The UNESCO lists potential threats to underwater cultural heritage. One threat is biological activity.
Biological impact of fungi, bacteria and woodborers: Bacteria-induced decay threatens wood in marine sites and even more so sites in fresh water. The attack of woodborers, or Teredo Navalis, also poses a considerable biological threat to submerged wood elements. This shipworm can destroy wood within a few months. As an example, the Baltic Sea was until recently free of Teredo Navalis as are the waters of the Arctic and Antarctic. This is one of the main reasons why shipwrecks are so well preserved in their waters.