Zebra mussels, distinctive striped freshwater mollusks, originated in the Black and Caspian Sea regions of Eurasia. These invasive bivalves likely arrived in North America in the 1980s, transported in ship ballast water to the Great Lakes. The first established population was discovered in Lake St. Clair in 1988. They rapidly spread throughout North American waterways, significantly impacting native ecosystems by altering food webs and outcompeting local species.
Fish That Prey on Zebra Mussels
Several fish species consume zebra mussels, though their effectiveness in controlling populations varies. Freshwater drum (Aplodinotus grunniens) use specialized pharyngeal teeth to crush mussel shells. Zebra mussels can constitute a significant portion of their diet, sometimes nearly half of their primary food sources.
Redear sunfish (Lepomis microlophus) also eat zebra mussels. Their unique pharyngeal teeth are well-suited for crushing shells, and some adult redear sunfish feed almost exclusively on them, showcasing their predatory capabilities.
Blue catfish (Ictalurus furcatus) are another species known to consume zebra mussels, particularly during warmer months. Their diet often shifts seasonally, and they lack a shell-crushing apparatus. Despite these fish preying on zebra mussels, their consumption typically does not curb the widespread proliferation of the invasive mollusk.
Birds That Consume Zebra Mussels
Diving ducks are major avian predators of zebra mussels, actively foraging in aquatic environments. Lesser scaup (Aythya affinis), greater scaup (Aythya marila), and common goldeneye (Bucephala clangula) frequently consume them. These birds dive to access mussel beds, often in shallow areas.
Zebra mussels can form a substantial part of their diets, especially during migration. Lesser scaup and common goldeneye often have zebra mussels dominating their stomach contents. Canvasbacks (Aythya valisineria) also eat them but prefer other aquatic vegetation. This predation can lead to localized reductions in mussel biomass.
Other Animals That Feed on Zebra Mussels
Other animal groups also feed on zebra mussels, albeit with varying degrees of impact. Crayfish, like the rusty crayfish (Orconectes rusticus), prey on smaller zebra mussels. An adult crayfish can consume a considerable number of mussels daily, contributing to localized predation.
Muskrats (Ondatra zibethicus), semi-aquatic rodents, opportunistically eat zebra mussels. They feed on various freshwater mussels and include zebra mussels when available. Their collective predatory pressure is less widespread or impactful compared to that exerted by fish and diving birds across larger aquatic systems.
Why Natural Predators Aren’t Enough
Despite a range of animals preying on zebra mussels, their natural predators are insufficient to control their rampant spread. One reason is the mussels’ extraordinary reproductive rate; a single female can release up to one million eggs annually. This prolific breeding capacity quickly overwhelms the consumption efforts of even numerous predators, leading to rapid population explosions.
Many specialized predators that naturally regulate zebra mussel populations in their native Eurasian habitats are absent in North America. The existing North American species, while adapting to consume the mussels, often lack the efficiency or numbers required to significantly reduce established populations. This absence of effective natural controls allows mussels to thrive unchecked.
Zebra mussels also colonize inaccessible surfaces, such as internal pipes of water infrastructure. Their ability to form dense colonies in protected environments, coupled with their sheer biomass, limits predation impact. Therefore, the combination of high reproductive output and limited effective natural enemies allows zebra mussel populations to persist and expand.