A reader asked us a very interesting question a while ago: what did shipworms (or “ship worms”) eat before there were ships, boats, piers, and other human-made wooden structures in the sea? Shipworms, the “termites of the sea,” are known for their destruction of wood via boring, and since they are saltwater creatures, ships and other such structures are often on the receiving end their furious drilling. However, as the reader observes, there must have been much less wood in the ocean before humans started putting it there, so what did shipworms eat before we supplied them with a food source?
We’ll begin with a word on shipworms, which is a term that refers to several species of clams with vermiform (i.e., “worm-shaped”) bodies; of course, their long, soft bodies are the reason they are called worms, even though, as clams, they are obviously aren’t worms. (The word “worm” is somewhat flexible, but no reasonable definition would classify clams as worms.) Like other clams (and oysters, mussels, and scallops), they are bivalve mollusks because they have a shell composed of two hinged parts. On shipworms, these shells are small and sharp and are on the anterior end of their bodies. The shells, operating like the head of a drill, are used to bore into wooden structures. The best-known species of shipworm is the Teredo navalis, which is found all over the world, although historically higher concentrations exist in the Caribbean Sea.
Shipworms can cause great destruction to the wood in salt water, although the rate of deterioration depends on the type of wood. Not surprisingly, softwoods like pine can be consumed by shipworms quite quickly; a pine tree could be destroyed by tunnels in less than four months if it is submerged in water with shipworms. Hardwoods like oak last longer, but even an oak tree would be riddled with tunnels in a little more than a half a year when subject to the relentless boring of shipworms. They are a force to be reckoned with, and are a classic example of humankind’s inability to fully conquer nature; to this day, there is no way to treat wood that totally eliminates the threat of shipworms.
As for our reader’s precise question, all we can do is offer some speculation. First, it is very hard to assess exactly how much more wood there is in the oceans now then there was a few thousand years ago. Presumably more because of the structures our reader pointed to – ships, docks, and so on – but how much this constitutes relative to the total amount of wood is something we aren’t prepared to answer. There is of course wood in the ocean that wasn’t put there by humans – think of all the driftwood scattered across beaches all over the world. Also, assuming there is vastly more wood in the oceans now then there was in the past, this has presumably only led to an increase in the total population of shipworms. When there weren’t boats and piers to eat, there wasn’t a food source to feed shipworms, and the scarcity of resources would have kept populations low. Limited resources are how all populations are kept in ecological check. So, shipworms would have had wood to eat before the advent of wooden structures in the sea, but there simply might not have been as many shipworms around.
In any case, this is our best attempt at an answer to a reader’s creative question. Given the enormous amount of wood that humans have added to the oceans, it does seem likely that there was a time when there was far less wood available in the sea, and thus any creature that depends on wood for sustenance would have had a harder time surviving. And since this is the case, all we can surmise is that there was once a time when there were far fewer shipworms floating around the ocean. Or perhaps the reader (along with us) has overestimated the human contribution of wood to the oceans, and in which case there is really no mystery to solve: there was always plenty of wood for shipworms to feast on.
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