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November 2, 2000 - VOL. 27, NO. 22
Protecting underwater rain forests: UT Austin scientists track impact of nitrogen, phosphorous on colorful world of coral reefs
|Deep beneath the waters of the Gulf of Mexico, scientists in scuba gear from UT Austin plant an odd-looking garden. The "crop" consists of watertight Ziploc bags full of seaweeds collected from a nearby coral reef. The bags also contain various amounts of nitrogen and phosphorous, the same kinds of nutrients that make lawns, flowers and food crops flourish.
The translucent packages are attached to a six-by-six foot PVC square frame with aluminum poles. Light reaching the bags through the water is continuously measured by light meters. After about eight hours, the frame is retrieved, the seaweed (or macroalgae) harvested and the scientists are ready to continue their experiments at the next location.
This strange activity is a part of the worldwide effort to protect and to learn more about the colorful colonies of minute creatures that make up the Earth's underwater gardens -- coral reefs. Coral are a combination of plant and animal: tiny polyps that build shells around their bodies, no more than a millimeter to several centimeters in size, and zooxanthellae, a microscopic form of algae that live in the polyp's tissue, providing its intense colors.
Scientists believe that coastal runoff, including everything from lawn fertilizers to sewage, spurs the growth of macroalgae, which look like large red, brown and green plants. Scientists believe macroalgae can grow so much they block light needed by zooxanthellae, eventually killing coral and turning the once rainbow formations deathly white.
Dr. K.H. Dunton, a research scientist and associate professor at UT Austin's Marine Science Institute at Port Aransas, said when large seaweeds proliferate, they form "underwater turfs growing up to six inches high. These turfs can eventually overgrow and smother the coral reef."
With graduate students Megan Scanlin and Harlan Miller, and Stein Fredriksen, a visiting scientist from Norway, Dunton is trying to determine whether nitrogen from coastal watersheds is ending up in reef communities. For the next two years, they will be studying the Flower Gardens National Marine Sanctuary, about 110 miles off the coast of Galveston, Stetson Bank, about 40 miles to the northwest, and Sonnier Bank, about 50 miles south of the Louisiana coast.
One of the largest sources of nutrients on the Gulf Coast is the Mississippi River. Since Sonnier Bank is closer to the river, scientists expect to see higher levels of nutrients in that area than in the Flower Gardens, Dunton said.
"The goal is to determine whether nutrients from inorganic fertilizers or wastewater that seep into Gulf Coast rivers and streams is restricted to areas immediately adjacent to the coastline -- or whether runoff is being carried into the Flower Gardens," Dunton said.
Coral reefs are a major economic engine for the tourist industry. They act as natural barriers, protecting beaches from erosion and storms, and serve as nurseries for economically important species of fish. Considered the equivalent of underwater rain forests, coral reefs also may be a potential source of new medicines. Some researchers believe that creatures living in reef environments may be sources of anti-tumor compounds, while coral themselves could prove useful in grafting bones.
"It's a question of diversity," Dunton said. "Coral reefs support a tremendous array of plant and animal species. Literally thousands of species of invertebrates and tropical fish live on coral reefs. Healthy fisheries have always been associated with coral reefs -- and in some areas of the world, the fisheries and the coral reefs have been totally wiped out.
"There is great concern over loss of coral reefs due to worldwide temperature increases. But there also is concern over the smothering of the reefs from algal blooms caused by excess nutrients entering the system," Dunton said.
The National Academy of Sciences estimates that algae blooms caused by excess nutrients are killing marine life and damaging marshlands along more than one third of the U.S. coast line. Scientists at the 9th Annual Coral Reef Symposium held in October in Indonesia warned that fully 25 percent of all coral reefs in the world already have been destroyed by pollution, global warming and other factors.
Dunton, who this year received the Teaching Excellence Award, is an expert in the ecology of marine plants such as seagrasses, kelp, marsh plants and algae. His work on the Texas coast primarily has involved research on growth and productivity of seagrass and marsh communities.
"The algae we incubate on the bottom are placed inside of plastic bags which are attached to a large frame and left on the bottom for six to eight hours," Dunton said. "The seaweeds are collected by divers from the reef and brought to the surface. We expose them to different levels of nutrients and then incubate them on the bottom and measure photosynthesis at the different nutrient levels.
"During the incubation, we continuously record light levels using underwater light meters so that we know how much light the plants have received. We do that several times during each research cruise at different sites, so we can gather information on algal growth at different nutrient concentrations at variety of locations," Dunton said.
Experts say the amount of nitrogen flushing from the Mississippi River into the Gulf of Mexico has tripled over the past 40 years. An enormous area devoid of bottom dwelling sea life -- known as the Dead Zone -- forms in the Gulf of Mexico every spring, and is believed to be related to runoff from the river.
"The Mississippi River plume, which includes the Dead Zone, is moving westward, and the reason for the Dead Zone is excess nutrients," Dunton said. "This could become a problem for the coral reefs, so we are trying to learn as much as we can about the present nutrient status."
The research is being funded by a grant from the National Undersea Research Program (NURP), which receives its funding from the National Oceanographic and Atmospheric Administration.
This month, Scanlin and another graduate student from Dunton's lab, Craig Aumack, will again visit these sites to collect additional measurements on a NURP research cruise. A follow-up cruise will take place in February.
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