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Christopher Roger’s Notes From the Field

December 30, 1998

Here is a picture of a male Fairy Shrimp that is the largest species ever found. It was discovered in 2006, living in only two pools south of Boise, Idaho. Its Latin name is Branchinecta raptor – B. raptor for short.

The other Fairy Shrimp in the picture is B. mackini, which is closer to the size of fairy shrimp at Mather Field. That gives you an idea how enormous B. raptor is! The female is even longer; more than 4 inches long! Why do you think the species name of “raptor” was chosen?

If you have time for a story, it is fascinating to investigate how and why the entire habitat of a species of fairy shrimp consists of two pools.

A few million years ago, the Juan de Fuca plate began pushing on the North American plate at the San Andreas Fault. The resulting collision pushed up the Sierra Nevada Mountains and, eventually, the Coast Ranges. This created a rain shadow, preventing rain from reaching what we now call Nevada.

Back then, all of Nevada and most of Utah, southeastern Oregon, southern Idaho and parts of eastern California and northern Arizona, were one huge lake called Lake Lahontan. This rain shadow dried Lahontan down to just a few lakes and created the Great Basin Desert.

Prevailing winds carried all that light, lake bottom soil north to the Paloose Plateau in Idaho. (Some of the richest wheat and potato producing soils in the world are now there). This wind-dispersed soil is called loess (pronounced “luss”). It is very deep in some places, even up to a few meters.

Now, here is where the story comes back to how the geology affects the fairy shrimp: The two pools where B. raptor is found are both on the original land surface, behind mountains. They are surrounded by loess, but the two mountains blocked the loess from burying their pools. This shrimp may once have been far more widespread, but its other pools were buried in loess long ago!

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