April 21, 2009 — An algae plume so large it can be seen by satellite appears to have flowed northward from South America to the Virgin Islands, two area scientists said Tuesday.
It was first spotted several weeks ago by fishermen and scientists as it headed northward. It has also reached Puerto Rican waters.
"The water is a different color than normal," said Richard Nemeth, who heads the Center for Marine Science at the University of the Virgin Islands. "It's kind of eerie, like pea soup."
The cloudy greenish water contrasts markedly to the normal clear blue water found in the Virgin Islands. Last Thursday and Friday the plume went down about 75 to 80 feet below the water's surface, but by Saturday the bottom edges of the plume began to mix with the water below it, Nemeth said.
"From satellite images, it looks like it's starting to break apart," he said.
Nemeth said he had heard about similar plumes during his 10 years in the Virgin Islands, but this is the first one he has seen firsthand.
The plume happens every year, but most years it doesn't travel this far north.
While no one disagrees that it originated in South America, Nemeth said he thinks it came from the Orinoco River, which exits Venezuela's northeast coast. Graciela Garcia-Molinar at the Caribbean Fishery Management Council in San Juan suggested that it came from the Amazon River, located further south than the Orinoco.
No matter where it originated, why it flowed so far north this year has scientists puzzling.
"That's a very good question," Nemeth said.
The implications for the territory's fish and reefs remains unknown, but Nemeth said that fish don't appear to swim in the plume.
"They seem to stay below the pea-soup layer," he said.
Garcia-Molinar suggested that when the plume departs, it may leave behind lots of nutrients to feed pelagic fish like marlin, tuna and dolphin, but UVI Adjunct Professor Simon Pittman said it remains unclear whether the algae that lands on the reef is good or bad for it.
Nemeth explained that it appears the algae plume is trapped in a gyre, a type of circular water mass that stays intact. This allowed it to flow so far north. Additionally, he said, the water seems cooler this year, which may help the algae plume stay intact longer.
Area scientists are busy trading notes on the algae plume, and the crews aboard the National Oceanic and Atmospheric Administration ship Nancy Foster, which is working in the area, are sampling the plume.
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