Although it is widely referred to as a “blob,” the belt is a collection of individual patches, said Brian Barnes, a researcher in the College of Marine Science at the University of South Florida.
“The projection we have for this year is that it’s going to be at least as big, if not a little bit bigger, than last year’s bloom,” said Barnes, who tracks the belt’s size and path. “But last year it was pretty bad.”
Here’s what you need to know:
What is the great Atlantic Sargassum belt?
Sargassum is a large, leafy brown seaweed that is abundant in the ocean. Its ability to float comes from the small berry-like orbs that sprout from the plant – gas-filled structures that mostly contain oxygen.
Sea grasses tend to stretch in island-like masses that stretch for miles. In the open ocean, these large rafts become important floating habitats that provide food, shelter and breeding grounds for a variety of marine life including fish, turtles, crabs and sea bird. Sargassum is also a primary nursery for a variety of commercially important fish, such as mahi mahi, jacks and amberjacks.
The large Atlantic Sargassum belt refers to a formation of floating seaweed that stretches mostly from the west coast of Africa to Brazil and around the Caribbean region, said Brian Lapointe, a research professor at Florida Atlantic University who studied of sargassum for more than 40 years. Lapointe estimated the belt to be about 5,000 miles long and 300 miles wide.
Experts emphasize that it is not one, giant blob, but a collection of blobs.
“You can’t take a boat from Africa to the Caribbean and see it all the way, not at all,” Barnes said. “It’s too heavy.”
The patches can vary in size, Lapointe said. Some clumps can be the size of a basketball while others can reach hundreds of meters or even miles, depending on ocean conditions.
Where are the seaweeds now?
Recent satellite images show patches south of the northern Caribbean islands and off the coast of the eastern Yucatán Peninsula, Barnes said. The seaweed has also reached the Gulf of Mexico, he added.
Experts expect the belt to move farther into the Caribbean in the coming months and begin washing up regularly on the region’s beaches throughout the spring, leading up to the summer months.
Alarming amounts of sargassum are beginning to show up on Mexican beaches. “But that’s the tip of the iceberg,” Lapointe said. “Some more from the sargassum belt.”
What happens when sargassum comes ashore?
Small amounts washing up on beaches probably aren’t cause for concern, Barnes said. “The effects will be minimal,” he said. “People just walk over it.”
But some of the larger patches could flood beaches if they float ashore. “If they come to your beach, it can cause pileups that are six feet high,” he said.
There’s also a big difference between having blobs of sargassum floating in open ocean waters and having them close to shore, said Francis Chan, director of the Cooperative Institute for Marine Ecosystem and Resources Studies at Oregon State University.
“You’re dropping a continent’s worth of nutrients into an ecosystem that’s used to having very little of it,” Chan said. “It’s like throwing a ton of mass into a large pool versus doing it inside a water bottle.”
When sargassum decomposes in an open water scenario, the large volume of liquid can dissolve the biomass efficiently. But when it passes through beaches where the water is shallow, the nutrients from the decaying algae can absorb the oxygen in the water and change the ecosystem.
“There aren’t many nutrients in these tropical beaches with clean water quality and now they have to contend with a ton of algae that will decompose and change the nutrient regime,” Chan said. “You can change the food web in this scenario.”
Last year’s record-setting growth caused severe problems in various communities. The US Virgin Islands, for example, declared a state of emergency after high concentrations of sargassum in St. Croix blocked a desalination plant, a main source of water for the island.
More broadly, sargassum overpopulation can threaten and kill critical nearshore ecosystems, such as coral reefs, sea grass beds and mangroves. Sargassum decay can also affect water quality, Barnes said, likening the process to making tea. When the seaweed decomposes, the organic matter “seeps” into the surrounding water, he said.
Seaweed also poses economic and human health threats. Tourists are not likely to frequent beaches blocked by sargassum, where bad piles prevent access to water and create bad conditions for swimming.
In the ground, rotting sargassum releases hydrogen sulfide, which can be dangerous to people with asthma or aggravate other respiratory conditions — and fills the air with a rotten egg smell.
“It’s there until it’s cleaned up, and it takes a lot of resources to do that in a timely manner,” Barnes said.
Will these flowers continue to grow?
Since 2011, when researchers first observed abnormally large accumulations of sargassum in the tropical Atlantic Ocean, the blooms have generally continued to grow year after year.
Why are they getting bigger? One theory is that as the human population increases, more nutrients flow into the ocean from activities such as deforestation, fertilizer use, agriculture and wastewater, Lapointe said.
The growth of the flower appears to be related to the seasonal flows of the river, he said. The flow from these large waterways provides a source of nutrients for the seaweed.
Some communities try to exploit the masses of seaweed that wash up on their shores, working to turn it into biofuel, fertilizer and building bricks. But because sargassum can contain heavy metals, including arsenic, Lapointe urges caution about repurposing the plant.
“Eventually, this will be the new normal,” he said. “As this problem gets worse, I think we’re going to see a lot of different management and mitigation measures being taken.”
