Our day starts off on the dock at Miner’s Bay. As I walk along the pier to start loading the boat, I glance down into the bay to see how clear the water is. The water clarity (turbidity) has a big impact on how much fun my day will be. I can see some perch lazily swimming below the dock, the sky is clear, and only a faint breeze ripples through Active Pass, all good omens for the dive ahead. Time to load up the boat with our freediving gear, kayaks, and survey equipment. We head out from the dock, and as we get up to speed, a brisk morning breeze runs across my face and I begin mentally preparing for the dive. We’ll survey around the low tide, and we’re right on time to meet our survey window. Things are starting to become routine for our crew of three (Rob Underhill, Joël Lavigueur, and I), this is just one of more than 20 days of eelgrass survey for our team this year. 

As we arrive at the site, I assess our surroundings. Every site is different and multiple factors can affect the eelgrass bed, both above and below the water. For example, are there many mooring buoys or docks in the area? What is the boat traffic like? Not only is this important for our safety while we’re freediving, but it can also be an important observation for monitoring. 

The next thing we check is visibility. How many metres down are we going to be able to see? Poor visibility, sometimes only a few feet, can result in much slower mapping and increases the reliance on the divers to map the entire bed. If the visibility is good, kayakers will map the nearshore edge successfully from the kayak. When the water is especially murky, we must dive down as deep as 6 metres, almost to the very bottom, to find the edge of the bed. 

Joël records as Rob snorkels on the surface, following the edge of an eelgrass bed at Veruna Bay, Saturna Island.

Some of the bigger beds can take hours to complete, and as the chilly water continues to seep into our wetsuits, we cut off our diving time at 2 hours. This ensures the safety of the divers by avoiding exhaustion and cold-water exposure. Before finishing our mapping, Rob and I swim through the bed, recording a video for our records, and observing the characteristics of the eelgrass, such as density and distribution. Recording these characteristics are important for monitoring the health of the beds over time. 

This video shows a series of clips of a typical survey day. Can you spot the juvenile salmon at the end?

Once we complete our survey, a little chilled and tired, we head back to Mayne Island and begin one of my favourite parts of this project, interpreting the data from our GPS waypoints. Using Geographic Information Systems (GIS) software, I get to see our survey data become a map of eelgrass right before my eyes. 

Why is this so exciting?

Thanks to a grant from the Government of Canada, we have been able to expand our eelgrass mapping beyond the shores of Mayne Island. In collaboration with the Galiano Conservancy Association, we have mapped eelgrass beds in the surrounding Gulf Islands in 2019 and 2020 including select sites around Mayne Island, Saturna Island, North Pender Island, Galiano Island, Valdes Island, Samuel Island and Parker Island. 

A slideshow of maps collected in 2020:

The data recorded at these new locations is considered a baseline. At most of our survey sites, the shape of the eelgrass beds had never been mapped before. In the future, scientists and ocean stewards can look back on this data and detect changes in the distribution and location of eelgrass beds in the Southern Gulf Islands.

How does eelgrass benefit the surrounding ecosystems and environment? 

Eelgrass meadows provide ecosystem services that many organisms, including humans, benefit from. These important functions include improving water quality, reducing coastal erosion, and carbon sequestration, all while providing habitat, food and oxygen for the surrounding marine community.

By providing these vital ecosystem functions, eelgrass beds support a diverse number of species and form the base of our many marine food webs. The diagram below shows the interconnectedness of our local marine food web, and the energy transfer, starting from eelgrass, all the way up to Southern resident killer whales.

Through the uptake of carbon dioxide and the use of the sun’s energy, eelgrass releases oxygen and organic material (growth) into the marine environment. Various invertebrates, like crabs and snails, feed on the eelgrass. Other invertebrates and algae, called epiphytes, live on the eelgrass and are themselves food for other organisms. This highly productive habitat provides food and shelter for many juvenile fish species, such as rockfish, salmon and flatfish. In their smaller, more vulnerable life stages, juvenile fish have a better chance of survival in these protected, prey-abundant areas. With salmon populations continuing to decline, eelgrass meadows are considered critical habitat for juvenile salmon survival. Many of the fish and invertebrates featured in our Sea Discovery articles also rely on eelgrass for habitat. 

Gathering baseline data and monitoring eelgrass beds enable us to understand these productive ecosystems further. Our work also leads to the protection and potential restoration of eelgrass in the Southern Gulf Islands.

In last year’s Eelgrass Meadows: Out of Sight and Out of Mind article, biologist Rob Underhill discussed the multiple reasons for the decline in eelgrass around the world and in the Strait of Georgia. Below are ways you can contribute as a community member to prevent the loss of eelgrass and maintain these vital ecosystems:

  • Avoid anchoring boats or installing docks and other structures in eelgrass meadows. Properly maintain your boating infrastructure to prevent derelict docks and boats. As we get into storm season, check that everything is secure.
  • Maintain forests and vegetation along creeks and streams to prevent erosion.
  • Minimize sedimentation of creeks and streams during construction activities by completing work in late spring or summer and initiating a re-vegetation plan immediately after construction.
  • Ensure your septic system is working properly and not leaking into nearby water bodies such as streams or the ocean. Make sure your compost and manure piles are covered to avoid excess nutrients and resulting algae blooms.
  • Use water-permeable surfaces on driveways and patios to reduce water flowing directly into the ocean.
  • Maintain and create wetlands in order to capture and slow surface water, and allow water to naturally filter into and replenish groundwater reservoirs rather than draining it straight into the ocean through ditches and drainpipes.
  • Volunteer with us as a Marine Citizen Scientist
Eelgrass survey training with Galiano Conservancy Association at Coon Bay, Galiano Island.


Islands Trust Eelgrass Habitat Mapping

Kennedy, L. A., Juanes, F., & El-Sabaawi, R. (2018). Eelgrass as Valuable Nearshore Foraging Habitat for Juvenile Pacific Salmon in the Early Marine Period. Marine and Coastal Fisheries10(2), 190–203. doi: 10.1002/mcf2.10018

Sea Change Marine Conservation Society

Six Reasons to Protect Eelgrass by Paul Shively


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