Northward range expansion of three non-native ascidians on the west coast of North America.
The solitary ascidians Microcosmus squamiger Michaelsen, 1927, Molgula ficus (MacDonald, 1859), and Styela canopus (Savigny, 1816) have been found beyond their previously known introduced range on the coast of California. The recent appearance in surveys confirms their presence within San Francisco Bay, indicating possible range expansions northward of more than 500 kilometers. All three species have spread across the natural biogeographic barrier of Point Conception, west of Santa Barbara, California. Species identities were confirmed using microscopy, and key distinguishing features were described. These records contribute to the increasing number of non-native species which are expanding their range northwards on the Pacific coast of North America, implicating both human vectors and ocean warming.