SYDNEY, Australia — Every day for a week, So Kawaguchi peered intently into the jars of cold water holding harvested krill eggs. None were hatching. In his laboratory in Hobart, Tasmania, on the edge of the Southern Ocean, he could see that the carbon dioxide he had pumped into the icy seawater had killed the eggs.

“We thought the krill might be more robust,” said Dr. Kawaguchi, a biologist who works for the Australian government’s Antarctic Division. “We were not expecting such a clear result.”

Those key moments in his laboratory more than seven years ago were pivotal in the career of Dr. Kawaguchi, who has been studying krill for 25 years. His recent research has led to dire predictions about how global carbon emissions will significantly reduce the hatch rates of Antarctic krill over the next 100 years.

Krill, typically about the size of a pinkie and similar in appearance to shrimp, are one of the most abundant animal species on earth, and a cornerstone of the Antarctic ecosystem. They form schools that can be miles long and miles deep, with thousands of crustaceans packed into each cubic foot.