Monday, June 5, 2000
‘termites of the sea’
HERE'S a quiz: 1. On his fourth voyage to the Americas
in 1502, Christopher Columbus lost all his vessels to: a. fire, b.
pirates, c. hurricane, d. shipworms.
2. Legend has it that to save his town, the Little
Dutch Boy plugged a hole in a wooden dike with his finger (or more likely
his entire arm). Who made that hole? a. vandals, b. woodpeckers, c.
lumberjacks, d. shipworms.
3. Why was so little wood found on the sunken liner
Titanic? a. it drifted away, b. there wasn't much to begin with, c. divers
took it as souvenirs, d. shipworms ate it.
OK, there's clearly a shipworm theme here, and indeed,
shipworms is the correct answer to all the questions. But in addition to
the facts above, there's something else interesting about shipworms: They
aren't worms. They're clams.
Shipworms get their name from their long, narrow,
cylindrical bodies. But the worm resemblance ends there. A closer look at
the creature reveals a shell at its front. This shell has two halves with
a gap in between, like a clamshell. In the gap pokes a muscular foot that
acts like a suction cup, holding the shell in place while its razor-sharp
edges scrape the wood ahead of it.
WHY scrape wood? Shipworms eat sawdust. The shipworm's
stomach has a pouch for storing sawdust and a special gland for digesting
wood particles. These termites of the sea also have an organ full of
bacteria that digest wood. The bacteria take nitrogen from the water and
convert it to protein for the worm, since wood doesn't supply protein. The
bacteria, in return, get nutrients from their host.
A shipworm begins life like most marine invertebrates:
as a tiny piece of meat in the plankton soup of the sea. When it finds a
piece of wood, the worm goes to work, using its shell to eat its way into
As the shipworm grows, so does the burrow. (The
creature's breathing siphons remain at the surface of the wood.) Depending
upon the species and the length of their wooden homes, shipworms can be as
short as 6 inches or as long as 6 feet.
Once a shipworm claims a home, its stuck there for
life. Even when researchers removed mature worms intact and uninjured,
they were unable to dig new burrows.
The damage shipworms cause is legendary. Greek
literature from 350 B.C. mentions them and early explorers dreaded them.
Shipworms are sometimes called the mollusk with the
million-dollar appetite. These creatures are credited with single-handedly
destroying the Hudson River piers in New York City. Researchers estimate
that untreated timbers, such as pier pilings, exposed to Hawaii's ocean
waters will last less than two years.
In recent history, East Coast researchers lowered
wooden panels about 5,500 feet to the ocean floor. When they recovered the
panels 104 days later, they were completely riddled with the wood-eating
This voracious appetite has a purpose. Large amounts of
wood get into the oceans by means of rivers, mangrove forests and humans.
Shipworms play an important role in reducing the amount of driftwood in
the world's oceans.
After writing this column, I wanted to see some of
these remarkable little clams so I paddled my kayak around the Ala Wai
Boat Harbor. I was disappointed. Nearly everything in the water is made of
concrete or fiberglass. The few wooden boats moored here are coated
thickly with protective paint.
But there's always the driftwood that washes up on the
beach. I'll never pass another piece.