Have you ever found yourself shoving dirty clothes into a closet as your dinner guests walk up the driveway? I have! Out of sight, out of mind, right? It’s a great strategy for early dinner guests, but unfortunately not so great when it comes to natural resource management. While they’re probably cleaner, our local eelgrass meadows are somewhat like my dirty clothes, often out of sight and out of mind. I hope this article will help bring to mind this important marine habitat that you may not often think about but are connected to in ways you may not know.

Before we begin, let’s bring eelgrass meadows to mind by bringing them to sight. View this short video to see what it looks like when our staff and volunteer free divers survey the edge of eelgrass meadows.

As you can see from the video, the water during our 2019 field season was abnormally clear, with visibility consistently around six metres. If you’ve ever done any local diving, you’ll know that’s about as good as it gets in the summer here. The great visibility allowed our underwater divers to easily see where the eelgrass is, so they could tell our GPS-wielding kayakers on the surface where to record waypoints. In combination with low winds and low tides, these perfect conditions allowed us to collect some great data on regionally important eelgrass beds, many of which had never been fully surveyed before! In 2019 we mapped the extent of eelgrass beds at nine locations including Gallagher Bay, Piggott Bay, North Miner’s Bay, Village Bay, Port Washington, Otter Bay, Clam Bay, Irish Bay, and Shell Beach.

Here is a slide show of the maps we collected.

Why Map Eelgrass?

Seagrasses around the world have gotten a lot of attention over the last 50 years as two things have happened. Firstly, seagrasses worldwide have declined significantly.1 For example, a local study released last year analysed historic air photos of Village Bay, Horton Bay, and Lyall Harbour on Saturna Island.2 Their results show an average decline in eelgrass area coverage of 41% between 1932 and 2016 in those bays. Secondly, we are increasingly aware of the important role seagrass meadows play, from providing fish habitat to sequestering carbon.3 4 For example, the Southern Resident Killer Whales exist on a diet of primarily Chinook and Chum Salmon, and food availability has been identified as one of the leading threats to their survival.5 Eelgrass provides habitat for juvenile fish, including salmon.6 For those reasons, conservation of salmon habitats such as eelgrass and bull kelp is considered an important component to preventing the extinction of the Southern Resident Killer Whales.

Despite knowledge of how important eelgrass is, and with concerns of its decline, we still don’t have a great idea of where is it within the Gulf Islands. That began to change in 2012 thanks to the efforts of Seachange Marine Conservation Society, and the Islands Trust Conservancy. They teamed up with other partners (including the Mayne Island Conservancy) to create a comprehensive map of eelgrass in the Islands Trust Area(link). This was an ambitious and much needed endeavour that provided for the first time a reliable map of where eelgrass occurred. The trade-off of covering such a huge area was that the mapping product was limited to a one-dimensional line around the islands noting presence or absence as detected by a towed underwater camera. While valuable, this first round of mapping did not provide the shape (extent) of the eelgrass beds. The Mayne Island Conservancy, under the direction of our past Executive Director Leanna Boyer, has been a leader in creating high definition maps of local eelgrass meadows as early as 2009. In fact, that work provides a model still used today.

Why has eelgrass declined?

In some parts of the world seagrass decline has been clearly linked to specific causes.  For example, in Chesapeake Bay, USA, the decline of eelgrass has been well documented and linked to a combination of reduced water quality and increased water temperatures.7 Locally, we have two sources of information describing a decline in area coverage of eelgrass: the historic air photo analysis completed by Nahirnick in 2018,8 and the field based monitoring completed by the Mayne Island Conservancy between 2009 and 2019. Unlike Chesapeake Bay, we lack data to show specific causes of decline. However, here are some potential or observed causes of eelgrass decline around Mayne Island:

  • Direct physical damage to plants from boat anchors.9 10 Though not widespread, there are a number of permanent mooring buoys installed in eelgrass beds, and obvious patches beneath the buoys where dragging anchor chains have scoured the eelgrass as the boat moves in the wind and current.
  • Increased Canada Geese populations. Canada Geese populations have increased exponentially since the 1970’s.11 Canada Geese were uncommon in the Gulf Islands until repeat government introductions between 1929 and 1991.12 Once exposed to grazing, eelgrass within reach of the geese can decline and not recover.13
  • Sediment in streams reduces water clarity. Eelgrass gets its energy from the sun. When the water becomes murky as a result of suspended sediments, the eelgrass begins to starve. Since eelgrass often grows in shallow bays where steams flow into the ocean, what happens on the land has a big impact on the eelgrass. Deforestation and construction can cause sediments to flow downstream into the bay, starving the eelgrass.
  • Pollution in streams reduces water clarity. Similar to sediments, fertilizers from agriculture and septic systems can flow downstream and cause unnatural algal blooms, starving the eelgrass.
  • Wave energy reduces water clarity. Especially near the shoreline, waves from boats or winds stir up the bottom sediments, reducing the water clarity and starving the eelgrass.
  • Reduction in salinity can be detrimental to eelgrass, especially in populations that are not adapted to severe changes in salinity.14 Decreases in salinity could result from increases in the volume of outflow from seasonal creeks at Village Bay, Campbell Bay, and Horton Bay. It is unknown how land clearing and development has affected peak water flow events through those creeks. Temporary decreases in forest cover (especially in the 1940’s and 1950’s from logging), in addition to increased ditching and drainage infrastructure may have increased peak flow through those creeks.
  • Wave energy washing away bottom sediments. In one instance we observed a significant loss of dense eelgrass from Miners Bay. Our leading hypothesis for that specific location is that storm energy at a low tide washed out the eelgrass roots, which at that location occur in a thin layer of sediment over a bedrock of shale.

What is the Mayne Island Conservancy doing to protect eelgrass?

  • We are improving knowledge of where eelgrass grows by mapping the extent of eelgrass beds around Mayne Island and surrounding waters. These maps will be added to our database and shared with government agencies, non-profit organizations, academic institutions, and community members to help inform decisions about marine management, including fisheries and infrastructure development. Next season, thanks to funding from the Government of Canada and our collaboration with the Galiano Conservancy Association, we’ll map the extent of another 10-15 priority eelgrass hotspots around the southern Gulf Islands. We just found out the Islands Trust Conservancy will also be investing resources to map eelgrass extent in the Islands Trust Area. We will coordinate with them to ensure our efforts are collaborative.
  • We coordinate long-term monitoring of three bays around Mayne Island to detect change in eelgrass extent (Miners Bay, Horton Bay, and Gallagher Bay), in collaboration with the Vancouver Free Diver Club.
  • We work with academic researchers to better understand the causes of eelgrass decline.
  • We work with private land owners to encourage land stewardship practices essential for healthy nearshore habitats.
  • We restore terrestrial habitats such as wetlands and forests to reduce impacts on eelgrass meadows from land.

What can you do as a community member?

  • 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.
  • 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.
  • 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

Conclusion

So while you may not often think about the eelgrass meadows growing around our shores, your actions on land have a direct impact on how they grow. Now that you know about the important things that eelgrass does for us, we hope you will keep eelgrass in mind when making choices about land development on your property or when choosing where to moor your boat. If you want to learn more about eelgrass, participate in mapping as a volunteer, get access to our geospatial data, or host us for a free consultation of your property, please contact us at info@mayneconservancy.ca.

  1. https://www.iucn.org/downloads/seagrass_status_and_health.pdf
  2. Nahirnick, K. (2018). Long-term Spatial-temporal Eelgrass (Zostera marina) Habitat Change (1932-2016) in the Salish Sea using Historic Aerial Photography and Unmanned Aerial Vehicle. Masters Study. University of Victoria
  3. 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
  4. Duarte, C. M., Sintes, T., & Marbà, N. (2013). Assessing the CO2capture potential of seagrass restoration projects. Journal of Applied Ecology50(6), 1341–1349. doi: 10.1111/1365-2664.12155
  5. Fearnbach, Holly & Durban, JW & Ellifrit, DK & Balcomb, KC. (2018). Using aerial photogrammetry to detect changes in body condition of endangered southern resident killer whales. Endangered Species Research. 35. 10.3354/esr00883
  6. 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
  7. Lefcheck, J. S., Wilcox, D. J., Murphy, R. R., Marion, S. R., & Orth, R. J. (2017). Multiple stressors threaten the imperiled coastal foundation species eelgrass (Zostera marina) in Chesapeake Bay, USA. doi: 10.7287/peerj.preprints.2544v2
  8. Nahirnick, K. (2018). Long-term Spatial-temporal Eelgrass (Zostera marina) Habitat Change (1932-2016) in the Salish Sea using Historic Aerial Photography and Unmanned Aerial Vehicle. Masters Study. University of Victoria
  9. https://www.youtube.com/watch?v=dPwKOjTDx9c
  10. Kelly, J. J., Orr, D., & Takekawa, J. Y. (2019). Quantification of damage to eelgrass (Zostera marina) beds and evidence-based management strategies for boats anchoring in San Francisco Bay. Environmental Management64(1), 20–26. doi: 10.1007/s00267-019-01169-4
  11. USGS, 2017
  12. Dawe and Stewart, 2010
  13. Rivers, D., & Short, F. (2007). Effect of grazing by Canada geese Branta canadensis on an intertidal eelgrass Zostera marina meadow. Marine Ecology Progress Series333, 271–279. doi: 10.3354/meps333271
  14. Salo, T., Pedersen, M. F., & Boström, C. (2014). Population specific salinity tolerance in eelgrass (Zostera marina). Journal of Experimental Marine Biology and Ecology461, 425–429. doi: 10.1016/j.jembe.2014.09.010

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