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Phytoplankton and zooplankton form the base of Lake Champlain’s food web, sometimes called the ‘lower food web.’ These microscopic floating plants, animals, and bacteria are the most numerous and most simple organisms. Complex predator-prey relationships lead to the top of the food web—predator fish such as largemouth bass, northern pike, lake trout, and salmon, and the people and animals that fish for these species. Forage fish, such as smelt and minnows, link the plankton community and the predator fish. Most fish, including predatory fish, feed directly on the plankton community when they are young.
Plankton communities are dynamic and strongly influenced by changes in their physical environment (often referred to as ‘bottom-up’ effects). Phytoplankton are microscopic plants—they require sunlight for photosynthesis for energy and nutrients, including phosphorus, to grow. In environments where there is excess phosphorus, phytoplankton, or algae, may grow abundantly. This can lead to algal blooms and is one of the reasons our water resource management efforts are focused on reducing phosphorus. Other environmental factors, such as temperature, also can influence phytoplankton growth. Cyanobacteria (blue-green algae), for example, prefer warmer water, thus increased temperatures that are predicted for the future may result in more cyanobacteria blooms. In Lake Champlain, cyanobacteria blooms frequently occur in areas with the highest phosphorus concentrations. Increasing phosphorus concentrations in other parts of the lake, coupled with notably warmer summer days, may contribute to the increasing number of blooms reported each year lake-wide.
Zooplankton are the “animal” brethren of phytoplankton. They also are small, single-celled organisms, but typically prey on phytoplankton and other microscopic organisms in the water column. Zooplankton also respond to bottom-up effects—fewer phytoplankton means less food, and changes in the type of phytoplankton may mean less good food is available for certain species of zooplankton. This, in turn, affects the fish that eat the zooplankton and so on up the food chain to the largest predators in the lake, such as Atlantic salmon and lake trout. ‘Top-down’ effects, such as changes in the predators that eat zooplankton, also can be very important. For example, large populations of zooplankton-eating (zooplanktivorous) fish will reduce zooplankton populations, which will result in less predation pressure on algae (phytoplankton). As a result, water clarity may decrease or more algal blooms may occur.
Changes in the Lake Champlain ecosystem as a result of invasive species have affected plankton communities in the Lake. Filter-feeding invasive zebra mussels consume large quantities of select plankton species, which has led to an increase in lake water clarity in shallow water and alters the food supply for fish and zooplankton that prefer these species as a food source. However, zebra mussels do not eat cyanobacteria, the plankton that cause the harmful algae blooms that are now common in some parts of Lake Champlain. The reduced competition for available nutrietnts and sunlight allows for cyanobacteria to flourish and bloom more frequently. Spiny water flea, an invasive crustacean found the Champlain Canal and Lake George in 2012, has the potential to disrupt the plankton communities in Lake Champlain by eating or outcompeting plankton, potentially affecting the entire food web.
Plankton Monitoring in Lake Champlain
Researchers at several academic institutions and State and Provincial agencies in the region are working to increase our understanding of this broad group of plants and animals. The Long-Term Water Quality and Biological Monitoring Project for Lake Champlain (LTMP) includes monitoring of plankton at 15 lake stations between April and October each year. Monitoring program staff count, identify, and measure phytoplankton and zooplankton at each of these stations. The Lake Champlain Research Institute at SUNY Plattsburgh, with funding from LCBP as part of the Lake Champlain Long-Term Monitoring Program, has documented several shifts in plankton community over the past few decades as new invasive species arrive and flourish in Lake Champlain and others decline. Continued monitoring and research of this important part of the Lake Champlain ecosystem is critical to understanding and predicting changes to the ecosystem as new species arrive, others decline, and our climate changes. To learn more about this program and view data, visit the LTMP website and view the “Biological Data Graphs” in the right column.
Phytoplankton ID Guides
- Pictorial Guide to Common Phytoplankton of Lake Champlain and the Lower Great Lakes (University of Vermont)
- Freshwater Plankton (Connecticut College)
- Great Lakes Water Life Photo Gallery: Great Lakes Algae (Great Lakes Environmental Research Lab)
Zooplankton ID Guides
- An Image-Based Key To The Zooplankton Of The Northeast USA (University of New Hampshire)
- Free-living and Parasitic Copepods of the Laurentian Great Lakes: Keys and Details on Individual Species (Great Lakes Science Center)
- Great Lakes Water Life Photo Gallery: Crustacean Zooplankton and Rotifers (Great Lakes Environmental Research Lab)
More on Plankton
For more information on how the Lake Champlain food web—including plankton—is changing, please visit our State of the Lake website.