The role of polychaetes in bioerosion of submerged mosaic floors in the Underwater Archaeological Park of Baiae (Naples, Italy)

The study investigated the role of boring polychaetes in the bioerosion of a submerged Roman mosaic floor in the Underwater Archaeological Park of Baiae (Naples, Italy). Three boring species, Dodecaceria concharum, Polydora ciliata, and Pseudopolydora antennata, were found. The initial colonization phases of boring polychaetes were investigated on experimental limestone panels placed underwater in the same marine area. The results showed that the ecological succession was characterized by a first stage of colonization with abundant spionids and a second stage with a boring mature community dominated by D. concharum. The study of silicone casts of the bored traces allowed confirmation that the ichnospecies belonging to the ichnogenera Maeandropolydora could be attributed to the action of spionid worms, whereas D. concharum is able to produce tongue- and ribbon-shaped borings (ichnogenus Caulostrepsis), and variously contorted galleries (ichnogenus Maeandropolydora) by settling inside borings produced by other polychaetes and increasing the complexity of the gallery system by modifying them. The study of the epilithic polychaete community highlighted that the site is characterized by a low hydrodynamism. Therefore, the most suitable in situ preservation interventions would be the covering of the mosaics with sand layers or geotextiles.