Often overshadowed by their coinhabitants from the animal kingdom, sea plants are vital members of marine ecosystems. In particular, macroalgae—commonly known as seaweed—provide habitats for many sea animals, produce oxygen via photosynthesis, and even combat global climate change by sequestering greenhouse gases. But can too much of a good thing become a bad thing? A team of researchers from the University of South Florida have recently uncovered a disturbing trend related to macroalgae growth in the Atlantic Ocean.

In their study, the team used global satellite imaging data from NASA to track growth and distribution of Sargassum algae from 2000-2018.  The largest macroalgae bloom on record—dubbed the “great Atlantic Sargassum belt”—was observed in the summer of 2018, spanning from the west coast of Africa to the Gulf of Mexico and weighing approximately 20 million metric tons.  Interestingly, the extent of Sargassum distribution dramatically increased starting in 2011, with nearly every subsequent year marked by a large mass of macroalgae extending across the ocean.  Although they were not able to identify a definitive cause for this increase, the researchers observed a correlation with elevated deforestation and fertilizer use along the Amazon River since 2010.  These practices are known to contribute to Sargassum growth by allowing more macroalgae-promoting nutrients to flow directly into the ocean.

Although macroalgae are usually beneficial, overgrown Sargassum can smother certain marine species and emit unpleasant sulfide gases when washed up onshore.  Unfortunately, because leftover macroalgae remaining in Atlantic waters during winter act as seeds for the following year’s bloom, large, harmful masses of Sargassum may become the norm moving forward.  This phenomenon illustrates an important and often overlooked consequence of human activity on the global ecosystem.

For more information: To read more about how macroalgae normally function to combat global climate change, check out this SITN article!

Managing Correspondent: Benjamin Andreone

News Article: Largest Seaweed Bloom in the World Discovered. U.S. News & World Report

Original Article: The great Atlantic Sargassum belt. Science

Image Credit: University of South Florida

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