Why This N. Oregon Coast Spot Has So Many Sand Dollars, Brown Waves, Clams

Published 11/12/2015 at 4:15 PM PDT
By Oregon Coast Beach Connection staff

(Seaside, Oregon) – One chunk of the north Oregon coast is known for three very unique situations: one is a periodic run of extremely brown waves, while another tinier stretch of it hosts an incredible amount of untouched sand dollars.

There is a connection, say local science experts. It's even connected to the awesome razor clamming you find in this area.

Most people don't know this, but the mouth of the Necanicum River is where you'll find more whole, unbroken sand dollars than anywhere else on the coastline. This happens only on either side of the river: at the extreme northern edge of Seaside or the southern tip of Gearhart.

Meanwhile, much of that area from Seaside up to Warrenton – about 20 miles – is prone to insanely brown waves. In fact, the city has information posted throughout town explaining this is a really good thing as it's the result of lots and lots of phytoplankton. Seaside, Oregon Hotels in this area - Where to eat - Map and Virtual Tour

The sand dolloars, brown waves and razor clams are directly related to the amount of nutrients in the waters off Warrenton, Sunset Beach, Gearhart and Seaside. It's a simple matter of the food chain, said Seaside Aquarium’s Tiffany Boothe.

“Most of the nitrates and phosphates are delivered via the Columbia River, but some also come down the Necanicum and other smaller coastal rivers,” Boothe said. “This is why there is such good razor clamming on almost all of Clatsop County beaches.”

The nutrients feed all the phytoplankton in the area, especially the diatoms. So much so that the diatoms bloom in such big numbers they create all those brown waves and gooey brown stuff.

In turn, sand dollars and razor clams feed on diatoms. With such a massive food source, this makes all of them quite prolific, down through the food chain.

The Clatsop Beach area has about two thirds of all the razor clam population on the entire Oregon coast.

What's intriguing about the brown waves is they occur in degrees (sometimes slightly brown, sometimes sludgy and disgusting-looking). But they also move up and down the beach.

“Looking down the beach you may notice that only a small section of the water is brown,” Boothe said. “At other times the whole surf zone looks like a muddy mess. What you are looking at when the diatoms have stained the surf brown is a bloom. Diatoms and other phytoplankton are always in the surf but certain ocean and weather conditions can create a 'bloom.' During these periods the diatoms or phytoplankton are reproducing at astonishing rates, but eventually the reproduction will slow and the bloom will disappear. Sand dollars and razor clams thrive where conditions are likely to produce blooms here and there.”

Then, there are those concentrations of sand dollar shells around the river. There are some reports the Nehalem Spit by Manzanita also has large amounts of them, but staff at Oregon Coast Beach Connection have confirmed that no other area in the state has as many as this spot between Seaside and Gearhart. Others have noticed as well.

Boothe said sand dollars live just past the surf zone in large colonies. When a sand dollar dies, its shell will end up on the beach, either via currents or strong wave action.

But why are so many whole and unbroken?

“Another reason you may find more sand dollar shells in one area verses another is human traffic,” Boothe said.

Less people equals more unbroken sand dollars.

This all still begs the question: if there is so much nutrient-rich ocean in this area for sand dollars, why do more wash up only here?

Exactly why is a bit of a mystery. However, Dr. Bill Hanshumaker, with the Hatfield Marine Science Center in Newport, said there are some possibilities.

One likelihood is simply the currents in the area, as many on the north coast believe. It's clear there are more such sand dollar beds, and for some reason the currents simply dump them in one spot.

The other two possibilities have to do with terrain, Hanshumaker said. One is that there is a very flat, gently sloping beach in that spot that reaches out closer to where the beds are. The other idea has to do with erosion in one area of the sand dollar beds, where the sediment they live in is simply more prone to being churned up and disturbed.

“Here on Seaside Beach, I always tell people looking for sand dollar shells, to park at 12th Ave. and walk the beach heading north,” Boothe said. “This is because a lot of people walk the beach between the Prom and the Cove, but few people walk north past 12th.”

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