RESUMEN
Ostreopsis spp. blooms have been occurring in the last two decades in the Mediterranean Sea in association with a variety of biotic and abiotic substrata (macroalgae, seagrasses, benthic invertebrates, sand, pebbles and rocks). Cells proliferate attached to the surfaces through mucilaginous trichocysts, which lump together microalgal cells, and can also be found in the plankton and on floating aggregates: such tychoplanktonic behavior makes the quantitative assessment of blooms more difficult than planktonic or benthic ones. Different techniques have been so far applied for quantifying cell abundances of benthic microalgae for research, monitoring and risk assessment purposes. In this context, the Benthic Dinoflagellates Integrator (BEDI), a non-destructive quantification method for benthic dinoflagellate abundances, was developed and tested within the EU ENPI-CBCMED project M3-HABs. This device allows mechanical detachment of cells without collecting the benthic substrate, providing an integrated assessment of both epiphytic and planktonic cells, i.e. of the number of cells potentially made available in the water volume from "resuspension" which could have harmful effects on other organisms (including humans). The present study confirms the effectiveness of the BEDI sampling device across different environments across the Mediterranean Sea and constitutes the first large-scale study of Ostreopsis spp. blooms magnitude in function of different macro- and mesohabitat features across the basin.