Experts at the Alfred Wegener Institute have, for the first time, experimentally measured the release of iron from the fecal pellets of krill and salps under natural conditions and tested its bioavailability using a natural community of microalgae in the Southern Ocean. In comparison to the fecal pellets of krill, Antarctic phytoplankton can more easily take up the micronutrient iron from those produced by salps. Observations made over the past 20 years show that, as a result of climate change, Antarctic krill are increasingly being supplanted by salps in the Southern Ocean. In the future, salps could more effectively stimulate the fixation of the greenhouse gas carbon dioxide in Antarctic microalgae than krill, as the team of researchers report in the journal Current Biology.