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Eelgrass: Its Habits and Habitats
By Anthony R. Wilbur
As shown on the left, the anatomy of an eelgrass (Zostera marina)
plant includes leaves, rhizomes (runners that connect one plant to the
next), and roots. Eelgrass, a flowering plant with all life cycles occurring
underwater, grows in intertidal and subtidal zones and tolerates wide
ranges in salinity and temperature. A variety of seafloor sediments, current
and tidal regimes, and shoreline types support eelgrass growth. For instance,
eelgrass can grow in high-energy environments among cobble substrates
by anchoring its roots in finer sediments deposited between the cobbles.
Eelgrass is, however, predominantly found in calm, marine embayments and
soft sediments (mud and sand). Light penetration through the water column
dictates the depth of eelgrass growth (i.e., clearer water supports deeper
growth), and there are areas in Massachusetts and Cape Cod Bay where eelgrass
was observed growing as deep as 40 feet.
Eelgrass forms one of the most—if not the
most—valuable, shallow marine habitats in Massachusetts coastal waters.
Individual plants, clusters of eelgrass, and extensive meadows are found
throughout state waters and support creatures ranging in size from microscopic
bacteria and larval crabs to foraging bluefish and diving ducks. It is
widely accepted that animals require habitat, but plants also need specific
habitat conditions to survive. Decreasing water quality, sediment contamination,
and seafloor disturbance are altering environmental features necessary
for eelgrass growth and survival, with potentially significant consequences.
The loss of eelgrass habitat transforms embayments from complex, flourishing
landscapes to homogenous seafloor habitats that do not provide equivalent
ecological services.
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Boston, MA 02114