The road along the east side of Tobago, running from the airport to the village of Speyside, passes dozens of small beaches where, in normal times, people lounge on the sand beneath palm trees and swim in the clear blue waters that lap at the shore. But on this mid-May weekend, sand and sea lay hidden beneath several feet of thick, brown seaweed.
Sargassum, a vine-like, floating algae, regularly circulates throughout the Gulf of Mexico and North Atlantic, where it forms the nearly 2 million-square-mile Sargasso Sea. Mariners recorded its presence as far back as Christopher Columbus’s time. The seaweed often washes up on beaches in the Gulf, the southern U.S. Atlantic coast and the northern Caribbean in spring and summer. But in 2011, it began showing up in unprecedented amounts, sometimes in places it hadn’t been seen before. On a single day in May 2014, for example, more than 8,400 tons of the stuff—the most ever recorded for a 24-hour period—buried a three-mile stretch of beach on Galveston Island, Texas.
As with many recent dramatic changes to the environment, the reason for the sargassum explosion appears to be a combination of factors resulting from climate change. That means scenes such as those in Tobago and Texas could be the new normal: an inconvenience for beachgoers and a potential economic disaster for those who earn their living from tourism and other coastal industries.
Mats of sargassum provide habitat and food for a wide variety of marine species, including sea turtles, fish, invertebrates, marine mammals and even birds, which depend on it to fuel over-water migrations. It rains down particulates to nourish creatures in the ocean’s depths. If the open sea is a desert, sargassum mats are its oases. They can help the beaches too: Driven onto shores by wind and waves, the algae mats add nutrients to the beach ecosystem and help build and strengthen dunes, which protect land and the structures behind them from storms.
But in such large quantities, sargassum has a dark side. For one, it tends to drive away tourists, who come to the shore for sand, not seaweed. Not all affected communities have the resources to remove the stuff, and even those that do find dealing with the increasing amounts a struggle. In addition, in Tobago and elsewhere, fishermen have been unable to fish in the thick seaweed. Heavy accumulations on the water may harm coral reefs and, on the beach, prevent sea turtle nesting.
Spikes of sargassum were first recorded in the Greater and Lesser Antilles (including Trinidad and Tobago) in 2011 and 2012. The problem appears to have begun many miles away. In recent years, the Amazon basin has experienced some of the world’s highest rates of deforestation. And without vegetation to hold soil in place, rain washes that soil and whatever it contains into streams and rivers. So when the Amazon basin saw greater than normal amounts of rain in 2011 and 2012, unusually high levels of nutrients such as nitrogen and phosphorus washed into Atlantic waters around the mouth of the Amazon River off the north coast of Brazil. Sargassum passed through this nutrient-rich water and responded by growing like, well, a weed. Ocean currents carried it from there to the Lesser Antilles and western Caribbean.
Jim Franks, a senior research scientist at the University of Southern Mississippi’s Gulf Coast Research Laboratory, recently created a website to collect eyewitness reports of large quantities of sargassum. Those reports confirm the seaweed is showing up in areas where before it had been seen only rarely or not all. Circulation patterns in the equatorial Atlantic even carried mats to Africa for the first time. Satellite data suggest the amount of sargassum in the Gulf of Mexico, Caribbean and Atlantic may hit an all-time high in 2015.
“For [Caribbean] communities, such an overwhelming influx is difficult to deal with,” says Franks, who has worked in the region for years. “It radically impacted tourism on some islands, creating economic and environmental hardship. I can’t overemphasize how important this is to the region,” he adds. “We need a well-thought-out strategy of response.”
Last summer, city officials in Galveston posted signs and handed out fliers touting the seaweed’s many virtues. The Galveston Park Board sent out 50 trained volunteers, dubbed the Bucket Brigade, to show beachgoers all the interesting little critters living in it. While these efforts didn’t change the fact that the beaches were covered, the city hoped they would change how Galveston visitors felt about the seaweed.
It didn’t. Most visitors think of a coast covered in sargassum as “a dirty beach,” says David Parsons, city manager in Port Aransas, Texas. This community on Mustang Island, just north of Corpus Christi, is developing machinery that uses a rake-like mechanism to pick up seaweed but leaves the surrounding wet sand. They hope to take the seaweed to remote parts of the beach to allow it to break down naturally—far from sunbathers and swimmers.
Tobago’s Division of Agriculture, Marine Affairs, Marketing and the Environment began removing sargassum from 16 beaches in early May, but officials noted that it continued to wash ashore in such quantities that efforts to clear it were futile. Some Caribbean islands use mechanical rakes and tractors to remove sargassum, but others have only hand rakes and animal-drawn wagons. Even when removing sargassum from the beach is possible, it raises the question of where to dump tons of decomposing vegetation.
One solution may be to dry and compact the seaweed into bales, and then use those bales as the base of new dunes. The theory is that these seaweed-based dunes will withstand waves and storm surges even better than natural ones. That won’t help beaches that don’t have dune systems, of course, which includes many of those in the Caribbean. Sargassum is sometimes used as fertilizer, but there’s not a high enough demand for that to make a dent in the amounts piling up. Dumping seaweed offshore may be an option, but it would also require heavy equipment and could potentially harm the marine environment.
Technology is at least helping us track the stuff. The University of Florida’s College of Marine Science posts links to real-time satellite observations of areas in the Gulf, Caribbean Sea and central Atlantic that can show the location of significant amounts of sargassum. In April, at a symposium held to discuss research and the economic and environmental effects of the “sargassum situation,” NASA and Texas A&M University at Galveston scientists unveiled the Sargassum Early Advisory System, or SEAS. This smartphone app combines satellite images with water current and wind data to predict where and when mats are likely to come ashore.
Such early warnings will be more helpful for communities with the resources to respond. Knowing an invasion is coming won’t always help vacationers, who tend to book trips several months in advance, and, of course, warning away tourists is exactly what affected communities don’t want to do. But until scientists and policymakers come up with better solutions, that may be their only choice.