A recent study by researchers at the University of South Florida reveals a troubling trend: seaweed blooms are expanding at an alarming rate across the world’s oceans. The research indicates a growing extent of these blooms. More specifically, they’ve increased by 13.4% per year on average over the past 20 years, most notably in the tropical Atlantic and western Pacific basin. This dramatic increase has many scientists worried about changing oceanic ecosystems and wider environmental effects.
Chuanmin Hu, USF professor of oceanography and co-director of the USF College of Marine Science’s Optical Oceanography Lab, is senior author of the paper. He noted that these rapid expansions of seaweed blooms were most visible after 2008. Back in 2008, the research team found key tipping points for three species of seaweed. Their work in different oceans extended through 2011 and 2012. Prior to 2008, large blooms of macroalgae such as this were pretty uncommon. The sole exception was sargassum in the Sargasso Sea.
The scientists used AI to rapidly and accurately sift through 1.2 million satellite images. These pictures, taken during the years 2003-2022, allowed them to recognize floating algal blooms. An artificial intelligence, or deep-learning model, helped researchers uncover the signals tied to these massive blooms. These results provide the most comprehensive picture of the distribution of algae across the world’s oceans to date. As far as marine research is concerned, this discovery is a historic breakthrough.
“What is noteworthy is that most increases in both floating macroalgae and microalgae scums occurred in the recent decade, in line with the accelerated global ocean warming since 2010,” stated the authors of the study. This observed relationship indicates that increased ocean temperature could potentially be a key driver of the positive trends in seaweed abundance we have been seeing.
Researchers pointed out that the rate of occurrence of blooms of microalgae, such as phytoplankton, is up only slightly—1% per year. Yet the recent explosion of macroalgae is most alarming of all. “On a global scale, we appear to be witnessing a regime shift from a macroalgae-poor ocean to a macroalgae-rich ocean,” said Hu. This shift would be nothing short of historic. It has the potential to affect radiative forcing in the atmosphere, alter light availability in the ocean, directly impact carbon sequestration, and indirectly affect overall ocean biogeochemistry.
Striking rings of blooms were recently seen off New Zealand’s remote Chatham Islands, as illustrated by a recent NASA capture. We thought we’d share this beautiful photo to illustrate how common this phenomenon is.
After analyzing the Kuroshio data, researchers said a regime shift in oceanographic conditions has already likely occurred. This change sets the stage for macroalgae to proliferate. This long-term shift cannot help but have profound implications for upper ocean stability and marine ecosystems.