Intertidal Organisms EZ-ID GUIDES


on this species


Zostera marina (Common eelgrass)

photo of eelgrass
Copyright © 2006 Mary Jo Adams


Like other seagrasses, eelgrass belongs to the family Zosteraceae.  Seagrasses are flowering plants but despite their common designation, are not true grasses.  They are more closely related to lilies.  Two species of eelgrass are found in the Pacific Northwest.  They are Zostera marina (common eelgrass) and Z. japonica (Japanese or dwarf eelgrass).

Native in the state of Washington, Zostera marina’s range spans the area from Alaska to California on the West Coast and is also found on the North American East Coast, in Europe, Asia, and the Middle East.  It is common in low intertidal and subtidal zones to a depth of 20-30 feet along sheltered areas with sandy or muddy beaches.  The dark green leaf blades are usually about ½ inch (8-10 mm.) wide but may be somewhat narrower.  The blades reach a length of 10 feet (3 meters) and are flat.  The inflorescence (flower clusters) grow on the tips of long shoots separate from the leaf blades.  Individual flowers produce a one-seeded fruit that looks like a grain of rice.  This species blooms from June through August.  Eelgrass does not grow in fresh water.

Common eelgrass forms meadows that provide rich habitat for many other species.  The eelgrass itself provides food for herbivores during the growing season and when it dies back in the fall, it becomes an important source of nourishment for detritovores.    Small organisms including diatoms, hydroids, caprellid amphipods,anemones, bryozoans, isopods, and bryozoans inhabit the blades.  Herring lay their eggs on eelgrass and eelgrass beds provide an important refuge for juvenile salmon.   Countless numbers of other species are also interwoven into the eelgrass community. 

Don’t confuse eelgrass with the surfgrass Phyllospadix.  Eelgrass grows in sheltered areas on a soft mud or sand substrate.  Surfgrass prefers higher energy beaches and attaches directly to rocks.  Aditionally, the inflorescence of eelgrass is on long shoots while the flowers of surfgrass form near the base.  Color can also help differentiate the two.  Eelgrass is dark green while surfgrass tends to be a brighter emerald green.  One final difference is that of blade width.  Eelgrass blades are more than 3/16th (4 mm.) wide and are often close to ½ inch wide.  Surfgrass blades are more narrow, 3/16th of an inch or less (2-4 mm.).    


This page was created by Mary Jo Adams on 9/5/06.