Marsh insect numbers continue to decline after 2010 oil spill

Tobie Blanchard, Hooper-Bui, Linda M.

News Release Distributed 04/24/13

BATON ROUGE, La. – The day after the explosion on the Deepwater Horizon oil rig – April 21, 2010 – Linda Hooper-Bui, an LSU AgCenter entomologist, had a graduate student sampling insect populations in the marshes of southeast Louisiana.

Hooper-Bui and her research assistants continued to sample the marshes using sweep nets and marsh grass cuttings throughout April and May of 2010.

The samples of healthy populations provided a benchmark she would use as she watched the number of insects living in the oiled marshes decline drastically.

“Where there were once chirps, snaps and buzzing, there is now silence in oiled areas,” she said.

Three years after the largest offshore oil spill in U.S. history, Hooper-Bui suspects volatile aromatic compounds found in oil – naphthalene and methylnaphthalene – could be part of the reason insect populations are not rebounding.

The scientist first noted the decline in September of 2010, five months after the spill.

“We thought it would be certain groups of insects that would be reduced, but it was really dramatic,” she said. “We would sweep, and there would be barely anything in the net in the oiled areas.”

Three insects she was particularly interested in were katydids, elongate grass bugs and acrobat ants. Katydids feed on the tips of marsh grass, the elongate grass bugs suck plant juices, and the acrobat ants live in the hollow stems of Spartina.

These insects were vital for the marsh’s larger food web. Also, all three would rarely be on the ground and have little contact with oil. Yet, as Hooper-Bui continued to sample in 2011 and 2012, the numbers of these insects in oiled areas were declining.

“I could smell the oil, and I went back to classic entomology, and I said, ‘well it’s like they are being fumigated,’” she said.

To test this theory, Hooper-Bui put crickets in floating cages for 24 hours at a time in oiled and nonoiled areas and looked at mortality rates. In her first test, 100 percent of crickets in the oiled area died. Seventy-five percent in the nonoiled area survived.

She said experiments in the field and in the lab indicated that a volatile aromatic compound was killing the insects.

Further analysis showed increasing levels of naphthalene and methylnaphthalene in the sediment. The amounts went up radically after the initial oiling event, leveled off, but continue to creep up.

“I am extremely concerned about this. We don’t have any idea where this is coming from. It’s a native component of the oil, but it is possible there is something out there that is producing this,” Hooper-Bui said.

Naphthalene, once the main ingredient in mothballs, is considered a repellent, but Hooper-Bui said it actually kills the insects. “It is used in museums to keep insects out of museum specimens in sealed containers,” she explained.

Naphthalene is also toxic to fish and shrimp. In birds it has shown to cause eggshell thinning. It is also dangerous to humans.

“Look up toxicity of naphthalene and the symptoms of human exposure,” Hooper-Bui said. “It is very eerily similar to what the people who live, work and play in the Gulf of Mexico have been complaining about.”

The scientist suspects this is probably one cause of problems, but perhaps not the only one.

Hooper-Bui received $318,000 from the Gulf of Mexico Research Initiative (GoMRI) with the Coastal Waters Consortium to study the effects of the oil spill on insects.

The marshes are vital to Louisiana, and insects are a good indication of marsh health.

“Ninety-seven percent by weight of all seafood caught in the Gulf of Mexico starts out its life in the estuaries. So if we don’t have healthy marshes, we don’t have a viable seafood industry,” she said.

The marsh also acts as the kidneys for North America, Hooper-Bui said. The marshes absorb nutrients that would increase the dead zone in the Gulf of Mexico, protecting the Gulf. In reverse the marsh also protects the coastal and inland cities because the more marsh we have, the more it reduces storm surge.

GoMRI is funding Hooper-Bui’s research through 2014, but she said she is writing more grant applications so she can continue her work in the marsh.

“People think of the marsh as a gross, stinky place, but I think it is this amazing, beautiful place,” she said.

Tobie Blanchard

4/24/2013 9:13:16 PM
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