Biotic resistance on the increase: native predators structure invasive zebra mussel populations

1. Abundant native predators, parasites and pathogens that switch to consuming a hyper-successful exotic species may be able to control the invasive population. Native predators may, however, need time to adapt to feed effectively on an exotic resource. In this case, mortality on an exotic population from native predators could increase over time even without a numerical increase in the predator population. 2. We measured mortality of zebra mussels (Dreissena polymorpha) in the Hudson River both in controls open to predation and in exclosures that excluded large predators to estimate mortality of zebra mussels from large predators and other causes. 3. We found that predation by the blue crab (Callinectes sapidus), and perhaps other predators, causes high mortality on zebra mussels in the Hudson River estuary. This predation apparently led to increased mortality and altered population structure in the invader over time. 4. Long-term data from the Hudson River suggest that components of the invaded ecosystem, like rotifers, are recovering through predator-caused release from zebra mussel grazing. Increased mortality on hyper-successful exotic populations over time may be a common phenomenon with both ecological and management implications.