Eelgrass
Eelgrass (Zostera marina) is the only true seagrass in Chesapeake Bay. It typically dominates in the higher salinity regions of the Bay including the lower York River.
Description
An eelgrass shoot typically consists of 3-5 strap-like leaves enclosed in a basal leaf sheath.
Salinity Range
Z. marina has a wide salinity tolerance of 10-35 ppt, but prefers salinities above 20 ppt.
Reproduction & Growth
Z. marina in the Chesapeake Bay region begins to flower in late winter, and releases its seeds in May. Germination begins in the fall as water temperatures drop below 68°F (20°C). Oxygen-rich waters inhibit germination of eelgrass seeds. Germination therefore typically takes place after burial into low-oxygen sediments.
Most eelgrass seeds fall directly from the parent plant into the sediment. However, reproductive shoots of eelgrass can float and seeds that remain attached can be transported many kilometers. The seeds remain viable for a year or less, so there appears to be little in the way of a long-term seed bank within Bay eelgrass beds.
Eelgrass commonly reproduces through vegetative growth by producing new leaves, rhizomes, and lateral shoots that push through the sediment. The rhizome stores food energy and the roots function both to anchor the plant and absorb nutrients. Individual shoots generally survive for one to two years and some vegetative shoots will differentiate and become flowering shoots during their second growing season.
Bay beds reach maximum abundances in the late spring, dieback in the summer as water temperatures rise above 74°F (23°C), regrow somewhat in the fall, and maintain low abundances throughout the winter. Summertime heat is particularly stressful for these populations, although the production of carbon reserves during other times of the year can improve summertime survival.
Distribution
Eelgrass is a temperate species that is widespread in northern latitudes, from the north Atlantic and north Pacific into the Mediterranean and Black seas. It is widely distributed along the North American coast from Newfoundland to North Carolina. Eelgrass populations in Chesapeake Bay are therefore growing near their southern temperature limits.
Benefits
Eelgrass beds provide food and habitat for blue crabs, young striped bass, bay scallops, waterfowl, and many other aquatic species. The beds also filter pollutants, reduce shoreline erosion, trap sediments, and add oxygen to the water.
Threats
Eelgrass in Chesapeake Bay is threatened by runoff of sediment due to deforestation, urban sprawl, and other watershed disturbances, which has significantly increased the turbidity of coastal waters, blocking needed sunlight. Climate warming also threatens Bay eelgrass. Eelgrasses prefer cool water and grow at the southern end of their thermal range in Chesapeake Bay. As Bay temperatures continue to climb, eelgrasses may not survive the heat. Learn more.
A “wasting disease” severely impacted eelgrass in Chesapeake Bay and the Virginia coastal bays in the 1930s, though there is little evidence it is prevalent in Chesapeake Bay populations at present. The infection is caused by a protist called Labyrinthula zosterae. The conditions that initiate broad-scale die-off from the disease are poorly understood, though higher infection levels are typically found under higher salinity conditions.
Visit the IUCN Eelgrass page for range maps, conservation status, and other details.