2: MARINE ORGANISMS AND ECOSYSTEMS AS MODEL SYSTEMS<br />
C. BONAVIRI, C. PIPITONE 1 , P. GIANGUZZA, B. HEREU 2<br />
Dipartimento di Ecologia Università di Palermo, Via Archirafi, 18 - 90123 Palermo, Italia.<br />
chiabon@libero.it<br />
1 CNR-IAMC, Sede di Castellammare del Golfo, Trapani, Italia.<br />
2 Department d’Ecologia, Universitat de Barcelona, Spain.<br />
PREDATION ON YOUNG PARACENTROTUS LIVIDUS SETTLERS:<br />
IMPLICATIONS FOR MEDITERRANEAN ROCKY<br />
INFRALITTORAL STABILITY<br />
PREDAZIONE SU GIOVANILI DI PARACENTROTUS LIVIDUS:<br />
IMPLICAZIONI PER LA STABILITÀ DEI SISTEMI INFRALITORALI ROCCIOSI<br />
MEDITERRANEI<br />
Abstract – Predation of young sea urchins settlers are often invoked as a key process in the control of sea<br />
urchins populations and therefore in the structure and stability of rocky infralittoral communities. In this<br />
study a number of decapod species were detected as predators of young settlers of the sea urchin<br />
Paracentrotus lividus and their predation rates estimated by laboratory experiments. Abundance of these<br />
predators also resulted significantly lower in barren than in macro algae forests, suggesting that lack of<br />
predation of juvenile sea urchins facilitates the stability of Mediterranean barren systems.<br />
Key-words: ecosystem stability, predator-prey interactions, sea urchin, crustaceans, hard bottoms.<br />
Introduction - In the last decades temperate infralittoral ecosystems have undergone a<br />
loss of habitat-forming algae. Erect macroalgae canopy can be massively reduced by<br />
perturbation (e.g., loss of top-down control of grazers, destructive harvesting) leading<br />
to a shift towards an alternative phase dominated by sea urchins and encrusting<br />
organisms named barren (Sala et al., 1998). Whether encrusting- and erect macroalgae<br />
dominated communities represent alternate stable states of rocky systems has not been<br />
proven (Knowlton, 2004). Sea urchins biomass and abundance maintain high in barren<br />
areas where few-months old individuals can be more numerous than in macro algae<br />
forests (Rowley, 1989). Echinoids are invertebrates with a planktonic larval phase and<br />
their population structure strictly depends on larval supply, settlement process and<br />
post-settlement mortality. Some authors suggest that mortality of young settlers could<br />
represent the bottleneck for sea urchin populations in erect macroalgae forests<br />
(Jennings & Hunt, 2010 and reference therein). Given that erect macroalgae are<br />
habitat-formers, they add physical complexity to the substratum by increasing species<br />
richness and functional diversity of mobile epifaunal organisms (Taylor, 1998).<br />
Density of small invertebrates is positively correlated with structural complexity of the<br />
habitat, being low in barrens and high in erect algae assemblages (Taylor, 1998). The<br />
fact that young settled sea urchins are vulnerable to predation by various small<br />
invertebrates (Scheibling & Robinson, 2008), may make erect algae systems less<br />
suitable for the survival of recruits. Mediterranean rocky littorals are characterized by<br />
either barren or macro algae forests (Sala et al., 1998). The sea urchin Paracentrotus<br />
lividus resides in both systems but displays always higher biomass and abundance in<br />
the former. Since the settlement of P. lividus is probably independent from the benthic<br />
assemblage (Hereu, 2004), the difference of the sea urchin population structure may<br />
depend on the post-settlement mortality between the two systems. Mortality of P.<br />
lividus recruits has been estimated to reach 75% during the first six months in a macro<br />
41 st S.I.B.M. CONGRESS Rapallo (GE), 7-11 June 2010<br />
104