A Eats B, Increasing C

In a recent issue of Science News, S. Milius reports on an "indirect effect" observed in many California bays. An invading species, the European green crab (Carcinus maenas), has decimated two native shellfish populations (both Nutricola sp.). The Nutricola crash means less competition for the eastern gem clam (Gemma gemma), a marginal invader that has lived in the bays for decades.

The gem clam arrived in California a century ago, transported there by the oyster shipping industry. Although an exotic species, eastern gem clams were considered harmless in San Francisco Bay. Now, however, with the Nutricola population crash, gem clam populations are exploding.

Froom the article:

"[Edwin Grosholz (Univ. of California, Davis)] found that the gem clams grew only half as fast in crowds of native clams as they did in dense colonies of their own."

"This isn't the first example of a new invader triggering a population boom in a previous invader, says Dan Simberloff of the University of Tennessee in Knoxville. 'But this was a particularly nice one.'"

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If you want more details on the west coast invasion by the European green crab, click here.