Abstract
This paper focuses on a faunistic inventory and the biogeographic pattern of Sardinian Porifera in a scarcely investigated Italian sea belonging to the Eastern Algero-Provençal Basin. The composition and structure of sponge fauna were studied in two priority habitats in two Marine Protected Areas (MPAs) of the North-Western Sardinian Sea. Shallow-water surveys investigated Posidonia oceanica meadows at five sites in the Asinara Island MPA and three karstic submerged caves in the Capo Caccia–Isola Piana MPA. The annotated checklist shows notably high values of taxonomic richness, confirming that P. oceanica meadows and karstic caves are key habitats for Porifera assemblages. Indeed, the sponge taxa recorded (n = 77) with 59 cave-dwelling and 45 taxa in seagrass meadows represent over 10% of the total Mediterranean sponge fauna, despite the small areas investigated, restricted biotopes and low sampling effort. This suggests that species richness is underestimated in circum-Sardinia seas. Internationally protected species (n = 6), rare species (n = 5) and Mediterranean endemic species (n = 14) were recorded. Previously investigated Posidonia meadows and caves share comparable values of species richness and endemicity with the Sardinian biotopes. The geographic range of species indicates that the biogeographic affinity of the NW Sardinian Sea sponge fauna is dominated by Atlanto-Mediterranean species. The three caves harbour a notably homogeneous sponge community, as indicated by the ca. 50% of shared species and high similarity index (> 83%). By contrast, the composition varies markedly among the five Posidonia meadows, which share only five species and display similarity values ranging ca. 20–60%. Unexpectedly when comparing these contrasting biotopes, faunal similarity is relatively low (< 40% shared species); indeed, Posidonia meadows harbour a notable number of cave-dwelling species in intermatte shaded microhabitats.
Highlights
The Mediterranean Sea is one of the world’s priority hotspots for conservation and is home to a wealth of endemic sponge species (Coll et al 2010; Pansini et al 2011; Pronzato et al 2012)
In accordance with the EU guidelines, we focused on two biotopes of conservation interest, Posidonia oceanica (L.) Delile (1813) meadows and submerged marine caves, and used Porifera assemblages as a model taxon in terms of five descriptors, i.e. taxonomic composition, species richness, endemicity, richness of species of conservation value, and richness of rare species
Two priority habitats were investigated and censuses of sponge fauna were conducted in shallow water along the Northern Sardinian Sea coast: i.e. at five sites of P. oceanica meadows along the southern coast of the Asinara Island marine protected areas (MPAs) (2–6 m depth; Asinara Gulf; Figure 1A) and three submerged karstic caves (Bisbe, Falco, Galatea) at the Punta Giglio Promontory, a rocky limestone promontory dating back to the Mesozoic Era within the Capo Caccia-Isola Piana MPA (3–9 m depth; Figure 1B)
Summary
The Mediterranean Sea is one of the world’s priority hotspots for conservation and is home to a wealth of endemic sponge species (Coll et al 2010; Pansini et al 2011; Pronzato et al 2012). Since ancient times, this semi-enclosed sea has been affected by human activity, and today its biodiversity is greatly endangered by habitat destruction, the overexploitation of bioresources and climate change (Médail & Quézel 1999; Halpern et al 2008; Costello et al 2010; Sala et al 2012). Historical data sets, mainly on marine protected areas (MPAs), are fundamental to understanding the accelerating changes occurring over time and space in the Mediterranean Sea
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