Some Aspects of the Bioerosion of Stone Artefact Found Underwater: Significant Case Studies

Within the framework of the project Restoring Underwater started in 2001, the ISCR Marine Biology sector with the ISCR Underwater Archaeology Operation Unit has begun a study of the deterioration of stone artefacts exposed to marine environments (Torre Astura – Nettuno; Baiae – Naples). These studies have allowed to better understanding the factor of degradation by biological, mineralogical, and petrographic analyses and to develop measures for the protection in situ of cultural heritage. Based on what was recorded, usually the bioerosion presents various degrees of gravity: limited and sporadic damage or very serious alterations. Depending on their chemical composition, the artefacts proved to be particularly susceptible to the action of corrosion exercised by perforating animal and plant organisms.This phenomenon becomes more significant in the case in which the artefacts remain exposed and in the same position for a long period of time. It is possible to confirm that the combined action of attack from clionides (sponges) and bivalves can lead, over time, to the total destruction of portions of the artefact (macroboring). As well as these more macroscopic types of damage, there was evidence of the widespread presence of microscopic bioerosion (microboring), caused by autotrophic and heterotrophic microorganisms, visible only through SEM observations, which, despite not creating large chambers, progressively undermine the resistance of the stone and facilitate the development of other biodeteriogens. This paper will be focused on the characterization of the bioerosion observed on different artefacts: the roman statues discovered underwater in the Grotta Azzurra, Capri and in the Campi Flegrei area (Naples –Italy), and the marble sarcophagi that are still on the seabed of San Pietro in Bevagna (Taranto – Italy).