Bryozoan transport in high-energy environments (Strait of Messina, Sicily)

The survey area, selected to study the bryozoan post-mortem dynamics, is located on the northern part of the Messina Strait. Both sides of the Strait are lined by the deep escarpments of the Scilla Valley, that descends from the Sill towards the Palmi Basin (Tyrrhenian Sea). Northward, the Calabria flank is more rough than its Sicilian opposite, where a structural high (central mound) acts as the seaward extension of Capo Peloro. The bottom, swept by strong tides and density currents, forms a variable mosaic of bare rocks, sand waves and megaripples. Modern sediments are a mixture of quartzose terrigenous particles and tephra enriched by a bryozoan-dominated component. Erect bryozoan species, grouped on the basis of colony structural form and style of fragmentation-disarticulation, are subdivided into rigid, flexible, massive and fenestrate morphotypes. Multivariate categorical analysis showed that the dispersal pattern of typified skeletal fragments is a selective process regulated to a large extent by a reconstructed network of sediment transport vectors. Fragments of rigid morphotypes decline progressively with increasing distance from source biotas. Flexible forms generate ubiquitous internodes; the relative abundance is a function of the module of transport vectors. Massive growths are meso-circalittoral in origin and experience a generally limited transport. Fenestrate morpho-types fracture into minimal pieces and suffer a marked depletion effect over the entire sampling area. In high-energy fields, bryozoan skeletal remains actually run along distinct routes, irrespective of submarine topography encountered during their dispersal phases.