Scientists study submerged populations of Coast seagrasses

By: Melissa Schneider / Published: Jul 23,  2009

Habitats have top economic values


(MOSS POINT, Miss.) — A team of scientists is surveying bays and a bayou at the Grand Bay National Estuarine Research Reserve to determine what factors make seagrass beds appear, disappear and reappear.

“Seagrass beds are one of the most important essential fisheries habitats,” said Hyun Jung “J.” Cho, assistant professor in the biology department at Jackson State University. “They provide nursery and foraging grounds for crabs, shrimp, fish and waterfowl.”

Seagrasses have many other benefits. Their roots hold sediment, which helps reduce increasing turbidity and curb sediment re-suspension. Above the ground, seagrass shoots help protect shorelines from erosion by buffering wave energy. And, because they remove nutrients from the water, sea grasses help prevent harmful algal blooms, which cause fish kills.

Seagrass beds also top the charts when it comes to economic value per acre, Cho said, making them some of the most valuable habitat in the world.

Surveys in recent years show that only two seagrasses are present at the Grand Bay National Estuarine Research Reserve: wigeon grass (Ruppia maritima) and shoal grass (Halodule wrightii).

While other seagrasses, such as turtle grass and manatee grass, were also present in the 1960s, they no longer are found in the Mississippi Sound, Cho said. A decrease in habitat quality and size likely made them disappear. Only wigeon grass and shoal grass can grow in current water conditions in the reserve area. Water quality should be improved and more habitat restored before trying to reintroduce those lost seagrasses.

In additional research, Cho and Patrick Biber, an assistant professor at The University of Southern Mississippi Gulf Coast Research Laboratory (GCRL), are using funding from the Mississippi-Alabama Sea Grant Consortium to work to develop protocols for propagating wigeon and shoal grasses and planting them in bayous. By collecting seeds from grass beds instead of uprooting the grasses, scientists keep the natural habitat intact. They germinate the seeds in a lab, grow them in an indoor tank and greenhouse and eventually plant them in bayous and estuaries.

A larger seagrass population should increase water quality and could lead to conditions favorable for future seagrass restoration of turtle grass and manatee grass.  

Scientists have tried transplanting wigeon grass using peat pots, peat pellets and biodegradable mats to help them take hold underwater.

Growing seedlings in peat pots and planting the entire pot in submerged sediment seems to be showing the most promise. But, seagrass restoration test plots in Bayou Cumbest and at GCRL are showing just how difficult it is to plant seagrasses and see them successfully take root.

“Only peat pots showed success, presumably because of the larger soil volume, allowing a more stable substrate for the plants to remain anchored after transplanting,” Biber said. “Transplants to Bayou Cumbest were monitored and survived up to six months after transplanting, at which time funding for this project was completed.”

There are several factors that make seagrass restoration challenging, Biber said. There is a lack of source material and plants often need to be harvested from already declining meadows. High plant mortality can be attributed to inappropriate water quality or sediment disturbance. And, plants often are washed away or underwater sediment is fluidized after seagrasses are planted.

“This makes the long-term success of seagrass transplanting particularly challenging in all but the most quiet and calm conditions, which are rare in the ocean,” Biber said.

In 2006, the year after Hurricane Katrina, scientists found unusually large amounts of wigeon and shoal grasses. Cho believes the wigeon grass may have been so abundant because Katrina possibly stirred the water bottom and exposed buried seeds to favorable growing conditions.

Due to the large fluctuation in abundance of wigeon and shoal grasses, long-term surveys using consistent methods are the only way to determine environmental factors and drivers that affect sea grasses and their long-term trends in this changing environment, Cho said.

“With only three or four years of data, you can’t really tell what is happening,” she said.

But, thanks to funding from the Mississippi-Alabama Sea Grant Consortium and other sources, Cho and her team have been able to do biannual surveys since 2005. She hopes to be able to keep the surveys going.

“Seagrass gets very little attention in the state,” she said. “In the Gulf Coast area, especially in Louisiana, the focus is on disappearing marshes.”


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