The Great Lakes support a broad diversity of life and ecosystems.
- Life in the Great Lakes ranges in size from the smallest blue-green bacteria, such as Microcystis, to the largest animal that still lives in the Great Lakes, lake sturgeon.
- Most life in the Great Lakes exists as microorganisms. Microorganisms such as phytoplankton and cyanobacteria are the most important primary producers in the lakes.
- The Great Lakes’ watershed supports organisms from every kingdom on Earth.
- Great Lakes biology provides many examples of life cycles, adaptations and important relationships among organisms, such as symbiosis, predator-prey dynamics and energy transfer.
- The Great Lakes ecosystem provides habitat for terrestrial and aquatic species. The Great Lakes are three-dimensional, offering vast living space and diverse habitats from the shoreline and surface down through the water column to the lake floor.
- Great Lakes habitats are defined by environmental factors. As a result of interactions involving abiotic factors such as temperature, clarity, depth, oxygen, pH, light, nutrients, pressure, substrate type and circulation, life in the Great Lakes is not evenly distributed temporally or spatially. Abiotic factors within the Great Lakes can change daily, seasonally or annually because of natural and human influences.
- Ecosystem processes (abiotic conditions, prey availability and predation) influence the distribution and diversity of organisms from surface to bottom and nearshore to offshore.
- Wetlands, including coastal marshes and freshwater estuaries, provide important and productive nursery areas for many aquatic and terrestrial species which rely on these habitats for protective structure, hunting grounds, migration stops, and raising offspring.
- Life cycles, behaviors, habitats and the abundance of organisms in the Great Lakes have been altered by intentional and unintentional introduction of non-native plant and animal species.