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Stability of the sponge assemblage of the Mediterranean coralligenous along a millennial span of time

April 16, 2013

Coralligenous is a Mediterranean hard substrate of biogenic origin, mainly composed of calcareous algae, growing in dimlight conditions. Sponges are one of the most representative taxa of the coralligenous assemblages, with more than 300 recorded species with different habits: massive, erect, boring and insinuating. When sponges die, their siliceous spicules remain trapped in the biogenic concretion, offering the opportunity to describe the coralligenous spongofauna over a very long span of time, virtually dating back to a large part of the Holocene period. The data reported here were obtained from portions of the cores from four blocks of coralligenous concretions. Each block was collected in a different locality of the Ligurian Sea: Santo Stefano Shoals, Bogliasco, Punta del Faro (Portofino Promontory) and Punta Manara. Radiocarbonage determinations indicate for these conglomerates a maximal age between 1600 and 3100 years. The spicules trapped in the cores show deep dissolution marks in the form of circular holes on their surface or present an enlargement of the axial canal. However, their original shape, generally intact, suggests the

absence of mechanical injuries and allows a tentative identification at specific level. The analysis of these old spicules reveals an ancient sponge assemblage composed of 30 recognisable species. This indicates that almost one half of the sponge community today settled on the coralligenous has been present in the conglomerates for their entire existence.

Bertolino M, Calcinai B, Catteaneo-Vietti R, Cerrano C, et al., in press. Stability of the sponge assemblage of the Mediterranean coralligenous along a millennial span of time, Marine Ecology, 2013, doi:10.1111/maec.12063. Article.

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