Duckweeds in competition
|Red algae versus duckweed||Other competitors: green algae and water fern|
|Algae and duckweeds are natural competitors.
In this sequence of photos (right) a population of duckweeds is progressively
reduced by growth of a red alga, species not determined. The top frame
shows the presence of both Lemna and Spirodela, while the lower
two frames show no Spirodela. Red-colored blue-green algae and
dynoflagellates are often the source of toxins that
kill other organisms, but we do not know if this alga secretes a toxin.
These populations were growing in an experimental water treatment system
for animal wastes.
Harmful Algal Blooms: Blue-Green Algae and Human Health, Thomas Morris, M.D., M.P.H., Medical Epidemiologist, North Carolina Harmful Algal Blooms Program, December 2000.
The Rise in Toxic Tides, What's behind the ocean blooms? Christine Mlot, Science New Online, September, 1997.
Harmful Algae and Phycotoxins Information Links, Stephen S. Bates, The International Society for the Study of Harmful Algae, May 2001.
Algal Toxins, from Field Manual of Wildlife Diseases, National Wildlife Health Center, U.S. Geological Survey, 1999-2001.
Photos "Death by Algae" courtesy of Paul Skillikorn.
Each photo at right depicts a different competitor for the duckweed:
Green algae: Since algae mostly grow submerged, duckweed competes with their growth by shading them and depriving them of the light needed for photosynthesis. However, some algae will be at the surface and compete with the duckweed for light and nutrients.
Water Fern (Azolla): The Azolla in the lower frame are hard to see. Their color is more olive-green than that of the duckweeds, and their fronds are bordered with a pink anthocyanin pigment. Azolla are known for their ability to harbor nitrogen-fixing bacteria, but this would not be an advantage in nitrogen-rich wastewaters.
Photos courtesy of Paul Skillikorn.
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Revised: April 25, 2003