USGS-Lake Ontario Biological Station, 17 Lake Street, Oswego, NY 13126, USA

Disruption of the benthic food-web in Lake Ontario: Consequences on native fishes

Over the past 150 years the biological communities of Lake Ontario have endured numerous disruptions. The present offshore fish community is dominated by exotic alewife, rainbow smelt, and various Pacific salmonines. It little resembles the historic community, which was dominated by coregonines, cottids, lake trout, sturgeon, Atlantic salmon, and burbot. Major changes in the fish community were brought about by the invasion of exotic species through man-made canals and more recently through ballast water discharge. Other significant factors driving fish community disruptions were eutrophication, deforestation, overfishing, and the intentional stocking of Pacific salmonids. The benthic macroinvertebrate community is presently undergoing rapid change. This change is coincident with the establishment and expansion of non-native Dreissena spp. during the late 1980s and early 1990s. For the fish community, the most alarming change in the benthic community is the sudden collapse of the Diporeia population, a deepwater amphipod and a staple in the diet of many native benthic species. Although this decline is believed related to the invasion by dreissenids, the exact mechanism has not yet been identified. The collapse of Diporeia was first noted in southeastern Lake Ontario. This observation coincided with the collapse of slimy sculpins in this same area along with shifts in the bathymetric distribution of lake whitefish (a commercially important species) and their subsequent decline in abundance. The collapse of Diporeia may also act as a bottleneck for early life stages of lake trout, and may impede the potential restoration of the bloater, Coregonus hoyi. The bloater, formerly abundant in Lake Ontario but extirpated by the late 1970s, fed extensively on Diporeia, and also provided forage for adult lake trout. We do not expect these native fish populations to recover unless the trend in Diporeia dynamics reverses.