Biological invasions in Lake Ontario: past, present and future

Abstract

Lake Ontario has an extensive history of biological invasions, extending more than 170 years. The rate of invasion began to increase during the 1870s, and accelerated after the opening of the St. Lawrence Seaway in the 1950s. Currently, there exist approximately 60 nonindigenous species (NIS) of vertebrate and invertebrate animals, protozoans, algae and aquatic macrophytes established in the lake. Fish are the most widely represented taxon (15 species), followed by algae (14 species), molluscs (11 species) and crustaceans (8 species), respectively. Vectors responsible for NIS introductions vary temporally and by taxon. Before 1920, deliberate release and solid shipping ballast were the dominant vectors for NIS introduction. Ships’ballast water was the dominant vector between 1961 and 2002. All algal species,and most of the crustaceans and protozoans, were introduced via ballast water discharge, whereas fish vectors consisted of deliberate introductions, canals, accidental introductions, ballast water discharge, and bait release. Identified mollusc vectors include solid or liquid ballast discharge, movement through canals and aquarium release. Since all transoceanic vessels entering the Great Lakes system must pass through Lake Ontario, these ships could potentially introduce new species, either by ballast water discharges or hull fouling. Approximately 17% of all the ships entering the Great Lakes with saline ballast water discharge into Lake Ontario, potentially exposing the lake to euryhaline NIS such as the crustacean Cercopagis pengoi and the diatom Thalassiosira baltica. Lake Ontario is the first port-of-call for 43% of non-ballasted vessels, which may expose port areas to NIS introduction via hull fouling. Additionally, about 5% of non-ballasted vessels will load and then discharge ballast water while operating on Lake Ontario, potentially allowing NIS contained in ballast residuals to establish in the lake. Alternative vectors, including the baitfish and aquarium trades, and particularly the commercial sale of live freshwater fishes for human consumption, may add to the complement of established NIS in the lake. NIS is now abundant components of the lake’s phytoplankton, invertebrate and fish communities, and jeopardize effective management of the lake. Despite recent implementation of ballast water exchange legislation, Lake Ontario remains highly vulnerable to future invasions. Management efforts must focus on identifying and eliminating vectors that may bring additional NIS to Lake Ontario and the other Great Lakes.