The Shellfish Farm News
October 2004
Rain!
A record-setting
spring and summer of low rainfall came to an abrupt halt
in late August this year and produced the wettest September
in recent memory. Rain is as important to shellfish farmers
as it is to “dirt” farmers, although for different
reasons. It is not the rain itself that is most important
to shellfish, but rather what the rain brings with it. As
the rain runs off the surrounding land it carries with it
nutrients like nitrogen and phosphorus that are required
for the growth of algae blooms. Phytoplankton is the single-celled
type of algae that feeds oysters, clams, mussels and scallops.
In wilderness
areas, nutrients that are washed into the ocean are in turn
carried back to the land by wildlife. For example, salmon,
bears, and eagles recycle nutrients from the ocean back
to the land with their feeding and migratory behavior. The
equilibrium of the nutrient cycle is altered when too many
nutrients are added or taken away from one part of the environment.
For example upland
development such as farms, housing and road construction
result in an overall increase in the amount and intensity
of nutrient run-off entering the ocean. This can cause excessive
algae blooms that cloud the water and have negative impacts,
for example by reducing the growth of seagrasses, thereby
affecting important fish spawning habitat In extreme situations,
die-off of the algal blooms can use up all the oxygen in
the water, suffocating all marine life and creating “dead
zones”. This startling situation now occurs in the
Gulf of Mexico, where there is a 7000 square mile dead zone
at the mouth of the Mississippi River resulting from decades
of excess nutrient input. Such wide-spread events have not
occurred on our coastline, probably due to the strong currents
and tidal – mixing of our waters, and to our comparatively
smaller population. However, as nutrient levels increase,
excessive blooms are as inevitable as the grass growing
on a fertilized lawn.
Shellfish graze upon algae blooms, thus reducing the severity
of the blooms and preventing their negative impacts. Therefore,
shellfish farming can buffer the negative impacts of upland
development. Scientists working in Chesapeake Bay on the
east coast of the United States have calculated that the
harvesting of 4000 to 8000 oysters removes the nutrient
input of one person over a period of one year. State governments
are promoting the planting of shellfish there to rehabilitate
the Bay and improve water clarity for fisheries habitat
and to re-establish a once-thriving oyster industry.
It
is unlikely that shellfish farming alone will rebalance
the nutrient cycle in our oceans. However, in combination
with other watershed management activities such as stormwater
control, shellfish farming can play an important role in
protecting the health of our coastal waters.
Dave
Mitchell is a Registered Professional Biologist and General
Manager of Fanny Bay Oysters Ltd.
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