The 2012 Great Lakes Water Quality Agreement states that “the Waters of the Great Lakes should support healthy and productive wetlands and other habitats to sustain resilient populations of native species.”
Assessment highlights
The Habitat and Species indicator includes assessments of Great Lakes coastal wetlands, tributaries and components of the aquatic food web with an emphasis on native species. Coastal wetland and aquatic food web conditions are variable across the basin, ranging from Good to Poor and Improving to Deteriorating, depending on the lake, habitat and species of interest. The health of individual species as well as biological communities in the Great Lakes reflects the availability and condition of their habitats, which are influenced by stressors such as changing climate, land use changes, pollution, and invasive species. Overall, the Habitat and Species indicator is assessed as Fair and the trend is Unchanging.
Although coastal wetland restoration and protection efforts have improved some coastal wetlands, other wetlands remain degraded. Wetlands of Lake Superior and those along the northern shorelines of lakes Michigan and Huron are generally in better condition than wetlands in lakes Erie and Ontario. For example, most of the wetlands in lakes Erie and Ontario have degraded plant communities as a result of nutrient enrichment, sedimentation, invasive species, past water level regulation or combinations of these factors. These stressors can allow some plant species such as invasive cattails and non-native species like European Common Reed (also known as Phragmites), Frog-bit and Water Chestnut to thrive, reducing biodiversity and habitat quality for native flora and fauna.
Amphibian, bird and fish communities in coastal wetlands tend to be healthiest where the footprint of human activity is the lowest. Coastal wetland amphibian and bird community health in each of the lakes are generally considered Fair to Good with Unchanging or Improving trends. However, species such as Western Chorus Frog and some marsh bird species have undergone long-term population declines. Coastal Wetland Fish communities are assessed as Fair in all lakes except Lake Erie where fish community health is assessed as Poor. This is due in part to Lake Erie coastal wetlands having higher average numbers of non-native fish species, which are more tolerant to disturbance.
Aquatic habitat connectivity assesses the percentage of tributary lengths that remain free of barriers impacting connection between the headwaters and the Great Lakes. The connectivity of tributaries is critical for migratory fish to reach spawning habitat and to maintain other ecological processes such as natural sediment transport. Tributary connectivity was reduced in each lake basin during the past century but is improving as a result of barrier removal and fish passage projects. These restoration efforts must also weigh the potential risk of creating spawning habitat for Sea Lamprey or allowing access of other non-native species into and out of the Great Lakes.
The Great Lakes aquatic food web is made up of many interacting species, from tiny algae (phytoplankton) and animals (zooplankton) to large fish. Changing nutrient conditions combined with the impacts of invasive species, especially dreissenid mussels (zebra and quagga mussels), are some of the most immediate stressors to Great Lakes food webs. Dreissenid mussels filter phytoplankton from the water column and alter the way nutrients are cycled through the lakes, resulting in reduced food for zooplankton, which impacts all other components of the aquatic food web including fish.
Phytoplankton communities are Deteriorating in all lakes except Ontario, but the reasons for this trend are variable. Lake Superior has maintained phytoplankton and zooplankton communities reflecting oligotrophic (low nutrient) conditions and is assessed as Good for phytoplankton and zooplankton, but gradual community shifts toward phytoplankton groups that thrive in warmer conditions may be occurring in response to climate change. In lakes Huron and Michigan, declines in the spring phytoplankton bloom resulted in decreased zooplankton biomass in past decades, but populations have stabilized in recent years. In Lake Erie, there has been a decrease in phytoplankton quality due to increases in the abundance of harmful cyanobacteria, but zooplankton communities are in Good condition due to high lake productivity.
Diporeia, a small bottom-dwelling invertebrate and an important food source for fish, severely declined in the 1990s and are in Poor status in all lakes except Lake Superior. The mechanisms causing these declines are complex and are not fully understood. However, dreissenid mussels have likely contributed to these trends by altering benthic habitat and reducing the amount of available food for other benthic organisms, such as Diporeia. In Lake Superior, Diporeia is assessed as Good and they remain a dominant component of some prey fish diets.
Phytoplankton, zooplankton, and benthic communities are important sources of food for prey fish and are essential to sustaining a healthy food web. The diversity of prey fish communities across the Great Lakes continues to change, although the direction and magnitude of those changes vary. The prey fish community is considered Fair overall based on the diversity and the proportion of native prey fish species in the Great Lakes. There have been fluctuations in the overall abundances of prey fish, which are influenced by both food availability and the number of top predator fish such as Lake Trout, Salmon, and Walleye. A balance between the numbers of predator fish and the available prey fish in the lakes is important for a sustainable Great Lakes fishery.
Sustainable fishery management, ongoing Sea Lamprey control, improving water quality, population rehabilitation stocking, restoration of spawning habitat, and declines in Alewives (a non-native prey fish) have contributed to improving Walleye and Lake Trout populations and increased reproductive success for Lake Trout populations. Wild-born Lake Trout make up nearly half of total harvest in U.S. waters of Lake Huron and account for more than 75% of the total catch from Canadian waters of the Lake Huron main basin and North Channel. There has also been evidence of increased natural reproduction of Lake Sturgeon in tributaries throughout the Great Lakes basin due in part to habitat improvements, dam removals, and stocking efforts, although changes in Lake Sturgeon status will take a long time to manifest due to the long lifespan of the species.
Only about one third of historically connected tributary lengths remain accessible to Great Lakes migratory fish
Populations of wild-born Lake Trout are increasing in Lake Huron and now occur at similar levels to hatchery-born fish, due to restoration efforts and increased reproductive success in recent years
Sub-indicators supporting the Habitat and Species assessment – Coastal Wetlands and Aquatic Habitat Connectivity
Sub-Indicator | Lake Superior | Lake Michigan | Lake Huron | Lake Erie | Lake Ontario |
Fair and Undetermined | Fair and Undetermined | Fair and Unchanging | Undetermined | Undetermined | |
Fair and Unchanging | Fair and Undetermined | Fair and Unchanging | Poor and Undetermined | Fair and Unchanging | |
Fair and Undetermined | Fair and Undetermined | Good and Unchanging | Fair and Unchanging | Fair and Improving | |
Fair and Undetermined | Fair and Undetermined | Good and Unchanging | Fair and Unchanging | Fair and Improving | |
Good and Unchanging | Fair and Unchanging | Fair and Unchanging | Poor and Unchanging | Poor and Unchanging | |
Fair and Improving | Poor and Improving | Fair and Improving | Fair and Improving | Fair and Improving |
Sub-indicators supporting the Habitat and Species assessment – Aquatic Food Web
Sub-Indicator | Lake Superior | Lake Michigan | Lake Huron | Lake Erie | Lake Ontario |
Good and Deteriorating | Fair and Deteriorating | Fair and Deteriorating | Poor and Deteriorating | Good and Unchanging | |
Good and Unchanging | Good and Unchanging | Fair and Unchanging | Good and Improving | Good and Unchanging | |
Good and Unchanging | Good and Unchanging | Good and Unchanging | Poor and Unchanging | Fair and Unchanging | |
Good and Unchanging | Poor and Deteriorating | Poor and Deteriorating | Poor and Unchanging | Poor and Unchanging | |
Poor and Unchanging | Poor and Improving | Poor and Improving | Poor and Improving | Poor and Improving | |
Good and Unchanging | Fair and Unchanging | Fair and Unchanging | Fair and Deteriorating | Fair and Improving | |
Good and Improving | Fair and Improving | Fair and Improving | Fair and Improving | Fair and Improving | |
Fair and Improving | Good and Unchanging | Good and Unchanging | Good and Improving | Good and Unchanging |
Status
