Invasion of the Zebra Mussel
They took the canal expressway across NY State in 1991-92
The invasion of the zebra mussel (Dreissena polymorpha) in the Mohawk River and elsewhere in the US was stunning in its speed. Since invasion they have had profound impacts on freshwater ecosystems. I looked into this invasion because of an interest in how the Erie Canal links the Mohawk and Hudson rivers with the Great Lakes ecosystem. This connection has, is, and will continue to be a pathway for invasive species.
Writing about the early spread of the zebra mussel, Charles O’Neil (NY Sea Grant) and Alan Dextrase (Ontario Ministry of Natural Resources) wrote that the “Erie Canal provided an expressway across New York State from Lake Erie to the Hudson River” (O’Neil and Dextrase, 1994). Thus this aquatic connection provides a fast pathway for a variety of invasive species, and isolation and containment can be difficult if not impossible. The zebra mussel and its colleague the quagga mussel, which prefers slightly deeper water, are here to stay – our ecosystem has been fundamentally transformed and there is no going back to pre-invasive conditions.
Zebra mussel (Dreissena polymorpha) from the Mohawk River near Canajoharie. Photo: JI Garver.
I first became interested in zebra mussels in the late 1990s after they had become common in the Mohawk. After seasonal drawdown of the locks on the Mohawk River, the mussel growth for the year was exposed, and the density of these organisms on rocks and concrete was amazing. The exposed mussels colonized the hard substrate at Lock E8 in Glenville, one of the removable dams that are lifted in the winter. I hadn’t appreciated at the time that I was looking at a new invasion that was pervasive in the watershed.
Zebra mussels and quagga mussels cause profound change in the aquatic ecosystems that they invade. They are filter feeders and because they can multiply in abundance they can severely deplete phytoplankton and zooplankton in the water column. While this filter feeding results in a marked increase in water clarity, it has a dramatic impact on other aquatic organisms that also rely on phytoplankton and zooplankton.
The documented population densities once zebra and quagga mussels get established are stunning. David Strayer with the Cary Institute of Ecosystem Studies and colleagues studied the establishment of zebra mussels in the Hudson (see Strayer and others 1996, 1999, and Strayer 2008). They estimated that in the freshwater tidal Hudson by the end of 1992 densities of zebra mussels were as high as 4000 mussels per square meter, they constituted > 70% of the biomass in the River, and they filtered a volume of water equivalent to the entire water column in 1 to 4 days (see Strayer and colleagues 1996 and 1999). As part of the reproductive cycle, the planktonic veliger larvae of zebra mussels are free-floating in the water column, but because the parents are filter feeders, cannibalism of larvae appears to help limit growth and expansion (Strayer et al., 1996).
Zebra mussels appear to have been introduced into the Great Lakes by ballast water and were widely recognized in Lake Erie by 1989. By 1993 they had not only spread across the Great Lakes but had crossed watershed boundaries and become fully established in both the Mohawk-Hudson as well as the Mississippi watersheds. Part of their success appears to have been due to their high fecundity – they are breeding champions. In addition to their fecundity, they have found a suitable environment, and hence they are thriving.
What have been the environmental consequences of this invasion? How have they affected different trophic levels of the aquatic ecosystems that they have invaded? In a 2004 Sea Grant publication, Charles O’Neil (NY Sea Grant) put these and other invasive species into perspective:
Non-native species have been called “biological pollution” due to their ability to negatively impact the ecosystem and the native populations of the flora and fauna that it supports. The combined effect of non-native species has been to alter the Great Lakes food web, as well as to alter trophic levels from the lowliest plankton to the top predatory fishes.
Zebra mussels were first recognized and widely abundant in western Lake Erie in 1989, and by the end of the year had spread rapidly across the entire Lake, and in the western parts of Lake Ontario. The spread of zebra mussels was explosive in 1990 and by the end of the year they occurred throughout the Great Lakes.
There are two freshwater avenues out of the Great Lakes, both artificial and both important pathways for invasive species. One is the Chicago Sanitary and Shipping Canal that connects Lake Michigan to the Illinois River, part of the Mississippi River. The other is the Erie Canal that connects both Lake Erie and Lake Ontario to the Mohawk and Hudson Watershed. The mussels took both of these un-natural paths out of the Great Lakes.
In 1990 the mussels started working eastward in the Erie Canal from Lake Erie, making it about a third of the way across NY State (O’Neil and Dextrase 1994). The invasion in the Mohawk occurred in 1991. By early 1992 they had followed the Erie Canal to the Mohawk River and were found at Herkimer and Amsterdam, and also in the Hudson River at Albany (O’Neil and Dextrase 1994). At the same time (1991) the mussels expanded into the Chicago Sanitary and Shipping Canal, and by 1992 had reached the confluence of the Illinois River with the Mississippi River. The zebra mussel appeared in Lake Champlain in 1993, presumably through the direct canal connection to the Hudson.
In the book “Quagga and Zebra Mussels: Biology, Impacts, and Control” Amy Bensen wrote a chapter entitled “Chronological history of zebra and quagga mussels (Dreissenidae) in North America,” which provides a review of the chronology of invasion. One interesting aspect of the escape out of the Great Lakes is how the mussels got into the Hudson River, because the invasion is inferred to have come in from two “fronts.” One front was earlier (1991) and is inferred to have been from a single point source near Catskill (May of 1991). The other front came through the more traditional invasive pathway, the Mohawk River. The two populations joined in the Hudson in 1992. Bensen writes:
“The initial invasion of the Hudson represented a large jump across country by the zebra mussel, as the nearest potential source populations were in Lake Erie in 1989 and Lake Ontario and the western part of the Erie Canal in 1990 (O’Neill and Dextrase 1994). A second invasion occurred in 1992, when zebra mussels were carried into the head of the estuary by fluvial transport from the Mohawk River. (The Mohawk itself was not infested until 1991 (O’Neill and Dextrase 1994).) The two populations merged in 1992.”
One thing that can stop zebra mussels is a lack of calcium in the water. To build shells they need to harvest calcium from river water. Thus, zebra mussels are calcium-limited, which means that they can only flourish in water with high levels of dissolved calcium. In a paper entitled “A calcium-based invasion risk assessment for zebra and quagga mussels (Dreissena spp),” Thomas Whittier of the Department of Fisheries and Wildlife at Oregon State University and colleagues note that risk of invasion is (and was) related to dissolved calcium in the water. They define risk based on calcium concentrations: very low (< 12 mg L–1 or ppm), low (12–20 mg L–1), moderate (20–28 mg L–1), and high (> 28 mg L–1). The Mohawk River has reported values of 30-40 ppm dissolved calcium, which is one reason it was a high-risk calcium-rich pathway and thus invasion was inevitable. However, many adjacent streams and rivers are calcium-limited (i.e., those in the Adirondacks), and hence are less likely to sustain significant populations. Most rivers and streams in New England and on the Atlantic slope are calcium-limited, and hence invasion is not expected in major waterways east or south of the Hudson.
Molluscivorous fish eat mussels. There must be some good news in all of this. Compared to native mussels (unionids), zebra mussels are thought to be more susceptible to grazing by fish because they are smaller and they have a thinner shell (Kirk et al., 2001). So a fair question is how well have the molluscivorous fish have done since invasion. There are a few fish in the Mohawk Watershed that have been documented to consume zebra mussels, and these include common carp, bull chub, white sucker, white perch, white bass, pumpkinseed, yellow perch, freshwater drum, round goby, and others (Kirk and others, 2001).
The last two fish on this list - freshwater drum (Aplodinotus grunniens) and the round goby (Neogobius melanostromus) - are of interest, in part because they too are invasive. The round goby is of interest because it is actively invading the Mohawk, and by 2019 it had entered the upper part of the watershed and has been captured in Utica. It is possible that this fish will have successfully invaded the Mohawk and then enter the Hudson River in the next five years or so. Given the density of zebra mussels, they should do just fine.
The rreshwater drum, or sheepshead, has already invaded the Mohawk and has been here since before the zebra mussels. Detection and monitoring is the cornerstone to understanding invasion, so new and novel approaches to monitoring are important. Freshwater drum are one of the few “soniferous fish” and they earn this distinction because they make drum-like noises.
Rodney Rountree and Francis Juanes designed an experiment that used passive acoustic monitoring in the Mohawk to determine the occurrence and abundance of freshwater drum. They recorded drum knocks in the Champlain, Erie, Seneca, and Oswego Canals. They write that it is “…believed that the freshwater drum migrated from the Great Lakes through the NYSCS [NY State Canal System] after first becoming established in the Mohawk River sometime in the last 30–40 years.” They hypothesize that the earliest invasion may have been immediately after reconstruction of the Erie Canal in 1918 (Rountree and Juanes, 2017). Their acoustic identification of drum may allow for a better understanding of population dynamics.
The changes resulting from the zebra mussel invasion are profound. David Strayer looked back at the impacts (Strayer, 2008). He wrote:
In the 20 years since zebra mussels (Dreissena polymorpha) first appeared in North America, they have become one of our most widespread and abundant freshwater animals, and have fundamentally transformed freshwater food webs and biogeochemistry. Indeed, few human impacts on North American fresh waters have been greater or more far-reaching than the arrival of this single species.
Have we learned anything from this invasion or are we doomed to repeat mistakes of the past? In his paper entitled “Twenty years of zebra mussels: lessons from the mollusk that made headlines” David Strayer concluded that the zebra mussel lived up to early prediction that it would spread widely and quickly, and cause considerable economic damage. However, the invasion is credited with giving rise to the study of invasion ecology, now an important pillar in ecology. It has also has important and major impacts on the public awareness and response to invasive species. The public is increasingly aware of alien species and the need for public policy to address the challenges of invasion.
This and other Notes from a Watershed are available at: https://mohawk.substack.com/
Further Reading
Kirk JP, Killgore KJ, Sanders LG. Potential of North American molluscivorous fish to control dreissenid mussels. US Army Corps of Engineers, Zebra Mussel Research Program. 2001 Jun;1.
Lucy, F. and Muckle-Jeffs, E., 2010. History of the zebra mussel/ICAIS conference series. Aquatic Invasions.
O’Neill, C.R., Jr. 2004. Biological pollution of the Great Lakes: the Nonindigenous aquatic species issue. NY Sea Grant, 2004.
O’Neill, C.R., and Dextrase, A. 1994. The introduction and spread of the zebra mussel in North America. In Proceedings of the 4th International Zebra Mussel Conference. Edited by A.H. Miller. Wisconsin Sea Grant Institute, Madison, Wis. pp. 433-446.
Ram, J.L. and McMahon, R.F., 1996. Introduction: the biology, ecology, and physiology of zebra mussels. American zoologist, pp.239-243.
Strayer, D.L., J Powell, P Ambrose, L C Smith, M L Pace, D T Fischer, 1996. Arrival, spread, and early dynamics of a zebra mussel (Dreissena polymorpha) population in the Hudson River estuary, Canadian Journal of Fisheries and Aquatic Sciences, 1996, 53:1143-1149, https://doi.org/10.1139/f96-038
Strayer, D.L., Caraco, N.F., Cole, J.J., Findlay, S. and Pace, M.L., 1999. Transformation of freshwater ecosystems by bivalves: a case study of zebra mussels in the Hudson River. BioScience, 49(1), pp.19-27.
Strayer, D.L. and Smith, L.C., 1996. Relationships between zebra mussels (Dreissena polymorpha) and unionid clams during the early stages of the zebra mussel invasion of the Hudson River. Freshwater Biology, 36(3), pp.771-780.
Strayer, D.L., 2009. Twenty years of zebra mussels: lessons from the mollusk that made headlines. Frontiers in Ecology and the Environment, 7(3), pp.135-141.
Whittier TR, Ringold PL, Herlihy AT, and Pearson SM. 2008. A calcium-based invasion risk assessment for zebra and quagga mussels (Dreissena spp). Front Ecol Environ 6: 180–84.