Abstract
Acquiring baseline data on highly diverse communities such as coralligenous ones is very valuable in order to determine possible shifts in communities and define strategies for their preservation. Distribution of sciaphilic epibenthic communities belonging to the `coralligene de la roche littorale´ was investigated at 30 photostations from 17 to 24 m depth on a rocky shoal off the island complex in the Gulf of La Spezia (Ligurian Sea, NW Mediterranean). Four communities displayed a sharp zonation: Paramuricea clavata characterised deeper, vertical surfaces, whereas on horizontal and medium inclination, sediment-covered substrata, Leptogorgia sarmentosa , together with Eunicella singularis and Eunicella verrucosa , characterised the upper stratum of the deeper community. Shallow vertical walls were characterised by a facies with sponges and zoantharians, whereas community dominated by large, massive colonies of Pentapora fascialis with a basal stratum of sciaphilic algal species patched with sediment on shallow rocky slopes of medium inclination. Bathymetric distribution of assemblages is influenced by high seawater turbidity (mean annual transparency: 11.9 ± 5.7 m at the western site, 6.2 ± 1.6 m at the eastern site), which induces a shift of the upper limit of distribution of these facies to unusually shallow depths. Quantitative data provide a baseline on the study site that will be useful to understand the influence of not only biotic and abiotic factors, but also mass-mortality events, particularly on these communities characterised by high resilience.
Highlights
In their classical work on vertical zonation of Mediterranean benthos, Pérès and Picard (1964)described the complex of communities thriving on hard substrates characterised by the presence of sciaphilic organisms, which they named ‘coralligenous biocenosis’
The carpeting madreporarians Leptopsammia pruvoti and Polycyathus muellerae grew on vertical substrate and Parazoanthus axinellae was present as epibiont on the sponge Axinella damicornis
The sciaphilic epibenthic communities identified at Tinetto shoal match those conventionally described for the northwestern Mediterranean under the name of ‘coralligène de la roche littorale’ (Pérès and Picard, 1964) rather well
Summary
In their classical work on vertical zonation of Mediterranean benthos, Pérès and Picard (1964)described the complex of communities thriving on hard substrates characterised by the presence of sciaphilic organisms, which they named ‘coralligenous biocenosis’. The diversity and richness of the Mediterranean coralligenous communities have been compared to those of tropical coral reefs (Ros et al., 1985) and their scientific importance has been stressed (Sarà, 1969; Laborel, 1987). Pérès and Picard (1964), mainly based on northern part of the western Mediterranean basin, is the basis for knowledge on coralligenous communities, together with studies on distribution and abundance of the most representative species (Laborel, 1961; Laubier, 1966; Sarà, 1969; True, 1970; Augier, 1982; Hong, 1982). The aim of the study was to investigate the species composition and percent cover of sciaphilic epibenthic assemblages belonging to the ‘coralligène de la roche littorale’ (sensu Pérès and Picard, 1964) on a sublittoral shoal off Tinetto Rock in the. Quantitative data provide a baseline on the study site that will be useful for temporal change detection
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