What types of organisms prey on Dreissena? Combining North American and Eurasian records, birds (36 species) and fish (15 species eating veligers and 38 species eating attached mussels) have been the most commonly reported predators (Molloy et al. 1997). The number of fish and bird species that have been documented as predators can be misleading, however, since most literature references contain records of only occasionally finding a few Dreissena in the stomachs of the predators listed. Records of field-documented predation also include copepod and coelenterate consumption of pelagic larvae and observations of leeches, crabs, crayfish, and mammals eating attached mussels (Molloy et al. 1997).
Birds have been the most intensively studied natural enemies of Dreissena (Molloy et al. 1997). Consumption of attached Dreissena has been recorded for at least 21 species in Eurasia and 20 in North America. Only five species — Greater Scaup (Aythyamarila), Goldeneye (Bucephalaclangula), Oldsquaw (Clangulahyemalis), Herring Gull (Larusargentatus), and White-Winged Scoter (Melanittafusca) — have been observed eating Dreissena both in Eurasia and North America. Five diving ducks — Tufted Duck (Aythyafuligula), Pochard (Aythyaferina), Greater Scaup (Aythyamarila), Lesser Scaup (Aythyaaffinis), and Goldeneye (B. clangula) — and one diving-rail, the Coot (Fulicaatra), are the most well-documented avian predators of Dreissena (Molloy et al. 1997).
Waterfowl frequently field-documented as predators of Dreissena in Europe or North America.
Molloy et al. (1997) indicated that 10 Eurasian and 5 North American fish species within five families have been field-documented as containing planktonic Dreissena larvae in their alimentary tracts: Cyprinidae (7 species), Clupeidae (3 species), Osmeridae (2 species), Percidae (2 species), and Percichthyidae (1 species). Consumption of Dreissena attached to substrates has been recorded for at least 13 fish families, including 14 species within 10 families in North America and 27 species within 9 families in Europe.
Examples of fish predators of Dreissena in North America. Freshwater drum, carp, round goby, and pumpkinseed are documented predators. Redear sunfish, river redhorse, and copper redhorse are predicted to be predators.
Examples of field-documented fish predators of attached Dreissena in Europe.
Only three species — the common carp (Cyprinuscarpio), pumpkinseed (Lepomisgibbosus), and round goby (Neogobiusmelanostomus) — have been field-documented as predators on both continents. Another 13 North American fish species have been mentioned in the literature as potential predators, based primarily on their documented feeding on other bivalve species in the field (Molloy et al. 1997).
Although predators, particularly fish and birds, have been documented on occasion to consume Dreissena at high rates (Molloy et al. 1997), this does not necessarily mean that they would be effective biocontrol agents. Practical constraints and ecological considerations are essential to implementation of a successful biocontrol project. Past biocontrol failures have made it very clear that extreme care must be exercised not to introduce a natural enemy that is not relatively host-specific. In this regard, natural enemies with wide host ranges cannot be seriously considered. Predators are typically not highly specific in their prey choices. There is, for example, no known predator (nor does one likely exist) that consumes only Dreissena (Molloy et al. 1997). Thus, a fish introduced to a water body from outside its natural range may prefer Dreissena as a prey item, but will also consume other aquatic organisms (likely other molluscs). Such predators may reduce Dreissena population densities, but their consumption of nontarget prey could potentially cause serious, adverse ecological impacts. Following their introduction, these predators would likely successfully reproduce and spread to other water bodies, where their presence might be undesirable. If technically and economically feasible, blocking reproduction among such introduced predators (e.g., stocking with sterile animals or those of a single sex) might possibly make their use acceptable in limited situations.
Besides their lack of prey specificity, predators have other characteristics that are likely to severely limit their usefulness as biocontrol agents. Predators would not likely provide the quick mussel kill typically desired in the infrastructures of raw water users. The financial cost of obtaining large numbers of predators (mass production?, mass harvesting from other areas?, etc.) to treat Dreissena-infested water bodies would likely be economically prohibitive. In addition, all currently known predators would be completely impractical for use in reducing mussel densities in the majority of confined Dreissena habitats within raw water infrastructures (e.g., pipes).
Could existing, indigenous predator populations be managed in their present habitats to maximize the role they naturally play in Dreissena control? French (1993) suggested that resource agencies should manage populations of drum, sunfish, and redhorse to improve their habitats and to reduce exploitation of large individual fish (i.e., the size that preys most intensively on Dreissena). Similarly, McMahon et al. (1994) also suggested improving habitat conditions for desired predators so that their populations would increase at a gradual rate and would be sustained through periods of reduced food. The technical and economic feasibilities of these ideas remain to be tested.
Management and Control Contents