Three Reasons Eelgrass is Declining—What’s Being Done?

Dredging

In an earlier post we showed how important eelgrass is to fish, and noted that eelgrass is declining worldwide. West coast eelgrass is affected by a combination of coastal development and nutrient pollution, direct displacement (such as dredging activities), and climate change.

Here’s why:

Eelgrass needs light. Urbanization and construction activities in coastal areas remove vegetated buffers, allowing more runoff into the water. Runoff carries sediment, which reduces water clarity. Also, nutrients from wastewater, stormwater, and other human activities can promote algae blooms, which also block light.

Dredging uproots eelgrass; filling buries it. These activities can completely decimate an eelgrass meadow even beyond the footprint of direct impact. It can take ten years or more for eelgrass to recover, if at all.

Climate change: as ocean temperatures rise, native plants feel the heat. Evidence shows that northern eelgrass populations will not adapt to warmer waters as easily as southern eelgrass populations might. Their photosynthetic engines just can’t keep cool enough. Also, as a consequence of climate change, sea level is rising, meaning eelgrass will have to move to keep the same relative depth. It can’t move far before a hardened structure such as bluff or even a seawall stops it.

The State of Washington is acting to restore eelgrass across Puget Sound. The Puget Sound Leadership Council established a target of expanding the total area of eelgrass beds by 20 percent by 2020. Major restoration efforts have already been undertaken, and more are underway. New plantings are proposed for the Nisqually, Skokomish and Elwha river deltas. In these places, restoration may have a better chance to succeed because of improved sandy substrate and restored water quality.

Section3B_Marine-Nearshore_AcresEelgrass

Acres of Eelgrass in Puget Sound

More information: shedding new light on eelgrass recovery and threats and human impacts on eelgrass.