Eelgrass forms a nearshore early warning system

  • Jul. 18, 2008 1:00 p.m.

Submitted by Ryan Duffy, Gwaii Haanas-At our ocean’s doorstep exist meadows that serve as an early warning system. Grazing upon information gathered from these meadows can help us understand how healthy our coastline is compared to others.Last week Parks Canada staff were making the most of July low tides while surveying seagrass meadows throughout the proposed Gwaii Haanas Marine Conservation Area Reserve. The monitoring program, now in its fifth year, provides information that can be compared to other national parks on the coast of British Columbia. Seagrass is not a seaweed (marine algae) or a true grass. Like its land dwelling relatives seagrass has green leaves, roots and flowers – however it chooses to reside below the tide. Seagrass occurs close to the coast, from the intertidal area to about 10 meters below the low tide. Parks Canada staff are particularly interested in a type of seagrass meadow – eelgrass (Zostera marina) – that occur in more sheltered locations such as protected bays on the east coast. As eelgrass occurs in nearshore waters, it is particularly vulnerable to the effects of human activities. This could include damage caused by boats anchoring at a popular location, to indirect human impacts such as excessive nutrients and sediments being washed into our oceans from land based activities. Monitoring eelgrass provides an early warning of coastal environment degradation, before it becomes too late to repair.Over 21 percent of Haida Gwaii’s coast is lined with eelgrass. Eelgrass meadows not only shelter an array of amazing creatures, such as the opalescent nudibranch, but are important spawning and nursery habitat used by juvenile herring, salmon, lingcod and rockfishes. Furthermore, other species such as great blue heron depend upon fish found within eelgrass meadows to rear their young.When Parks Canada staff visit eelgrass communities around Gwaii Haanas they observe and measure three things. Firstly, how much human disturbance an individual meadow has been exposed to (minimal in Gwaii Haanas). Second, how much material, such as algae, is growing on the seagrass leaves. Algal growth may make seagrass communities less productive and reflect abnormally high amounts of nutrients within the water. Finally, juvenile fish are caught using a seine net, identified, measured and released. Changes to fish populations or the numbers of species can also reflect changes within eelgrass communities.How does Gwaii Haanas compare against its Pacific coast cousins? Previous surveys suggest that Gwaii Haanas eelgrass meadows may be in better health than others monitored in the Gulf Islands and Pacific Rim. In Gwaii Haanas significantly more fish species have been caught, some meadows containing over 22 species, and less pollution has been detected. Although Gwaii Haanas eelgrass meadows are in good health at present, we need to continue monitoring if we are going to hear the alarm of this early warning system.

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