Kathleen Sayce, August 15, 2016
In mid summer on the Columbia River Estuary a color change appears in the water, red to purple, and persists into early fall. It’s a natural red tide, when billions of single celled animals, ciliated protozoans, called Myrionecta rubra (also called Mesodinium rubrum) bloom. The bloom is particularly striking from the high span over the shipping channel, on the south end of the 101 bridge near Astoria. It is not toxic, but it is very red.
|The band of purplish-red water is a colorful streak of Myrionecta rubra cells, seen from the Astoria-Megler bridge on August 14th, 2016.|
The cells are less than 100 micrometers long, and have two rows of cilia between two round body sections, which give this tiny animal the swimming dexterity of a jet fighter. They look like two round balls of different sizes stuck together. The beating rows of cilia allow it to jump ten to twenty body lengths in one movement, which would be like a 6-feet-tall human jumping sixty to one hundred twenty feet.
Seen under the microscope, they spin, dash and turn with amazing speed. The red color comes from a red alga that lives inside the cell. The algae cells are not permanent residents; each cell lives around 30 days inside the protozoan. There may be several algae cells in each Myrionecta organism, and carbon fixed through photosynthesis by the algae feeds the protozoan.
During warm, sunny weather the blooms form in long streaks in the Columbia River Estuary between the jetties to above (east) of the Astoria-Megler bridge. Sometimes they also form in Youngs Bay, and can be seen on that causeway and bridge. In some years, the entire river looks like it’s running with blood instead of water. Most years, the bloom is in streaks surrounded by otherwise normal-colored water, green to gray to blue.
One spectacular year in the 1990s, the Myrionecta bloom in local waters coincided with a dinoflagellate bloom, of Ceratium species. Dinoflagellates are often golden to warm red in color. That year, the dinoflagellates were golden orange. The combination of strong red-purple and gold from billions of organisms of different colors in different parts of the river gave the water a very weird red-orange color combination. Ceratium organisms gathered in warmer shallow water, and Myrionecta tended to the deeper waters of the main channels, so the colors were blended together in some areas, and distinctly separate in others. Both blooms stopped as the storm season got underway that fall.
This species prefers lower salinity water, and warm weather. August and September are the usual months to see the long red to purple streaks. Cool storms disrupt the bloom in fall, and by mid to late October, unless weather has been unusually calm, it’s gone again for the year. Individual cells turn up in plankton samples throughout the year, however, it's only late summer to early fall when their numbers rise into the billions and become visible to us.
Myrionecta has been seen and collected in the surf zone along the north coast beaches in Oregon and south coast beaches in Washington, on each side of the river. It’s also been found in Willapa Bay, and the Willapa and Palix Rivers.
In Alaska, residents say that when the fireweed blooms, summer is almost over. Here, when we see the red tide of Myrionecta rubra on the Columbia from the Astoria-Megler Bridge, we know fall is going to arrive in a few weeks.