Mollusc associations from a cold-water coral environment (Apulian margin, S Italy)

A quantitative study by means of multivariate analysis was carried out on molluscs yielded by 8 small cores, up to 40 cm long, recovered in 2010 (CoralFISH EU-FP7 Project) along the Apulian margin off Santa Maria di Leuca (S Italy), 525 to 784 m depth. The mainly silty seafloor of this area is characterized by mound-like and elongated topographic features (50–300 m wide and up to 25 m high) whose upper part is generally olonized by cold-water coral communities. Shells were picked from 31 core levels and then identified – when possible – to species, revealing a diverse fauna including 79 benthic taxa (37 Bivalvia, 3 Scaphopoda, 39 Gastropoda) out of 112 recognized in the area by sorting 24 contextually recovered box-corer samples. The dominant taxon is the small infaunal bivalve Kelliella miliaris; among other relevant elements, Abra ongicallus, Notolimea crassa and Alvania cimicoides are also mud-related, while Heteranomia squamula, Delectopecten vitreus, Asperarca nodulosa and Bathyarca pectunculoides thrive on hard substrates. The multivariate analysis (clustering, MDS) was conducted on a 79 species x 29 samples abundance matrix, defining three groups (A to C); they were analyzed in terms of the dominance and similarity contributions of species and proved to belong to different habitats as regards bottom type and relationships with corals. A and B are quite homogeneous; the former is restricted to coral mound tops and appears to be related to coral branches or rubble, while the latter is found both in inter-mound areas and on the mound upper flanks and links to a frankly muddy seafloor. Conversely, group C is heterogeneous and interpreted as transitional; the MDS dispersion of its levels led to perform a second step analysis on a reduced matrix. This revealed at least three different transitional stages (C2 to C4) between coral rubble and mud habitats. C3, found at or near mound tops just below mud-related faunas, appears closer to group A; C4, mostly epresented at the NE base of mounds, is more similar to B; C2 occurs quite randomly and includes a mixed fauna. The mollusc groups and stages studied herein match quite well with both macrohabitats and thanatofacies recognized in the area by means of bottom samples and submarine video surveys (APLABES Project, HERMES Project).