Scientists Discover The Largest Seaweed Bloom Across The World

Scientists of the USF School of Marine Sciences make use of the satellite observations of NASA for discovering the biggest seaweed growth in the world called the Great Atlantic Sargassum Belt (GASB), as reported in Science.

They made a confirmation that the belt of brown macroalgae known as Sargassum forms its shape in response to ocean currents, which is based on numerical simulations. It can grow so much that it covers the surface of the tropical Atlantic Ocean from the west coast of Africa to the Gulf of Mexico. This happened last year when more than 20 million tons, heavier than 200 fully loaded aircraft carriers, floated in surface waters and some of them caused havoc on the coasts bordering the tropical Atlantic, the Caribbean Sea, the Gulf of Mexico and the Gulf of Mexico.

The team also made use of environmental and field data for suggesting that the belt is seasonally shaped in response to two key nutrient inputs: one derived from humans and one natural. In the spring and summer, the discharge of the Amazon River adds nutrients to the ocean, and these discharged nutrients may have increased in recent years due to increased deforestation and the use of fertilizers. In the winter, the outcrop off the coast of West Africa provides nutrients from the deep waters to the surface of the ocean where the Sargassum grows.

"The evidence of nutrient enrichment is preliminary and is on the basis of limited field data and other environmental data, and we need more research to confirm this hypothesis," said Dr. Chuanmin Hu, of the School of Marine Sciences at USF, who He led the study and studied Sargassum used satellites since 2006. "On the other hand, based on the last 20 years of data, I can say that it is very likely that the belt is a new normal," Hu said.

Hu led the work with the first author, Dr. Mengqiu Wang, a postdoctoral scholar in his Laboratory of Optical Oceanography at USF. The team included other members of USF, Florida Atlantic University and Georgia Institute of Technology. The data they analyzed in NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) in 2000-2018 indicate a possible regime change in Sargassum blooms since 2011.

"The scale of these blooms is truly enormous, which makes global satellite images a good tool to detect and track their dynamics over time," said Woody Turner, manager of the Green Forecast Program at NASA headquarters in Washington.

In scattered doses in the open ocean, Sargassum contributes to the health of the ocean by providing habitat for turtles, crabs, fish and birds, and produces oxygen through photosynthesis like other plants. "In the open ocean, Sargassum provides great ecological values, which serve as habitat and shelter for various marine animals, and I often saw fish and dolphins around these floating mats," Wang said.

But too much of these algae make it difficult for certain marine species to move and breathe, especially when the layers cover the coast. When it dies and sinks to the bottom of the ocean in large quantities, it can choke corals and seagrasses. On the beach, the rotten Sargassum releases hydrogen sulfide gas and smells like rotten eggs, which could pose health problems for people living on beaches that have asthma.

2011: A turning point

Prior to 2011, most of the pelagic Sargassum in the ocean was mainly floating in patches around the Gulf of Mexico and the Sargasso Sea. The Sargasso Sea is located at the western end of the central Atlantic Ocean and is named after its popular algae resident. Christopher Columbus reported for the first time on Sargassum of this ocean of crystal-clear waters in the fifteenth century, and many sailors of the Sargasso Sea are familiar with these algae.

A recipe for a flowering of fatality and sadness

The team identified the key factors that are critical for the formation of flowering: a large population of seeds in the remaining winter of a previous flowering, the entry of nutrients from West Africa in winter, and the entry of nutrients in the spring or summer of the Amazon River. In addition, Sargassum only grows well when salinity is normal and surface temperatures are normal or lower.

By: Preeti Narula

Content: https://www.sciencedaily.com/releases/2019/07/190704191408.htm