In a "sneak peak" revealing a grim side effect of future warmer seas, new NASA satellite data find that the vital base of the ocean food web shrinks when the world's seas get hotter.
That discovery has scientists worried about how much food marine life will have as global warming progresses.
The data show a link between warmer water - either from the El Nino weather phenomenon or global warming - and reduced production of phytoplankton of the world's oceans, according to a study in the journal Nature.
Phytoplankton are the microscopic plant life that zooplankton and other marine animals eat, essentially the grain crop of the world's oceans.
Study lead author Michael Behrenfeld, a biological oceanographer at Oregon State University, said the recent dramatic drop in phytoplankton production in much of the world's oceans is a "sneak peak of how ocean biology" will respond later in the century with global warming.
"Everything else up the food web is going to be impacted," said oceanographer Scott Doney of the Woods Hole Oceanographic Institute. He was not involved in the study.
A satellite commissioned by NASA tracked water temperature and the production of phytoplankton from 1997 to 2006, finding that for most of the world's oceans when one went up the other went down and vice versa.
As water temperatures increased from 1999 to 2004, the crop of phytoplankton dropped significantly, about 200-million tons a year. On average about 50-billion tons of phytoplankton are produced yearly, Behrenfeld said.