The effects of wood anisotropy on the mode of attack by the woodborer Teredo navalis and the implications for underwater cultural heritage Anne Marie Eriksen a , David John Gregory a, * , Chiara Villa b , Niels Lynnerup b , Knud Bo Botfeldt c , Arne Redsted Rasmussen c a Conservation and Natural Sciences, Environmental Archaeology and Materials Science, National Museum of Denmark, I.C. Modewegsvej, Brede, Dk-2800 Kgs. Lyngby, Denmark b Laboratory of Biological Anthropology, Department of Forensic Medicine, Faculty of Health Sciences, University of Copenhagen, Frederik V's vej 11, Dk-2100 Copenhagen, Denmark c Department of Natural History Conservation, School of Conservation, The Royal Danish Academy of Fine Arts, Schools of Architecture, Design and Conservation, Esplanaden 34, Dk-1263 Copenhagen, Denmark article info Article history: Received 19 April 2015 Received in revised form 18 November 2015 Accepted 19 November 2015 Available online 29 November 2015 Keywords: Shipworm Computed tomography (CT) scanning Underwater cultural heritage In situ preservation Wood anisotropy 3D-models abstract Marine borers such as the shipworm, Teredo navalis, can cause great destruction to wooden archaeo- logical remains in the marine environment. The focus of this study was to investigate whether shipworm preferentially settle on one orientation of the wood over another, i.e. radial, tangential or transversal and if the resulting tunnels are oriented in a specific direction according to the fibres within the wood. This was investigated using Computed Tomography (CT) scanning and subsequent 3D modelling as a method of both quantifying the severity of attack by shipworm and examining the orientation of the tunnels. Panels of pine, cut in tangential, radial and transversal planes, were placed in the sea at a location where shipworm was known to be abundant. After attack, the panels were weighed, X-rayed, entrance holes counted and 3D CT models created. All results show a difference between the three planes. The specific direction of the single tunnels could be evaluated using the CT models, since the individual tunnels could be isolated, and followed throughout the panel. The results show that the radial plane suffered a more severe attack than either of the two other planes. These results have implications for archaeological interpretation and conservation. For example, the results show that ancient ships built with timbers cut in a radial plane (e.g. Viking Ships or other structural elements cut in radial plane) may be more prone to attack and thus require more protection than those built in tangential or transversal plane should they be raised (difficulties lifting due to fragility) or preserved in situ. © 2015 Published by Elsevier Ltd. 1. Introduction When exposed to open seawater, waterlogged archaeological wood can be subject to rapid degradation by xylotrophic (wood eating) organisms such as the shipworm, Teredo navalis (Mollusca: Teredinidae). T. navalis is the most common species of shipworm in Danish waters and can deteriorate wooden structures within months (Hochman, 1973). An adult T. navalis can release one to two million larvae at a time, which are ready to settle on wood after one to three weeks (Roch, 1940). Distribution of the larvae can happen via currents, or as “passengers” in ship's ballast water. Furthermore, as adults T. navalis can be spread by driftwood (MacIntosh et al., 2012). After settlement on the wood surface, the pelagic larvae metamorphose into an adult shipworm and start boring into the wood. Knowledge about the orientation of the shipworm's preferred attack orientation is scarce and observations have lead to the understanding that shipworm bores along the grain of the wood (Evens, 1990; Køie et al., 2000). Wood is an intrinsically anisotropic material, produced by the specific deposition of anatomical elements during the life of a tree (Gregory et al., 2007; Hoadley, 1990). The stem of the wood consists * Corresponding author. E-mail addresses: anne.marie.eriksen@natmus.dk (A.M. Eriksen), david.john. gregory@natmus.dk (D.J. Gregory), chiara.villa@sund.ku.dk (C. Villa), nly@sund.ku. dk (N. Lynnerup), kbb@kadk.dk (K.B. Botfeldt), arr@kadk.dk (A.R. Rasmussen). Contents lists available at ScienceDirect International Biodeterioration & Biodegradation journal homepage: www.elsevier.com/locate/ibiod http://dx.doi.org/10.1016/j.ibiod.2015.11.018 0964-8305/© 2015 Published by Elsevier Ltd. International Biodeterioration & Biodegradation 107 (2016) 117e122