Award: OCE-1638958

Intellectual merit Marine phytoplankton, the microscopic photosynthetic microbes, are responsible for about half of photosynthetic oxygen production on Earth and form the base of most aquatic food webs. They are sensitive to climate change, rising temperatures in particular. Their ability to survive and adapt to warming is key to the aquatic ecosystem resilience to global climate change, but much remains unknown. In this project, the researchers determined the physiological, ecological and evolutionary responses of phytoplankton to rising temperature and changing nutrient levels. The research team found that phytoplankton can adapt evolutionarily to rising temperatures, increasing their optimum (Topt) and maximum (Tmax) temperatures for growth. There may also be a trade-off where high-temperature adapted populations grow less well under low temperatures. Researchers also found that nutrient limitation may preclude successful adaptation of phytoplankton to high temperature, consequently, a simultaneous increase in temperature and a decrease in nutrient concentration, predicted to occur in many parts of the ocean, may be more detrimental for phytoplankton than the effects of these two stressors separately. While adapting to high temperature, phytoplankton also change their carbon and nutrient content, cell size and shape, and the composition of fatty acids, which may have consequences for major biogeochemical cycles, food webs, and human nutrition. This research also found that temperate habitats where temperatures fluctuate seasonally have species with a greater range of optimum temperatures compared to the tropical habitats where temperatures are more constant. This diversity in temperature traits may help phytoplankton adapt to novel environmental conditions, including high temperatures. The results of this project increase the general understanding of how marine phytoplankton may respond to warming and help predict how ecosystems may change in the future. Broader Impacts The results of this project were disseminated through numerous scientific conferences, invited seminars and peer-reviewed publications. Three postdoctoral associates, two graduate students and several undergraduate students were trained on this project. They learned diverse experimental and field sampling techniques, data analysis, modeling and manuscript writing. Grad students and postdocs also received training in mentorship of undergraduate students. Two of the postdocs received tenure-track positions, one in the US and another one in Europe, and both graduate students are continuing their academic path as postdoctoral researchers. A middle school teacher from a rural district in MI received training in scientific methods and hands on research in aquatic ecology and climate change. Last Modified: 04/13/2021 Submitted by: Elena G Litchman