Local News

Weekend plankton bloom raises concerns over "red tide"

SITKA, ALASKA
Alice Johnstone has lived for twenty-five years on Thimbleberry Bay, about three miles from downtown Sitka. The bloom began sometime early Sunday morning in her area.

“It kept getting thicker and thicker, and brighter and brighter, and I thought, Something’s happening. Maybe it’s red tide.”

Johnstone says she never doubted that it was a natural phenomenon. Both the Sitka police and the Coast Guard received reports of a suspicious substance in the water: callers thought it could be anything from bunker oil to something resulting from fill being placed to expand the Sitka airport. Luckily, cooler heads prevailed.

“We went out and caught some plankton with a plankton net.”

David Wilcox is a seventh-grader in his very first day of camp at the Sitka Sound Science Center. Reese Warren was also in on the effort to identify the bloom.

“Well, we pulled it out of the water and they go into this jar, and then we squeezed to make the extra water go away. So we’ve got the extra water in the jar with a whole bunch of plankton in it.”

After that, it was just a matter of studying the plants in the jar to figure out what was making the water red. It turned out to be a form of dinoflagellate – or marine plankton — called Noctiluca scintillans. It’s not what causes paralytic shellfish poisoning, according to Paul Norwood, an instructor at the science camp, but it’s not far off.

“They are closely related. That’s not to say that it is safe to eat the clams, of course. Especially butter clams tend to store PSP toxins in their tissue for a long time after exposure. In the first sample there were hundreds of Noctilunca scintillans, the rather harmless ones, but there were also a couple of dinoflagellates from a genus that’s potentially a bearer of toxins.”

So if it’s a relatively harmless red algal bloom, does that mean we’ve overly fearful about the infamous red tide? Norwood doesn’t think so. Dangerous red tides aren’t always red. Norwood believes you can’t be too cautious when it comes to PSP.

“As long as the water’s red, and it’s a dinoflagellate that causes it, you can call it a red tide. And the poisoning that’s sometimes associated with red tide is sometimes associated with red tide, and sometimes there’s no red tide but the toxin is present. So just because you’re seeing the waters dyed red, that’s a definite warning sign, and I would not ever eat clams when the water’s dyed red. But even if it’s not dyed red, then there’s still a risk.”

This current bloom appears to be tapering off. One byproduct of Noctiluca is ammonia, and in high concentrations the plankton can make their own environment uninhabitable. There can also be localized fish kills when a large biomass of Noctiluca depletes the oxygen supply.

Norwood says this outbreak is really not all that unusual, it just happens to be occurring where we all can see it. That confirms what Alice Johnstone has observed. Several years ago she was traveling along the shoreline of Admiralty Island.

“We were flying and we could see the heads of bays somewhere over in that area that were bright red, but I’ve never seen anything like this here.”

And a couple of final notes on Noctiluca: it does like the heads of bays because, as Dean Stockwell, a faculty member at the UAF School of Fisheries and Ocean Sciences says, Noctiluca is a plant that eats things, and there are usually a lot of nutrients in the runoff at the heads of bays. Noctiluca will also eat Alexandrium, the type of algae responsible for PSP, so they often don’t coexist. But, that doesn’t mean they can’t. Alexandrium has been found in the water in both Juneau and Ketchikan this year. Moreover, the toxin cannot be cooked out of clams, mussels, or scallops. The only safe clam is one that has been tested for the presence of PSP.
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