August 18, 2010

Scientists find oil at Gulf of Mexico toxic to fish

Scientists have found evidence that oil has become toxic to marine organisms in an area in the Gulf of Mexico that supports spawning grounds of commercially important fish species.

Researchers describe 'a constellation' of oil droplets mixed with sediment. Phytoplankton, the base of the marine food web, is found to be in poor health nearby.

Researchers from the University of South Florida said Tuesday (Aug 17) that, in preliminary results, there appear to be droplets of oil among the sediments of a vital underwater canyon where clouds of oil from the BP spill were found.

"So, indeed, the waters have a level of toxicity that needs to be recognized, and I think these were some of the first indicators that the base of the food web-the bacteria and the phytoplankton-may be affected," said David Hollander, chief scientist on a research vessel that just returned from a 10-day trip in the gulf.

More than 200 million gallons of oil leaked into gulf waters from BP's broken well until it was capped last month. The company used millions of gallons of chemical dispersant to break up the oil as it gushed off the Louisiana coast.

Researchers peering into the murk described what they saw using a process involving ultraviolet light.

"We were able to detect sediments that had oil covering them. It wasn't like a drape, don't get me wrong, like a blanket of oil; rather, it looked like a constellation of stars that were at the scale of microdroplets. They seemed to be at every location we looked east of the wellhead, and interestingly and surprisingly, at the top of the DeSoto Canyon to the east," said Hollander.

He described the DeSoto Canyon as an underwater geologic feature that is thought to bathe the Continental Shelf with nutrient-rich waters.

"In subsurface waters east of the wellhead, phytoplankton-microscopic, plant-like organisms that form the base of the marine food web-was found to be in poor health. In those locations, phytoplankton was repressed, or "feeling a toxic response to those waters," he added.