LSU Researcher Investigates Deepwater Horizon’s Effects on Coastal Insects

by Zac Lemoine

Deep in the marshes and bayous of Louisiana, the sounds of millions of insects, hundreds of frogs and other creatures can be heard buzzing, croaking and splashing through one of the most delicate ecosystems in the United States. Today, in the third year after the Deepwater Horizon blowout, those sounds — once deafening — are less common.

Linda Hooper-Bui, associate professor in the LSU Department of Entomology, takes samples from the coast three years after the Deepwater Horizon oil spill.

Like many researchers at LSU, Linda Hooper-Bui, associate professor in the LSU Department of Entomology, who primarily researches ant colonies, focused her research efforts on the impact of the estimated 4.9 million barrels of oil released during the time the Macondo well leaked into the Gulf of Mexico.

“We are working in the salt-water marshes and coastal dunes,” said Hooper-Bui. “We’re asking questions related to stressors. It’s not just oil; it’s oil dispersants, cleanup activities and whatever restoration plans are in progress. … All of this is factored in.”

The oil spill is not what brought Hooper-Bui to the coast of Louisiana. She had been studying ant colonies in the marshes for years as part of a larger group, looking holistically at the changes in the Gulf area. They have benchmark data to measure the impact of sea level rise, land subsidence, marsh destruction or restoration and climate change.

These data, collected both before the oil spill and after in oiled areas and similar unoiled reference sites, offer a great deal of information on the changes in the marsh ecosystem. According to Hooper-Bui, her team has seen native species decrease and invasive species fluctuate.

“Our work is focused on insects,” said Hooper-Bui. “Mainly we focus on ants, because ants are closely associated with the soil and plant life.”

Because of the monumental devotion of resources and time, research relating to the oil spill has become the primary focus of a number of researchers, who often adapt or postpone previous research. Because of the all-encompassing nature of the oil spill research, some have jokingly begun to refer to each year as a season, much like a television show, with the period between April 2010 and April 2011 serving as the premiere season.

With the onset of spill season one, the data collected by Hooper-Bui and her colleagues proved invaluable in measuring the immediate impact of the oil and the lasting changes still unfolding today.

“In oil spill season one, we saw a radical decrease in almost every species we looked for – these include insects and spiders,” said Hooper-Bui. “It was catastrophic.”

Linda Hooper-Bui and her group studies ant colonies living along the coast of Louisiana. After the Deepwater Horizon oil spill in 2010, she has seen a striking decrease in ant populations.

While direct contact with the oil and potential devastating effects to the food chain could have led to the death of the insect populations, evidence suggested other factors were involved.

In order to better measure the impact oil had on insects, Hooper-Bui and her team constructed cages designed to float in the marsh area. The cages included food and, as a result, were entirely self-sustaining. Essentially, the insects in the cages were only coming in contact with the air in the marsh.

“The marsh is often covered with water because of tides and wind-driven water, but there are times when there is a low tide or a strong north wind that the sediment is exposed,” said Hooper-Bui.

The exposed sediment is key to what she believes is killing the insect populations.

When the waters are pushed back or withdrawn due to tide, a scene appears that is very different from the wind-swayed cord grass rising up through the brown waters of the coast. Something that looks similar to cracked pavement emerges.

A hardened surface of oil paves the sediment along the coastline. The pavement-like top is made of long strand hydrocarbons, weathered by the mile-long journey from the break in Macondo and the dozens of miles it traveled through the Gulf to reach the Louisiana coast. Add exposure to the sun and, while unsightly, it’s not too harmful to the plant and animal life because most of the harmful toxins have been stripped away or weathered to acceptable levels. What remains under the hardened surface is another story.

When the surface is exposed, the sun heats the dried oil to the point of cracking, exposing the softer oil beneath. The oil bubbling up through the cracks is less weathered and contains many of the short strand hydrocarbons. It is this unweathered oil that Hooper-Bui believes is causing the drastic drop in insect life.

Using the cages of insects, Hooper-Bui tracks insects along the coastline and 60 feet in from the coast. The differences were substantial. In 2010, immediately following the spill, there was a 60 percent drop in insects closest to the coast. Hooper-Bui’s team found 30-40 insects per sample 60 feet inland, and only 10 insects per sample along the coast.

While the impact was drastic in the first year, Hooper-Bui expected insect life to spring back, but that didn’t happen. In 2011, the inland sites remained the same, but the insects along the coast dropped again — to one-third of a bug per sample. Her most recent samples, taken in April, show no insects along the coast in oiled areas.

“We’ve heard the oil coming into the marsh is so weathered its non-toxic. … Well, the insects are telling us something different,” said Hooper-Bui. “The insects are dying and they’re not coming in contact with anything but the air. There is something toxic. This is the canary in the coal mine.”