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Intriguing Connection to Clams, Diatoms, Brown Waves and Washington / Oregon Coast

Fascinating connection to clams, diatoms, brown waves and the Washington / Oregon coast

Posted on 11/13/22 at 5:19 p.m
By employees of the Oregon Coast Beach Connection

Fascinating connection to clams, diatoms, brown waves and the Washington / Oregon coast

(Warrenton, Oregon) – Two small stretches of coast from Washington and northern Oregon have something odd in common that also sets them apart from the rest of the region. A larger-than-average population of diatoms makes for the odd phenomenon of brown waves and an enormous density of razor clams—as well as many whole sand dollars (at least in one area). (Photo by Long Beach Brown Waves Oregon Coast Beach Connection)

The Long Beach peninsula on Washington’s southern shore and Clatsop Beach on the tip of the Oregon coast both flank the Columbia River. It, in turn, dumps an incredible amount of nutrients into the surrounding areas, creating a slightly different ecosystem than the rest of the Oregon and Washington coast.

For an area – right around the Necanicum River in Seaside – that meant a lot of whole sand dollars, probably more than you can find anywhere else. Whether the same situation exists on the Washington side along the peninsula isn’t clear, but experts say it’s worth a look.

Clatsop Beach includes Seaside, Gearhart and Warrenton – approximately 20 miles. Both it and the Long Peninsula are prone to the eerie sight of thick brown waves, which some visitors initially mistake for pollution. They can turn sticky brown, sometimes with an odd kind of brown sludge. However, it’s just a bunch of phytoplankton: a specific type known as diatoms. It’s not pollution – and that’s a good thing.

Razor clam, diatom brownshaft and whole sand dollar populations are directly related to diatoms. It’s simply a matter of the food chain, said Tiffany Boothe of the Seaside Aquarium.


Aerial view of brown waves at Seaside (Oregon Coast Beach Connection)

“Most nitrates and phosphates are delivered down the Columbia River, but some also come down the Necanicum and other smaller coastal rivers,” Boothe said. “That’s why almost every Clatsop County beach has such good razor clams.”

Sand dollars and razor clams feed on diatoms. With such a massive food source, this makes them all quite productive up the food chain.

The Clatsop Beach area is home to about 90 percent of all razor clam populations on the entire Oregon coast. The Long Beach area on the Washington coast also has a significant population.

What makes the sand dollars so prolific here is a bit of a mystery. An important factor is that they wash up on a secluded stretch just around the Necanicum River, at the very northern edge of Seaside and the southern part of Gearhart. With fewer people, not as many step on them or pick them up. The diatoms are the other important factor.

But there is something about the topography of the nearshore environment that allows them to be ripped out of their habitat and washed ashore.

Boothe said sand dollars live in large colonies just behind the surf zone. When a sand dollar dies, its shell lands on the beach, either by currents or strong wave action.

dr However, Bill Hanshumaker told the Oregon Coast Beach Connection a few years ago while he was at the Hatfield Marine Science Center in Newport that there are a few possibilities.

One possibility is simply the currents in the area, as many on the north coast believe. It is clear that there are more sand dollar beds like this, and for some reason the current simply dumps them in one place.

The other two possibilities have to do with terrain, Hanshumaker said. One is that there is a very flat, gently sloping beach at this point that gets closer to the beds. The other idea has to do with erosion in an area of ​​the sand dollar beds where the sediment they live in is simply more prone to being disturbed and disturbed.

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