Waters near a Tulum resort are brown from Sargassum, a seaweed-like algae, on June 15, 2019 in Tulum, Mexico. /VCG Photo
Scientists have spotted the largest seaweed bloom in the world, stretching from West Africa to the Gulf of Mexico and consisting of 20 million metric tons of biomass.
According to satellite observations, the seaweed band, called the Great Atlantic Sargassum Belt, now covers an 8,850 kilometer-long stretch, and scientists suggest the situation could become the new normal.
"In the open ocean, Sargassum provides great ecological values, serving as a habitat and refuge for various marine animals," wrote co-researcher Dr Mengqiu Wang, from the University of South Florida College of Marine Science.
But excessive seaweed brings about negative effects. It starves marine creatures of oxygen in the water, and leaves unpleasant odors on the beaches, scientists explained.
The study, titled "The great Atlantic Sargassum belt," was published in Science on Friday.
A worker uses a rake to clean up piles of Sargassum, a seaweed-like algae, from a beach on June 15, 2019 in Tulum, Mexico. /VCG Photo
Both human and nature factors have contributed to this serious environmental problem, scientists said.
They found that algal blooms in the ocean were partly due to the increase in nutrients brought from the Amazon River in the spring and summer each year, as well as human activities including deforestation and use of fertilizers.
Total fertilizer usage in Brazil increased by 67 percent between 2011 and 2018.
Changes to ocean circulations and increased iron sediments from airborne dust are also thought to be contributing factors, the study's co-researcher Chuanmin Hu told Katie Langin from Science last year, calling them "educated speculation."
Mexico's Riviera Maya Caribbean tourist towns of Cancun, Playa del Carmen and Tulum are being inundated with tons of foul-smelling seaweed-like algae called Sargassum that has turned the pristine blue waters brown and littered the white sands beaches. /VCG Photo
A recurrent phenomenon
Massive seaweed bloom was first discovered in 2011 when the brown sea plant inundated Caribbean beaches, trapping sea turtles and emitting a foul smell.
"It was unprecedented, we'd never seen it before," Hazel Oxenford, a fisheries biologist at the University of the West Indies in Cave Hill, Barbados, was quoted by Langin in the same article.
But what was thought to be a one-off phenomenon made a comeback a few years later, damaging the local ecosystem. Last year, the Barbados government declared a national emergency.
Satellite imagery shows that the blooms have recurred nearly every year since 2011. The area there is surrounded by currents traveling from South America to Africa and then back to South America.
Langin says the clockwise loop gets ruptured from January to May, and flows moving towards the west bring Sargassum up the Brazilian coast toward the Caribbean.