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Algae

Algae As Environmental Problems



Red tides are events of great abundance (or "blooms") of red, brown, or yellow-colored dinoflagellates of various species. These algae synthesize biochemicals, such as saxitoxin and domoic acid, which are extremely poisonous and can kill a wide range of marine animals, as well as humans who eat shellfish containing the toxins. The toxic syndromes of humans associated with dinoflagellate toxins are known as paralytic, diarrhetic, and amnesic shellfish poisoning.



Scientists cannot yet predict the environmental conditions that cause red tides to develop, although it seems that they are related to the availability and ratio of nutrients to temperature. Red tides are natural phenomena, but some scientists believe that human interference may have increased the frequency of these phenomena in some regions.

The dinoflagellates involved with toxic dinoflagellate blooms are commonly of the genera Alexandrium, Dinophysis, Nitzchia, or Ptychodiscus. The algal toxins can be accumulated by filter-feeding shellfish such as clams and oysters. If these are eaten while they contain red-tide toxins, they can poison humans or animals in the local ecosystem. Even creatures the size of large whales can die from eating fish containing large concentrations of dinoflagellate toxins.

In addition, freshwater algae can cause problems when they are overly abundant. Algal blooms can cause foul tastes in the water stored in reservoirs, which may be required by nearby towns or cities as drinking water. This can be a significant problem in naturally productive, shallow-water lakes of the prairies in North America.

Eutrophication is another major problem that is associated with algal blooms in lakes that are receiving large inputs of nutrients through sewage disposal or the runoff of agricultural fertilizers. Eutrophication can result in severe degradation of the aquatic ecosystem when large quantities of algal biomass sink to deeper waters and consume most of the oxygen during their decomposition. The anoxic (deficiency in oxygen) conditions that develop are lethal to the animals that live in the sediment and deep waters, including most species of fish. Because the primary limiting nutrient in fresh waters is usually phosphate, inputs of this nutrient can be specifically controlled by sewage treatment, and by the banning of detergents containing phosphorus. This has been done in many areas in North America, and eutrophication is now less an environmental problem than it used to be.

Resources

Books

Buchanan, B.B., W. Gruissem, and R.L. Jones. Biochemistry and Molecular Biology of Plants. Rockville, MD: American Society of Plant Physiologists, 2000.

Freedman, B. Environmental Ecology. 2nd ed. San Diego: Academic Press, 1995.

Pritchard, H.N. and P.T. Bradt. Biology of Nonvascular Plants. St. Louis: Mosby, Inc., 1984.

Raven, Peter, R.F. Evert, and Susan Eichhorn. Biology of Plants. 6th ed. New York: Worth Publishers Inc., 1998.


Bill Freedman

KEY TERMS


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Accessory pigments

—Pigments such as the carotenoids, xanthophylls, and phycobilins, which can absorb solar radiation, and pass some of the absorbed energy to chlorophyll pigments for use in photosynthesis.

Bloom

—An event of great abundance of phytoplankton, to the degree that the water is distinctly colored by the algal pigments.

Epiphyte

—A plant which relies upon another plant, such as a tree, for physical support, but does not harm the host plant.

Eukaryotic cell

—A cell whose genetic material is carried on chromosomes inside a nucleus encased in a membrane. Eukaryotic cells also have organelles that perform specific metabolic tasks and are supported by a cytoskeleton which runs through the cytoplasm, giving the cell form and shape.

Gyre

—A zone of spirally circulating oceanic water, that tends to retain floating materials, as in the Sargasso Sea of the Atlantic Ocean.

Macroscopic

—A size range that can be seen without magnification.

Microscopic

—A size range that cannot be seen without magnification.

Mutualism

—A symbiotic relationship between two species that is mutually beneficial.

Periphyton

—Unicellular algae that occur on the surfaces of the rocks and larger plants of aquatic ecosystems.

Phytoplankton

—Microscopic algae that occur suspended in the water column.

Primary photosynthetic pigment

—This refers to the green-colored, chlorophyll pigments of algae and higher plants. These absorb red and blue light, to make the energy available to drive photosynthesis.

Thallus

—A single plant body lacking distinct stem, leaves, and roots.

Zooplankton

—Minute animal life that lives in water.

Additional topics

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