This 'floating rainforest' is threatening entire ecosystems

The overwhelming threats of the golden floating rainforest

Imagine standing on the deck of the research vessel, surrounded by the vast, endless expanse of the ocean. The deep blue waves extend as far as your eyes can reach. And then, the scene transforms. At the surface of the water, you’re greeted by sun-kissed fronds reflecting the warm sunlight. Its beauty lies in its intricate layers, resembling golden mats adorning the water’s surface, swaying in rhythm with the ocean’s gentle movements.

It’s a mesmerizing display, a true work of art by Mother Nature herself. The Sargassum is a sanctuary, a floating oasis teeming with life. This ecosystem has been here long before even voyager Christopher Columbus embarked on his voyage across the vast Sargasso Sea, expressing concerns in 1492 that his ship might become ensnared by it. Beneath the surface, schools of fish dart in and out of the Sargassum‘s shelter, seeking refuge and sustenance.

But despite the beauty, the life it holds, it is also a bringer of death. And the latest research shows it’s slowly spreading across the globe.

A $3.2 million grant from the National Oceanic and Atmospheric Administration (NOAA) is set to change the game for coastal communities grappling with the unpredictable and massive seaweed phenomenon known as the ‘Great Atlantic Sargassum Belt’.

Sargassum – a genus of brown seaweed – grows in the calm and crystal-clear waters of the Sargasso Sea, an immense region of biodiversity spanning 2 million square nautical miles (5.2 million square kilometres) located to the east of Bermuda in the Atlantic Ocean.

I think I’ve replaced my climate change anxiety with Sargassum anxiety.

Patricia Estridge, CEO of Seaweed Generation

Unlike traditional shores, the Sargasso Sea is delimited by the swirling ocean currents that form the North Atlantic Subtropical Gyre. Within the open ocean, clusters of Sargassum create a vibrant ecosystem referred to by ocean explorer Sylvia Earle as a “golden floating rainforest”. Suspended by buoyant gas-filled ‘berries,’ this seaweed serves as sustenance, refuge, and breeding grounds for various creatures, including crabs, shrimp, whales, migratory birds, and approximately 120 fish species.

Sargassum plays a singular role as the primary spawning grounds for European and American eels and provides shelter for around 43 other species classified as threatened or endangered. Moreover, it offers a safe haven for the early stages of sea turtle hatchlings and juvenile fish. Ten species are exclusive inhabitants of this extraordinary environment. The Sargasso Sea also hosts a significant commercial fishery with an estimated annual value of approximately $100 million USD.

However, in recent years, substantial quantities of Sargassum have shifted westward, forming what scientists have termed the Great Atlantic Sargassum Belt. As of March 2023, this belt extended over 5,000 miles (8,000 kilometres) in length and 300 miles (500 miles) in width. It comprises interconnected, island-like masses that can span extensive distances. When it washes ashore, it does not uniformly blanket beaches; some areas may remain relatively clear or experience only mild effects.

Nevertheless, the collective volume this year is almost overwhelming. The significant growth of Sargassum in recent years is attributed to various factors, including increased nutrient levels, rising sea temperatures, changes in ocean currents, and deforestation in the Amazon rainforest.

“I think I’ve replaced my climate change anxiety with Sargassum anxiety,” says Patricia Estridge, CEO of Seaweed Generation, a UK startup working to make seaweed commercially viable.

For the past decade, researchers have scrutinized this expanse of marine greenery stretching from West Africa to the Florida Keys, but foreseeing where the Sargassum will land has remained a significant challenge. The seaweed’s movements are influenced by a combination of ocean currents, temperature, and nutrient availability.

Offshore it’s not a problem. The problem is for these inshore communities.

Dr. Brian Barnes

Predicting when and where Sargassum will wash ashore has been a significant challenge, and efforts to develop forecasting systems aim to address this issue and help coastal communities better prepare for its arrival. For example, Miami-Dade County in Florida (USA) allocated a substantial budget of $6 million in 2022 to address the removal of Sargassum from merely four well-frequented beaches.

“Offshore, we can monitor it with satellites,” says Dr. Brian Barnes, an assistant research professor with USF’s College of Marine Science. “We’ve been doing this for years and have some pretty high-tech techniques to really identify where the Sargassum is and have some idea of where it’s going, but again offshore it’s not a problem. The problem is for these inshore communities.”

Barnes leads the charge in developing a ground-breaking Sargassum forecasting system to provide advanced warnings to inshore communities. The existing capabilities of weather satellites offer resolutions of approximately one kilometre by one kilometre. However the NOAA grant will empower the researchers to access finer-resolution satellites, allowing them to focus on Sargassum patches within a range of three to four meters.

Every year we’re seeing more and more countries reporting an influx.

Shelly-Ann Cox, Chief Fisheries Officer for the Barbados government

“That’s the scale you really need to be looking at in order to identify Sargassum patches that are meaningfully going to impact a region,” Barnes says. Currently the new forecasting system can anticipate the beaches Sargassum is approaching approximately two to three days in advance. “Which is not enough time to set out like a floating barrier or something like that. But it is enough time to stage equipment. Get your dump trucks ready.”

The initial brunt of Sargassum’s impact was keenly felt in the Windward Islands of the Caribbean. Shelly-Ann Cox, serving as the Chief Fisheries Officer for the Barbados government, has dedicated more than a decade to addressing Sargassum-related challenges. She vividly characterizes the repercussions, both environmental and economic, as nothing short of catastrophic: “Every year we’re seeing more and more countries reporting an influx, and the devastating impacts on tourism, fishery sectors and transport.”

Recently, Sargassum’s unwelcome arrival blocked the inflow of water into a desalination plant in the U.S. Virgin Islands, leading to disruptions in the water supply in 2022. “Nuclear power plants and things will sometimes have water inflows, and so they’re very interested in knowing that there’s a patch that’s going to be impacting this particular location,” Barnes explained.

However, a more fundamental issue revolves around the proper disposal of Sargassum. While some have proposed its use as a fertilizer, the presence of substantial heavy metals – especially arsenic – raises concerns about its suitability for plant cultivation. Even composting poses risks, as it might enable arsenic leaching into groundwater, eventually infiltrating drinking water sources and the broader food chain.

No one [has been able to] think of a commercially viable solution for Sargassum.

Patricia Estridge, CEO of Seaweed Generation

These concerns have prompted several Caribbean nations to prohibit Sargassum composting. When considering industrial applications, the extensive processing necessary to eliminate heavy metals proves economically unviable. “There are so many climate-positive uses for seaweed, but then there are many different seaweeds in the ocean,” says Estridge. “No one [has been able to] think of a commercially viable solution for Sargassum.”

Although it feels like an ocean away, the Sargassum phenomenon is not confined to the Atlantic Ocean alone and looms as a problem for coastal communities in the Pacific and Indian Oceans. Having demonstrated its ability to spread from the North to South Atlantic, it is believed that Sargassum could establish itself as a potentially invasive species in these other ocean regions.

Given similar environmental conditions in the Pacific and Indian Oceans, Australian coastal communities may soon face unpredictable and massive Sargassum influxes. These could have profound ecological and economic implications, disrupting tourism, fisheries, and water supply infrastructure.

As communities around the world grapple with the complexities of Sargassum influxes, the USF’s pioneering efforts in Sargassum forecasting offer hope and resilience for a more prepared future.

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