2. Invasive species: Invasive species are especially prevalent in intertidal areas with high volumes of shipping traffic, such as large estuaries, because of the transport of non-native species in ballast water. San Francisco Bay, in which an invasive "Spartina" cordgrass from the east coast is currently transforming mudflat communities into "Spartina" meadows, is among the most invaded estuaries in the world. Conservation efforts are focused on trying to eradicate some species (like "Spartina") in their non-native habitats as well as preventing further species introductions (e.g. by controlling methods of ballast water uptake and release).