Wednesday, September 26, 2012

Late Summer Red Tide: Myrionecta

Written September 17, 2012, published late September 2012

In late summer to early fall each year, water in the lower Columbia River, from Tongue Point to the entrance, turns purple to blood red. This so-called red tide is not toxic, and has been happening here for many decades. It’s caused by the rapid growth of a tiny ciliated protozoan (a single-celled animal with rows of tiny movable hairs, called cilia), Myrionecta rubra, which lives in brackish to salt water. It was formerly called Mesodinium rubrum

Aerial photo of Chinook Basin on Baker's Bay, during late summer when Myrionecta is blooming. Myrionecta patches are very dark; while waters with low levels of this protozoan are green. Photo by Kathleen Sayce

Myrionecta rubra looks like two balls stuck together, one slightly smaller than the other. It has two rows of cilia where the balls join, which move in rhythm like flexible, very fast beating galley oars. The whole animal is so small that in a water sample without magnification, all you can see is a red blur in the water. Under a light microscope, Myrionecta cells live only a few minutes before they overheat and die, rupturing the cell wall and spewing the intercellular contents out into the water. When healthy, they zip around as though jet propelled, bouncing off the edges of the slide, and rocketing from one side to another, fast, agile, tumbling, and changing directions with ease. 

Myrionecta cells look red because inside each cell, which is 50 µm long and 20 µm wide, are even tinier red algae, each one a few microns in diameter. Green plants have green plastids called chloroplasts, which were once free-living green photosynthetic bacteria. Myrionecta’s red plastids are red algae that have learned how to live inside cells; they can also live on their own as well. This relationship is often called a symbiosis, because the algae give the cells in which they live sugars for food, being photosynthetic, and gain a protective cell wall to live within. 

Myrionecta is around most of the year in brackish to salty water. In the years when I collected water samples to look at plankton species, I saw them in samples from the Columbia River, the Columbia plume offshore, in the ocean surf, in Willapa Bay, and also on rivers, including the Palix and Willapa Rivers. During August to October, they become very abundant. A few cells in the water don’t change the color, but billions of cells turn the water blood red. 

Sailboat ont the Columbia River near Desdemona Sands off Astoria, sailing through a dense red patch of Myrionecta. Aerial photo by Kathleen Sayce.

This color change is easily seen from the Astoria-Megler Bridge on Highway 101. The darkest colors can be seen as streaks and swirls, especially from the spans over the north and south channels, or from an airplane. The red color appears in August, first as a purplish tinge to otherwise blue waters, strengthens in September, and persists until fall storms begin, usually sometime in October. During this period, the number of Myrionecta cells in the water is easily in the millions of cells per cubic meter of water. The next time you are sitting in your car on the high span at the south end of the bridge in late summer or early fall in warm dry weather, watch the water and see if Myrionecta rubra is ‘blooming.’ 

Unlike many harmful algal blooms, this dramatic red bloom happens every summer and early fall with no bad side effects.  Myrionecta rubra doesn’t make biotoxins, does not make seafood poisonous, or cause illness or death in fish, birds or humans. It’s been going on for many decades. Not all blooms in local waters are so benign, but this particular one doesn’t seem to be a problem. 

Wednesday, September 19, 2012

Fossil mammoth teeth tell us about past climates and plant communities

Written August 7, 2012, published September 2012

There is a fossil Columbian mammoth tooth in the museum at the Pacific County Historical Society, South Bend, WA. The tooth was found in the 1930s, in floodplain sediments along the North River. Mammoth fossils from the Pleistocene Epoch are common throughout North America, and in Washington. During the Pleistocene, mammoths lived from Alaska and Canada to Nicaragua and Honduras. Two mammoth species wandered over from Asia into Alaska and Canada, and two species were indigenous to and widespread in North America, including the Columbian mammoth. 

Figure 3. Mounted composite skeleton of a Columbian-type mammoth made from skeletal elements recovered in the 1870s from the
‘swamps’ at the Copelin Ranch along Latah Creek in Spokane County (site 06). When assembled in 1886 in the Field Museum of Natural History in Chicago, Illinois, this ‘mammoth’ was considered to be the first fully mounted specimen, albeit a composite from several individuals, of a mammoth in North America. (Photo from Higley, 1886.)
Washington Geology, vol. 27, no. 2/3/4, December 1999, page 25 “Some Notable Finds of Columbian Mammoths
from Washington State” Bax R. Barton

The Columbian mammoth, Mammuthus columbi, is the state fossil. Bax Barton wrote in Washington Geology (Vol. 27 (2/3/4), 1999, page 23) “Of the 39 counties in Washington, only heavily forested counties on the west side of the Cascade mountains (for example, Skamania and Wahkiakum) and less populated counties on the east side (for example, Ferry and Pend Oreille) have thus far failed to produce mammoth fossils.” The Columbian mammoth was up to 13 feet tall and just under 10 tons, eating around 500 pounds of vegetation per day. This mammoth had long tusks, and was not very hairy, unlike other mammoth species, and also unlike mastodons. 

Mammoth tooth on display at Pacific County Historical Society, South Bend, WA. It was collected from the floodplain of the North River in north Pacific County. Photo by Kathleen Sayce.
This single fossil tooth from the North River tells us what plant communities and climate were like during glacial maxima (when continental ice was most widespread) in the Pleistocene. Mammoths did not live in forests. They grazed on open grasslands, eating grasses and sedges, with sages, mosses, ferns and aquatic plants as minor foods. Grasses and sedges were extensive during glacial maxima because that climate was cooler and drier than today’s. These shifts promote a long-term seesaw between forests and grasslands. Forests shrink during glacial maxima, and expand during warm wet periods. Periods of cold dry weather promote grasslands and sedges. Warm wet periods promote forests, such as today’s climate. Today, the present climate promotes trees. 

Sea level also seesaws between ice ages and temperate periods. During glacial maxima, sea level was as much as 350 feet lower than today. The continental shelf was a wide rolling plain, dissected by rivers flowing from modern day estuaries in deep valleys, including Columbia, Willapa and Grays Harbor. These river valleys can still be seen on bathymetric charts as deep canyons, along with larger side channels; finer stream details are buried under marine sediments. 

Mammoths weren’t the only animals to flourish during the Pleistocene; freshwater river habitats for fish in those streams on the plains were extensive compared to present day. 

Mammoth teeth are common fossils for two reasons. One, teeth are hard, and generally persist with relative ease compared to other body parts. Two, over their lifetimes, each mammoth had six or more full sets of teeth. As grazers, they wore teeth down quickly, and replaced them in sets. Shark teeth are common marine fossils for the same reasons: teeth are hard, and sharks constantly grow new teeth to replace worn and damaged ones.  

As the climate warmed, forests expanded, grasslands shrank, and mammoths found their preferred food plants disappearing. Their teeth were designed for grasses and sedges, not conifer trees. The last mammoths died out around 10-11,000 years ago, based on dating the youngest known fossils from the Midwest. There are gold deposits buried on the continental shelf, and mammoth fossils are out there as well, along with a lot of shark teeth.