Lake Michigan, the third-largest of the Great Lakes and the fifth-largest globally by surface area, is entirely within the United States. This freshwater body spans approximately 22,400 square miles (58,000 square kilometers) and supports a complex ecosystem. Its diverse habitats, including rocky shores, sandy dunes, and varying water depths, contribute to the wide array of life it harbors. The lake’s cold, clear waters and extensive shoreline create conditions for a rich aquatic and terrestrial community.
Fish Species
Lake Michigan supports diverse native and introduced fish species. Historically, about 150 native fish species, including Lake Trout, Lake Sturgeon, Lake Whitefish, Walleye, Yellow Perch, and Muskellunge, inhabited the lake. By the early 2020s, this number declined to about 68. Lake Trout, once a top predator, faced severe population declines due to overfishing and the invasive Sea Lamprey. Lake Whitefish remain a commercially harvested species, often found in deeper, colder waters.
Non-native species have altered the lake’s food web. The parasitic Sea Lamprey arrived in the early 20th century, contributing to the collapse of native predator fish populations by feeding on them. Alewives, an invasive species, became abundant after 1949, leading to the introduction of Pacific salmon (Chinook and Coho) in the 1960s for population control. These salmon, along with Rainbow Trout (Steelhead) and Brown Trout, now form a significant sport fishery.
Other introduced species, like the bottom-dwelling Round Goby, compete with native species for food and habitat. Yellow Perch, a native species, have seen their numbers decrease by approximately 80% since 1990, impacting both the ecosystem and recreational fishing. Efforts are underway to restore native fish populations, including the long-lived Lake Sturgeon, which was nearly eliminated by overfishing. The current fish community reflects the interplay of native resilience and the impacts of introduced species and human activities.
Invertebrate Life
Lake Michigan’s waters contain diverse invertebrate life, playing fundamental roles in the aquatic food web. Invasive zebra and quagga mussels, which arrived in the Great Lakes in the 1980s and 1990s, are among the most impactful. These filter feeders consume plankton, increasing water clarity but altering nutrient cycles and reducing food availability. Their dense colonization of the lakebed has changed the benthic environment.
Crustaceans are another group, including native amphipods like Diporeia, a historical food source for many fish species, which have decreased due to invasive mussels. Copepods and cladocerans, microscopic crustaceans, are crucial zooplankton components, feeding on phytoplankton and serving as food for larger organisms. Invasive spiny water fleas and fishhook water fleas are also present, preying on native zooplankton and impacting the food web.
Aquatic insects, such as mayflies, stoneflies, and caddisflies, spend their early life stages in the lake’s waters. Their presence can indicate good water quality, as many are sensitive to environmental changes. Larval insects and worms, like chironomids and oligochaetes, inhabit the lake bottom, contributing to decomposition and serving as food for bottom-feeding fish. These invertebrate communities are essential for nutrient cycling and supporting higher trophic levels.
Birds and Mammals Connected to the Lake
Lake Michigan’s ecosystem supports birds and mammals that depend on the lake and its shorelines. The lake serves as a stopover point for migratory birds, offering feeding, resting, and breeding grounds. Waterfowl such as ducks and common mergansers, along with gulls and common terns, are frequently observed on the lake’s surface and along its shores.
Predatory birds like bald eagles and ospreys are drawn to the lake for its abundant fish populations. Other species, including the common loon and various wading birds like the great blue heron, utilize the lake’s waters for foraging. Diverse coastal habitats, from sandy beaches to wetlands, provide nesting sites and cover for avian residents and visitors.
Mammals also rely on Lake Michigan’s resources. River otters and mink are often found along the lake’s edges and in tributary areas, where they hunt for fish and other aquatic prey. Beavers and muskrats construct their homes in the lake’s wetlands and feed on aquatic vegetation. These mammals, along with others like coyotes, utilize the shoreline vegetation for cover and travel corridors.
The Microscopic and Plant World
The foundation of Lake Michigan’s food web consists of its microscopic and plant communities. Phytoplankton, free-floating microscopic algae, form the base of this food web, converting sunlight into energy through photosynthesis. Common types include diatoms, green algae, and cyanobacteria. These tiny organisms are the primary food source for zooplankton and small fish.
Zooplankton are microscopic animals that graze on phytoplankton, transferring energy up the food chain. This group includes copepods and cladocerans, crucial links between primary producers and larger consumers. The abundance and composition of phytoplankton and zooplankton have been influenced by factors such as invasive mussels, which filter plankton from the water column, and nutrient levels.
Bacteria are pervasive in Lake Michigan’s waters, playing a role in decomposition and nutrient cycling. They break down organic matter, returning essential nutrients to the water column, which then become available for plant and algal growth.
Aquatic plants, both submerged and emergent, thrive along the lake’s edges and in shallower areas. Floating-leaf pondweed, wild celery, coontail, and various species of cattails are examples of plants that provide habitat, oxygen, and food for numerous aquatic organisms and waterfowl. These plants help stabilize sediments and support nearshore biodiversity.