Stability of the sponge assemblage ofMediterranean coralligenous concretions along a millennial time span

Abstract

The Mediterranean coralligenous substratum is a hard bottom of biogenic origin, mainly composed of calcareous algae, growing in dim light conditions. Sponges are among of the most representative taxa of the coralligenous assemblages, with more than 300 recorded species of 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 core samples collected from four 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. Radiocarbon age 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 the species 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 coralligenous substrata has been present in the conglomerates for their entire existence.

Comparison between the sponge fauna living outside and inside the coralligenous bioconstruction. A quantitative approach

“…Moreover, in the coralligenous habitat, the presence of pockets of soft-sediments allows the contemporary presence of both hard-and soft-bottom species (Ballesteros, 2006) and the peculiar structure leads to the entrapment of sediments that can represent a sort of black box, telling the story of the ancient assemblages (Bertolino et al, 2014). Scheffers et al (2010) demonstrated that in Curaçao reefs, cryptic suspension feeders, especially sponges, covered more than 60% of the inner cavity surface.…”

“…Bertolino et al (2013), sectioning big coralligenous blocks into slices identified the presence of 27 exclusively endolithic species giving an idea of the richness of this group inside the coralligenous substrata. Moreover, it was stated that the diversity of coralligenous sponges has remained stable over a millennial span of time, and this extended stability may be related to the en- vironmental stability of the inner habitat of the conglomerates (Bertolino et al, 2014).…”

Temporal variability of sedimentation rates and mobile fauna inside and outside a gorgonian garden

“…This lack of information has been reinforced by recent studies focusing on the diversity of Porifera (Bertolino et al . ; Calcinai et al . ).…”

“…As highlighted by Ballesteros (2006), knowledge about the actual biodiversity hosted by this habitat has yet to be characterized. This lack of information has been reinforced by recent studies focusing on the diversity of Porifera (Bertolino et al 2014;Calcinai et al 2015). There is an increasing interest in the characterization of the distribution of this peculiar habitat (Martin et al 2014), but a shared monitoring approach has still not been developed yet.…”

Marine bioerosion of lapideous archaeological artifacts found in the Grotta Azzurra (Capri, Naples, Italy): Role of microbiota and boring Porifera

“…Probable high levels of chemical erosion are also shown by characteristic circular marks of dissolution (Fig. 9B) present on spicules (Bertolino et al, 2014).…”