Mid-winter limnological surveys of Lake Erie captured extremes in ice extent ranging from expansive ice cover in 2010 and 2011 to nearly ice-free waters in 2012. Consistent with a warming climate, ice cover on the Great Lakes is in decline, thus the ice-free condition encountered may foreshadow the lakes future winter state. Here, we show that pronounced changes in annual ice cover are accompanied by equally important shifts in phytoplankton and bacterial community structure. Expansive ice cover supported phytoplankton blooms of filamentous diatoms. By comparison, ice free conditions promoted the growth of smaller sized cells that attained lower total biomass. We propose that isothermal mixing and elevated turbidity in the absence of ice cover resulted in light limitation of the phytoplankton during winter. Additional insights into microbial community dynamics were gleaned from short 16S rRNA tag (Itag) Illumina sequencing. UniFrac analysis of Itag sequences showed clear separation of microbial communities related to presence or absence of ice cover. Whereas the ecological implications of the changing bacterial community are unclear at this time, it is likely that the observed shift from a phytoplankton community dominated by filamentous diatoms to smaller cells will have far reaching ecosystem effects including food web disruptions.
Bibliographical noteFunding Information:
We thank the officers and crews of CCGS Griffon, USCGC Neah Bay and R/V Lake Guardian along with Technical Operations personnel from Environment Canada who ably assisted with the sampling program. The manuscript benefited from the insights of many colleagues, including R. Adrian, T. Glavina de Rio, K. R?hland, J. Saros, E. Silow, D. Straile and S. Wilhelm. This material is based upon work supported by the National Science Foundation under grant no. OCE-1230735 (RMLM, GSB). Additional support was provided by the Ohio Sea Grant College Program (grant R/ER-081 to RMLM and GSB), New York Sea Grant (grant R-CE-29 to MRT), the Lake Erie Protection Fund (grant 430-12 to RMLM) and the U.S. Environmental Protection Agency (grant GL-00E00790-2 to EDR). The work conducted by the US Department of Energy Joint Genome Institute was supported by the Office of Science of the US Department of Energy under Contract No. DE-AC02-05CH11231 and Community Sequencing Project 723 (RMLM, GSB, RAB).
© 2015 Society for Applied Microbiology and John Wiley & Sons Ltd.