Back on the British Virgin Islands, Horton says it’s been an “educational journey” since the rafts of Sargassum wafted in back in 2011.

The island natural resources officials have learned “what to do, what not to do, when to leave it so it can be incorporated in the sand; when to actually step in, clean it, and move it along.”

That journey has had its ups and downs. The downs were most obvious when, in 2011, Horton saw that an abundance of Sargassum can deplete oxygen in the water when it decays.

“Because marine life needs oxygen, some were not able to survive,” Horton explains. “We had a lot of fish, sharks, and eels that ended up dying. That’s when we got a big understanding of the negative impacts of seaweed once it’s in a large quantity.”

A boat in the BVI surrounded by Sargassum.

Right now she’s thankful that the majority of the Islands’ sea turtle population is in the northern area of the islands, where there’s less of Sargassum, which emits the strong, rotten-egg smell when it begins to decay. That’s because when the seaweed begins to decompose, a process that starts about 48 hours after it washes ashore, it releases hydrogen sulfide, a colorless, poisonous gas.

Because it’s in an outdoor environment, that gas hasn’t caused major health issues after immediate exposure. But that doesn’t mean it’s not causing any harm: Research recently conducted by the Tropical Disease Unit at Toronto General Hospital and the Harvard T.H. Chan School of Public Health determined that decomposing Sargassum releases ammonia alongside the hydrogen sulfide gas, which can cause respiratory, skin, and neurocognitive symptoms.

During an eight-month period of 2018, there were 11,000 cases of acute Sargassum toxicity reported on the neighboring islands of Guadeloupe and Martinique. The illness can cause heart palpitations, shortness of breath, dizziness, vertigo, headache, and skin rashes.

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