The photographs in this post show a small piece of water-logged driftwood about 30 cm long and riddled with holes and tunnels caused by two different types of wood-boring sea creatures. The larger borings are about 1 cm in diameter and many are lined with a smooth calcareous material that has become stained through burial in the beach sediments. These larger borings may be familiar to beachcombers as being made by Shipworms, Teredo navalis Linnaeus. I have talked about these worms – which are not really worms but bivalved molluscs – elsewhere in the blog.
Less familiar, are the much smaller holes and burrows in this piece of soft wood. These have been made by Gribbles, Limnoria lignorum (Rathke). Gribbles are very small marine isopod crustaceans. Crustacea is the major grouping that includes the crabs, prawns, and sandhopper types of animal. Isopods are a bit like the terrestrial woodlice that you see in gardens – they have an ‘armoured’ body with lots of limbs and joints; and their body is flattened from top to bottom – compared with amphipods such as sandhoppers in which the body is flattened from side to side. Gribbles are very small and their length rarely exceeds 3.5mm.
Shipworms can burrow into hard wood but Gribbles prefer wet, cool and soft wood, like the bases of exposed pilings on piers and jetties. The pictures here show the infestation damage caused by both Gribbles and Shipworms that leads to the destruction and disintegration of the timber.
Revision of a post first published 29 May 2010
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