Microbial response to different phytoplankton-derived dissolved organic matter sources in the Ross Sea, Antarctica

Rachel E Sipler1, Jenna Spackeen2, Jeff McQuaid3, Erin Marie Bertrand4, Quinn N Roberts2, Steven Baer5, David A Hutchins6, Andrew E Allen7 and Deborah Ann Bronk8, (1)Virginia Institute of Marine Science, Gloucester Point, VA, United States, (2)Virginia Institute of Marine Science, College of William & Mary, Gloucester Point, VA, United States, (3)J. Craig Venter Institute, La Jolla, CA, United States, (4)Dalhousie University, Halifax, NS, Canada, (5)Bigelow Lab for Ocean Sciences, East Boothbay, ME, United States, (6)University of Southern California, Marine and Environmental Biology, Los Angeles, CA, United States, (7)University of California, San Diego / J Craig Venter Institute, Scripps Institution of Oceanography, La Jolla, CA, United States, (8)College William & Mary/VIMS, Gloucester Point, VA, United States
Abstract:
Western Antarctic shelves are highly productive regions that play an important role in global carbon and nitrogen cycles, specifically serving as a critical sink for carbon dioxide. Fixed carbon is stored within the phytoplankton cell as particulate organic matter or released into the surrounding water as dissolved organic matter (DOM). These phytoplankton-derived sources of organic matter support higher trophic levels as well as heterotrophic bacterial growth and respiration. The composition of the phytoplankton-derived organic matter is a function of the taxa as well as the environmental conditions under which it is produced. Phytoplankton community composition within western Antarctic Seas changes throughout Austral spring and summer with early production dominated by ice algae, switching to pelagic diatoms and flagellates later in the season. The goal of this study was to compare the response of Ross Sea microbial communities to DOM produced by ice algae or late season diatoms, specifically recent isolates of Pseudo nitzschia obtained from the Ross Sea. During 5-day bioassay studies, exudates from a natural ice algal community and from Pseudo nitzschia sp. isolates were added to natural microbial communities collected from two different Ross Sea locations, an ice-edge and an ice-covered site. The bacterial response to the DOM additions was greatest in the ice-covered community with a 5 and 3-fold higher bacterial abundance in the ice algae DOM and Pseudo nitzschia DOM treatments, respectively, relative to the control. The ice edge bacterial community responded similarly to both sources with a ~2-fold increase in bacterial abundance compared to the control. Unlike the bacterial response, there was little difference in chlorophyll a concentrations between treatments, indicating that phytoplankton growth was not stimulated or inhibited by our additions.