Dreissena in Lake Ontario 30 years post-invasion

Abstract

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/m²). Round goby densities were estimated at 4.2 fish/m² 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.

Keywords: Dreissena polymorpha; Dreissena rostriformis bugensis; Lake Ontario; Long-term changes; Neogobius melanostomus.

Fig. 1.

Location of stations in Lake Ontario sampled for Dreissena during August–September 2018. Ponar stations (black circles), Benthic Imaging System (BIS, white circles), or both Ponar and BIS (grey circles).

Fig. 2.

Deployment of the Benthic Imaging System (BIS). Left: BIS on deck of R/V Lake Guardian; right: BIS being deployed from starboard side of R/V Lake Guardian. Position of cameras and lights are indicated.

Fig. 3.

Round goby in screen shots from down-looking (A) and side-looking (B) cameras at station 37 (24 m depth) in Lake Ontario in 2018. For scale, the yellow and black squares on the BIS feet are each 24 × 24 mm. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 4.

Long-term dynamics of zebra (black lines, triangles) and quagga (red lines, circles) mussel density (left graphs) and biomass (right graphs) in Lake Ontario. Vertical bars are standard errors. Lake-wide density and biomass were calculated as weighted averages from four depth zones. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 5.

Length-frequency distributions of Dreissena spp. >5 mm in length in Lake Ontario in 2008, 2013, and 2018. The average lengths (L) of mussels >5 mm ± standard error for each year are given.

Fig. 6.

Proportion of Dreissena <5 mm in different depth zones of the total density in 2008, 2013, and 2018 in Lake Ontario. Vertical bars are standard errors.

Fig. 7.

Round goby and mussel distribution with depth in the nearshore of Lake Ontario in September of 2018. Upper panel: round goby densities (fish/m²) by depth estimated using down-looking camera of the Benthic Imaging System. Note: depths <11 m and >35.5 m were not sampled. Lower panel: change in percentage of mussels 3–12 mm in size (grey triangles) and density of round goby estimated using Benthic Imaging System. Distance-weighted least squares regression (r = 0.64, P < 0.001) was used to indicate the trends.