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By BILLY SINGLETON
Daily News Staff Writer
Record-breaking sunlight and heat in recent weeks has yielded an unusually widespread plankton bloom throughout southern Southeast Alaska. The phenomenon is lending a striking turquoise color to much of the area’s waters, including those around Ketchikan.
Scott Walker, the Ketchikan area commercial fisheries management biologist for the Alaska Department of Fish and Game, has observed local waters by floatplane for years. He said last week that the bloom might be the largest he’s ever seen.
“We had a bloom last year, but it was nothing like this year,” Walker said. “Now, like the entire countryside is that way.”
Walker said that the color appears with the most intensity on the west coast of Prince of Wales Island. It ceases around Thorne Bay and Sea Otter Sound in the north, but as of Thursday, he wasn’t sure how far south of Alaska it might extend.
University of Alaska Ketchikan biologist Barbara Morgan said on Monday that the culprit is phytoplankton — tiny, photosynthesizing organisms that drift with the current. Their gold and whitish color, combined with reflected blue skies, give the water its cloudy, greenish effect.
Specifically, these plankton fall under the categories of diatoms, dinoflagellates and coccolithophores.
Based on her recent tests, Morgan said the water is currently safe for swimming and fishing, but she warns against harvesting shellfish for personal use.
Though it’s not associated with any visible changes to the water, a harmful plankton species has been measured in the Ketchikan area in recent weeks.
Southeast Alaskan Tribal Ocean Research issued an advisory July 17 warning against harvesting shellfish after the phytoplankton Alexandrium was measured at Seaport Beach in Saxman. Alexandrium produces the toxins that can cause paralytic shellfish poisoning in humans who have consumed shellfish that have ingested the plankton.
Nicole Forbes, an environmental specialist at the Ketchikan Indian Community, said that shellfish in the greater Ketchikan area could also pose a risk of paralytic shellfish poisoning.
“I think it’s safest to assume that it’s not just at Seaport Beach,” Forbes said on Monday. “I wouldn’t take that risk.”
Strict testing requirements mean that commercially available shellfish are still safe, Morgan said.
None of the plankton species reported so far are toxic to salmon. But, according to Morgan, clouded water could discourage salmon from entering the area, which could lead to a shorter window of time for fishermen in the inside waters to catch them.
“What I’ve noticed in the past is that salmon don’t really like going into this opaque water that we have right now because they can’t see very well,” Morgan said. “… So they lay off shore where the phytoplankton bloom isn’t happening, and they wait until it disappears or thins out and then they come shooting in and just go right upstream.”
Walker, of Fish and Game, agreed that thick plankton blooms likely pose challenges to the fish, though he said he wasn’t aware what kind of specific effects they might have.
There do appear to be some benefits to the phenomenon, including water oxygenation.
“They are photosynthesizing, … and so they are also producing a lot of oxygen,” she said. “Worldwide, the phytoplankton in the oceans make out about half of the oxygen in the atmosphere. So not only are they not depleting the oxygen, they’re actually making a lot of oxygen.”
Phytoplankton also serve as food for zooplankton, which feed fish.
As for the future, Morgan said she expects climate change to contribute to more intense plankton blooms.
“We are seeing increased temperatures periodically, and that is affecting algal blooms on a global scale,” she said. “… My expectation, the expectation I think of scientists in general, is that we will see more of these kind of events happening with global climate change becoming more and more exaggerated as time goes by.”
According to Morgan, the effects of larger blooms would depend on what kind of plankton are present.
“Depending on the species, it could either be good … or it could be really detrimental,” she said. “If we had a bloom of this magnitude that was a toxic variety, that would have a big effect.”