The importance of cellulose content and wood density for attack of waterlogged archaeological wood by the shipworm, Teredo navalis

Archaeological wooden remains are at risk of rapid degradation by the shipworm, Teredo navalis, whenexposed to open seawater. An earlier study has shown a difference in the extent of attack based on thestate of preservation of the wood. The current study aims to examine in more detail how shipworm attackcorrelates to the state of preservation, as measured by density, and the amount of residual cellulose, andif it is thereby possible to estimate when attacks will occur based on the level of deterioration. Thisknowledge would have practical implications for in situ preservation of wooden natural and culturalheritage underwater as it may be able to predict whether a wooden object is in danger of being attacked.The results confirm that there is a significant correlation between the extent of deterioration of thewood and the shipworm attacks. Samples with low density (< 100 kg/m3) and a low cellulose content(≤ 24% weight/dry weight) showed no attacks (rating 0). Attacks (rating 1–2) were first observed whenthe density of the wood was ≥ 134 kg/m3, with concomitant cellulose contents of ≥ 29%. Severe attack(rating 3–4) was observed on samples where the density was ≥ 292 kg/m3and cellulose contents of ≥ 48%.