Large slick’ could be huge plankton bloom

By Houma Today
22 March 2011

 HOUMA — Scientists at a Cocodrie marine-research center say a miles-long discolored patch on the Gulf originally feared to be oil may actually be a huge algae bloom — the kind that fuels the annual dead zone off Louisiana’s coast.


The patch, estimated to be 100 miles long and six miles wide by the Coast Guard, was tested by Coast Guard officials this weekend and found to contain only trace amounts of petroleum.

This slick is separate from the oily substance that washed up on Grand Isle and Fourchon beach this weekend.

Nancy Rabalais, director of the Louisiana Universities Marine Consortium research station in Cocodrie, said scientists from the lab steamed through the "slick" Monday about 15 miles off the coast of Cocodrie to take samples. They believe the slick is actually a huge, thick concentration of phytoplankton, the plant species of the microscopic critters at the bottom of the ocean food chain.

Rabalais said they’re currently testing to see which species of phytoplankton make up the bloom, and whether they are toxic. Large plankton blooms of toxic algae can sometimes cause fish kills and disruptions in the marine environment.

Rabalais said high flows of the Mississippi River are likely pushing nutrient-rich sediment from farms upstream into the Gulf. The nutrients and warm springtime waters fuel an explosion of algae growth that will eventually die off and sink to the Gulf floor, causing the summertime phenomenon known as the "dead zone," which forms annually off Louisiana’s coast.

"That’s the stage we’re in right now," Rabalais said.

As the dead plankton sinks to the Gulf bottom and decomposes, the process eats up all of the life-sustaining oxygen on the Gulf floor. That creates a huge area of "dead" water that marine life must either flee or die.

Last year’s dead zone measured between 6,500 to 7,800 square miles.