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Algae blooms, runoff suffocating Atlantic Canada’s eelgrass beds: Dalhousie study

A lions mane jellyfish passes over a bed of eel grass. - Nick Hawkins
A lions mane jellyfish passes over a bed of eelgrass. - Nick Hawkins

Eelgrass has meant a lot to coastal Nova Scotians.

Until recent years it was something to be collected along the shore each fall and banked against stone foundations to keep the draft out.

It also served as a good mulch for gardens.

For goggled-eyed children prowling the shallows on long summer days eelgrass meadows were a new world in which to chase exotically armoured creatures.

Those meadows are in trouble.

And a new report by researchers at both Dalhousie University and the Canadian Healthy Oceans Network breaks down how all of us who live along the shore because we love it there, have our share of the blame.

“Essentially we created a metric that resembles a report card,” said Grace Murphy, a post-doctoral researcher at Dalhousie.

Over two years they looked at the human impacts on individual eelgrass beds in 180 bays around Atlantic Canada. Each of those bays got its own flower shaped graph ranking the level of impact of ten human activities ranging from clearing land for yards and development to agriculture runoff, commercial fishing, aquaculture and invasive species.

In each of those bays they then looked at individual eelgrass beds and how they were each affected by nearby developments.

What they found was great variation of both impact and causes. Prince Edward Island’s eelgrass beds suffer most from agriculture runoff. Probably the worst offender of all our impacts, the fertilizers and nitrogen spread on the fields ends up feeding algae blooms in the water that creates two problems.

Dr. Tri Nguyen-Quang of Dalhousie's Agricultural Campus holds cyanobacteria, or blue-green algae. - Contributed
Dr. Tri Nguyen-Quang of Dalhousie's Agricultural Campus holds cyanobacteria, or blue-green algae. - Contributed

It shades out the eelgrass beds, hurting the plants, and in blooming, consumes oxygen from the water asphyxiating the creatures living in the habitat itself. A similar problem is caused by fish plants pumping their effluent into the bays.

“We found 64 per cent of bays in Atlantic Canada are negatively impacted by nitrogen loading,” said Murphy.

While there’s less intensive agriculture along Nova Scotia’s side of the Northumberland Strait, most of the land along the coast has been cleared for cottages and homes to provide those prized waterview lots. In clearing the forest we remove the hedge that slows the flow of nutrients and sediments into the meadows that then choke them out.

On the Atlantic Coast the main offenders are commercial fishing, invasive species and shoreline development.

Though not prized swimming grounds for most humans, Murphy warns the eelgrass beds are vital nursery habitat for both finned and clawed creatures.

Her hope is that both the people living along the water and administrators – be they regional planners or staff at Fisheries and Oceans Canada – use the tool her team has created when making calls about what we do and don’t do near the water we all love to look at.


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