For students who want to learn something scientifically and socially valuable in a short time. A 15 minute lecture is followed by time for questions. Sponsored by the Shapiro Science Library.
The problem of invasive species homogenizing our ecosystems with unwanted organisms that damage, degrade, and exterminate native species is widespread across the terrestrial and aquatic habitats of the Great Lakes region. Two of the most pernicious of these species are the zebra and quagga mussels, which were introduced to the lakes through ballast water exchange by foreign freighters. Unlike Asian carp, which are our current barbarians at the gate, mussels are here and have devastated food webs where they have proliferated. Their filtering activities, which remove algae from the water column, in conjunction with declining nutrient levels in Lake Huron especially, have led to a trophic cascade, which has depressed algae, zooplankton, forage fish, and severely impacted the salmon fishery of Lake Huron. Several unintended consequences of these changes include the almost elimination of alewife (main forage of salmon) from Lake Huron, and since the alewife eat larval forms of fish with planktonic stages, we have seen: 1. Lowered salmon populations, and 2. Increases in native species with planktonic larvae, including emerald shiner, walleyes in Saginaw Bay, and to some degree lake trout and lake herring. Lake Huron and probably other Great Lakes (e.g., Michigan) are shifting toward more historical, pristine conditions, and their water quality, algal, zooplankton, and forage fish populations are beginning to closely resemble those found in Lake Superior.