Eelgrass
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 algae) 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, the use of 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 years.(2)
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 cakes.(3) 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 fibre.(4)
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 nearby 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, 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, and provides nutrients
to deep sea ecosystems as remote as thermal vent communities 30,000
feet below the surface.
In addition to its biological roles, eelgrass is physically important to shoreline ecosystems and human development. 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 with large machinery, 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 cover plants. This can come from logging, construction and 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 Section.
Additional Links & References
Websites
- Sea Change Marine Conservation Society
- Children's Lesson on Eelgrass
- Eelgrass Biology
- Eelgrass Facts: Puget Sound Shorelines
Articles
- Archipelago Marine Research Ltd. 2000. Subtidal Survey of Physical and Biological Features of Portge Inlet and the Gorge Waterway.
- Pojar, J. et al. Plants of Coastal British Columbia. B.C. Ministry of Forests and Lone Pine Publishing. 1994. (Plant field guide book.)
- Port Townsend Marine Science Center
- Wright, M. 2002. Eelgrass Conservation for the B.C. Coast: a Discussion Paper
- SeaChange Marine Conservation Society (Word Document)
