Biology Reference
In-Depth Information
decades,” says the USGS's Jim Cloern. “On top of our regular seasonal vari-
ability we're getting larger regime shifts originating from the ocean.”
The new blooms coincided with a cooling of the ocean of the Pacific
coast and affected productivity in the saltier portions of the bay. These
areas now experience blooms in fall and winter as well as spring. The
cooler conditions also nurtured bumper crops of Dungeness Crab and
English Sole. When these predators arrived in the bay, they found some
tasty exotic clams to eat and the clam population declined—setting the
stage for larger and more frequent bay phytoplankton blooms.
Beyond the microscopic phytoplankton sustaining the base of the bay's
food web, bigger and more complex plants grow in the shallows and along
bay margins. These plants not only provide shelter for other organisms to
live but eventually decompose into the detritus eaten by filter feeders and
into the organic matter that supports the entire bay ecosystem.
Growing at the edge of the bay is a challenge for plants. The pull of
tides and waves churns soil, alternately uprooting young shoots and bury-
ing stems in the mud. Plant seeds also have difficulty sprouting in salty
soil; seed coats must absorb enough water to break and sprout. This
shrinks the germination window to a few months during the rainy season,
even for species that tolerate high salinity when mature. Constant immer-
sion in water can suffocate tissues. And constant exposure to salty or alka-
line soils and seawater can desiccate even the hardiest plants. Plants
adapted to marshes use several common strategies to overcome these
problems. Hollow, air-filled roots and stems help deliver oxygen to sub-
merged tissues. In addition to generating seeds, many marsh plants clone
themselves via creeping rhizomes and runners. Such clones can make up a
substantial portion of any pickleweed, salt grass, or tule patch. The result-
ing tangle of runners often forms a thick mattress that helps anchor the
stems above.
Salinity, submergence, and competition all influence what species can
grow where in a salt marsh. Of these, coping with the salt delivered by
seawater requires the most specialized adaptations. Species found only in
saltier soils—also known as
halophytes
—can tolerate levels of soil salinity
that will inhibit or even kill potential freshwater marsh plants. The ability
to withstand high salinities is costly, however. Adaptations for salt toler-
ance consume energy and nutrients that could otherwise be spent on
growth and reproduction.
Marsh plants minimize such salt stresses in several ways, mostly by
