Sargassum seaweed stretches from Gulf of Mexico to Africa, Harbor Branch scientist says

Think there's a lot of Sargassum seaweed on Treasure Coast beaches this Fourth of July weekend?

You ain't seen nuthin' like the “Great Atlantic Sargassum Belt."

A team of scientists including  Brian Lapointe, a research professor at Florida Atlantic University’s Harbor Branch Oceanographic Institute at Fort Pierce, have discovered a mass the stuff stretching from West Africa to the Gulf of Mexico.

What they've dubbed the “Great Atlantic Sargassum Belt” is the world's largest algae bloom (Seaweed is a macroalgae,) extending 5,500 miles and weighing more than 20 million tons.

The massive bloom and the Sargassum covered beaches may become the “new normal,” according to a study the team published in the journal Science.

Earlier this week Lapointe told TCPalm Sargassum, the seaweed with small air-filled "berries" that floats in island-like masses on the ocean and has been washing up on Treasure Coast beaches, emits hydrogen sulfide and can contain high levels of arsenic and heavy metals.

More:Seaweed on local beaches has arsenic, emits hydrogen sulfide, scientist says

Sargassum isn't toxic to touch, but touching some of the organisms living in it, such as jellyfish larvae, can cause skin rashes or blisters.

Normal amounts of Sargassum are a boon to many types of sea life, providing food and habitat for numerous species of fish and resting sites for baby sea turtles.

But huge mats of Sargassum can cause problems for marine life, blocking sunlight sea grass needs to grow and, when the seaweed dies and sinks to the ocean floor, smothering sea grasses and corals.

Natural and human causes

Lapointe and his fellow scientists — Mengqiu Wang, Chuanmin Hu and Brian Barnes, all of the University of South Florida; and Joseph P. Montoya from the Georgia Institute of Technology — studied 19 years of satellite images from NASA to see how the bloom has exploded since 2011.

To figure out why, they analyzed fertilizer consumption patterns in Brazil, Amazon deforestation rates, Amazon River discharges and nitrogen and phosphorus measurements from the western parts of the central Atlantic Ocean near the Amazon outflow.

The data suggested a combination of natural causes, exacerbated by human activities.

In the spring and summer, Amazon River discharges add nutrients to the ocean. Those nutrients may have increased in recent years because of more deforestation and fertilizer use in the Amazon basin.

More: University of South Florida's Sargassum tracking site

Just like fertilizer runoff feeds algae blooms in the St. Lucie River and Indian River Lagoon, nitrogen and phosphorus running out the Amazon into the ocean feed Sargassum blooms.

The Sargassum bloom that began in 2011 is, Lapointe said, "the result of nutrient accumulations since 2009, resulting from stronger upwelling in the eastern Atlantic and excessive Amazon River discharges in the western Atlantic.”

Other studies have suggested the bloom has grown in part because climate change has increased the ocean water temperature.