More than one quiet day lying on a beach or casting a fishing line has been interrupted by the sharp pain caused by the bite of a greenhead horse fly.

But this bane of coastal enthusiasts could end up helping scientists measure the health of Louisiana’s coastal marshes as restoration of the disappearing land continues.

New research from two LSU Agriculture Center scientists is the next step to developing a checklist of what insects and other critters marsh soils should include and can be detected by a simple test.

The quest began simply enough with a cup of coffee shared between Claudia Husseneder, professor of molecular biology, and Lane Foil, professor of entomology. It was 2010 and the Deepwater Horizon was still spilling oil into the Gulf of Mexico, and by the time the coffee was done, the two researchers had come up with an idea of measuring the impact of the oil on marsh habitat.

Foil worked with horse fly research for years and had a familiarity with where and how they could be collected while Husseneder works with genetics. The plan they came up with was to not only conduct horse fly population comparisons between multiple oiled and unoiled sites along Louisiana’s coast, but to also look at the genetic diversity difference between the two groups.

It seemed like a good indicator because the greenhead horse fly is native to the state and is dependent on the spartina grass marshes of the coast, Foil explained. The larvae feed on other invertebrates within the tidal zone in the soil and on a variety of organism as the larvae continue to grow.

These larvae are at the top of the food chain, so if something in the environment affects other organisms, it should show up in the greenhead horse fly population.

“They are like the lion invertebrate in the marsh,” Husseneder said.

What they found through the help of grants from the National Science Foundation and the Gulf of Mexico Research Initiative is both the population and the genetic diversity of the greenhead horse fly in the oiled areas were greatly reduced compared with unoiled areas. In addition, the genetic analysis showed that although there was some movement of genetic material into the oiled areas, there wasn’t much movement out.

“That gives us some hope that when you go out this year the oiled and nonoiled areas might be closer,” Husseneder said.

These early results were published recently in the journal Nature.

Now, the two scientists are starting on a three-year, $2 million Gulf of Mexico Research Initiative grant to compare horse fly population levels using upcoming collections this year and genetic material from 2011.

One part of that research also will include a comparison of the stomach contents of the horse fly populations from oiled and unoiled areas over time to give an indication of what the flies are eating. This, in turn, indicates what organisms are present in each marsh area.

This identification of horse fly food is done by looking for one unique genetic marker that each species or group of species share. In essence, this could result in a checklist of organisms, on a genetic scale, of what a healthy marsh looks like or if there are problems that should be addressed. A simple soil sample and equally simple test could give the results.

“This species doesn’t live outside of the spartina marshes,” Lane said.

As such, the annoying, painful greenhead horse fly could be the canary in the coal mine or the harbinger of good tidings for the future in coastal marsh rehabilitation.

Follow Amy Wold on Twitter, @awold10.