Most organisms meet their carbon and energy needs solely on photosynthesis (phototrophy) or solely on ingestion/assimilation of organic substances (heterotrophy). However, there is increasing recognition that mixotrophs, which combine phototrophy and heterotrophy in a single organism, are important components of planktonic food webs. Based on prior work, the investigators have confirmed the ubiquitous nature of mixotrophs in Arctic and Antarctic waters and hypothesize that a possible consequence to the warming of Arctic surface waters is that pico- and nano-mixotrophs will become more abundant in the region. Using water samples from across the Arctic, the investigators will conduct laboratory experiments to better understand the environmental conditions that trigger mixotrophic activity. Such experiments will also provide information on how the microbial food web will function in a warming climate and how such changes will potentially affect higher trophic levels, such as fish. This work will provide a possibly transformative re-orienting of our current view of surface water food webs structure and dynamics and nutrient flows in a changing Arctic. The project will train a post doctoral scientist, graduate, and undergraduate student. In addition, the project includes outreach to local schools in urban Philadelphia, and collaboration with a Falmouth, MA. high school art teacher as part of novel art-science projects (STEAM).
As Arctic water temperatures warm, the investigators predict a two-fold effect on the marine food web. First, they predict an increased contribution to primary production from pico- and nano-phytoplankton. Second, they predict an impact on bacterial consumption owing to the fact that many of the pico- and nano-phytoplankton species exhibit mixotrophic behavior. The investigators propose a number of laboratory experiments on strains of algal groups that have been identified as mixotrophic species and are found in Arctic waters. Arctic marine isolates will be acquired from the Roscoff Culture Collection and the National Center of Marine Algae. Species specific mixotrophic activity and grazing rates will be determined across a range of environmental conditions that trigger and/or stimulate mixotrophy, such as high/low light and high/low nutrients. From these species specific measurements, along with qPCR analysis to determine species abundances in water samples from across the Arctic marine environment, the potential impact of mixotrophic activity can be assessed on an Arctic-wide basis. Finally, to determine and compare the levels of mixotrophic activity in environmental samples without relying on ingestion experiments the investigators will develop a gene-based method of activity based upon RNA sequencing and the results of the environmental response experiments discussed above. This will be important for prediction in a warmer world.
