1st Record: CA/San Francisco Bay (Meehan et al. 1989) Introduction of Macoma petalum to San Francisco Bay could have occurred as early as the 1850s in solid ballast, or in the late 1800s-early 1900s with Eastern Oysters (Crassostrea virginica). However, the molecular detection of its occurrence did not occur until 1988 (Meehan et al. 1989; Carlton and Cohen 1995).
CA/San Francisco Bay to Sacramento San Joaquin Delta (Meehan et al. 1989; Cohen and Carlton 1995); Port Sonoma/CA/San Pablo Bay (2004, Cohen et al. 2005)