Over the last 50 years, phytoplankton production has gone down by 40 percent as climate change has warmed the oceans that cover 70 percent of our planet. Responsible for half of all photosynthesis that occurs here on Earth, these tiny microorganisms sitting on the sunlit sea surface transform light into oxygen and nutrients, protecting our aquatic food web. Without them, the ocean would be a barren wilderness.
Source: How Citizen Science Is Saving Our Oceans | GOOD
Understanding a Secchi Disk and how to use one: Act Now
