Small marine organisms reacting to warmer oceans may dramatically affect the climate by the end of the 21st century, Michigan State University researchers say. Warmer oceans will cause populations of marine microorganisms called phytoplankton to thrive near the poles but shrink in equatorial waters, they said. Since phytoplankton play a vital role in the food chain and the world\'s cycles of carbon, nitrogen, phosphorous and other elements, a drastic drop in their numbers could have measurable consequences for Earth, an MSU release said Thursday. Phytoplankton also play a key role in regulating atmospheric carbon dioxide levels, and thus global climate, so the shift could cause significant change, the researchers said. \"If the oceans continue to warm as predicted, there will be a sharp decline in the diversity of phytoplankton in tropical waters and a poleward shift in species\' thermal niches, if they don\'t adapt to climate change,\" MSU graduate student Mridul Thomas said. Phytoplankton are small but they flourish in every ocean, consuming as much carbon dioxide through photosynthesis as all the terrestrial plants combined, the researchers said. David Garrison, program director in the National Science Foundation Division of Ocean Sciences, said the study addresses fundamental question of future impacts of a change in phytoplankton populations. \"This is an important contribution to predicting plankton productivity and community structure in the oceans of the future,\" he said. \"The work addresses how phytoplankton species are affected by a changing environment, and the really difficult question of whether evolutionary adaptation to those changes is possible.\"