The citizen science web platform has expanded rapidly since its first foray in 2007, when it asked the public to classify images of galaxies and identify stars, disks and such like. By last year, Zooniverse had taken on cancer with Cell Slider, which was transformed into an app less than 12 months later.
As with all its projects, Plankton Portal is about using the human eye to determine things that an algorithm still cannot sufficiently well. In this case, it's the different species of plankton, their distribution and behaviour (things like, how deep they are meandering in the ocean -- since plankton captures CO2 from the atmosphere and redistributes it, its location is an important indicator of how the carbon cycle is faring).
Plankton are well-suited to this kind of project, considering they can range from just a few picometres in length to a few centimetres. Of these tiny creatures, Plankton Portal is focusing largely on zooplankton (animals) as opposed to their plant counterparts (phytoplankton) and bacterioplankton and virioplankton.