The microscopic plants that form the foundation of the ocean’s food web are declining, reports a study published July 29 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.
Researchers at Canada’s Dalhousie University say the global population of phytoplankton has fallen about 40 percent since 1950. That translates to an annual drop of about 1 percent of the average plankton population between 1899 and 2008.
The scientists believe that rising sea surface temperatures are to blame.
“It’s very disturbing to think about the potential implications of a century-long decline of the base of the food chain,” said lead author Daniel Boyce, a marine ecologist.
They include disruption to the marine food web and effects on the world’s carbon cycle. In addition to consuming CO2, phytoplankton can influence how much heat is absorbed by the world’s oceans, and some species emit sulfate molecules that promote cloud formation.