Eelgrass meadows are one of the world’s richest and most productive marine ecosystems, providing habitat for a diversity of fish, invertebrates, birds and mammals. Also, eelgrass ecosystems play an important role in ensuring resiliency against climate change as they remove a large amount of carbon from the atmosphere and turn it into oxygen.
The European Green Crab is one of the most unwanted invasive species worldwide for its tendency to disrupt the balance of marine ecosystems. It first arrived in San Francisco in 1989 by ship and within 10 years, larvae of the invasive species was unknowingly transported to Vancouver Island’s west coast. Today, European Green Crabs have been detected in locations throughout Barkley and Clayoquot Sounds, including Pacific Rim National Park Reserve, but have not yet been observed on the East coast of Vancouver Island.
European Green Crab invasions have resulted in a loss of eelgrass meadows. The invasive crab burrows into the muddy ocean floor as it forages for food, uprooting eelgrass plants. Green crab populations spread and grow quickly as the aggressive species can thrive in a wide variety of temperatures and salinity levels. Parks Canada is monitoring European Green Crab to track changes in population size and impacts on eelgrass ecosystems.
Climate change consequences in the ocean environment include increased storm frequency and rainfall, sea level rise, rising ocean temperatures and ocean acidification. Eelgrass plays an important role in ensuring resiliency against climate change. Eelgrass roots stabilise muddy and sandy seabeds. The dense canopy of leaves absorb wave energy, which reduce shoreline erosion.
Although temperate eelgrass meadows store 10 times less carbon than tropical seagrass meadows, eelgrass meadows still store a large amount of “Blue Carbon” compared to other unvegetated marine habitats. Since eelgrass meadows provide valuable habitat to a range of species and are not expected to be directly affected by increased ocean acidification, they may help compensate for the potential loss of other habitats such as mussel beds.
The unique ability for eelgrass to protect against shoreline erosion, store a large amount of “Blue Carbon” and provide habitat in an increasing acidic ocean climate are a few of the reasons that Parks Canada values the protection and preservation of eelgrass environments.
Recreational and industrial marine activity occurring in or near eelgrass meadows can result in destruction of portions of eelgrass beds either from direct contact like dragging anchors, boat propellers physically cutting eelgrass blades or boat engines dragging through eelgrass meadows disturbing the soft bottoms. Eelgrass meadows can also be damaged by repeated trampling by people or hauling boats, including kayaks onto eelgrass meadows at low tide.
European Green Crab
Eelgrass meadow with boat prop scars (photo: Luba Reshitnyk/Hakai Institute)
How is Parks Canada monitoring eelgrass meadows?
Eelgrass meadows can be thought of as the “canaries” of the marine ecosystem because of their sensitivity to changing environmental conditions and human interference. This makes them an effective monitoring subject for understanding wider changes in local marine environments.
The Parks Canada Coastal Health Assessment Eelgrass Monitoring Program
Over the past three years Pacific Rim National Park Reserve, Gulf Island National Park Reserve and Gwaii Haanas National Marine Conservation Area Reserve have been working with scientists from the Hakai Institute to map eelgrass monitoring sites using Unmanned Aerial Systems (UAS, aka drones).
Monitoring European Green Crab abundance
In Pacific Rim National Park Reserve, Parks Canada also monitors populations of European Green Crab and their potential impacts on eelgrass habitats. We also test measures to control green crab abundance and continue to conduct surveys to assess the health of eelgrass ecosystems in the national park reserve.
At Pacific Rim National Park Reserve, Parks Canada is collaborating with other coastal sites, government departments, and environmental groups to monitor changes in eelgrass meadow extent and health over time, including: Gulf Islands National Park Reserve, Gwaii Haanas National Park Reserve, Hakai Institute, Department of Fisheries and Oceans Canada.
A total of 74 fish species, comprised of 305,152 individuals, were caught and released from 2004 to 2018 in the Pacific Rim National Park Reserve eelgrass monitoring program. Overall, eelgrass fish assemblages are persistent and stable over the study period. The aerial extent of 22 eelgrass meadows in the national park reserve were assessed in 2016 and 2017 and these surveys will continue on a bi-annual basis to assess future changes in meadow extent.
Evaluation of European Green Crab removal methods showed areas and months when green crab catch was higher. This information will be used in future efforts to control the spread of the invasive species. Continued monitoring of green crab densities will contribute to our understanding of how these populations change overtime and allow us to make informed management actions. Additional monitoring of eelgrass meadows will also ensure early detection of habitat loss and trigger additional management actions.