Changes in the Benthic Macroinvertebrate Community of Southwestern Lake Ontario Following Invasion by Dreissena Mussels, the Amphipod Echinogammarus ischnus, and the Round Goby Neogobius melanostomus: A Long-term (1983-2014) Perspective

Abstract

Successive invasions of the Laurentian Great Lakes by zebra (Dreissena polymorpha) and quagga (D. bugensis) mussels, the amphipod Echinogammarus ischnus, and the round goby (Neogobius melanostomus), all of Ponto-Caspian origin, have altered benthic macroinvertebrate communities, but the impacts of these invasions may differ short- and long-term and in magnitude. Changes in diversity and abundance of benthic macroinvertebrate communities at long-term cobble and artificial reef study sites in southwestern Lake Ontario were quantified using dome suction sampling in July and September 2014, following invasion of the round goby after the year 2000. Using Non-metric Multi-dimensional Scaling (nMDS), Analysis of Similarities (ANOSIM) and Similarity Percentages (SIMPER), abundance estimates for native benthic macroinvertebrate taxa were compared with past sampling years (1983, pre-invasion of dreissenids; 1991-1992, early post-invasion of dreissenids; and 1999-2000, ~10 years post-invasion of dreissenids and early post-invasion of E. ischnus). Oligochaetes were the dominant taxon in 2014 (1193.9 ± 18.3 [SEM] m-2 at the cobble and 982.3 ± 32.2 m-2 at the reef sites, July and September abundances combined), followed by E. ischnus (101.2 ± 2.1 m-2 at the cobble and 599.9 ± 5.5 m-2 at the reef sites), and Chironomidae (63.4 ± 26.5 m-2 at the cobble and 215.9 ± 19.3 m-2 at the reef sites). By 2014, chironomid richness had increased >100% since 1991-1992. For the first time during the 31 year sampling period, gastropods and sphaeriid clams were absent, which contributed to low Simpson’s Diversity in 2014. Between 2000 and 2014, D. bugensis almost completely replaced D. polymorpha, and E. ischnus replaced Gammarus fasciatus as the dominant amphipod. Results in 2014 were in strong contrast with those reported from 1983, 1991-1992, and 1999-2000, when gastropods and sphaeriid clams, as well as the native amphipod G. fasciatus, were dominant members of the benthic macroinvertebrate community. These results suggest that the 2014 benthic macroinvertebrate communities underwent greater change after invasion of the round goby than the communities did after the dreissenid and E. ischnus invasions (~1990 and ~1994, respectively). The loss of gastropods and native clams, coupled with increases in oligochates and chironomids at the study sites, likely will have important effects on benthic and pelagic food webs in Lake Ontario.