In the Strait of Messina (Sicily, Central Mediterranean Sea) strong tidal currents, very irregular hydrological regime and related solid load, and local seismic activity cause sediment instability; this area represents therefore a case study of a naturally disturbed soft-bottom environment. In this paper, mollusk and polychaete assemblages of the northern part of the Strait were described. Composition, community structure, eco-ethological features, trophic guilds and sediment-type relationships were studied in 64 stations sampled located between 3.5 and 50 m depth in October 1992 by means of a Van Veen grab. A total of 131 species (65 molluscs and 66 polychaetes) were identified. A dense population of the tubicolous polychaete Ditrupa arietina was recognized, together with the occurrence of other species tied to a high sedimentation rate, such as Corbula gibba and Tellina distorta, as well as widespread, mud-tolerant species (e.g. Chone spp., Hyalinoecia tubicola). Diversity (H¢) showed a peak at intermediate depths (10/20 m) and a clear decrease beyond this depth, corresponding to the Ditrupa core population. Multivariate comparison between sediment features and community composition throughout the bathymetric gradient showed a narrow ecocline between two environments subjected to opposite hydrodynamic constraints. In the shallower zone, a wide typology of trophic-ethological guilds was related to community patchiness, in contrast to a greater functional uniformity of the deeper assemblage, dominated by sessile, semi-infaunal suspension feeders. A possible role played by a phase of increased rainfall to increase bottom instability, locally emphasized by a previous human activity, is also discussed.
A case study of mollusc and polychaete soft-bottom assemblages submitted to sedimentary instability in the Mediterranean Sea.
COSENTINO, ANDREA;GIACOBBE, Salvatore
2006-01-01
Abstract
In the Strait of Messina (Sicily, Central Mediterranean Sea) strong tidal currents, very irregular hydrological regime and related solid load, and local seismic activity cause sediment instability; this area represents therefore a case study of a naturally disturbed soft-bottom environment. In this paper, mollusk and polychaete assemblages of the northern part of the Strait were described. Composition, community structure, eco-ethological features, trophic guilds and sediment-type relationships were studied in 64 stations sampled located between 3.5 and 50 m depth in October 1992 by means of a Van Veen grab. A total of 131 species (65 molluscs and 66 polychaetes) were identified. A dense population of the tubicolous polychaete Ditrupa arietina was recognized, together with the occurrence of other species tied to a high sedimentation rate, such as Corbula gibba and Tellina distorta, as well as widespread, mud-tolerant species (e.g. Chone spp., Hyalinoecia tubicola). Diversity (H¢) showed a peak at intermediate depths (10/20 m) and a clear decrease beyond this depth, corresponding to the Ditrupa core population. Multivariate comparison between sediment features and community composition throughout the bathymetric gradient showed a narrow ecocline between two environments subjected to opposite hydrodynamic constraints. In the shallower zone, a wide typology of trophic-ethological guilds was related to community patchiness, in contrast to a greater functional uniformity of the deeper assemblage, dominated by sessile, semi-infaunal suspension feeders. A possible role played by a phase of increased rainfall to increase bottom instability, locally emphasized by a previous human activity, is also discussed.Pubblicazioni consigliate
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