A record-breaking mass of smelly seaweed stretching from West Africa to the Gulf of Mexico has been identified using satellite imagery.

Researchers at the University of Southern Florida used satellite imagery to determine that the giant floating mass of seaweed is a whopping 8,850 kilometers (5,000 miles) long. It weighs an estimated 20 million metric tons or the equivalent of 1.6 million double-decker buses.

Scientists first noticed that seaweed was spreading rapidly across the Atlantic and growing in mass in 2011.

“There’s a huge amount of Sargassum in a place where it’s never been seen before,” said Mengqiu Wang, co-author of the study, which was published in the journal Science.

Wang said the seaweed was of “great ecological value” to marine life such as fish, crabs, shrimps, and turtles that use it as a habitat or food source. But excesses of Sargassum like the recent explosion cause some problems for marine life, as dead Sargassum sinks to the ocean floor and can “smother corals and seagrasses”, according to the university’s press release.

Sargassum also releases a sulfur gas that smells like rotten eggs as it decays, which has caused problems as it washes up on tourist-filled coasts in Mexico and the Caribbean.

The rotting seaweed can attract insects and the gas given off affects asthma sufferers, causing what Wang said was a “public health concern.”

According to Expansion , a Mexican business magazine, hotels in Quintana Roo saw a decrease in visitors in June due in part to the heaps of unsightly, foul-smelling seaweed washing up on the beaches. The local government even declared a state of emergency over the Sargassum situation, local media reported.

The seaweed explosion is also indicative of bigger problems, Wang said. Researchers believe ocean chemistry must have changed “in order for the bloom to occur so quickly,” she said, likely caused by nutrients seeping into the water from widespread deforestation and fertilizer use.

While the effects of deforestation are widespread and contribute to our ongoing climate crisis, Wang said that the Sargassum bloom is primarily a concern for beachgoers and does not seem to be creating any severe problems in the ocean itself just yet.

“If we could effectively block the Sargassum from landing on the beaches, that could be a good way to go,” she told CNN.

Wang added that governments in affected regions could find strategies “to make it useful,” citing seaweed’s potential use as biofuel or fertilizer. More research into the Sargassum may also uncover other uses.

“We still have a lot of work to do to understand the phenomenon,” Wang said.

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