A&M International Biologist, Students Study Endangered Seagrasses

They sway with the ebb and flow of the tides, pockets of green that darken the waters of Corpus Christi Bay and other parts of the Laguna Madre, with no hint of the enormity of their significance to the complex food chain above and below water.

Texas A&M International University Associate Professor of Biology Dr. Jerilyn Jewett- Smith has been studying the seagrasses found in the subtidal Laguna Madre and other South Texas estuaries for the past 15 years.

Her doctoral dissertation focused on seagrasses and her current research seeks to identify the impacts of water quality changes on the rare seagrass known as clover-grass or star-grass (Halophila engelmanii).

"I consider this seagrass something like the canary in the coal mine. It's a clear indicator that something is amiss if this plant is in trouble. If we lose it, the ramifications on the rest of the food chain are enormous. Since these are rare seagrasses, we suspect that they will be the first to be affected by changes in the system, such as stress created by pollution," she said.

Dr. Jewett-Smith is investigating if DNA testing can be used to identify the impact of changes in light quality due to the on-going brown tide on the seagrasses.

Assisted by two A&M International student research assistants, Jose Luis Egremy and Rosie Garza, she has been gathering samples which are cleaned and ground. The DNA is extracted and polymerase chain reaction techniques are used to generate bands that can be examined to show if the grasses are genetically similar or diverse.

Preliminary results of the research show that star-grasses from Red Fish Bay had a high degree of genetic similarity, which suggests that most of the grasses originated locally. On the other hand, the analysis suggests that the genetic traits of star-grasses from Corpus Christi Bay may be less similar.

Jewett-Smith suggests this may be due to the ongoing blooms of brown tide that are reducing the amount of light that the underwater plants need for photosynthesis. As a result of this environmental stress the number of star-grass varieties that can survive in the region are being limited.

"The loss of these rare seagrasses could spell certain ecological disaster," she explained. "For starters seagrasses are a primary food source for the green sea turtle, which is itself an endangered species. The grasses are home for a myriad of sealife which use the the grasses for cover from predators, nutrition and breeding areas. Redfish, a favorite of sport fishers, would be affected by a reduction in the amount of seagrass. The complexity of the chain can be quite mind- boggling when you begin to break down its components," she said.

Jewett-Smith said the jury is still out on what has prompted the brown tide.

"We're now in our seventh year of brown tide blooms. It is considered a natural phenomenon, but marine scientists are unclear as to what has triggered it. Some research suggests that reduced freshwater inflow to the estuaries during the drought triggered the tide. Others have noted physical changes in the inlet geography, prompting current changes. Some suggest global warming, but this is dificult to prove. There will be a symposium on brown tide at the Estuarine Research Federation meeting in November and we hope to have a clearer picture from the data presented there," she said.

Jewett-Smith hopes her research can help to determine the severity of the brown tide impact on sea grasses.

"As I said earlier, this coal mine canary needs to be kept breathing for us to have a fully functional system. It's loss would drastically change the ecosystem," she concluded.

For additional details, contact Dr. Jewett-Smith at (210) 326-2586 or email to jjewett@tamiu.edu.

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