The Bay’s International Guest
A bay’s health is measured by the diversity of its biological species. So when an international guest — a clam — drops into San Francisco Bay and starts eating the food supply of the ecosystem’s resident clams, scientists worry that the Bay will suffer. Potamocorbula amurensis was found hitching a ride on a ship from Asia in 1986. Within a year, there were 1,500 of them per square foot in some parts of the Bay. The tiny, inedible clam thrived in the saltier conditions of drought years. Scientists thought the newcomer would decline with the generous rainy season of 1992—1993, but their numbers are holding. Are they a danger to the Mya arenaria, the Bay’s edible softshell clam? Perhaps not. Of the 20 mollusks that live in the Bay, 18 came from other places, including the softshell clam. In fact, our Bay is one of the most altered estuaries in the world. Jim Carlton, scientist at Willioams College/Mystic Seaport, calls it “an accidental zoo.” Yet there is no convincing evidence that any native species is extinct as the result of a new species, Carlton says.
Excerpted from “The Bay’s International Guest,” by Jane Kay, “Bay in Peril,” Examiner, October 1993, p. 14.