Today’s Image of the Day from NASA Earth Observatory features a satellite view of a harmful algal bloom (HAB), or red tide event, along the shoreline of Rio de Janeiro, Brazil.

The clear waters along the coast appear to be dark red as a really of the unusually widespread phytoplankton event. 

According to a report from NASA, phytoplankton blooms are common this time of year in Rio de Janeiro, but (unlike this particular outbreak) they typically contain species that are beneficial to the ecosystem.

The red tide consumed more than 200 kilometers of the coastline and persisted for more than eight weeks.

Priscila Lange, an expert in the Department of Meteorology at the Federal University of Rio de Janeiro, said the red tide event is “very worrying” due to its potential impacts on the marine food web. She and her colleagues believe that weeks of cloudiness and rain triggered the event. 

“Once there was light, the red folks – dinoflagellates, Mesodinium rubrum, etc. – bloomed like crazy!” said Lange.

She explained that in early December, the red tide reached Arraial do Cabo and “darkened the waters of Rio’s most pristine scuba dive paradise.”

The false-color image was captured by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite on December 26, 2021. 

Image Credit: NASA Earth Observatory

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By Chrissy Sexton, Earth.com Staff Writer