Copper accumulation in the digestive caecae of Limnoria quadripunctata holthius (Isopoda : Crustacea) tunnelling CCA-treated wood in laboratory cultures

To investigate the mechanisms by which the isopod Limnoria in tolerates cop per, chromium and arsenic when tunnelling CCA-treated wood in the marine en vironment, digestive caecae of specimens of L. quadripunctata from CCA-trea ted and untreated Pinus sylvestris is sapwood were examined using transmiss ion electron microscopy (TEM) and energy dispersive X-ray detection (EDX). Copper-containing granules were found to be present in the small cells of t he digestive caecae (midgut) of Limnoria from both treated and untreated wo od. However, individuals tunnelling treated timber contained a greater numb er of granules, with six types of morphology being distinguished of which o nly two were present in Limnoria from untreated wood. The presence of coppe r-containing granules in Limnoria from untreated timber may be explained by the ability of this isopod to acquire and store copper from seawater for u se in enzymes and blood pigments. The increased number of copper granules i n individuals tunnelling treated wood was believed to result from elevated levels of this element in the food substrate. This ability to store copper allows these organisms to tolerate this metal in the wood substrate and may explain how this organism is able to attack CCA-treated wood in service. N o chromium, or arsenic, was detected in the digestive caecal cells.