Long-term increases in shell thickness of zebra mussels (Dreissena polymorpha) in the Hudson River

Since zebra mussels (Dreissena polymorpha) appeared in the Hudson River in 1991, their shell thickness (mass at a given shell length) has increased substantially. This may be a result of increases in predation pressure and alkalinity in the river, and probably affects the susceptibility of mussels to crushing predators, as well as the ultimate fate of mussel shells in the ecosystem.