What is Eelgrass?
Eelgrass plants form “meadows” on the sea bottom, where many creatures take shelter among the grass-like leaves. Despite its name and appearance, eelgrass (Zostera marina) is neither a seaweed (marine alga) nor a grass. It is a perennial flowering plant that lives in salt water and has dark green, ribbon-like leaves that are 2-12 mm wide and between 20 and 100 cm long. The dense meadows or beds are sometimes exposed at low tide. Eelgrass forms the basis of a complex food web in estuaries and other sheltered marine areas.
Where does eelgrass grow?
Eelgrass grows at and below the low tide line in up to 6m of water. It is common in estuaries, tidal flats and protected areas such as pocket beaches. Like all plants, eelgrass relies on photosynthesis, using sunlight to convert carbon dioxide and water to sugars. Therefore, it requires relatively clear water; turbid (murky) water prevents the plants from receiving enough light. Eelgrass is widely distributed along the coastlines of the northern hemisphere, from subtropical to arctic coastal regions.
Large eelgrass meadows are abundant in the sheltered waters of Portage Inlet and the Gorge Waterway, except for high current areas such as the Gorge narrows. The area covered by these meadows is approximately 80 hectares, representing 80% of the total eelgrass present in all the CRD harbours. Comparison with historic studies of the area indicates that eelgrass beds have expanded considerably in recent years1. These expansive meadows are an important asset for the ecology of these waters.
Victoria Harbour supports some small areas of eelgrass in the Selkirk Waters (north of Point Ellice bridge), near Shoal Point and southwest of McLoughlin Point.
In Esquimalt Lagoon, eelgrass is common along the west side of Coburg Peninsula, along the west shore of the lagoon and at the entrance.
How does eelgrass reproduce?
Eelgrass flowers are tiny and inconspicuous, with both female and male parts on the same spike. Pollen is spread either on or under the water surface by currents. After fertilization, the seed develops within a capsule, which eventually ruptures and releases the seed. After being dispersed by waves and currents, the seed sinks to the bottom and germinates. Eelgrass can also reproduce vegetatively, i.e. asexually. The plants have underground, horizontal stems called rhizomes that spread and produce shoots.
How have people used eelgrass?
Local First Nations including the Straits Salish, Nuu-chah-nulth, Haida and Kwakwaka’wakw, ate eelgrass rhizomes, either fresh or dried in cakes2. The Seri Indians of Mexico harvested Eelgrass fruits and processed them as grain, and wove the leaves into baskets and blankets. Eelgrass has also been used in various parts of Europe and the USA as a soil conditioner, roof thatch, insulation and paper fibre3.
Why is eelgrass important?
Eelgrass meadows support a complex web of interrelated creatures, thanks largely to billions of microorganisms such as bacteria, diatoms and algae. These microbes attach to eelgrass leaves and form a film that is grazed upon by larger animals. Microbes also help to break down dead plant matter. This material, called detritus, provides the primary nutrients for many of the plants and animals that live in and near eelgrass beds. The structure of eelgrass plants also provides sheltered habitat for many species. Some of the more easily recognizable members of eelgrass communities include:
- Fish such as juvenile Pacific salmon, herring, pipefish, sole, perch and smelt
- Invertebrates such as isopods, amphipods, polychaete worms, crabs, sea stars, clams, snails, anemones, sea urchins and many others
- Birds including many species of diving and dabbling ducks, geese, herons and gulls
- Mammals such as harbour seals and river otters
The importance of eelgrass to juvenile salmon is of particular concern since salmon in turn affect many other ecosystems, and are important to the economies and cultures of human communities. When young salmon first emerge from streams as smolts, eelgrass beds in estuaries provide them with a sheltered area where they can gently acclimate to the salt water. The abundant food allows them to grow large enough to survive in the ocean.
Detritus is also exported to other ecosystems. It nourishes terrestrial plants, either through the feces of birds or by being washed up on shore. Detritus can also be washed out to sea by currents, providing nutrients to deep sea ecosystems as remote as thermal vent communities 10,000 m below the surface.
In addition to its biological roles, eelgrass is physically important to shoreline ecosystems and man-made structures. Its rhizomes help to trap sediment and anchor shifting sands, and its leaves dampen wave action. This helps to prevent beach erosion.
What threatens eelgrass? Eelgrass beds can be destroyed by dredging, which is often done to construct ports, wharves and other coastal structures. Dredging also stirs up sediments that can bury eelgrass plants. Construction of seawalls, breakwaters, groynes and other structures can alter coastal sediment processes that are necessary to retain the fine sediment in which eelgrass grows. Structures such as docks and wharves can “shade out” eelgrass, preventing sufficient sunlight from reaching the plants. Excessive sediment from streams can reduce light penetration and bury plants. This can be caused by logging, construction or natural events in watersheds, and be transported by streams to coastal areas where eelgrass grows. Pollution, including nutrients (e.g. fertilizers) and chemicals (such as oils, heavy metals, pesticides, solvents, etc.) can damage or kill eelgrass. When eelgrass beds are exposed at low tide, they can be subject to trampling by people.
How Can I Help Protect Eelgrass?
For information on protecting eelgrass, please refer to our How Can I Help?
Additional Links & References
- Archipelago Marine Research Ltd. 2000. Subtidal Survey of Physical and Biological Features of Portage Inlet and the Gorge Waterway.
- Pojar, J. and A. MacKinnon Plants of Coastal British Columbia. B.C. Ministry of Forests and Lone Pine Publishing. 1994. (Plant field guide book.)
- Wright, N. 2002. Eelgrass Conservation for the B.C. Coast: a Discussion Paper