Seaweed is making its way across the globe: Scientists at the University of Florida in St. Petersburg’s College of Marine Science used NASA satellite observations to find and document the biggest bloom of macroalgae in the world.
Called the Great Atlantic Sargassum Belt, this giant area of brown algae stretches from West Africa to the Gulf of Mexico, said a NASA press release. Based on computer simulations, the team confirmed that this odd belt of seaweed develops its shape in response to ocean currents. The team, which published their findings in Science, demonstrated how satellite imagery can help monitor changes in massive seaweed blooms worldwide.
“The scale of these blooms is truly enormous, making global satellite imagery a good tool for detecting and tracking their dynamics through time,” said Woody Turner, manager of the Ecological Forecasting Program at NASA Headquarters in Washington.
Chuanmin Hu of the USF College of Marine Science led the study and has analyzed Sargassum with satellite imagery for the past 13 years. His team, which included scientists from University of South Florida (USF), Florida Atlantic University, and Georgia Institute of Technology, studied data from NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) between 2000 and 2018. They found that there was a possible regime shift in Sargassum blooms since 2011.
Massive amounts of ‘Sargassum’ are shown along the coastline in Cancun, Mexico. (Photo Credit: Michael Owen)
The satellite imagery showed that major blooms occurred annually between 2011 and 2018, except in 2013. This data and field measurements suggest that there wasn’t a bloom that year because Sargassum seed populations measured during winter 2012 were very low, according to Dr. Mengqiu Wang, a postdoctoral scholar in his Optical Oceanography Lab at USF.
A side-by-side comparison of ‘Sargassum’ levels in the lower Florida Keys and an open ocean. (Photo Credit: Brian Lapointe, Ph.D., Florida Atlantic University’s Harbor Branch Oceanographic Institute /Mengqiu Wang – USF)
Prior to 2011, most free floating Sargassum was mainly found in patches around the Gulf of Mexico and the Sargasso Sea. However, in 2011, Sargassum populations started to emerge in places they weren’t located before, such as the central Atlantic Ocean. Even though Sargassum can foster ocean health by providing a good habitat for ocean animals and generate oxygen via photosynthesis, too much of this algae could be a nuisance to marine species and overpopulate shorelines. It’s likely that the ocean’s chemistry might have altered for the seaweed bloom to grow at such a fast rate.
The Great Atlantic Sargassum Belt’s density. (Photo Credit: NASA / Earth Observatory / Data provided by Mengqiu Wang and Chuanmin Hu, USF College of Marine Science)
According to the study, there are some key factors that are important for bloom formation: a big seed population in the winter left over from the previous bloom, nutrient input in the spring or summer from the Amazon River, and nutrient input from West Africa upwelling in the winter season. It’s possible that discharged nutrients increased over the past few years because of increased deforestation and fertilizer use, however, the team will need to conduct more research to confirm if this hypothesis could be true. Sargassum needs normal salinity and surface temperatures in order to bloom well.
“This is all ultimately related to climate change, as climate affects precipitation and ocean circulation and even human activities [that can lead to Sargassum blooms], but what we’ve shown is that these blooms do not occur because of increased water temperature,” Hu said. “They are probably here to stay.”
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