Ocean algae blooms alarm scientists, threatening tourism

Floating algae are rapidly expanding across the world's oceans, a trend that concerns scientists and could negatively impact marine ecosystems, fisheries, and tourism. An analysis of 1.2 million satellite images from 2003 to 2022, aided by artificial intelligence, revealed a significant global increase in these algae.

While microscopic algae are vital for oxygen and carbon cycles, the study focused on macroalgae, which are visible to the naked eye. Although these larger algae also play important roles in healthy ecosystems, excessive amounts in coastal waters and on beaches can be detrimental. The research, published in Nature Communications, provides the first global assessment of floating algae, highlighting a "substantial increase" that suggests conditions are becoming more favorable for widespread algal blooms.

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Published regional studies have already existed, but our work provides the first global picture.

Globally, floating microalgae grew by about 1% annually between 2003 and 2022. However, some regions experienced much faster expansion, with the tropical Atlantic and western Pacific seeing an increase of 13.4% per year. Scientists observed large patches of seaweed appearing in areas where they were previously absent starting in 2008.

"On a global scale, we seem to be witnessing a transition from macroalgae-poor oceans to macroalgae-rich ones," said Chuanmin Hu, a professor of oceanography at the University of South Florida. He noted that the spread of floating algae is likely due to a combination of factors, varying by region, including warming ocean temperatures. The consequences can be severe, as seen in increased mortality of marine mammals like sea lions due to toxins transmitted through the food chain during harmful algal blooms.

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On a global scale, we seem to be witnessing a transition from macroalgae-poor oceans to macroalgae-rich ones.