Eelgrass in Canada

Key results

• Eelgrass is widespread on the Pacific, Atlantic and Arctic (Hudson Bay) coasts of Canada
• Most of the mapped eelgrass sites in James Bay (Hudson Bay) are in recovery following major declines
• For the information included, the majority of eelgrass sites in Canada are single observations or sites for which the most recent observations are more than 10 years old (historical)^{Footnote 1} 

Eelgrass sites in Canada, 2020

How this indicator was calculated

Note: The eelgrass distribution maps presented here should not be considered complete, as eelgrass is known to occur in other locations. The maps are a reflection of collected and published material on eelgrass, as of March 2020. Various data sources, with different data collection dates, have been combined. Eelgrass site categories include historical sites (data more than 10 years old), single observations and multiple observations within the last ten years, and sites where restoration efforts have occurred. In addition, site designations may represent individual eelgrass beds or larger areas with multiple eelgrass beds. See Table 1. Status of eelgrass sites for more information. Additional details are available in the detailed data table (Excel/CSV; 136 KB).
Source: Environment and Climate Change Canada (2020).

The importance of eelgrass to ecosystems was shown after a widespread wasting disease outbreak along the Atlantic coast of North America in the 1930s resulted in a 90% loss of eelgrass. It is estimated that populations of migratory Brant geese along the Atlantic coast, which rely heavily on eelgrass outside the breeding season, declined by as much as 90%.^{Footnote 2} Declines of clams, lobsters, crabs, scallops, cod and flounder were also reported following the loss of eelgrass.^{Footnote 3}

Eelgrass beds are highly productive and several studies have indicated that eelgrass beds contribute to the sequestration of "blue carbon" in marine sediments, providing a valuable ecosystem service in coastal areas.^{Footnote 4,Footnote 5}

Eelgrass decreases can be associated with a number of environmental stressors that can work together to cause cumulative effects. Examples of environmental stressors include, physical disturbances from human activities or storm events and increased water temperature due to climate change. Other stressors, such as excessive nutrients causing an increase in algae and sedimentation can smother eelgrass or reduce light penetration. Invasive species, like European green crab, can also negatively affect eelgrass distribution.

Canada does not have a national scientific monitoring program with standardized methodologies for assessing eelgrass sites. Eelgrass data collection is ongoing, with data collected from many different sources using various methods. Data trends are difficult to detect as there is high natural variability in eelgrass beds over time and the interpretation of observed changes may not be consistent between measured variables. For example, a common stress response of eelgrass plants is to flower, thereby dispersing their seeds. This response may lead to an increase in eelgrass distribution that could mask the detection of the initial stress.

For the majority of documented eelgrass sites in Canada, there is only a single observation indicating the species' presence at a specific location. Some sites have monitoring data that include information about measures such as extent, shoot density, biomass and leaf length over multiple years.

About the indicator

What the indicator measures

The indicator shows compiled information on the distribution of eelgrass sites in Canada, including historical observations. It provides a snapshot of the locations where eelgrass has been studied in Canada.

Why this indicator is important

Eelgrass is a common seagrass species in Canadian coastal waters and has been described as an ecosystem engineer, because it physically changes its environment creating habitat and resources for other species. Eelgrass health is well-correlated with the success of many commercially harvested fish species, as eelgrass beds serve as nursery areas for juveniles.^{Footnote 6} Changes in eelgrass growth and distribution can have significant effects on coastal marine and estuarine (where fresh water meets sea water) ecosystems. Given the many ecosystem services provided including carbon sequestration, eelgrass has been designated an ecologically significant species in Canada. However, despite the environmental and economic benefits of seagrasses in general, their populations are declining globally.^{Footnote 7} 

Healthy coasts and oceans

This indicator supports the measurement of progress towards the following 2019 to 2022 Federal Sustainable Development Strategy long-term goal: Coasts and oceans support healthy, resilient and productive ecosystems.

Related indicators

The Canadian species index indicator tracks average population trends for vertebrate species in Canada (including marine vertebrates) and is a good proxy measure of overall biodiversity trends.

The Status of key fish stocks and the Harvest levels of key fish stocks indicators address the condition and management of wild fish stocks.

Canada's conserved areas indicators report the amount and proportion of Canada's terrestrial and marine area that is conserved.

Data sources and methods

Data sources

Eelgrass data used in this indicator were gathered and provided to Environment and Climate Change Canada by academic, government and community sources and were combined into a single inventory. 

Methods

Eelgrass sites were mapped using location and site history information. 

Caveats and limitations

The indicator contains information on eelgrass sites for which data has been provided. Other eelgrass sites exist.

Seasonal and annual variation in eelgrass beds is large. Furthermore, changes may not be consistent between measured variables: as an example, below-ground biomass can decrease while above-ground biomass is increasing. Structural differences in eelgrass beds occur along environmental gradients. Trends are, therefore, difficult to determine, and require several years of data. Note that an increase in leaf length or canopy height is a common response to light limitation and is a sign of stress, although such an increase can also occur in plants growing at the furthest extent of their potential depth range.

Data are collected from many different sources, each potentially using different methodologies. As such, considerable care must be taken when comparing and interpreting data from eelgrass sites.

Data quality and the geographical precision of mapping varies between data providers.

Resources

References

Department of Fisheries and Oceans (2009) Does Eelgrass (Zostera marina) meet the criteria as an ecologically significant species? Canadian Science Advisory Secretariat Science Advisory Report 2009/018. Retrieved on September 10, 2018.

Ganter B (2000) Seagrass (Zostera spp.) as food for brent geese (Branta bernicla): an overview. Helgoland Marine Research 54: 63–70. Retrieved on October 5, 2020.

Greiner JT, McGlathery KJ, Gunnell J, McKee BA (2013) Seagrass Restoration Enhances "Blue Carbon" Sequestration in Coastal Waters. PLOS ONE 8(8): e72469. Retrieved on October 5, 2020.

Hitchcock JK, Courtenay SC, Coffin MRS, Pater CC and van den Heuvel MR (2017) Eelgrass bed structure, leaf nutrient and leaf isotope responses to natural and anthropogenic gradients in estuaries of the Southern Gulf of St Lawrence, Canada. Estuaries and Coasts 40: 1653. Retrieved on September 10, 2018.

Muehlstein LK (1989) Perspectives on the wasting disease of eelgrass Zostera marina. Diseases of Aquatic Organisms 7:211-221. Retrieved on October 5, 2020.

Poppe Katrina L, Rybczyk John M (2017) Carbon sequestration in a Pacific Northwest eelgrass (Zostera marina) meadow. Northwest Science 92(2): 80-91. Retrieved on October 5, 2020.

Postlethwaite VR, McGowan AE, Kohfeld KE, Robinson CLK, Pellatt MG (2018) Low blue carbon storage in eelgrass (Zostera marina) meadows on the Pacific Coast of Canada. PLOS ONE 13(6): e0198348. Retrieved on October 5, 2020.

Rhode Island Coastal Resources Management Council (2018) Rhode Island's Coastal Habitats. Retrieved on October 5, 2018.

Smithsonian Institution (2018) Seagrass and Seagrass Beds. Retrieved on September 10, 2018.

Unsworth RKF, Nordlund LM, Cullen‐Unsworth LC (2018) Seagrass meadows support global fisheries production. Conservation Letters 12: e12566. Retrieved on September 10, 2018.

Related information

North American Blue Carbon, 2017

SeagrassNet, Global Seagrass Monitoring Network