Who lives in Sargassum?

 Floating mats of Sargassum are home to many species, from spawning eels to loggerhead turtles.  Check out this slideshow from Smithsonian to see some of the many species found in these floating ecosystems.

 

Sea Invaders

Sargassum muticim is an invasive species.  Originally found in Japan, it has spread throughout the world's temperate waters, reeking havoc on local ecosystems. The floating  Sargassum block sunlight from reaching the depths of the water, affecting native species.

 

Sargassum muticum reached Ireland in 1995. The following map shows how it has spread in the following decade.

Sargassum and its Ecosystems

 

Baby sea turtles forage in mats of Sargassum.

 

Sargassum plays an important role in the life cycles of many animals.  Some use the floating mats to breed or for cover, while others live their whole lives living on or around the seaweed. Many eels spawn in Sargassum patches.  Loggerhead turtles are believed to use the drifting Sargassum mats for cover and protection as they mature.  The sargassum fish has appendages that mimic the shape of the seaweed. Birds search the mats for organisms to eat. Once a mat loses its buoyancy, it sinks to the ocean floor, providing nutrition to organisms on the ocean floor.

The Wide Sargasso Sea

 

There are many stories of ships stuck in the Sargasso Sea.

Located in the Atlantic, the Sargasso Sea has long been the stuff of legends. Columbus and his crew were becalmed in the Sargasso Sea in 1492 for three days. His may have been one of the first written accounts of Sargassum as he described the seaweed floating around his ships in the still sea.

What makes the Sargasso Sea so still?  Bound by open water on all sides, the Sargasso Sea lies within the Northern Atlantic Subtropical Gyre. Ships passing into the Sargasso Sea are sometimes becalmed by its doldrums. The mats of Sargassum are rumored to have entangled the becalmed vessels.

You may have heard of this part of the Atlantic where ships disappear.  The Bermuda Triangle lies within the Sargasso Sea.  Stories about the Sargasso Sea abound, from Jules Verne's Twenty Thousand Leagues Under the Sea to one of my favorite novels, Jean Rhys's Wide Sargasso Sea. In her prequel to Jane Eyre, Rhys constructs a novel in which the sea acts as a metaphor for the life of Antoinette, who is, in several ways, becalmed both before and after her marriage to Mr. Rochester.

Sargassum and Coastal Ecosystems

 

Sargassum blocking the sun above a reef.

   

In the 2019 article The Complex Case of the Seaweed That Is Drowning Ecosystems in the Caribbean, author Rodrigo Pérez Ortega interviewed Rosa Elisa Rodríguez Martínez, an ecologist studying coral reefs at the National Autonomous University of Mexico’s institute of Marine Science and Limnology.  Located in Puerto Moralos, twenty-four miles south of Cancun, Martinez had been studying the effects of  Sargassum blooms on the local ecology.

Martinez was one of the first scientists to understand the effects the  Sargassum bloom would have on the coral reefs of the Mexican Caribbean. Starting in 2015, with some respite in 2016 and 2017, the amount of Sargassum washing in increased substantially. The deteriorating water quality coincided with seagrasses near beaches dying off, followed by coral reefs dying from disease.

The increase in  Sargassum is complex, with some blame going to discharge from Brazilian farmers, upwelling, and climate change. Once the  Sargassum reaches the beaches it dies off, causing a “brown tide” as it decomposes in the water. The mass of decomposing material cuts down how much light reaches seagrasses and causes low oxygen levels and higher ammonium and sulfate levels in the water. The deteriorated water and decomposing seaweed have caused wildlife mortality in at least 78 species. Corals have also started dying off from “white syndrome.” Thus far there is no conclusive evidence that the  Sargassum is causing the death of the coral, but it coincides with  the arrival of the  Sargassum bloom in 2018.  Scientists are studying the heavy metals in  Sargassum as well at the macrofauna living on the seaweed to more fully understand its impact and the effects of removing  Sargassum.

Sargassum is having a negative impact on the local community. Tourism suffers due to  Sargassum blooms, leading to layoffs in the local communities.  Economic hardship leads to an increase in crime. Although people are paid to collect the seaweed, the problem is overwhelming.

Read the article!

Too much sargassum? Convert it!

The article Researchers convert washed-up seaweed into biofuels and fertiliser in Oceanographic explores work by researchers from Universities of Exeter and Bath to come up with a method to make harvesting sargassum to make chemicals and biofuels financially sustainable.

Coastal communities in Central America have been plagued by the sargassum blooms which, along with the Covid pandemic, have crippled the tourism industry. Local fisheries also suffer.

Removing the seaweed and processing it has been cost prohibitive, as the first steps include harvesting the seaweed, washing the salt water out, then drying it.  Rather than removing the salt, researchers are working on a salt-based biochemical conversion. The process involves releasing sugars which feed a yeast to produce a palm oil substitute while preparing residual seaweed for hydrothermal liquefaction.

Researchers are looking to create liquid fuels, plastics and fertilizers. They are hoping seaweed biorefineries can create local solutions to the problem of sargassum. At the same time, they plan to tackle another problem associated with sargassum: plastic.  The plastic debris found in sargassum will be processed along with the seaweed.

 Check out the article!