San Francisco Bay Expeditions 1993-1997
Like most estuaries, San Francisco Bay has suffered a large number of invasions of both marine and terrestrial species of plants and animals over the past 200 years, many of which have resulted in the replacement of native species with weedy alien species that are better competitors. In fact, San Francisco Bay marine communities are now dominated by species that are not native to the west coast; most of these marine invasions are suspected to be the direct result of shipping practices. Prior to the early 20th century, the newcomers arrived primarily in solid ship's ballast or with species imported for aquaculture (sometimes inadvertently included in the packing materials); now they are most commonly carried in the enormous volumes of ballast water exchanged daily between ports by modern shipping. The rate of successful invasions seems to have increased in the past decade or two. We are attempting to recognize and document the spread of additional alien marine species in the Bay during the 1990s through a series of field trips fondly known as the San Francisco Bay Expeditions.
A small group of intrepid biologists has completed four, one-week "rapid assessments" of float-fouling communities around San Francisco Bay approximately annually between 1993 and 1997. Our group field trips in October 1993 (S.F. Bay Expedition I), July 1994 (S.F. Bay Expedition II), May 1996 (S.F. Bay Expedition III), and October 1997 (S.F. Bay Expedition IV) have been supplemented by other collecting 1993-1998 by individuals. We sampled 20-25 sites during each Expedition; the sites were primarily marinas or boat-launch ramps spaced around the Bay and up into the Delta region. The core team of volunteers participating in all four expeditions was Andy Cohen, Jim Carlton, John Chapman and Claudia Mills. Other expeditioneers included Jean Chapman, Sarah Cohen, Jeff Crooks, Terry Gosliner, Kathleen Halat, Leslie Harris, John Holleman, Mike Kellogg, Gretchen Lambert, John Rees, Doris Sloan, Luis Solarzano, Jan Thompson, Bob Van Syoc, Kerstin Wasson, Anna Weinstein and more.
Primary background for this project can be found in the PhD dissertations of James T. Carlton ("History, Biogeography, and Ecology of the Introduced Marine and Estuarine Invertebrates of the Pacific Coast of North America," University of California at Davis, 904 pp, 1979 - new index available on the web) and Andrew N. Cohen ("Biological Invasions in the San Francisco Estuary: A Comprehensive Regional Analysis," University of California at Berkeley, 465 pp, 1996). These 2 studies, 20 years apart, have provided a terrific backbone for our understanding of bioinvasions in San Francisco Bay.
A comprehensive public report on invasions in the San Francisco Estuary system entitled "Nonindigenous Aquatic Species in a United States Estuary: a Case Study of the Biological Invasions of the San Francisco Bay and Delta" by Andrew N. Cohen and James T. Carlton (1995) includes findings from the First San Francisco Bay Expedition in 1993 - this document may still be available on the web, but not in its original location. Several shorter research papers on invasions by alien species in S. F. Bay were published in 1995 - see Volume 122, number 2 of Marine Biology, including papers on Philene auriformes, a New Zealand nudibranch; Maeotias inexspectata and Blackfordia virginica, two Black Sea hydromedusae; and Carcinus maenas, a European crab. A few small papers have appeared elsewhere. A flashy, short review of what is going on, authored by Cohen and Carlton, was published in the January 22, 1998 Science, titled "Accelerating invasion rate in a highly invaded estuary." The subject was also explored on National Public Radio's January 23, 1998 Science Friday in an interview program between Ira Flatow and Andy Cohen.
San Francisco Bay and the associated estuary system now supports populations of over 220 documented non-indigenous species. Some of these, like Potamocorbula amurensis, a small clam from Asia, Sphaeroma quoyanum, a small boring isopod from Australia and New Zealand, and the Atlantic saltmarsh cordgrass Spartina alterniflora, are now among the most important animals in the bay in terms of both biomass and their role in controlling biological systems in the bay. Many of the invading species are of much lesser importance, but the entire assembladge has changed forever the nature of the marine communities in San Francisco Bay. Bodega Bay, the next large bay to the north is well on its way to a similar change in marine community structure.
In the next year or two we should be putting together several more manuscripts from our results. We also expect to continue sampling - the October 1997 samples may be paired with another set following what was an unusually wet El Niño winter in central California.
I am specifically working up a historic study of the hydroids and medusae in San Francisco Bay, comparing what was present in 1937 when C. M. Fraser monographed the Hydroids of the Pacific Coast with what we have found in the Bay in the 1990s. This paper made its debut in poster form at the June 1995 Conservation Biology meeting in Ft. Collins, Colorado, entitled "Where Have all the Flowers Gone? The Disappearance of Hydroids and their Medusae from San Francisco Bay." The poster has also been on display on the lower floor of the main laboratory at the Friday Harbor Laboratories, with a 1998 update.
Similar rapid assessment surveys for exotic marine species occurred in Puget Sound in September 1998 and May 2000, in Willapa Bay in May 2000 and on the Washington outer coast in August 2001. Whereas the fauna of San Francisco Bay is dominated by introduced non-native species, Puget Sound and most of the Washington outer coast are still dominated by the native fauna and flora, and discovering exotic species there has been a different kind of challenge. I took part in similar surveys in Prince William Sound, Alaska in August 1999 and Kachemak Bay, Cook Inlet, Alaska in August 2000. Rapid Assessment surveys for nonindigenous marine species were also conducted in Southern California and New England in August 2000.
site is maintained by C. E. Mills and all photographs are copyrighted
by the author
** This page was established March 1998; last updated 30 August 2001 **
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