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article imageEssential Science: Big seaweed bloom triggers pollution concern

By Tim Sandle     Jul 15, 2019 in Science
Scientists have discovered the biggest seaweed bloom in the world. This is a record-breaking belt of brown algae, from West Africa to the Gulf of Mexico. It’s here to stay for the long-term, and this means ecological trouble.
Marine biologists working at the University of South Florida (USF Innovation) used NASA satellite observations in order to discover the mass bloom of microalgae. The bloom has been named the Great Atlantic Sargassum Belt. The sargassum is native to the Sargasso Sea.
20 metric tonnes of seaweed
The bloom weighs 20 metric tonnes and it stretches from west Africa to the Gulf of Mexico. The sargassum bloom follows the Antilles Current and thrives in saltwater, which enables the mass to grow over such a large span.
When parts of the algae wash up on beaches, the debris generates a malodorous stench (caused by hydrogen sulphide). While the mass can aid some forms of wildlife, such as providing a food source for seabirds, it can also produce a thick overlay which can block sunlight, which affects some marine life. In addition, when the large mats die and sink the decaying mater can kill coral.
The vast pool of brown seaweed did not suddenly appear, researchers have been tracking the phenomenon since 2011. The issue is that each year it becomes bigger and bigger, leading to the largest bloom of macroalgae ever recorded.
State of Emergency
The growing brown mass is causing problems, not least in Mexico. In June 219, the Mexican state of Quintana Roo declared a state of emergency over sargassum.
Started at the beginning of the 1990's seaweed farms have become a source of revenue for thousa...
Started at the beginning of the 1990's seaweed farms have become a source of revenue for thousands of women on the Island of Zanzibar
Marco Longari, AFP/File
The state described the situation as an “imminent natural disaster.” Adding: “The arrival and decomposition of large quantities of sargassum should be addressed with a double perspective, of guaranteeing the protection and use of the natural environment, and consequently, guaranteeing the normal development of human health”.
June saw triple the 600 cubic meters that arrived during May, which was more than five times the quantity that washed up in April, in the region alone. Furthermore, scientists in Mexico and the U.S. have detected high levels of arsenic and heavy metals in sargassum, based on seaweed that washed up on Quintana Roo beaches.
Last year, the floating biomass also overwhelmed Caribbean beaches, prompting the government of Barbados to declare its own national emergency.
Big stink
The smell from the seaweed that washes up on beaches is a serious issue, according to The Guardian. Reporting on the Caribbean, the newspaper describe show the noxious smell has had a significant effect on the tourism (the combination of the sight and smell left beaches highly unattractive).
On land the effects are also problematic, where the gas released has destroyed some electric units, like televisions and eroded metals. There are also concerns with human health. Some people living close to beaches have complained of headaches, nausea and skin irritation.
Origins
According to one of the researchers, Chuanmin Hu there’s a clear link to climate change and the marine biomass. "The ocean's chemistry must have changed in order for the blooms to get so out of hand," Hu states in a research brief, adding that the sargassum reproduces from fragments of a parent plant, and it has several initiation zones around the Atlantic Ocean. The brown mass develops faster when nutrient conditions are favorable.
Another causative factor is fertilizers and other nutrients, potentially washing in from the Amazon River and then nourished by upwelling from deeper waters off the coast of West Africa.
Seaweed
Seaweed
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Hu’s team have conducted an 19-year analysis, drawing imaging data from a satellite instrument that calculates wavelengths of light reflected from the ocean surface (carried on NASA's Moderate Resolution Imaging Spectroradiometer (MODIS)). This helps to chart how the bloom has developed. Writing in The Atlantic, journalist Ed Yong notes: “To satellites that detect infrared, sargassum blazes like a bonfire.”
The analysis reveals that between 2000 and 2010 there was little seaweed in the central Atlantic (most appeared in the Gulf of Mexico and Sargasso Sea). However, from 2011 large blooms began to appear, becoming., by 2019 a vast band. In 2018 this amorphous mass stretched for 5,500 miles (8,850 kilometers).
By winter the mats dissipate, or they contribute to new blooms in the coming year. A big concern from the research is that the mass is the new normal – expect more seaweed; lots of it, each year.
Research paper
The discovery has been published in the journal Science. The research paper is titled “The great Atlantic Sargassum belt.”
Essential Science
The Shearon Harris Nuclear Power Plant in New Hill  North Carolina  is a nuclear power plant with a ...
The Shearon Harris Nuclear Power Plant in New Hill, North Carolina, is a nuclear power plant with a single Westinghouse designed pressurized-water nuclear reactor operated by Duke Energy.
NRC via Wikimedia
This article is part of Digital Journal's regular Essential Science columns. Each week Tim Sandle explores a topical and important scientific issue. Last week we found out that scientists working at Google are investigating cold fusion technology, to be used as an energy source.
The week before the topic was world’s first artificial intelligence created universe simulation to examine the effect of dark energy on an expanding universe.
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