Aquarium of the Pacific - Online Learning Center - Species Print Sheet
Although grass-like, eelgrass is technically a flowering plant that grows submerged in salt water. The salt tolerant plants form eelgrass meadows or beds that are both a biologically diverse ecosystem and a primary producer. They provide the base for a complex nearshore food web that starts with diatoms coating the plant blades to form an attachment for bacteria, fungi, and detritus. They act as a critical nursery and shelter for many species of fishes, shore and seabirds, and invertebrates. These beds also guard against erosion by dampening wave energy from storms and stabilize substrate. Sensitive to pollution, eelgrass is an indicator species for water quality.
At the Aquarium
Our plants, located in the Shorebird Sanctuary, were donated by the Stewards of the Los Cerritos Wetlands located in Long Beach, California. Collection of eelgrass, a protected species, is prohibited in California except under a special permit which the Aquarium has.
Widely distributed on the US Pacific & Atlantic coasts, coast of British Columbia, Canada north to Alaska’s Seward Peninsula, and in Europe.
These flowering salt-tolerant plants grow in the sandy mud of tidal flats and creeks in sheltered bays, inlets, salt ponds, and at the mouth of estuaries. The blades of the plants are either submerged or partially floating.
The thick white rhizomes are branching with numerous roots and a leaf spaced at nodes 1.0-3.5 cm (0.39-1.4 in) apart. In shallow waters the dark or emerald green leaves of the eelgrass plant are ribbon-shaped with rounded tips and are up to 0.9 m (3 ft) in length. The leaves are longer and wider in deeper waters at a maximum depth of usually no more than 6 m (20 ft). Flowers are enclosed in transparent leaf sheaths.
Eelgrass reproduces asexually through growth of rhizomes that create large beds or meadows in the wetlands, and sexually by seed germination. Male and female flowers are present on the same plant but they mature at different times, preventing self-fertilization. The male plant releases pollen in the form of long filaments that remain suspended in the water until waves or currents carry them to a female plant where fertilization takes place. Seed-bearing shoots develop that eventually break off and float to the surface. The shoots release buoyant seeds.
In intertidal waters the plants have a seasonal biomass cycle building up in the spring and summer, flowering from June into August, and then dying back in the fall to become detritus in the winter.
Leaves and rhizomes contain air spaces that help keep the blades buoyant. Seeds are also buoyant.
In 1930 “Wasting Disease” decimated almost all of the eelgrass beds on the Atlantic coasts of North America and Europe. As a consequence beaches and sandbanks eroded away, fisheries closed, and some wildlife species disappeared. The partial recovery of these beds is now threatened by 21st century human-caused impacts.
Eelgrass beds are threatened by commercial, industrial, and residential development that replaces wetlands and by urban runoff that pollutes the wetlands.
Deep water eelgrass is much different than shallow water eelgrass. Leaves of deep water eelgrass are longer and wider. There is a higher rhizome biomass but there is no seasonal biomass, that is, the plants do not die back. There are either no flowers or only a few.
Historically, eelgrass has had many uses. First Nation people and Native Americans used eelgrass for food, roofing, basket weaving, smoking deer meat, and as a cure for diarrhea. Early settlers used the plants as thatching for roofs, as fuel and mulch for potato beds, banking houses and barns, a substitute for bedding, and as a conditioner for soil. Industries used eelgrass in the manufacture of paper, to make cigars, as upholstery and packing materials, and as a gelling agent. During World War II when cotton was scarce, it was used to make nitrocellulose.