The sedimentary dynamics of Sabellaria alveolata bioconstructions (Ostia,Tyrrhenian Sea, central Italy)

Sabellaria alveolata(Linnaeus 1767)is a polychaete able to build bioconstructions of different thickness,size and patchiness,in intertidal and subtidal environments.Its biological features have been the object of numerous studies worldwide.The worm reefs are formed by millions of tubes built by sand and shells(whole or in fragments)bonded together with a strong glue produced by the worm itself.Hence,Sabellaria alveolata represents a sedimentological asset for the coastal protection,since it contributes to create natural barriers against storm waves and erosion,and supplies the beach with new sandy deposits.This work shows a multidisciplinary approach to studying a bioconstruction of Sabellaria alveolata along the Latium coast(Ostia,Tyrrhenian Sea,central Italy),proposing image analysis as a novel technique to investigate worm reefs,along with classical sedimentological/ecological tools.The Sabellaria bioconstructions have been analysed at different scales of observation,suggesting the more appropriate strategies to develop a reliable model illustrating the different growth steps of these bioconstructions.

Sediment provenance of a carbonate bioclastic pocket beach—Le Dune(Ionian Sea,South Italy)

This study focuses on the analysis of a carbonate bioclastic pocket beach located along a coastal sector of the Apulia Ionian Sea,Le Dune beach,South Italy.The beach develops for about 800 m and it is exposed to the south-westerly and southerly seas.Coastal sediments range from very coarse to medium-fine sands and they are mainly composed of bioclasts(more than 90%)which include molluscs,foraminifers,echinoderms,algae branched,bryozoans,spicules of sponges and arthropods.The study area is one part of a marine protected reserve characterised by 15 different habitats of the typical Mediterranean submerged populations and the presence of Posidonia oceanica meadows.The aim of our research is to highlight the correlation between physical and biological processes influencing Le Dune beach dynamics and its sediment provenance by analysing the textural and compositional characteristics of beach sands,which is fundamental for pocket beach conservation.The beach sand analysis,deriving from textural,compositional and bioclast investigations,underlines that one of the main indicators of the beach dynamics is the bioclast component,which provides relevant information about sand provenance and sediment transport.The beach constitutes a semi-close system only nourished by the shells of organisms and by the erosion of headlands and dunes without important sediment interchange with adjacent littoral sectors.