With the help of a comprehensive literature study on the biodegradation of wood in marine environments with special emphasis on the aggressive marine borer, Teredo Navalis, the environmental conditions for their activity and spread will be clarified. Data on marine environmental parameters such as temperature, salinity and dissolved oxygen content that are paramount for the spread of marine borers, will be collected, harmonised and mapped for the Baltic sea in a GIS. All data are synthesised into a tool for assessing the potential spread and hence decay of the underwater cultural heritage. The tool will be verified by assessing recent historical environmental data (available for the past 20 years).