UP TO 700 million litres of oil, plus nearly 7 million litres of dispersant chemicals, all threaten some of the most important marine and coastal habitats of the US. When the leak from the Deepwater Horizon well stopped – for now, at least (see “Oil spill memory will fade fast”) – on 15 July, it was time to take stock of a grim scene.
Even as the engineers complete their job, an army of ecologists is gearing up for an arduous campaign to document the damage and chart the eventual recovery. “This is almost like a war footing,” says , a biological oceanographer at the University of South Florida in St Petersburg.
The Gulf of Mexico has become, in effect, a colossal ecological laboratory. “It’s like the biggest science experiment ever,” says , a coastal ecologist at Texas A&M University in Corpus Christi. “Unfortunately, it’s a completely uncontrolled experiment.”
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“It’s like the biggest science experiment ever – but completely uncontrolled”
Some of those in the thick of the action already possess years of ecological data, providing a firm baseline against which to determine the spill’s effects. Others had to rush into the field to get samples before the oil spread too far.
The region’s fragile coastal marshes are a top priority. As the oil neared the marshes, a team led by of Louisiana State University in Baton Rouge visited 32 sites east and west of the mouth of the Mississippi, taking samples of salt marsh plants and sediments. “We know some of those sites are oiled now,” says Turner, who’ll return to survey the damage in September.
Here, New Scientist profiles some of the other projects that will document the ecological legacy of the biggest offshore oil spill in American history.
OIL MUNCHERS
Oil-munching microbes have had a busy few months digesting the oil, gas and other hydrocarbons produced by the Gulf leak. Identifying which bugs were out there before the spill and which are there now provides a vital clue to how ecosystems are reacting to the spill.
at the University of Georgia in Athens collected microbes in the northern Gulf in late March, providing a snapshot of the community before the leak sprung. DNA fragments are extracted from water samples and used to identify the bugs present. Hollibaugh and others are heading back to the same sites next week to collect more samples.
Jay Grimes at the University of Southern Mississippi in Hattiesburg has found an increase in cold-water bacteria. He says measurements from the deep-water plumes of oil show oil is being consumed by these species. The next step will be to find out how fast this is happening in order to say how quickly the plumes will disappear.
SHIFTING SANDS
What can shifting sands tell us about the oil spill? Its extent, deep under water.
Crabs, oysters and other benthic critters spend a lot of time shuffling sand on the ocean floor and could die if the oil gets into their burrows. Such changes in the ocean floor could therefore be used to map the oil’s spread along the seabed. And that’s just what geologist at the University of Southern Mississippi in Hattiesburg hopes to do when he heads to the Gulf study sites in September to collect sediment cores.
His colleague Charlotte Brunner will look at – tiny organisms that live mostly in oxygen-rich pores in the sand of the seabed. She is looking for changes in the mix of species. Those that need a lot of oxygen are likely to be suffocated by the spill, allowing species that can survive on low oxygen levels to thrive. Foraminifera are at the bottom of the food chain, so such changes could have widespread consequences.
A DEADLIER DEAD ZONE
Oil is bad and so are excess nutrients washed from farmland. What’s unclear is what happens when the two meet.
Even before the spill, this summer’s dead zone in the Gulf of Mexico was forecast to be since systematic studies began there in 1985. This oxygen-starved region of water forms off the coast each summer, when agricultural nutrients fertilise massive algal blooms. As the algae die, sink and rot, oxygen is sucked from the water.
To find out if the oil has made it worse, at the University of Maryland’s will cruise the Gulf in September, towing a device called ScanFish. Resembling a section from an aircraft wing, it will “fly” up and down the water column, measuring temperature, oxygen, organic material, and zooplankton populations.
In parallel, Roman’s team will map fish populations and use the results to produce a 3D map of the dead zone and oil, and show how these two environmental problems are affecting the distribution of zooplankton and fish.
Crucially, the data can be compared with results from cruises run every year since 2003. The concern is that as well as being toxic to plankton and fish, oil could extend the anoxic dead zone: bacteria that feast on oil can further deplete oxygen levels, and slicks on the surface may block the uptake of oxygen from the atmosphere.
GENE GIVEAWAY
The oil seems to be getting into the Gulf’s every nook, but just how widespread are its toxic effects? The answer may be written in the genes of marine fauna.
When these creatures are exposed to oil, a gene called CYP1A is activated, which helps them break down the most toxic hydrocarbons. Joe Griffiths at the University of Southern Mississippi in Hattiesburg is using CYP1A-activation to track oil exposure.
But there’s a wrinkle in the system. Organisms can encounter oil for many reasons, including natural seeps and other pollution besides the BP leak. To track the effects of BP’s oil, Griffiths wants to measure the CYP1A in oysters, fish and crabs he collected before they were hit by the spill. And he wants to collect more samples now, so he can measure the oil in the water and CYP1A at the same time. But his first share of the funds BP pledged for tracking the accident’s impact has run out, and it isn’t clear that the next round is coming soon.
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● For scientists studying the Gulf of Mexico’s deep-water corals, the moment of truth comes this week. Since May, three sites studied by a team from the US Geological Survey have been sitting under the massive slick. The researchers planned to return to their field sites on 22 July – their first visit since the blowout – to see if the corals have been damaged by undersea plumes of oil and dispersant.
● Big fish like tuna and dolphins eat smaller fish in the middle of the water column. But because oil spills usually happen in shallow waters – not 1500 metres below the waves – nobody knows how midwater fish and their relationships will be affected. Joseph Torres at the University of South Florida will visit the well site in September to gather fish for autopsies. He is anxious about what he will find: midwater fish are delicate as they live in what is normally a rare pristine environment.
● Female blue crabs migrate from estuaries out to sea to lay their eggs. As the larvae return after a month in open water, many are showing up with blotches of what seems to be oil lodged beneath their shells. This is worrying because they are an important source of food for other estuarine creatures, and the adults support an important commercial fishery.
