The Lagoon of Venice is a complex mosaic of benthic habitats, which are strongly controlled by benthic fluxes (exchanges of nutrients, oxygen, sediment, organic matter, contaminants, etc.) between the bed and the overlying water column. Turbulent energy production and dissipation, bed shear stress and velocity gradients control these fluxes and vertical gradients of such parameters in the benthic boundary layer depend in turn on the bed physical features, i.e. its hydrodynamic roughness, defined by sediment type/size and morphology, and are strongly mediated by biology. Biology-mediated processes can enhance or reduce seabed stability at several space-time scales, so that biogenic seabed roughness is essential for understanding benthic fluxes, thereby dictating habitat classification, and informing conservation efforts.

To support the characterization and comparison of biogenic benthic roughness in relevant habitats, two sites were selected: (i) a subtidal flat presenting seagrass/algae coverage and a dense colony of Pinna nobilis in the central lagoon; (ii) the edge of a creek entering an intertidal flat in the northern lagoon, with seabed featuring sponges, oysters and other epifaunal and vegetation cover. Both sites have an average water depth of 1.5 – 2 m. For each site, a photogrammetric survey over a 72 m2 area (12 x 6 m) was carried out by scientific divers. Structure-from-Motion (SfM) analysis of the collected images allowed to produce a digital terrain model with a high spatial resolution (accuracy under 1 cm). Preliminary analyses on the local spectrum of altimetric fine-scale variability are presented, and related to biogenic features. Main results support the linking of physical bed roughness to habitat structure and composition.