An invasive isopod is on the move in Southeast Alaska. It’s been found in both Ketchikan and Sitka.
But the organism affects only one creature: the blue mud shrimp.
If you’ve never heard of the blue mud shrimp, then this invasive isopod probably isn’t a concern of yours now — but it should be.
Listen to this story:
I have lived in Southeast Alaska my whole adult life, and never even heard of blue mud shrimp until I got an email from Karen Johnson, a naturalist in Sitka and member of the local Fish & Game Advisory Committee.
On Labor Day, we were out at Starrigavan Beach in Sitka at a minus tide digging for blue mud shrimp. Johnson brought along a pump made from plastic pipe, sort of an oversize version of something you might use to pump the bilge in your skiff.
Johnson heard about the blue mud shrimp by way of Dr. John Chapman, a fisheries professor at Oregon State University.
Chapman is why Karen Johnson was up at dawn, digging for an invertebrate that no one has really paid much attention to up here until now.
“Think of it more like you’re in a coal mine, and the canary just died,” Chapman said.
The isopod is called Orthione griffenis, or O. griffenis, and it finds its way up under the carapace of adult blue mud shrimp — and only blue mud shrimp. Although it’s a parasite, Chapman says O. griffenis is far from microscopic.
“So in the head, there’s a huge bulge on the side, that if it were scaled up to be your size and my size, that’d be like having a little dog or a cat under your armpit sucking your blood,” Chapman said. “You would see it.”
The isopod eventually kills its host shrimp, and soon the remaining shrimp can’t find each other to reproduce, rendering a blue mud shrimp population extinct. This is already happening in coastal areas of California, Oregon and Washington. And now O. griffenis is in Alaska, in what could be the largest infestation yet discovered.
Tammy Davis is the invasive species coordinator for the Alaska Department of Fish & Game in Juneau. Like many of us, she hadn’t been concerned about blue mud shrimp until she met John Chapman. But now she’s concerned.
“They’re really important for circulating nutrients and oxygen in the sandy substrates where they’re established,” Davis said. “Similar to the role that earthworms play in gardens.”
In this case, the garden is the intertidal zone, which Chapman considers to be as full of life as an ocean reef, except upside-down. Blue mud shrimp play a critical role in this environment, most of the time invisible to us, unless you’ve got a shovel.
Karen Johnson and I spent over an hour sinking holes all over this beach until finally, we hit paydirt.
Johnson stood in a hole about 3 feet wide, and over a foot deep. In her hand, she had our quarry, a blue mud shrimp. This one was a juvenile, maybe 2 inches long. No parasite is present, but Johnson popped it into a specimen bottle. Johnson said she would be mailing the specimen, along with several others, to Chapman.
John Chapman and his research team don’t just want to study the isopod O. griffenis. They want to understand the mechanism of its arrival in North America in ballast water aboard ships from Asia, and how it travels long distances in its larval stage between intermediate hosts, to finally find blue mud shrimp in Ketchikan and Sitka.
And then Chapman wants to kill it.
“This is an introduction that if we can stay on top of it, we might find out how this thing works,” he said. “And then if we do that, of course, we’re gonna throw wrenches in all the gears we can find. We, humans, are excellent at causing extinctions. Why don’t we cause the extinction of something that’s bad?”
Helping to cause the extinction of a cat-sized, blood-sucking parasite, which is threatening an obscure shrimp critical to the health of our ecosystem? That’s worth getting up early for.