Global floating algae blooms are expanding

Area of Science:

• Marine biology
• Oceanography
• Remote sensing

Background:

• Algal blooms, including microscopic algae (phytoplankton) and larger macroalgae, have increased in various ocean regions over the past two decades.
• A comprehensive global assessment of these algal increases has been lacking.

Purpose of the Study:

• To quantify the global distribution and trends of macroalgal mats and microalgal scums using satellite imagery.
• To analyze changes in algal bloom areas from 2003 to 2022.

Main Methods:

• Analysis of 1.2 million satellite images using artificial intelligence (AI).
• Quantification of macroalgal mats and microalgal scums across global oceans.
• Statistical analysis of expansion rates over a 20-year period.

Main Results:

• Macroalgae blooms covered a cumulative area of 43.8 million km².
• Significant expansion rates observed: macroalgae at 13.4% per year (since 2003) in the tropical Atlantic and western Pacific, and microalgae at 1.0% per year (since 2003).
• Expansion rates for macroalgae accelerated significantly since the 2010s.

Conclusions:

• Ocean warming and eutrophication are probable drivers of observed algal bloom trends.
• A potential regime shift favoring macroalgae and specific microalgae species is suggested.
• Findings have significant implications for ocean ecology, carbon sequestration, and marine economies.