The driftwood lay abandoned by a storm-driven high tide, far from the ebb and flow, sculpted by the elements and set in a gallery of chaotically arranged, sun-baked tree bones.
By chance the 10-foot-long piece, a large hunk missing, stood upright among its horizontal companions.
The posture caught my eye; the shipworm tracks that created a honeycomb of tunnels caught my attention.
I grew up in Maryland with the story of the Dove (of Ark and Dove fame, the ships that brought colonists from England in 1634), which was so damaged by shipworms that it sank on the way home.
Ironically, a replica with an unprotected hull built 341 years later was almost destroyed by shipworms. Mariners called them termites of the sea, but they’re neither termites nor worms, but a mollusk.
There are many species, but they all have a voracious appetite.
"Everybody that has untreated wood pilings in the Port Gardner area has a shipworm problem," said Port of Everett terminal manager Dave Cavanaugh, who sees irony in the law of unintended consequences.
"Since the waterway has been cleaned up over the last 30 years, a lot of marine life has come back, like sea lions and harbor seals … and shipworms."
Creosote worked against shipworms but it’s not used any more; the chemical ACZA helps, he said. But untreated pilings can be honeycombed and useless in two to four years.
The port’s answer is to gradually replace wood pilings with steel ones.
Bankia setacea is the most common shipworm in Puget Sound, according to Megan Dethier, research assistant professor of biology at the University of Washington’s marine labs in Friday Harbor.
It’s often called teredo, but teredo is uncommon north of Oregon, she said.
Bankia setacea, sometimes called the giant Northwest shipworm, starts out small, but its rate of growth would make it a star in a horror flick.
One study showed that in six months, shipworms in the harbor at Vancouver, B.C., grew about 20 inches, said Alan Kohn, University of Washington professor emeritus in the zoology department.
Shipworms start out as free-swimming larvae about the size of a grain of sand. If they’re in luck, chemical signatures will guide them to untreated wood.
They immediately enter, leaving only tiny holes as a clue. By the time the infestation is found, it’s usually too late — they’ve grown more than a yard long and have destroyed the wood with pencil- to finger-width tunnels.
The key to its burrowing is a tiny pair of shells at the front end with ridged surfaces that, as the worm rocks ist head back and forth, shave away minuscule wood pieces to create both food and a circular tube.
The pieces are ingested, with some cellulose in the wood turned into glucose (and energy) by bacteria.
While boring and eating, the worm keeps growing. It’s anchored near the entry point, also feeding on plankton sucked through a siphon, with another siphon expelling what it’s eaten in pellet form.
At the end near the entry, featherlike structures can close the burrows if the siphons are retracted.
Dozens or hundreds of shipworms may be working in a piling or plank, but they avoid crossing each other’s calcium carbonate-lined burrows. The lining may help keep bacteria out or create a smoother surface for the soft body, Kohn said.
Given its solitary existence, reproduction is through the miracle of self-fertilization.
If you see short, narrow grooves or shallow tunnels, then the wood is probably also home to gribbles, isopods about the size of a grain of rice that remain near the surface, Kohn said.
I’m glad they have a taste for wood and not humans, or else we would be talking horror movies.
Columnist Sharon Wootton can be reached at 360-468-3964 or www.songandword.com.
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