Lake Champlain’s food web links all its inhabitants, from microscopic plankton to fish, birds and other wildlife. At the base of the web, sometimes called the 'lower food web,' are the most numerous and simplest organisms, primarily phytoplankton and zooplankton. 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 people who fish for these species and others. Forage fish, such as smelt and smaller perch, 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). All phytoplankton require phosphorus to grow and will grow abundantly in locations where concentrations are high. This can lead to algal blooms and is one of the reasons our water management efforts are focused on reducing phosphorus. Other environmental factors, such as temperature, can also influence phytoplankton growth. Cyanobacteria, for example, prefer warmer waters, thus the increased temperatures associated with global climate change are predicted to result in more cyanobacterial blooms. In Lake Champlain, cyanobacteria blooms occur frequently in areas with the highest phosphorus concentrations. Increasing phosphorus in other parts of the lake, coupled with notably warmer summer days, may contribute to the increasing number of blooms reported each year.

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. This, in turn, affects the fish that eat the zooplankton and may be felt throughout the food web. ‘Top-down’ effects, such as changes in the predators that eat zooplankton, can also be very important. Large populations of zooplankton-eating fish will reduce zooplankton populations, which will result in less algae consumption and more phytoplankton. As a result, water clarity may decrease or more algal blooms may occur.

Changes in the Lake Champlain ecosystem due to invasive species have affected plankton communities in the Lake. For example, filter-feeding invasive zebra mussels consume large quantities of plankton, which has led to an increase in lake water clarity in shallow water. Clearer water allows more sunlight to penetrate deep waters, thus promoting aquatic plant growth. Less plankton in the water also means that fish depending on them for food have less to eat. Spiny water flea, an invasive crustacean found in waterbodies adjacent to the Lake Champlain Basin, 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

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. 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)

• 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)