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No Golden State for Zebra Mussel
The infamous zebra mussel - crustacean purveyor of wrack, ruin and general? clogging to Great Lakes plumbing and power plant cooling systems - might find California much less hospitable, according to a recent study. Only 44% of 160 sites on rivers, canals, lakes and reservoirs statewide offer the right conditions for colonization by this striped-shelled European terror.
According to the S.F. Estuary Institute study, zebra mussels require an environment that is rich in calcium, fresh to mildly brackish, warm-to-cool and alkaline, with plenty of hard substrates and low enough flow speeds to allow young to settle and adhere. Researchers Andy Cohen and Anna Weinstein screened the sites for five important environmental variables (salinity, dissolved calcium, pH, temperature and dissolved oxygen) and ranked 54% as having no or low potential for colonization, 2% as moderate and 44% as high. Among the most inviting spots were coastal watersheds, the west side of the Sacramento Valley, the lower San Joaquin River and the southern Delta, not to mention critical water conveyance facilities such as the Delta Mendota Canal; the California, South Bay, Los Angeles and Colorado River aqueducts; the All American Canal; and their associated reservoirs.
Researchers were surprised, however, by how many waterways and waterworks would fail to prove cozy mussel motels. "Zebra mussels exploded so fast in the Great Lakes that everyone got the impression they could live anywhere," says Weinstein. But zebra mussels might have a hard time getting to California, let alone surviving here. The upper Sacramento River system, for example, doesn't have enough calcium to keep the mussel happy - zebra mussels need more calcium, about 15-30 ppm, than any other freshwater bivalve to maintain their shells. San Francisco Bay, for another example, is too much of a constant mix of fresh and salty. Researchers have never found zebra mussels abundant where salinities fluctuate above 2 parts per thousand (in the Bay-Delta's case, this would roughly be downstream of Antioch).
With no watery superhighway to travel, the worrisome mussel may also find it not so easy to reach the Golden State from the Great Lakes or the Oklahoma River 2,000 miles away (the nearest infested area). There's not a lot of trailered boat traffic - one major pathway of introduction - between Lake Michigan and the S.F. Bay-Delta watershed, and even if there was, most mussels along for the ride would be dead and dried out upon arrival (as were those found recently by California border guards). "An invasion is not inevitable, "says Weinstein, "but we need to be vigilant."
Vigilance, at the moment, means educating border inspectors and passing out boater leaflets, as well as a state-federal task force aimed at stopping the spread on the west slope of the Rockies at the 100th meridian. Another step might be to identify invasion hot spots, so they can be the focus of boater education, monitoring and advance planning for containment and eradication. Such hot spots are likely to be "popular recreational reservoirs with lots of interstate boat traffic, where hospitable conditions combine with lots of opportunities for introduction," says Weinstein. For more mussel information see Now in Print.
Contact: Anna Weinstein (510)231-9539
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