Ripple effects: The four biggest threats to coastal ecosystems in Canada
Canada’s unequalled coastlines are both picturesque and protective — filtering water, storing carbon, reducing the effects of storm surge, and supporting marine biodiversity and local communities — yet Canada is not doing a good job of protecting them.
From estuaries, salt marshes, mudflats and seagrass meadows to sand or gravel beaches and rocky tidal zones, coastal ecosystems are threatened. But what are those threats, and what can we do to address them?
Climate change
Coastal regions are especially affected by climate change — from extreme temperatures like the 2021 heat dome that infamously “cooked” an estimated billion sea creatures out west, to increasing storm surges and flooding on the east coast. Sea levels are also rising, changing tidal flows into wetlands and putting some at risk of flooding. The impacts of these changes are often worse because they are occurring in areas already heavily modified by people.
Hard armouring
Canada’s coastal population is large and growing, which has resulted in extensive modification of many shorelines and coastal areas. Urban and agricultural development has resulted in the drainage of coastal wetlands, and we often see “hard armouring” — structures like seawalls, rocky “riprap,” retaining walls and dikes — built to protect shoreline infrastructure from rising sea levels and damaging waves. While these structures may seem like a simple solution to reduce coastal flooding, they can have serious impacts on surrounding ecosystems.
Coastal ecosystems like wetlands and beaches are naturally dynamic and will shift as sediments are moved around by waves and tides. Hard armouring prevents this natural ebb and flow and can actually worsen coastal erosion as sediment is washed away from shore. This process creates additional problems as fine sediments in nearshore waters prevent light from reaching seagrass meadows, stunting plant growth. Over time, healthy ecosystems will shift landward in response to rising sea levels, but human-made barriers create a phenomenon known as “coastal squeeze”: a slow process by which coastal ecosystems are squeezed between human-made structures on one side and rising sea levels on the other. The result is fragmented habitats and the loss of the species that depend on them.
This infographic above shows three scenarios. The third scenario shows how “hard armouring” in the form of a boulder wall prevents the inward migration of the nearshore ecosystem that would naturally happen with sea level rise, “squeezing” out the species supported by this ecosystem and reducing the amount of carbon it can store.
Nutrient overload
Salt marshes and seagrass meadows prevent excess nutrients from agricultural fertilizer, pollutants from urban runoff, and sediment from rivers and streams from entering marine ecosystems. But too many nutrients in these nearshore ecosystems increases sunlight-blocking algae, impairing seagrass growth and its ability to store carbon. Elevated nutrients also make marsh plants grow rapidly but with less energy put into their roots and rhizomes, weakening marsh “platforms,” increasing erosion and releasing stored “blue carbon” from the ecosystem.
Blue carbon is carbon stored in the plants, algae and sediments of coastal ecosystems. Learn more.
Invasive species
Invasive species not only outcompete native species, but they also threaten the Canadian coastline’s most important marine plants. European green crabs, for example, are found on east and west coasts and their burrowing literally uproots seagrasses and salt marsh vegetation.
Introduced species can also have a negative effect on coastal wetlands. While native to much of North America, Canada geese have become overabundant in southwestern coastal B.C. These geese have always migrated through the region in spring and fall, but in the mid-1900s, a new population of young birds was intentionally introduced to the region. Limited predators and the temperate climate created ideal conditions for these birds to stay year-round and start breeding. This new resident population has since expanded, shifting the ecological balance as they forage on native marsh vegetation and uproot large areas of tidal marsh habitat. The damage causes major erosion in estuaries and loss of habitat for native species like Pacific salmon.
The solution? Reduce, restore and regulate — and transform
Coastal wetlands play a critical role in addressing the dual crises of biodiversity loss and climate change, making it crucial that we address the multiple and overlapping threats that degrade these ecosystems.
But to do so, we need to transform our relationship with the coast. First, we need to reduce stressors on coastal wetlands by managing invasive species and sources of pollution. Then we need to restore already degraded habitats by, for example, replanting native vegetation to stabilize shorelines and filter water or creating tidal channels to reestablish the natural movement of tides in estuaries and salt marshes.
These steps need engagement from all levels of government — municipal, provincial, federal and Indigenous — to coordinate coastal protections, as well as enforce existing regulations to safeguard these habitats.
Next in this blog series, we’ll look at how WWF-Canada’s conservation teams and their partners are working to reduce threats, including steps that individuals like private landowners can take to better steward coastal ecosystems.