War of the Sponges

From June, 1994 (update #21)

MONTREAL, Quebec -- To judge by some recent newspaper headlines, freshwater sponges are taking on zebra mussels -- and winning. The "Chicago Tribune," for example, declared that it's "High Noon for Zebra Mussels," running a sub-headline that read, "Sponges are gunning for pesky mollusk in Lake Michigan, Erie." The gist of the story was that freshwater sponges have been found in abundance at several Great Lakes locations attached to, and covering, zebra mussels. The story implied that freshwater sponges could conceivably help solve current zebra mussel proliferation problems by killing the mussels. McGill University's Anthony Ricciardi, author of a 1993 "Canadian Journal of Zoology" review of sponge taxonomy, distribution and ecology for eastern Canada, has been studying sponge/zebra mussel interactions for several years. He provided "ZMU" with the following comments on these newspaper reports:

"(1) Regarding the overgrowth of dreissenid mussels by sponges and its potential impact. Freshwater sponges in the St. Lawrence River (primarily Eunapius fragilis and Ephydatia muelleri) overgrow zebra and quagga mussels on canal walls, rocky substrates, woody debris, and occasionally on unionid bivalves. Mussels may be completely overgrown by E. fragilis as early as June; mussels on canal walls and other permanent substrates may remain covered with sponges for six months or more, and appear to suffer adverse effects due to this fouling. "Despite their competitive ability, it is very unlikely that sponges will significantly reduce dreissenid mussel populations on a large scale, although they may outcompete them on a local scale (e.g., on a canal wall). Dreissenids apparently have no mechanism to prevent fouling and overgrowth, but their high recruitment rate would prevent them from being displaced from a habitat.

"(2) Regarding observations of increased sponge abundance in the Great Lakes. Reported increases in the numerical density of sponge colonies are meaningless. A large sponge may fragment to form several independent colonies. Estimates of percent coverage or biomass per unit area are more ecologically relevant measures of sponge abundance and would provide a better idea of whether sponge growth is increasing.

"(3) Regarding the notion that 'sponges need clean water.' This statement is misleading. While some species are noticeably absent from heavily polluted waters, others are tolerant of highly eutrophic conditions -- even waters with high coliform levels or high levels of siltation. Some species can tolerate dissolved oxygen levels as low as 0.8 mg per liter." Ricciardi also noted that the sponge genus Spongilla (perhaps featured in newspaper articles because the name sounds like the movie monster Godzilla) is not a likely variety of sponge to harm zebra mussels. Ricciardi is currently preparing his observations of sponge/zebra mussel interactions for journal publication.

ID: 199406-6.

The Zebra Mussel Update was a 4- to 8-page quarterly national newsletter published by the University of Wisconsin Sea Grant Institute from May 1990 through May 1997. The ZMU documented the spread of the zebra mussel -- an exotic nuisance mussel -- through North America's freshwater environments, especially the Great Lakes, and on efforts to control it.