Pisaster brevispinus (Stimpson, 1857)

Starfish are not common within San Francisco Bay because they are intolerant of fresh water. They are present only near the Golden Gates, in places where there is a strong influence from the truly marine environment on the outer coast. In seasons with relatively high rainfall, such as winters in which we experience a strong el niño, echinoderms like starfish can die in large numbers as freshwater floods from up the Sacramento River to lower the salinity to lethal levels. This is a normal occurrence insofar as these starfish have only been able to make their way into the Bay in part because of the heavy water use by agriculture, usage that raises the salinity in the Bay enough to support the existence of a truly marine fauna in some places.