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SAVING THE BLUE CRAB
Excess Nutrients in the
Chesapeake Bay Make Survival Difficult
| Recently, the blue
crab has been in the headlines because of reduced catches by commercial and recreational
Chesapeake Bay crabbers. While harvesting is a major factor in affecting the crab
population, loss of habitat has also contributed to the problem. To understand how this
loss of habitat occurs, it is first necessary to understand how excess nutrients affect
the Bay. The Chesapeake Bay is like a soup. Both are
composed of many ingredients. |
But just as too much
of any ingredient can spoil the flavor of the soup, too much of a particular substance can
harm the Bay. The current problem with the Bay is too many nutrients. Nutrients are
substances that help plants grow. The most important nutrients are nitrogen and
phosphorus. Plant and animal matter (including human waste), fertilizer, and even
deposition from car exhaust and power plants all contain nutrients. If not treated, these
nutrients will find their way into creeks, rivers and eventually the Bay. |
How Excess Nutrients Harm
the Bay
| Once the nutrients are in the
Bay, they become food for plants. But excess nutrients cause too much plant growth,
especially algae (microscopic floating plants). When there is too much algae,the water
becomes cloudy and blocks the light needed by underwater plants called submerged aquatic
vegetation (SAV). Algae can also coat the leaves of the SAV, further reducing the amount
of light received by the plants. SAV are very important to blue crabs because they provide
food, shelter and nursery areas. Research has shown that the density of juvenile crabs is
ten times greater in SAV beds than in unvegetated Bay areas. |
An excess amount of algae can
also cause other problems. When the algae die, they settle to the bottom where they are
naturally decomposed by bacteria. During this normal decompositional process, the bacteria
use dissolved oxygen from the Bay's bottom waters. When large amounts of algae are
decomposed by bacteria, the removal of dissolved oxygen is substantially increased. This
dissolved oxygen is needed by blue crabs and other organisms living on and near the
bottom. The resulting low dissolved oxygen concentrations drive blue crabs from their
preferred habitat and kill many of the small bottom organisms on which the blue crabs
feed. This situation worsens in the summer when several natural factors act to further
lower the amount of dissolved oxygen in the Bay's water. The low dissolved oxygen
conditions caused by excess nutrients are the primary reason large bottom sections of the
Bay are unsuitable as blue crab habitat. |
What is Being Done about
Excess Nutrients
| Reducing nutrient
pollution has been a priority of the Chesapeake Bay cleanup for over a decade. Progress is
being made due to the combined efforts of citizens, industry and the government.
Since 1985, Maryland has greatly reduced phosphorus and
nitrogen pollution. We are already seeing results in the Bay and its tributaries such as cleaner water
and more Bay grasses. These improvements show that the cleanup is on the right track. |
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What You Can Do to Help
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Presently, many people are trying to
restore the Chesapeake Bay by reducing the nutrients that ultimately harm the habitats for
blue crabs and many other organisms. Actions that help improve Bay conditions include
reducing the use of lawn fertilizers, carpooling, and planting trees. Become involved in
Maryland's Tributary Strategies - a program designed to involve the public and local
governments in activities to reduce nutrient pollution and help the State reach a 40
percent nutrient pollution reduction goal for the Chesapeake Bay. |
| For more information on what you can do to help the Bay, call
the Maryland Department of Natural Resource's Tidewater Ecosystem Assessment Division
at (410) 260-8630; e-mail: tparham@dnr.state.md.us; The Alliance for the Chesapeake Bay, (410) 377-6270; or the Maryland Department
of Natural Resources Tributary Strategies, (410) 260-8710. |
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