Naval Shipworm (Teredo navalis)

Shipwrecks are great! They are about the best dive sites that you can dive to. They stir the imagination, provide a dose of history on the side, and most of the time have plenty of amazing stuff to look at as well! And the older the wreck is, the better. The problem with most really old ship wrecks is that most of them have deteriorated and all but disappeared a long time ago. This unfortunate state of affairs is largely caused by the naval shipworm. Because the shipworm eats wood.

Here is an example of shipworm damage. On the left is a frame from the Danish ship Sophia, that sunk in 1645. Notice the damage caused by the shipworm. On the right, a well preserved frame from the Vasa. This photo is taken by myself at the Vasa Museum in Stockholm.

 The naval shipworm is a saltwater clam that has a long, reddish, wormlike body. It can be found in temperate and tropical salty waters all over the world.

The shipworm is a common cause of damage to submerged timber structures and the hulls of wooden boats and -yes indeed- sunken wooden ships. It is one of the main reasons that old, wooden ship wrecks have disappeared. The shipworm eats the wooden parts of wrecks, basically leaving only the metal parts remaining, scattered around the seabed.

The Vasa is a prime example of a wreck NOT eaten by the shipworm. The ship sunk in 1628, and was still in near-perfect condition when it was raised in 1961. It is now on display at the Vasa-Museum in Stockholm. As you can see from the photos above, old wooden ships are preserved remarkably well in the depths of the Baltic Sea. The water is cold, dark, and low in oxygen. Most importantly, the Baltic Sea water is brackish water. This means it is low in salinity. And this accounts for the absence of the shipworm that in most other seas eats up all the wooden parts of old wrecks, because the shipworm needs salty water to survive.

There are plenty of wreck dive sites in the Baltic that are suitable for divers of all levels of experience. Check out my earlier text about some great wreck dive sites in the Baltic Sea.

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