Aquatic Invasive Species Part 1: What are they?

By Gabriella Marchesani
July 04, 2024

Lake Champlain is home to 51 non-native species. In this series, we will discuss what those species are, how they impact the lake and its economy, and how to manage them. This series is a partnership between Lake Champlain Sea Grant and Lake Champlain Basin Program, developed and written by Gabriella Marchesani, a science writer at LCSG and a boat launch steward at LCBP. In this column, she will reflect on encounters at the boat launch, interview experts to clear up misconceptions, and prepare basin residents for some incoming species.

Before we dive into aquatic invasive species (AIS) and their impacts on Lake Champlain, what exactly is an invasive species? As an aquatic invasive species boat launch steward, I receive an array of responses from boaters, scuba divers, anglers, birders, and concerned citizens launching their watercraft into Lake Champlain. Married couples amusingly ask, “can we get rid of this invasive?” while pointing at their spouses. Anglers often complain about their fishing competitors, the double-crested cormorants. Older Lake Champlain locals reflect on the time zebra mussels were unheard of 40 years ago, while now found growing on anything they can attach their bristles to. Invasive species are defined as non-native species who cause harm to the economy, the ecosystem, or to human health in the new environment they colonize..

Non-native species in Lake Champlain are not necessarily bad! In fact, most fish species bringing anglers to Lake Champlain, including bass, salmon, and perch, are non-native species. While introduced in Lake Champlain, these species have not negatively impacted the aquatic ecosystem and become invasive. Others have become problematic. Of the 51 established non-native aquatic species in Lake Champlain, including plants, animals, and pathogens, about a quarter are currently considered invasive. Most of them were first introduced in the 1800s, via the Great Lakes by ocean cargo ships mainly coming from Europe and Asia.

In response to the threats AIS pose, environmental organizations have taken measures to control their spread. But why is invasive species management necessary? Why should we prioritize one species over the other? Can we prevent the arrival of new invasives? Why have some introduced species evolved to coexist in non-native ecosystems? These are all valid questions when considering invasive management, especially considering humans are responsible for spreading them.

Food Web Dynamics

While quantifying the impacts of AIS on Lake Champlain is difficult, the increase of several invasives has threatened the abundance and diversity of natives, impacting the way species interact in the lake, or the food web. Aquatic invasives play stressor roles in food webs by altering the flow of energy, and thus the state of the ecosystem. For example, invasive spiny waterfleas eat the native zooplankton that young sport fish such as bass, walleye and yellow perch feed on.

Think of these relationships as a seesaw with all pathways of production and energy scattered across each side of the beam. If you add a non-native species to one side, the beam might still remain balanced, and trophic relationships can continue to play out in a balanced manner. However, if a non-native species exists too far on one side of the balance, it can disproportionately impact the food web. When native species lack defense mechanisms against invasive species, invasives can dominate their niches, often resulting in a decline in biodiversity. In the Great Lakes, invasive alewife fish species are known to throw off the balance by consuming native zooplankton, which can deplete the food source for native fish. This decline in native zooplankton and preying on larvae can disrupt the balance and lead to a decline in native fish populations. Alewives invaded Lake Champlain in the early 2000s. While they have outcompeted native smelt, scientists have found they’ve become the primary food source for Atlantic salmon and lake trout, and potentially a primary driver for the wild lake trout population rebound.

Recreation, Tourism, and Local Economies

Lake Champlain brings many tourists from across the United States and Canada during the summer for boating, kayaking, and swimming—all activities impacted by invasives. Aquatic invasive plants such as Eurasian watermilfoil form thick mats in shallow areas of a lake which can foul propellers, jam impellers, and cause bilge-pump failure in boats. Dense mats of invasive water chestnut result in losses to shoreline property values. Zebra mussels, an invasive mollusk, create dense colonies that can clog water intake pipes, boat motors, and foul boat hulls and engines. They are also known for their sharp shells when stepped on, cutting swimmers’ feet.

The list of threats posed by AIS goes on as they continue to outcompete native species. Overall, considering that invasive species are the second leading cause of biodiversity loss, after habitat destruction, monitoring their impact on Lake Champlain is necessary. We can ensure the protection of wildlife and a healthy state of the lake by preventing the spread of AIS and supporting native species. To read more in depth about aquatic invasive species’ impacts to Lake Champlain check out AIS in the Lake.

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