The marine phytoplankton—also called microalgae—account for about half of all photosynthesis on Earth and, through the plankton food web that they support, they both underpin the marine food chain and play a central role in the global carbon cycle strongly influencing the Earth’s climate.

Living at the surface of the sea the phytoplankton are particularly sensitive to changes in sea surface temperature. A recent study of global phytoplankton abundance over the last century concluded that global phytoplankton concentrations have declined due to rising sea surface temperatures as a consequence of current climate change.

Researchers at Plymouth University's Marine Institute in the U.K. need to know much more about these changes. That’s why they’ve created the Secchi citizen science app and are asking for citizen scientists for help. Citizen scientists can lend a hand by making a simple piece of scientific equipment called a Secchi Disk and using the Secchi App, available for both Apple iOS and Google Android devices.