Blooming seaweed

July 2019: Analysis of the Great Atlantic Sargassum Belt establishes a direct relation between the blooming seaweed and higher nutrient levels in the ocean. The ocean’s chemistry changes following higher nutrient discharge from the Amazon river in response to increased deforestation and fertiliser use since 2010.

Summary

Analysis of the Great Atlantic Sargassum Belt establishes a direct relation between the blooming seaweed and higher nutrient levels in the ocean. The ocean’s chemistry changes following higher nutrient discharge from the Amazon river in response to increased deforestation and fertiliser use since 2010.

Information

Emerging reports observe a record breaking bloom of macroalgae called the Great Atlantic Sargassum Belt (GASB). The belt forms its shape with ocean currents, expanding from the west coast of Africa to the Gulf of Mexico. Numbers estimate that in 2018 alone the belt contained more than 20 million tonnes of biomass, indicating an exponential increase in seaweed since 2011. New evidence indicates that the seaweed is reacting to changing ocean chemistry that is more nutrient rich, establishing a direct connection with increased nutrient discharge from the Amazon river due to higher deforestation activities and fertiliser use that intensified in 2010. In small patches, the seaweed provides habitats for turtles, crabs and fish by means of producing oxygen via photosynthesis and in serving as habitat for marine animals.

Implications & Opportunities

The extensive bloom challenges marine species to move and breathe freely, especially in coastal areas. Species such as turtles reportedly struggle to swim through the belt and to safely reach their nesting grounds. When the seaweed dies, it sinks to the ocean floor smothering corals and seagrasses while on the beach it releases hydrogen sulphide gas (smelling like rotten eggs), severely impacting local tourism industries and local fisheries. Countries such as Barbados or Mexico have declared national emergencies and are struggling with time-consuming, expensive, and often inefficient attempts of collecting and removing the seaweed from coastal areas, thereby impacting the ecological health of their beaches.

Limitations

The study only uses limited field data and estimated environmental factors to model and project the complex growth patterns of the GASB; hence the results should only be seen as indicative.

Sources

Wang, M., Hu, C., Barnes, B. B., Mitchum, G., Lapointe, B., & Montoya, J. P. (2019). The great Atlantic Sargassum belt. Science, 365(6448), 83–87. doi:10.1126/science.aaw7912 

BBC. (2019). Sargassum: The biggest seaweed bloom in the world. Retrieved from https://www.bbc.co.uk/news/science-environment-48869100