Phytoplankton form the base of the food pyramid. Scientific American reports that these tiny organisms that cannot be seen without a microscope are declining in numbers according to a report published on July 29th in Nature.
"The tiny organisms, known as phytoplankton, also gobble up carbon dioxide to produce half the world's oxygen output—equaling that of trees and plants on land. But their numbers have dwindled since the dawn of the 20th century, with unknown consequences for ocean ecosystems and the planet's carbon cycle". Follow the link to read the full article.