July 20, 2019

Andrew Campbell 

Scientists at the University of South Florida St. Petersburg Marine Science Institute have discovered the unprecedented increase of brown algae through the NASA satellite observation technology, extending from West Africa to the Gulf of Mexico. The scale has never been seen before, and it is probably not a short-term phenomenon.

 
Because it is made up of Sargassum, scientists named it the Great Atlantic Sargassum Belt. Sargassum is large brown algae that will proliferate on an enormous scale, like a floating island. In 2011, Sargassum began to grow in large numbers in places that had not occurred in the past, such as the Mid-Atlantic, and then reached the coast on a large scale, affecting the local environment and economy.

 
Woody Turner, who was the manager of the ecological forecasting project at NASA headquarters in Washington, said, " The scale of these blooms is truly enormous, making global satellite imagery a good tool for detecting and tracking their dynamics through time "The research host, Hu Chuanmin, a scholar at the University of South Florida Marine Science Institute, published the findings in the journal Science. He has been using satellites to study Sargassum since 2006. Hu Chuanmin said, " The ocean's chemistry must have changed in order for the blooms to get so out of hand." Sargassum reproduces through fragments of parental individuals and may have multiple initial growth areas around the Atlantic Ocean. When nutrient conditions are favorable and the physiological clock is also suitable for reproduction, it accelerates growth.
 

According to computer simulations, the researchers confirmed that the shape of the Atlantic Sargassum belt is formed along the ocean current. It is large in size and covers the tropical Atlantic surface from the west coast of Africa to the Gulf of Mexico. In 2018, more than 20 million tons of Sargassum floated on the sea (which weighed more than 200 full-loaded aircraft carriers), affecting recreational activities on the tropical Atlantic, the Caribbean, the Gulf of Mexico and the eastern coastline of Florida. Hu Chuanmin and Dr. Wang Mengqiu, a postdoctoral fellow at the University of South Florida's Optical Oceanography Laboratory, completed the study. The research team assembled scholars from the University of South Florida, Florida Atlantic University and Georgia Institute of Technology.
 

The ecological function of Sargasso is to provide a habitat for marine life. When Wang Mengqiu visited the Gulf of Mexico last year, he saw dolphins swimming in the Sargassum. Scientists analyzed NASA's medium-resolution imaging spectrometer (MODIS) data from 2000 to 2018 and found that from 2011, the growth of the algae may cause an ecosystem shift, which leads to rapid reorganization of the ecosystem and a new stable state. Wang Mengqiu said that in the satellite imagery, except 2013, there will be a large number of breeding every year from 2011 to 2018. In addition, there was no increase in 2013, as the number of seeds of Sargassum in previous winter was unusually low.

 
Before 2011, the free-moving Sargassum in the ocean was found around the Gulf of Mexico and the Sargassum Sea. The Sargassum Sea is located in the western part of the Mid-Atlantic Ocean and is named after the large number of Sargassum. In the open ocean, the patches of Sargassum provide sea turtles, crabs, fish and bird habitats, and like other plants, produce oxygen through photosynthesis to maintain ocean health. But once it is too much, it will crowd out marine life, especially near the coast.
 

The team established a key factor in the hyper proliferation of Sargassum: winter leaves a large number of seeds due to the previous increase, plus the nutrients of the upwelling in West Africa in winter, and the nutrients brought by the Amazon River in spring or summer.
 

Scientists believe that in recent years, deforestation and rising of fertilizer use may increase the nutrient emissions. However, Hu Chuanmin emphasized that the evidence of excessive nutrient is still in the initial stage, and the available information is limited. The team needs more research to confirm whether this hypothesis is true. In addition, Sargassum grows well only when the salinity is normal and the surface temperature is normal or cooler.

 
Dr. Paula Bontempi, deputy director of NASA's Department of Earth Sciences and responsible for managing NASA's marine life and biogeochemical programs, said: "Earth's ocean biogeochemistry is changing in response to natural and human forcing. The Great Atlantic Sargassum Belt suggests that we may be witnessing ecosystem shifts in our ocean that could have important implications for marine organisms and ecosystem services, which humans depend on." 
 

"This is ultimately related to climate change, because climate affects precipitation and ocean currents and even human activities (which may lead to the bloom of Sargassum), but we have confirmed that the proliferation of Sargassum is not caused by an increase in water temperature, but rather a long-term change. May stay there all the time."

Photo:Webshot.