Ecology of The San Francisco Estuary - Introduced Species

Introduced Species

Species introductions have been increasing since at least the 19th Century as a function of increasing trade and traffic. Introductions include numerous taxa, including copepods, shrimp, amphipods, bivalves, fish and both rooted and floating plants. Many pelagic species have been introduced most recently through ballast water releases from large ships directly into the Estuary. As a result, many of these introduced species originate from estuaries around the Pacific Rim, particularly copepods such as P. forbesi and L. tetraspina. The Amur River clam originates from Asia, and has created significant and drastic changes to the ecology of the LSZ, primarily by diverting pelagic food to the benthos and into an accelerated microbial loop.

Species have also been introduced via attachment to sporting boats which are trailered between regions. This is the probable source of a number of low salinity plants like Egeria densa and water hyacinth (Eichhornia crassipes). These plants have created profound changes in the Delta by disrupting water flow, shading phytoplankton, and providing habitat for piscivorous fish like the striped bass, Morone saxatilis, itself intentionally introduced in the late 1800s from the Chesapeake Bay. The freshwater quagga mussel, originally from Europe, is expected to be introduced by boaters within the next two to ten years, in spite of precautionary measures.