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The Problem with Invasive Species

There are 5 non-native aquatic species present in Chautauqua Lake.  

  1. Eurasian water milfoil (EWM; Myriophyllum spicatum)
  2. Curly-leaf pondweed (CLP; Potamogeton crispus)
  3. Brittle naiad (Najas minor)
  4. Water chestnut (Trapa natans)
  5. Starry stonewort (Nitellopsis obtusa)

Eurasian water milfoil (EWM) and curly leaf pondweed are widely distributed in the lake’s littoral zone. Both have been in the lake for many decades and have altered the natural biodiversity by out-competing native plants.  Although some argue that they have become an integral part of the lake’s ecosystem and are kept in check by herbivores (insects that feed on plants), the evidence of this is lacking.  From the Vermont Federation of Lakes and Ponds“Unfortunately, we (humans) interfere with ‘Mother Nature’ all the time by introducing invasive species – knowingly or unknowingly. It is our responsibility to work to control or eradicate invasive species to protect the native species and the ecosystems they have unbalanced”.

Eurasian water milfoil came to North America from Europe, Asia, and Northern Africa, where 20+ types of native species feed upon it and keep it in check.  Here, natural controls (insects, bacteria, fungi) are few to none and milfoil is a widespread and serious problem in lakes throughout the US and Canada. Dense milfoil infestation interferes with all types of recreation, and can reduce water circulation leading to warmer water and fish mortality.  Milfoil grows quickly and reaches the surface within 6 weeks after mechanical harvesting.  Best case scenario (2.5 acres/day x 5 days/week X 6 weeks), CLA has capacity to cut 450 acres over a 6 week period, compared to a 4000 acre littoral zone that has had up to 2345 acres of milfoil in past years.  Since 2019, mechanical harvesting has been augmented with herbicide treatments, and the acreage has shrunk to 1140 acres in 2023. We are moving in the right direction.

Some facts about milfoil:

  • Grows to surface in 3’ – 15’ and forms canopy through lateral growth 
  • Displaces native plant species 
  • Will continue growing in fall after native plants shut down 
  • Reproduces primarily through fragmentation (harvesting, boat traffic) and a piece just a few inches long can start a new plant
  • Regrows to the surface in 6 weeks after mechanical harvesting
  • Natural senescence at the end of each season results in large amounts of decaying biomass that contribute to nutrients in the water column and muck build up on the lake bottom

Curly leaf pondweed is native to Eurasia, Africa, and Australia, and here are no natural controls in North America.  It forms dense surface mats which interfere with all types of recreational use. It overtakes and outcompetes native plants, which is likely to result in lower diversity. While some claim it provides critical fish habitat, other sources state that it’s dense stands provide unsuitable shelter, food, and habitat for native animals.  This plant grows abundantly very early in the season, prior to the start of the mechanical harvesting season and when it naturally dies off by mid-summer, it’s senescence contributes to the nutrients in the water column, litters the shorelines with decaying plant matter, and contributes to muck accumulation on the lake bottom.  Chemical herbicide controls should be applied as early as possible in the spring to prevent turion formation and reduce reproduction, and when the biomass is low to minimize nutrient release. 

Some facts about curly leaf pondweed:

  • Grows up to 4”/day, well before other native plants
  • Leaves are alternating on the stem and have wavy edges, similar to a lasagna noodle
  • Reaches the water surface in June, before CLA harvesting starts 
  • Forms dense stands in up to 16’ of water
  • Reproduces by forming turions, which can stay dormant for years in the soil 
  • Plants can sprout in Fall, overwinter under ice, and begin growing in early spring
  • Natural senescence (late June/July) releases phosphorus at a time when algae is starting to grow

Brittle naiad, also called “water nymph” is native to Europe, Africa, and Asia, and has no natural controls in North America.  It is an extremely fragile plant, and it propagates by stem fragments and seeds.  Thick clusters of brittle naiad can displace native vegetation and interfere with fishing & boating.  It is a difficult plant to control since mechanical harvesting of this brittle plant distributes it further, and chemical controls may not kill the seeds. 

Some facts about brittle naiad:

  • Typically found in water 1- 4’ deep.
  • Prefers calm, slow moving water, often around docks and shorelines.
  • An annual plant, which forms seeds that are stored in the bottom sediment

Water chestnut,  is native to Europe, Asia and Africa where the plant is kept in check by native insect parasites. These insects are not present in North America and the plant, once released into the wild, is free to reproduce rapidly. It rapidly colonizes areas of freshwater lakes and ponds and slow-moving streams and rivers where it forms dense mats of floating vegetation, causing problems for boaters and swimmers and negatively impacting aquatic ecosystems. In Chautauqua Lake, water chestnut is most often found in the outlet. Vigilant monitoring and hand-pulling has so far managed to keep it from widely spreading.

Some facts about water chestnut:

  • Rooted aquatic annual plant that regrows each season.  
  • Typical stem length from the root on the bottom to the rosette on the surface is 6-7’.
  • Reproduces by seeds that fall to the bottom and germinate each spring.
  • Seeds can live in the bottom sediment for up to 12 years!

Starry stonewort, native to northern Eurasia, is a new and expanding threat to our lake.  Per the NY DEC, Starry stonewort negatively impacts native species by outcompeting native plants that provide food and shelter for native invertebrates and fish. Its dense mats of vegetation also negatively impact native fish spawning and phytoplankton (small native aquatic plants that are eaten by fish and invertebrates).  This is a growing concern in Chautauqua Lake, with an estimated 90 acres found in the 2023 survey. Mechanical harvesting has been trialed in 2023, but is risky in terms of dispersing fragments.  DASH (Diver Assisted Suction Harvesting) will be tested in 2024 as well as chemical based controls.

Some facts about starry stonewort:

  • Prefers deep, slow moving water.
  • Actually a submerged annual macroalga not a plant.
  • Can form dense masses up to 10’ deep.
  • Reproduces by fragmentation and by bulbils that remain viable in the sediment and overwinter.