A Necessary Nuisance: The Undervalued Functions of Non-native Aquatic Plants

Julian Burgoff

I am grateful to to Julian Burgoff for giving Conservation Sense and Nonsense this opportunity to publish his guest article that adds to our extensive collection of articles about the benefits of non-native plants and the damage done by herbicides to needlessly destroy them. Julian Burgoff is an avid bass angler and aspiring fisheries ecologist from western Massachusetts. He is currently a master’s student with the Massachusetts Cooperative Fish and Wildlife Research Unit at UMass- Amherst where he studies juvenile river herring age, growth and habitat use in coastal Massachusetts lakes and estuaries. He is passionate about lake ecology and the management of aquatic vegetation in lakes and hopes to work in a field related to lake conservation and warmwater fisheries management in the future.

Conservation Sense and Nonsense

Natural resource managers and scientists in the United States often use divisive, warlike language when referring to both terrestrial and aquatic plants they consider to be “invasive” species, devolving the complexity of ecological interactions into good vs evil rhetoric. Like terminology used by the US government to define groups such as undocumented immigrants, nonnative “invasive” species are often referred to by natural resource managers and scientists in this country as “alien” and “exotic,” causing “nuisance infestations” and economic and ecological “harm.” This demonization of non-native species is illustrated by the title of a seminar conducted last spring by the State of Connecticut’s Agricultural Experiment Station Invasive Aquatic Plant Program regarding the relatively recent proliferation of Hydrilla Verticillata in the lower Connecticut River:

Despite the hyper-negative perception cast upon non-native species, the reality is that non-native organisms often provide important ecosystem services in highly altered landscapes and waterbodies that are often completely overlooked and highly undervalued by the scientific community.

Aquatic plants harbor an immense amount of aquatic life in lakes, ponds, and rivers. They stabilize lake and river bottoms, sequester/cycle nutrients, provide oxygen, improve water clarity, and serve as important habitats for all aquatic life from small macroinvertebrates (larval insects) and zooplankton (free-floating microorganisms) to large predatory fishes. The aquatic plant communities in lakes and rivers of the United States are subject to sustained stress via anthropogenic disturbances to land and water. Land use changes including corporate agriculture, development and expansion of impervious surfaces, wastewater pollution and damming of rivers have all contributed to dramatic changes in aquatic ecosystems and their aquatic plant communities since the colonial invasion of the North American continent.

Non-native aquatic plants have long been blamed for their supposed negative ecological impacts to lake and river ecosystems. As a response to eutrophication (i.e. nitrogen and phosphorous enrichment from human activities), non-native aquatic plants can grow in extremely dense stands that are perceived to outcompete native aquatic vegetation, decrease water quality (e.g. lower dissolved oxygen), and reduce foraging efficiency for predatory fish. While this may be accurate at various spatial/temporal scales, the prolific growth of non-native aquatic plants also serves a multitude of benefits for lake and river ecosystems and the organisms that they support.

Non-native aquatic plants have a tremendous capacity to improve water quality in freshwater ecosystems. In tropical climates like Florida, floating plants such as Hyacinth (Eichhornia crassipes) and Water Lettuce (Pistia stratiotes) sequester nutrients from the water and produce allelochemicals (chemical compounds released by plants) that, along with physically shading areas of the water, can reduce harmful algal blooms.

Photo: Kevin Copple
Cyanobacteria bloom on Lake Hatchineha, Kissimmee, Florida

 In the northeast, Water Chestnuts (Trapa natans) provide similar ecosystem services in terms of shading, nutrient cycling, and competition with algal taxa. Non-native submerged aquatic plants such as Eurasian Milfoil (Myriophyllum spicatum) and Fanwort (Cabomba caroliniana) also compete with algae and cyanobacteria via allelopathy and physically collect suspended sediment and algae particles from the water column, improving water clarity.

Photo: Jody White
Eurasian Milfoil in a tidal tributary of the Potomac River
Dense Eurasian Milfoil in an urban central Massachusetts lake
Dense stands of Fanwort with holes/edges of clear water in an otherwise turbid, hyper-eutrophic Central Massachusetts lake

All of these plants provide habitat for a diverse array of macroinvertebrates and zooplankton, and thus contribute essential prey resources to feed the higher organisms up the food web like fishes.

Source: https://www.caryinstitute.org/eco-inquiry/teaching-materials/hudson-river-ecology/water-chestnut-high-tide-day
Depiction of the interactions between plants, macroinvertebrates, zooplankton and fishes underneath beds of water chestnut on the Hudson River

Not all fisheries and aquatic ecologists are blind to the ecosystem services provided by non-native aquatic plants. Researchers following the recovery of submerged aquatic vegetation on the Potomac River and Upper Chesapeake Bay since the 1980s have documented the important role that hydrilla played in reestablishing water clarity and facilitating the regrowth of native aquatic plants such as Eel grass (Vallisneria americana) and Coontail (Ceratophyllum demersum). Long-term assessments of aquatic plant communities in these ecosystems failed to reveal the catastrophic impacts to native flora and fauna biodiversity claimed by the Connecticut Invasive Aquatic Plant Program. Similarly, a study regarding the impacts of hydrilla on the biodiversity of plants, fish and waterfowl in 39 Florida lakes conducted on multiple time scales found no significant effects on metrics of ecological health. A quote from the abstract of this article depicts the main findings:

“Our conclusions support the hypothesis that hydrilla in these Florida lakes has occupied a mostly vacant ecological niche and has not affected the occurrence or relative composition of native species of aquatic plants, birds, and fish.”

“Lack of exotic hydrilla infestation effects on plant, fish and aquatic bird community measures,” Mark Hoyer, et. al.

There seems to be a common pattern with aquatic plant “invasions”. Water quality suffers due to human activities which affect the ability for native plants to grow, opening a niche for more tolerant species to proliferate and this in turn often remediates conditions enough to allow native taxa to reestablish. Where native aquatic plant communities remain intact and water quality remains high, the degree to which “invasion” of non-native aquatic plants occurs is often buffered by the integrity of the existing native plant communities. The notion that non-native aquatic plants enter an ecosystem and completely overtake the native plant community is rarely, if ever, an actual phenomenon realized in nature. In my view, the trouble comes when humans seek to selectively intervene with species interactions and try to control aquatic plant communities with quick fixes like herbicides and algicides as band-aids to cover up the consequences of poor water quality. These “management” efforts often result in a net loss of ecosystem services, biodiversity, habitat, and water quality.  The pictures below illustrate this phenomenon.

Variable-leaf Milfoil (Myriophyllum heterophyllum) growing amongst native Yellow Water-lily (Nuphar lutea) in an eastern Massachusetts lake
Variable Milfoil left to rot after a chemical herbicide treatment in a neighboring eastern Massachusetts lake

Where I live in Massachusetts there are dozens of small ponds and lakes that are sprayed with herbicides annually to treat “nuisance” aquatic vegetation. Most aquatic plant “control” here is driven by the desires of lakefront property owners who are concerned with their property values and want to transform the lakes they live on into swimming pools (full of toxic cyanobacteria, I suppose). A select few private lake management companies (e.g., Solitude Lake Management) enjoy a monopoly over the lake management market in this region and are endorsed by herbicide manufacturers to put chemicals into our water in the name of ecological “restoration”. Unfortunately, there is often extremely limited pre and post water quality monitoring, and almost never in-depth pre and post monitoring for impacts to indicators of biotic health (native plant communities, zooplankton/macroinvertebrate communities, fish etc.) following these treatments.

 While this issue is not studied nearly enough by independent scientists (i.e. those not representing institutions funded by chemical manufacturers), numerous studies have shown that lake herbicide treatments can have negative impacts to water quality, native plant communities, zooplankton communities, fish and wildlife. I have witnessed firsthand the negative consequences of herbicide use to “control” non-native aquatic plants ever since I was a kid. I’ve seen numerous lakes with abundant milfoil populations turn from crystal clear water to pea soup, with dense cyanobacteria blooms following chemical treatment.

Some of the healthiest lakes are those which have never been subjected to large-scale herbicide treatments. One such lake, Lake Bomoseen, is one of the most important fisheries in the state of Vermont, offering trophy Brown Trout, Largemouth Bass and Smallmouth Bass angling opportunities. Since the 1980s, the lake has supported an abundant population of Eurasian Milfoil. An excellent example of the ecosystem services achieved by allowing species interactions to occur unmolested over time, Lake Bomoseen supports an extremely healthy native aquatic plant community in addition to the dense stands of Eurasian Milfoil present around the lake. In 2022, the Lake Bomoseen Association, comprised of select individuals who own property around the lake, requested a permit from the Vermont Department of Environmental Conservation for the use of an herbicide ProcellaCOR to treat the entire littoral zone (i.e. the area of the lake where plants grow) of the lake over a 3-year period. This spurred a tremendous amount of public dissent. Lakefront property owners, local anglers, and hundreds of Vermont citizens concerned with the use of chemicals in the lake have united and made their voices heard on the issue. The Vermont Fish and Wildlife Department submitted a review of the treatment application to the Vermont DEC, stating that the proposed treatment was a threat to the health of the lake and the integrity of its fish populations. An excerpt from the review sums up the position of the VT Fish and Wildlife on this proposed treatment:

“Lake Bomoseen supports high-quality sportfish fisheries that rely on a diverse healthy aquatic plant community, which may be harmed by wide-scale application of pesticide, thus impacting these sportfish populations and the public benefits they support. The pesticide application at the scale proposed presents a risk to fishing as a public benefit.”

Vermont Fish and Wildlife

The proposal is still under review by the VT DEC, which if approved, would be the largest lake-wide herbicide treatment ever conducted in the state of Vermont. More information about this issue and how you can support the folks fighting to stop this treatment can be found here.

My observations of aquatic plant communities and their importance as habitat for fish have led me to pursue a career in fisheries and aquatic ecology. Before I had ever read a single piece of scientific literature, I had internalized many of the complex interactions between fish and aquatic plants based off of intuition derived from thousands of hours of on the water experience fishing in eutrophic, heavily vegetated Massachusetts ponds and lakes. To this day I am obsessed with fishing in thick aquatic vegetation. In the summer months on a hot sunny day I will actively seek out lakes with the densest aquatic plants I can find to chase after big bass hiding in the matted cover. I share this passion with thousands of anglers across the country.

Native aquatic plants can grow in dense stands, too. This is a cavernous mat of Elodea canadensis over +/- 9ft of water in a bay on southern Lake Champlain
Releasing a Largemouth Bass extracted from the canopy pictured above

Next time you go to your local lake or river, spend some time looking at the aquatic plants that inhabit that body of water. If you have the opportunity, go under the water to observe how fish utilize and interact with stands of aquatic plants. Notice all the life that resides within the plants and try to appreciate the organisms that you encounter, regardless of where in the world they may have originated.

Julian Burgoff
Amherst, MA