Hood Canal changes color again, thanks to plankton bloom

Hood Canal has changed colors again, shifting to shades of bimini green, as it did in 2016, when satellite photos showed the canal standing out starkly among all other waters in the Northwest.

Hood Canal has changed colors as a result of a plankton bloom, as shown in this aerial photo taken in Northern Hood Canal.
Photo: Eyes Over Puget Sound, Washington Ecology

The color change is caused by a bloom of a specific type of plankton called a coccolithophore, which shows up in nutrient-poor waters. The single-celled organism produces shells made of calcite, which reflect light to produce the unusual color.

Observers are now waiting for the clouds to depart, so we can get new satellite images of the green waters.

The plankton bloom started June 1 in Quilcene and Dabob bays, according to Teri King of Washington Sea Grant. It came about a week earlier than last year and has since spread through Hood Canal. Observers in the Seabeck area reported seeing the bloom the past few days. The bimini green color, which gets its name from an island in the Bahamas, is especially noticeable when the sun comes out.

Coccolithophores are known for dominating other phytoplankton when there is a shortage of nutrients, such as nitrogen, in the water. We usually get an influx of nutrients when it rains, so I’m not sure how long the bloom may last. I’m told, however, that the white calcite shells, called coccoliths, can stick around after the organism has died, although they eventually sink to the bottom.

Electron microscope image of plankton Emiliania huxleyi

The species of coccolithophore in Hood Canal is believed to be Emiliania huxleyi, shown in the microscopic photo on this page. They don’t produce any known toxins harmful to people or marine life, experts say, and they can be eaten by small fish and larger zooplankton.

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