Planktonic Responses to Simulated Warming and Elevated Iron Availability in McMurdo Sound: Community Composition and Microbial Interactions

Erin Marie Bertrand1, John McCrow2, Kai Xu3, Zhi Zhu3, David A Hutchins4, Rachel E Sipler5, Jenna Spackeen5, Deborah Ann Bronk6, Jeff McQuaid2 and Andrew E Allen7, (1)Dalhousie University, Halifax, NS, Canada, (2)J. Craig Venter Institute, La Jolla, CA, United States, (3)University of Southern California, Biology, Los Angeles, CA, United States, (4)University of Southern California, Marine and Environmental Biology, Los Angeles, CA, United States, (5)Virginia Institute of Marine Science, Gloucester Point, VA, United States, (6)College William & Mary/VIMS, Gloucester Point, VA, United States, (7)University of California, San Diego / J Craig Venter Institute, Scripps Institution of Oceanography, La Jolla, CA, United States
Abstract:
Western Antarctic shelf systems are home to high rates of primary productivity. The impact this production has on carbon cycling and higher trophic levels depends in part on rates of export as well as nutrient drawdown, both of which are influenced by phytoplankton community composition. Using bottle incubation bioassays from two field seasons in McMurdo Sound (Jan 2013, Jan 2015), we show that increases in temperature and iron availability had a profound influence on productivity and planktonic community composition. In 2013, chlorophyll increased over 10-fold upon a 4C increase in temperature over 10 days. In 2015, after one week, increases of 3 and 6 degrees C enhanced chlorophyll a production 3 and 4- fold respectively. Iron addition further enhanced chlorophyll production at all experimental temperatures. In both field seasons, initial eukaryotic communities were dinoflagellate, ciliate and Fragilariopsis- dominated, but increases in temperature enhanced the contribution of the pennate diatom Pseudo-nitzchia as assed via both microscopy-based cell counts as well as metatranscriptomic determination of active community composition. In addition to providing molecular insight into phytoplankton responses to elevated temperatures, metatransriptomic assessments also afforded a window into bacterial community composition and activity changes as a result of elevated temperature and changing micronutrient fields. Elevated temperature preferentially enhanced eukaryotic over bacterial contributions, as measured both by changes in cell abundance as well as mRNA attribution. These results support the notion that projected West Antarctic warming could lead to profound alterations in phytoplankton – bacterial interactions as well as key changes in overall community structure that could have implications for carbon cycling and trophic structures in the coastal Southern Ocean
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