Has the Hudson River fish community recovered from the zebra mussel invasion along with its forage base?
In the first decade after zebra mussels (Dreissena polymorpha) appeared in the Hudson River, the biomass of zooplankton and deepwater macrobenthos fell by ∼50%, while the biomass of littoral macrobenthos rose by >10%. These changes in the forage base were associated with large, differential changes in the abundance, geographic distribution, and growth rates of openwater and littoral fish. In recent years, populations of zooplankton and deepwater macrobenthos have risen towards pre-invasion levels, while littoral macrobenthos remained unchanged. We therefore hypothesized that the abundance, distribution, and growth rates of openwater fish species would shift back towards pre-invasion levels, while littoral fish species would not change. Our analysis of large data sets for young-of-year fishes found no systematic change in the abundance or geographic distribution of either group of fish in the Hudson. We did find a marked increase in growth rates of openwater fish, but no change in growth rates of littoral fish, in support of our hypothesis. Our study shows that the ecological effects of a biological invasion may change over time.