But many of these marsh and mudflat denizens shouldn't be calling the San Francisco Bay home because it isn't. Home is in reality, the Atlantic Coast, Asia, Europe, and Australia. As many as 200 species of marine invertebrates have been introduced to the San Francisco Bay by humans, either accidentally or purposefully, in the last 130 years. The concern of the mitten crab is multi-faceted. The crabs dig burrows that may be destructive to levees and earthen dams.
Mitten crabs are also an intermediate host for a parasitic liver fluke that affects humans.
Both the mitten crab and the Asian bivalve are prolific breeders and, in vast numbers, can have an impact on the availability of food for native animals. In such high numbers, these filter feeders deplete plankton as a food source. The East coast cord grass is yet another of the many invaders of the Bay. The plant was intentionally brought in to be used in the restoration of a salt marsh in Fremont. Since that time it has expanded to new areas of the bay and can be found on both the east and west side.