Orange plankton bloom is not a good sign for ecological health

If you notice an orange tint to the waters of Central Puget Sound, it’s not your imagination. It is a dense plankton bloom dominated by the dinoflagellate Noctiluca scintillans.

Noctiluca scintillans bloom comes ashore at Saltwater State Park in Des Moines on Monday of this week.
Video: Washington Department of Ecology

Noctiluca is often seen in some numbers at this time of year, but it may be a bit more intense this time around, according to Christopher Krembs, an oceanographer with the Washington Department of Ecology. Christopher tells me that the orange color may stick around awhile.

The orange-colored species does not produce any toxins found to be harmful to humans, but it is not exactly a friendly organism either. It often shows up in marine waters that are out of balance with nutrients or impaired in some other way. It can gobble up other plankton that feed tiny fish and other creatures, but it does not seem to provide a food supply that interests very many species — probably because of its ammonia content. Consequently, Noctiluca is often referred to as a “dead end” in the food web.

A plankton bloom at the north end of Vashon Island gets a distinct edge from the tidal currents flowing through Colvos Passage.
Photo: Eyes Over Puget Sound, Ecology

I had a lot of discussions with Christopher and other plankton biologists earlier this year while writing a series of articles about the importance of plankton to the entire Puget Sound food web — right up to orcas. A primary point to the series was to describe how excessive nitrogen from human sources may be upsetting the balance in Puget Sound.

For a deeper dive into plankton, please take a look at this package of stories in the Encyclopedia of Puget Sound titled “Nutrient Pollution,” with a special focus on plankton in the second story in this list:

Christopher Krembs manages a program that assesses water conditions throughout Puget Sound, including aerial views of the surface waters, where he often observes different types of plankton, as well as jellyfish and other creatures that provide clues to water quality. See the webpage Eyes Over Puget Sound, where he expects to post his latest report next week.

The waters in Budd Inlet turned green from a plankton bloom near Olympia.
Photo: Eyes Over Puget Sound, Ecology

His flight on Monday revealed intense blooms of Noctiluca throughout Central Puget Sound, including the waters near Vashon Island.

“What is striking is the very high phytoplankton biomass in Central Sound and not so much in South Sound and other places from the air,” Christopher said in an email. “The jury is still out when the monitoring data come in.”

He’s not sure why the Noctiluca bloom is occurring right now. May was a record-dry month, he noted, and rain-fed rivers are running low. On the other hand, snow-fed rivers are running fairly high, while the mighty Fraser River in British Columbia has dropped down from its previous levels.

Rivers can bring nitrogen down from the uplands to feed the phytoplankton, which capture the energy of the sun to grow and multiply rapidly.

As Christopher points out, we need more studies focused on the base of the food web, which supports our salmon populations and ultimately thousands of species in and around Puget Sound. Clues that could help us understand how to recover Puget Sound are likely to be hidden in the water, where basic biological responses result from water chemistry and circulation patterns throughout Puget Sound.

As a result of the current Noctiluca bloom, the Department of Ecology has posted a discussion as part of its “Puget Sound Nutrient Watch” series on the blog ECOconnect. Efforts to reduce nutrient loading in Puget Sound are being discussed in a workgroup called the Puget Sound Nutrient Forum, which anyone can follow online or in person.

One thought on “Orange plankton bloom is not a good sign for ecological health

  1. Thanks for keeping the spotlight on this topic. Do you see much movement toward action as opposed to discussions and some hand wringing? It seems like the same problem is across most of the country waters (the Mississippi River for example) with not much progress to solutions or improvements.

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