Biology Reference
In-Depth Information
ened to allow the huge hulls of navy battleships and port vessels to nose
into dock without grounding. McGrath's team began scrutinizing present-
day harbor conditions closely to see if they would sustain an eelgrass bed
after construction. They found that fill from the transbay BART tunnel
project now blocked the original path of the waves. They worried that al-
tered currents might rob the area of the newly placed dredged material, or
smother the new beds with silt, or pour sand right back into the shipping
channel. For this reason, the team carefully modeled tidal circulation, bot-
tom elevations, and how far the waves penetrated into the harbor before
designing the new meadow. To hold in the sand, the team proposed a jetty
extending across the mouth of Middle Harbor.
Years of permitting negotiations later, the bay commission gave its
blessing to the project. McGrath's construction team first lined the fill area
with fine-grained silts and clays to provide a stable base, then gradually
began adding sand. Monitoring stations tracked when each batch of addi-
tional sediment had settled enough to add the next. About 5.2 million
cubic yards of material were added to the harbor—enough to fill San Fran-
cisco's War Memorial building 28 times. By 2010, the bottom of Middle
Harbor averaged about six feet deep.
Since then, the nearly 180 acres of shallow-water habitat has gradually
come back to life. Least Terns and Brown Pelicans started feeding in the
restored area almost immediately, and eelgrass has recolonized the bottom
on its own. A new harbor park, operated by the regional parks district, of-
ficially opened to the public in 2004. It attracts families, kayakers, and
shorebirds, but it also offers an unusual example of state-of-the-art con-
tainer shipping and underwater restoration occurring side-by-side.
Hundreds if not thousands of acres of oyster beds once corrugated bay
shallows. The 15 thousand tons of oyster shell deposits—all from Olympia
Oysters (
Ostrea lurida
) dredged from bay waters each year by mining op-
erations—are a testament to the former abundance of this native bivalve.
As part of the effort to restore submerged habitats, scientists are now try-
ing to return native oysters to the bay.
Though an intrinsically important native species, oysters, like coral
reefs in tropical seas, are being eyed for the habitat they provide. Their
corrugated, tear-shaped shells provide solid three-dimensional structure
to a soft, muddy bay floor. Species ranging from tunicates to anemones,
and bryozoans to other shellfish, need a hard surface to settle on and grow.
Between the loss of bay rocks to navigational blasting and the demise of
