Dreissena in Lake Ontario 30 years post-invasion

We examined three decades of changes in dreissenid populations in Lake Ontario and predation by round goby (Neogobius melanostomus). Dreissenids (almost exclusively quagga mussels, Dreissena rostriformis bugensis) peaked in 2003, 13 years after arrival, and then declined at depths <90 m but continued to increase deeper through 2018. Lake-wide density also increased from 2008 to 2018 along with average mussel lengths and lake-wide biomass, which reached an all-time high in 2018 (25.2 +/- 3.3 g AFTDW/m(2)). Round goby densities were estimated at 4.2 fish/m(2) using videography at 10 to 35 m depth range in 2018. This density should impact mussel populations based on feeding rates, as indicated in the literature. While the abundance of 0-5 mm mussels appears to be high in all three years with measured length distributions (2008, 2013, 2018), the abundance of 5 to 12 mm dreissenids, the size range most commonly consumed by round goby, was low except at >90 m depths. Although the size distributions indicate that round goby is affecting mussel recruitment, we did not find a decline in dreissenid density in the nearshore and mid-depth ranges where goby have been abundant since 2005. The lake-wide densities and biomass of quagga mussels have increased over time, due to both the growth of individual mussels in the shallower depths, and a continuing increase in density at >90 m. Thus, the ecological effects of quagga mussels in Lake Ontario are likely to continue into the foreseeable future. (C) 2020 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved.

Automated summary

We conducted a study on the changes in dreissenid populations and predation by round goby in Lake Ontario over a period of three decades. The study found that dreissenid populations peaked in 2003 and then declined at depths less than 90 meters but continued to increase at deeper depths until 2018. The overall density of dreissenids in the lake also increased from 2008 to 2018, along with the average mussel lengths and biomass. The study also estimated the density of round goby in 2018 and examined its impact on mussel populations based on feeding rates. Despite indications of round goby affecting mussel recruitment, no decline in dreissenid density was found in the nearshore and mid-depth ranges where round goby has been abundant since 2005. These findings suggest that the ecological effects of dreissenid mussels are likely to persist in Lake Ontario.