Photo of Lake Willoughby captured by Farrah Ashe
A Comprehensive Suitability Assessment of Vermont Waterbodies for Spiny Water Flea (Bythotrephes longimanus), Zebra Mussel (Dreissena polymorpha), and Starry Stonewort (Nitellopsis obtusa)
Authors: Farrah Ashe, Nikki Boudah, Kelsey Colbert, Kait Jones and Will Sutor
Partnered with:
Vermont Department of Environmental Conservation
Table of Contents:
Executive Summary / Page 2Introduction / Page 2
Background / Page 3
Approach / Page 3
Findings / Page 6
Discussion and Recommendations / Page 11
Literature Citations / Page 15
Acknowledgements:
We would like to thank our partner Josh Mulhollem of the Vermont Department of Environmental Conservation (DEC) for his guidance throughout the course of this project. He provided our team with the waterbody data used in the report and answers to our many questions during the entire process. We thank him for the time he dedicated to us and the resources which he was able to provide for our team.
Executive Summary:
According to the Vermont Department of Environmental Conservation (Agency of Natural Resources, 2017), the waterbodies of Vermont are vulnerable to invasion from zebra mussels, spiny water flea, and starry stonewort. There is currently a lack of state-wide knowledge on which waterbodies are hospitable to these three organisms. By understanding this, the state can assess where the greatest needs are, and focus their efforts on prevention and monitoring in those locations. If no action is taken to determine waterbodies at high risk for invasion, more affordable preventative measures will no longer be an option. This is problematic because invasive species can drastically alter ecosystems, resulting in the need of mitigation or eradication efforts further down the road which can cost the state orders of magnitude more than preventative measures or monitoring in the early stages of invasive species establishment (USGS, 2017).
The goal of this project was to conduct a statewide analysis to determine which Vermont waters are at the highest risk of introduction and establishment of these three invasives. This was accomplished by reviewing relevant scholarly literature on the three focal species and the environmental conditions they can tolerate. Tolerance information was then organized to determine high, moderate, and low priority waterbodies at risk for invasion from each invasive species. This data was compiled and used with the vessel travel data to create an ArcGIS map on the state waterbodies for each invasive species. Using these tools, we were able to recommend to the DEC the waterbodies that should be prioritized for monitoring and spread prevention.
Introduction:
Vermont’s waterbodies are currently inhabited by seventeen invasive species and threatened by fifteen more invasives in neighboring watersheds (Agency of Natural Resources, 2016). The spiny water flea, starry stonewort, and zebra mussels are three of the seventeen species currently found in parts of Vermont and all three are expected to continue invading Vermont’s waterbodies. Preventing further spread of invasives is critical to conserving Vermont’s biodiversity, as invasives can lack natural predators and therefore outcompete native species. Spread of invasive species also poses a risk to human health as invasives can clog water pipes and impact the quality of fish and water humans are consuming. It is also important to recognize that most of these aquatic invaders are spread between waterbodies as a direct result of human activity. Known invaders such as the zebra mussel, can easily cling to boats or trailers. They can also be spread into new locations due to a lack of public knowledge around baitfish regulations (Agency of Natural Resources, 2016). Mitigating the negative impact aquatic invasive species impose can be aided with public education but if it is not addressed, more extensive preventative measures must be implemented. The result of the high cost of eradication can place a great fiscal burden on local communities.
The purpose of our project is to therefore determine which waterbodies in Vermont are susceptible to invasion by one or all of these species, and the level of risk for invasion based on water quality characteristics. The goal of this report is to help the reader better understand the risk invasives pose on the areas they are inhabiting, and to emphasize the importance of conducting a statewide analysis to determine which Vermont waterbodies are most at risk for invasion of the spiny water flea, starry stonewort, and zebra mussel.
Background:
Studies have shown that nonindigenous species pose a severe threat to the health of waterbodies throughout the state of Vermont (Modley, 2008). The introduction of an invasive species can change food webs by destroying native food sources, alter ecosystem functions such as changing water chemistry, and degrade the habitat quality of other organisms. Furthermore, the presence of a nonnative species can decrease native species biodiversity and even cause localized extinction in an ecosystem (USGS, 2017). As a result, the spread of invasive species throughout the state is not only detrimental to Vermont’s ecology but are also financially costly to mitigate (Clavero and Garcia-Berthou, 2005).
The zebra mussel (Dreissena polymorpha), spiny water flea (Bythotrephes longimanus) and starry stonewort (Nitellopsis obtusa), are three aquatic invasive species that have been identified in waterbodies of Vermont. Each of these invaders has been known to cause harm to the ecosystems that they infiltrate, and therefore present a serious concern to the state. Zebra mussels, for example, can attach themselves to any surface in the water including other native clams and mussels causing asphyxiation and eventually death (Johnson and Padilla, 1996). Due to their aggressiveness, and also effective domination of ecosystems that they invade, zebra mussels have been known to alter the structure and function of waterbodies around the world (Karatayev et al., 2002). According to the USGS Ecological Survey, both the spiny water flea and starry stonewort pose similar ecosystem-altering threats to aquatic ecosystems as the zebra mussel. The spiny water flea has the capacity to completely shift the trophic structure of an ecosystem through its insatiable appetite for crustacean and zooplankton. Such effects have shown significant reductions in these two species, crucial to nutrient cycling within aquatic systems (Kelly, 2013). Similarly the starry stonewort can have negative impacts on fish spawning, foraging, and nesting habitat, altering the ecosystem and abundance of aquatic species (Pullman, 2010; Midwood et al., 2016). As a result, many states have begun to require mitigation and prevention efforts for these three aquatic invaders at the state and local level (e.g. analyses and risk assessments of critical bodies of water) (Kipp et al., 2017).
Vermont has not formulated a comprehensive environmental suitability and vessel-based introduction risk assessment for these three aquatic invasive species. Therefore, a statewide analysis of these three invasives that are currently in and threatening the waters of Vermont is needed. Our assessment will determine the waters in Vermont which are at the highest risk of introduction by vessel travel and establishment in native suitable habitat. This will help the state of Vermont determine which aquatic ecosystems should be prioritized for invasive prevention planning, monitoring, and control measures in the future.
Approach:
We chose to focus on three invasive species for the main portion of this project. Zebra mussels were chosen because of their severe negative impacts in Lake Champlain and Lake Bomoseen in Vermont. Studies have shown that these invaders clog water intake pipes, pose a hazard to recreationalists, and harm the native biota and natural food web of these lakes (Modley, 2008). Due to its natural history, there are large amounts of scientific literature on zebra mussels and the factors controlling their growth, reproduction, and subsequent spread (Cohen, 2017; Feng & Papes, 2017; Karatayev et al., 1998; McMahon, 1996; Wu et al., 2010). We also chose this species from the request of our partner due to these reasons and the need for prioritizing waterbodies to better focus prevention and monitoring efforts. The spiny water flea was chosen because of its recent invasion into Vermont (first observed in Lake Champlain in 2014) (Voorhees et al., 2015). This lack of study poses a problem to the state water managers on understanding the best control and prevention methods to use in Vermont, as well as, understanding the spread paths of the species. Starry stonewort is also a relatively new invasive species to the waters of Vermont found in 2015, with its most recent invasion into the waters of Lake Derby of Derby, VT (VT DEC, 2016). The last two species presented the opportunity to gather a wealth of scholarly information on these species to aid in the knowledge of our partner, the VT DEC, and help in finding limiting factors to their survival in Vermont waters.
In order to best determine the level of risk for invasion of each waterbody in Vermont, information on the habitat requirements of the three species was compiled and assessed. We analyzed the scholarly literature on each of the three species in order to understand which lake characteristics were necessary for survival, growth, and reproduction to determine population establishment if the species were to be introduced into the ecosystem. This included research on water pH, conductivity, salinity, hardness, depth, dissolved oxygen, chlorophyll-a concentration, and total phosphorus, among the other water quality parameters that were pertinent to the required habitat profile of the nonnative species. We then compiled the found tolerance ranges from the literature into a spreadsheet. This allowed for easy comparisons of the lake data we received from our project partner.
Our community partner gave us the lake data in groupings by the environmental parameters. The averages that were not already found in this data were calculated to a daily, yearly, and then overall average for each waterbody. Each of the parameters were set as “meets” or “does not meet” for each of the three species. If the waterbody only had one measurement which was taken to represent the whole, this was noted and marked with an asterisk. The waterbodies that has no data were marked with “N/A”, indicating that the data was not available. Some of the data that were collected were done so in the spring (e.g. total phosphorus and hardness). This was used because spring is one of the times of the year in which dimictic lakes (the lake type of most Vermont lakes) experience turnover and therefore the nutrients that were previously layered throughout the water column are most evenly mixed (Nunberg, 1988). This data was then compiled into one spreadsheet. The risk of an invasion occurring given successful introduction was classified into three different categories: low risk, moderate risk, and high risk. Here we defined this risk being the risk of establishment of the invasive species if introduction were to occur. High risk waterbodies fall within two or more of the environmental tolerance parameters or contain two or more parameters with “meets” for that species. Moderate risk waterbodies contain one environmental tolerance parameter that was met, due to natural lake fluxes. Low risk waterbodies do not have any of the parameters that were met. We also noted the difference between waterbodies with low data (only one year of data) versus those which had multiple years of data collection. These specific low data values are well marked so if they need to be explored further on an individual basis, they can be considering the unknown variance that the data could have with using only one year of data to represent the waterbody.
We utilized vessel travel data from the DEC’s greeter program, a program designed to track boater behavior and inspect boats to better understand the transportation of invasives. The greeter data was listed for two different risk factors: risk from last waterbody and risk from time since in last waterbody. These two factors were first categorized on a 1-3 level of risk (1 being low, 2 being medium, and 3 being high). For the risk of last waterbody: 3=The last waterbody visited contains at least one invasive species that is not currently found at the lake where the inspection occurred. 2=It is unknown if the last waterbody visited contains any AIS of concern consisting mostly of out-of-state waters. 1=The last waterbody visited does not contain any AIS that are not already found in the lake where the inspection occurred. For the time since the last launch the categories were: 3=the watercraft was last used in a lake other than the one where the inspection occurred within the last 5 days. 2=the watercraft was last used in a lake other than the one where the inspection occurred within the last 2 weeks but not within the last 5 days, or, it is unknown when the watercraft was last used. 1= the watercraft was not used in a lake other than the one where the inspection occurred within the last two weeks. This data was then summed and recategorized as 2-3 being low risk, 4 being medium risk, and 5-6 being high risk vessels launching. This data was then used to create an ArcGIS shapefile and subsequently a map. State waterbody data (VT Priority Lake/Pond data from vtanrgis public access data) were added to a map of Vermont. The calculated risk percentages attribute was then chosen to be represented as a pie chart for the three risk categories. This map was created to provide a visual to aid in the understanding of the overall risk including the boat travel introductory risk in addition to our environmental suitability establishment risk.
Findings:
Our team created a spreadsheet which contains the environmental parameters and the waterbodies of Vermont listed by name and location (by longitude and latitude). In this spreadsheet, chlorophyll-a concentrations, pH, alkalinity, hardness, and total phosphorus concentrations are listed (refer to Table 1 for a sample of the chlorophyll-a data).
Lake_ID / Chlorophyll-a limits in the environment for starry stonewortAMHERST / meets
ARROWHEAD MOUNTAIN / meets
BEEBE (HUBDTN) / meets
BERLIN / N/A
MEMPHREMAGOG / meets
METCALF / meets
NINEVAH / meets
SHELBURNE / does not meet
SILVER (BARNRD) / meets
SOUTH (EDEN) / meets
SOUTH BAY / meets
SPRING (SHRWBY) / meets
ST. CATHERINE / meets
STAR / meets
STRATTON / meets
SUNRISE / meets*
SUNSET (BENSON) / meets
SUNSET (BRKFLD) / meets
TICKLENAKED / meets
VALLEY / meets
WAPANACKI / meets
WILLOUGHBY / meets
WINONA / meets*
WOODWARD / meets
We chose not to include dissolved oxygen as one of the final environmental parameters, because the dissolved oxygen varies with the water depth and the lake layers (Rao et al., 2008). The hypolimnion could be anoxic, while the other more shallower layers are still able to contain sufficient oxygen levels to sustain growth and reproduction of the invasive species. For example, despite their temperature sensitivity, spiny water flea will move vertically in the water column to find the optimal conditions suitable for dissolved oxygen concentration. Table 2 contains a list of the Vermont waterbodies that are stressed due to low dissolved oxygen levels. This omission is unlikely to affect our data, but in the future this parameter could be significant. Especially if there is a moderate match in suitability, where one environmental parameter is not met while others are.
Waterbody Name / Town / Latitude / LongitudeLake Eden / Eden / 44.72 / 72.5
Elfin Lake / Wallingford / 43.47 / 72.99
Ewell Pond / Peacham / 44.37 / 72.17
Fern Lake / Leicester / 43.87 / 73.07
Great Hosmer Pond / Craftsbury / 44.7 / 72.37
Lake Parker / Glover / 44.72 / 72.23
Sabin Pond (Woodbury Lake) / Calais / 44.4 / 72.42
Shelburne Pond / Shelburne / 44.38 / 73.17
Spring Lake (Shrewsbury Pond) / Shrewsbury / 43.5 / 72.92
Stiles Pond / Waterford / 44.42 / 71.93
Ticklenaked Pond / Ryegate / 44.18 / 72.1
Valley Lake (Dog Pond) / Woodbury / 44.43 / 72.43
Walker Pond / Hubbardton / 43.74 / 73.14
Furthermore, it is important to note that depth was not assessed in our study because of its variability within a lake’s profile. While we did acquire the maximum and mean depths of each waterbody studied from the state, it wasn’t appropriate for any of our focal species. Depth did not impact the spiny water flea, because conditions in the water column vary and the species is able to move vertically. We also found that depth wasn’t appropriate for starry stonewort and zebra mussel, because both species inhabit shallow waters that are present in all lakes.
Each of the environmental parameter records was then added to a master spreadsheet categorized by each species separately. The number of waterbodies that met the species habitat parameters allowed us to calculate a quantitative value for risk of establishment. This final spread looks similar to Table 1, but instead contains a risk column with the waterbodies marked as “low”,”moderate”, and “high”.
Table 4: Denotes our tolerance range data gathered from the literature. All tolerance ranges are listed next to their subsequent source. Ranges that did not possess maximum values were left blank.