This paper reviews the international literature on the natural enemies of Dreissena spp. and discusses the biology and ecology of organisms known to be involved in their predation (176 species), parasitism (34 species), and competitive exclusion (10 species). Research on natural enemies, both in Europe and North America, has focused on predators, particularly birds (36 species) and fish (15 and 38 species eating veligers and attached mussels, respectively). Other field-documented predation includes consumption of pelagic larvae by copepods and coelenterates, and consumption of attached mussels by leeches, crabs, crayfish, and rodents. Cannibalism of veligers by adult zebra mussels has also been reported. Ciliates and trematodes are the most commonly reported obligate parasites, with occasional records of suspected bacterial or ascetosporan infection. Mites, nematodes, leeches, chironomids, and oligochaetes have been observed to be associated symbiotically within the mantle cavity, but with few to no adverse effects. Organisms capable of competitively displacing zebra mussels from hard substrates include sponges, amphipods, algae, bryozoans, hydrozoan coelenterates, and other bivalve species (including interspecific competition among Dreissena spp.).

Although the vast majority of the organisms that are natural enemies in Europe are not present in North America, ecologically similar species do exist on this continent, and zebra mussels represent a novel and abundant organism for these native predators, parasites, and ecological competitors — the new natural enemies of Dreissena. However, the idea that these organisms could eliminate zebra mussel populations, even in limited areas of North America, is far more hopeful than realistic. As in Europe, there will likely be isolated reports of major impacts by natural enemies, and on the whole we will likely see a cumulative effect of a suite of enemies having a constant, but limited, role in suppressing zebra mussel populations.