How It Looks From Here

Can a bird’s eye view of the shore predict seagrass health?

Researchers studying estuaries in Western Canada say yes. Aerial images of coastal development along the Salish Sea predicted seagrass health.

The Salish Sea is a biologically rich body of water with 419 islands and 4642 miles (7470 km) of coastline making it an important habitat for seagrass. It is connected to the Pacific Ocean and borders the US and Canada.

The researchers used historical aerial photographs dating back to 1932 and drone photos as recent as 2016 to assess seagrass coverage in three estuaries in the Southern Gulf Islands of British Columbia. At the same time, they looked at development on the ground such as residential housing density and shoreline activities to predict changes to seagrass density and health.

Seagrass beds serve as critical nurseries for the marine food web, create oxygen, sequester carbon and stabilize coastal waters.  Seagrass, which are sun-loving plants, need clear water and protection from human disturbance to grow into healthy, productive meadows. Fragmentation, or splitting meadows into smaller patches, changes their ability to protect the coast and serve as a habitat for marine animals.    

The findings, published in the Journal of Coastal Research, found that eelgrass coverage declined by an average of 45.1% while meadow fragmentation increased by an average of 66.3% during the 84 years studied. This was in line with global trends in seagrass decline which is estimated to be about 2 football fields per hour.

Increased coastal activity and development can impact seagrass health directly and indirectly. And the Salish Sea has undergone a population boom the researchers noted. Boat propellers and anchors can physically injure plants and fragment beds. Coastal development brings increased pollution and runoff affecting water quality and plant growth. Even structures like docks create shade and impede seagrass growth.

“In this analysis, aerial photography was an effective tool for quantifying eelgrass change over time and assessing trends in landscape-level coastal environmental indicators,” said the researchers.