Science Calls on Sailors with Secchi App

When a team of UK-based scientists learned that the population of the Earth’s marine phytoplankton had declined 40 percent since 1950, they set out to find the cause. Phytoplankton is the ocean’s primary producer, and a decrease in its population could mean trouble for oxygen production, food chain supply and climate regulation. 

 A citizen science project: the Secchi App

The scientists quickly realized there weren’t enough marine biologists to cover the whole ocean, so they created a citizen science project—the Secchi App—and asked sailors around the world to help collect research. 

With a homemade Secchi disk and a simple app, any sailor can become a scientist Here’s how it works: sailors measure Secchi Depth (the clarity of seawater) using a Secchi disk (any round piece of white plastic, such as a bucket lid, attached to a measuring tape). They lower the disk into the water and note the depth at which the disk is no longer visible from the surface. Then, they upload results to Secchi, a free app, which tracks data to a central database. Eventually, these results will help research if—and why—plankton populations are changing. To get involved, visit


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