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Advancing Sea Oat Biology: Advancing Dunes

Richard_Hodel_t.jpgReprinted from Coastwatch, a publication of North Carolina Sea Grant.
by Sharon Settlage

Burned feet. That’s what you can get if you attempt to make your way barefoot past the dunes on a hot summer day. Temperatures in the sand near dunes can reach 146 degrees.

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Eva Gonzales.jpgDr. Eva Gonzales’ study of sea oat biology has been featured in Coastwatch, a publication of North Carolina Sea Grant. Gonzales is an assistant professor in Appalachian State University’s Department of Biology.

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Former Appalachian State University graduate student Richard Hodel used DNA analysis to study differences in sea oat populations along the Gulf and Atlantic coasts.

But what about the beach grasses, like the beautiful sea oats rippling in the wind that seem unbothered by the blazing hot sand? How do they survive the harsh combination of burning sand, sun and salt spray? Unlike most other plants, sea oats are adapted to those severe conditions — even prefer them.

A recent study funded by North Carolina Sea Grant found that Atlantic Coast sea oats are truly unique. Biologist Eva Gonzales at Appalachian State University and former graduate student Richie Hodel used DNA analysis to study populations of sea oats, or Uniola paniculata, along the Gulf and Atlantic coasts. Hodel, who graduated in summer 2011, is now a Ph.D. student at the University of Florida.

The genetic evidence shows differences between populations within the species. These data might explain anecdotal observations that indigenous sea oats grow better in North Carolina than Gulf Coast sea oats.

Nurseryman Steve Mercer and others have known for years that sea oat seedlings are best raised from seeds gathered near the spot where they are to be transplanted. They cite lessons learned from the late David Nash, who was an N.C. Cooperative Extension agent for Brunswick and New Hanover counties.

“I expect that most Master Gardeners and nursery operators will recommend local stock for most species, including sea oats,” says Spencer Rogers, Sea Grant coastal construction and erosion specialist.

After Hurricane Isabel in 2004, many plantings on the Outer Banks required in-state seeds. “Later, the N.C. Department of Transportation planting specifications for Highway 12 required seed sources within 100 miles,” Rogers continues.

More Sea Oat Science

Back in the 1970s, Ernie D. Seneca, then at North Carolina State University, had Sea Grant funding to study dunes and dune grasses. Seneca collected seeds from Atlantic and Gulf localities and measured the growth rates of the sea oats under various temperature and light conditions. His study showed three growth types — a Virginia and North Carolina population, an Atlantic Coast Florida population and a Gulf Coast population. Georgia and South Carolina sea oats were not included in his study.

A Florida Sea Grant-funded study in 2004 at the University of Florida also found that geographic source was significant in affecting sea oat growth rates when planted in different locations. One of the researchers, Michael Kane, was instrumental in providing Florida sea oat samples for the Appalachian State study.

The recent work by Gonzales and Hodel is unique because they used modern DNA sequencing to show genetic differences in plants from different localities.

Their study indicated that Gulf Coast and Atlantic Coast sea oats are different on a genomic level. The research team sampled leaves from sea oats in Texas, Louisiana, Mississippi, Alabama, east and west Florida, Georgia, South Carolina and North Carolina.

A Needle in a Haystack

Graduate student Hodel had a formidable task before him when he started his project work in Gonzales’ lab in winter 2009. Gonzales had samples of geographically spaced plant material, the sequence of sea oat chloroplast DNA, and a hunch that there might be different DNA sequences between Gulf Coast and Atlantic Coast sea oats. She had no idea what, if any, differences there might be.

Much like a forensic criminologist would identify an individual suspect, Hodel performed PCRs, or polymerase chain reactions, and sequenced DNA from chloroplasts to find specific differences among individual plants. Amongst the 16,000 base pairs of DNA that he sequenced, he found five nucleotide differences.

Once he knew he could detect genetic differences, his job shifted to the field. Hodel drove to the coasts of Texas, Louisiana, Mississippi and Alabama to sample plants every 50 kilometers — about 31 miles — or so.

Louisiana, he said, was the most challenging, because many areas were swampy and without dunes. No dunes means no sea oats.

Other samples were provided by scientific collaborators or were previously collected by Gonzales. Most North Carolina samples were obtained during beach trips by Hodel or his lab mates.

Back at the lab, Hodel used computer analysis to show that the five genetic differences between his plant samples could be boiled down to two distantly related populations: a Gulf Coast or western lineage and an Atlantic Coast or eastern lineage.

Gonzales and Hodel speculate that the mangrove forests of southern Florida formed a natural barrier that isolated the plants during millions of years of sea oat evolution. Without intermixing, the chloroplast DNA sequences drifted into two major genotypes.

Given their scientific evidence indicating that sea oats are genetically different, Gonzales and her team concluded that sea oats from the Gulf Coast are best kept on the Gulf Coast and Atlantic Coast sea oats should not be planted on the Gulf. However, their sampling indicated several cases of intermixing in man-made restored dunes. “There is an area around Charleston, S.C., that is so mixed up. They had planted everything,” Gonzales says.

Gonzales plans to take advantage of the “mixed-up plantings” in the Charleston Harbor area to study whether locally adapted plants are truly better. If the hypothesis that local plants grow better is correct, then her team will find that the Gulf Coast type performs more poorly on the Atlantic Coast than native plants. “The experiment has already been planted,” says Gonzales.

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North Carolina Sea Grant, based at N.C. State University, facilitates university-based research to answer complex questions about the state’s diverse coastal ecosystems and meet the needs of coastal communities. This research fuels outreach and education programs that promote discovery, learning, new research and awareness across the state and nation.