The ratio of carbon isotopes in three common species of tuna has changed substantially since 2000, suggesting major shifts are taking place in phytoplankton populations that form the base of the ocean's food web, a new international study finds.

“The change we observed in tuna, which are near the top of the marine food web, reflects profound changes in physiology or species composition occurring at the bottom of the food web,” said Nicolas Cassar, professor of biogeochemistry at Duke University’s Nicholas School of the Environment. Read more.