(Bloomberg) -- Algal blooms in coastal areas increased in size and frequency during the first two decades of this century as the world’s oceans warmed, according to an analysis of about 760,000 satellite images. 

Phytoplankton blooms are accumulations of microscopic algae that form characteristic fluorescent swirls on the surface of oceans, rivers and lakes that, when large enough, can be seen from space.

These algae are an essential nutrient for marine animals, from fish to whales, but the proliferation of blooms has become a major environmental problem worldwide as some out-of-control growth has produced toxic or harmful effects. 

Over 80% of the world’s coastal countries experienced algae blooms between 2003 and 2020, according to a paper led by Lian Feng, a researcher at the Southern University of Science and Technology in Shenzhen, China. The research, published on Wednesday in the journal Nature, found blooms had increased by 59.2% in frequency and 13.2% in size over the 17-year period.

These changes have a significant correlation with the warming of the oceans as a result of man-made climate change, the paper found. Oceans have a high capacity to capture heat and have absorbed almost 40% of the carbon dioxide that humans have emitted from burning fossil fuels since 1750.  

Scientists analyzed images from NASA’s Aqua satellite and found the largest bloom areas were along the coastal areas of Europe, representing one third of the total area impacted, and North America,  with 21.5% of the affected waters. Regions in the Southern Hemisphere, and especially Africa and South America, experienced more frequent blooms. 

While the analysis did not distinguish between safe and harmful blooms, toxins produced by some species of algae can lead to poisonous outbreaks that in the past have sickened or even killed animals and humans. In other cases, the decay of dense blooms has depleted oxygen in the waters below, forming so-called “dead zones” that can result in mass die-offs of fish. 

The research is the first attempt at setting up a system to detect and monitor algae blooms at a global scale, and at high resolution. It is also a step toward understanding how oceanic currents, the nutrients they carry and the animals that feed on them are shifting as waters warm.

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