The survival of Teredo navalis L. in timber wrapped in TERRAM4000 and a plastic membrane

Abstract

Since in situ preservation of archaeological material has become more widespread (European Union, 1992) the need to stop an active attack of Teredo navalis, a wood-boring mollusc, on waterlogged archaeological wood has become more urgent. The aim of current study is to examine the ability of two plastic materials (TERRAM4000 and a plastic membrane) to stop both initial attack by T. navalis and their effects on wood with active woodborer degradation. Blocks of pinewood were submerged in the southern part of the Kattegat in Denmark, where shipworm is known to be prolific. After settling and attack had been confirmed, the blocks were removed and wrapped in either TERRAM4000 (polypropylene and polyethylene) or a proprietary plastic membrane (polyethylene), normally used on fishing piles or piers, as a protection against shipworm in Denmark. An optical oxygen sensor was packed together with each block to measure the amount of available oxygen around the wood. After one week the oxygen level around the test blocks wrapped in the plastic membrane had dropped drastically and lead to the death of all shipworms within the test blocks after one-four weeks. Although no new shipworm attacked the wood wrapped in TERRAM4000, the geotextile did not impede the passage of oxygenated seawater, as living individuals were found in the blocks after 46 weeks of wrapping and submersion.