Original Article

The ISME Journal (2015) 9, 990–1002; doi:10.1038/ismej.2014.197; published online 17 October 2014

Oceanographic structure drives the assembly processes of microbial eukaryotic communities
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Adam Monier1,2,3,5, Jérôme Comte1,3,4, Marcel Babin1,2, Alexandre Forest1,2, Atsushi Matsuoka1,2 and Connie Lovejoy1,2,3,4

  1. 1Takuvik Joint International Laboratory, Centre National de la Recherche Scientifique (France, CNRS UMI 3376), and Département de Biologie, Université Laval, Québec, QC, Canada
  2. 2Québec Océan, Université Laval, Québec, QC, Canada
  3. 3Institut de Biologie Intégrative et des Systèmes (IBIS), Université Laval, Québec, QC, Canada
  4. 4Centre d’Études Nordiques (CEN), Université Laval, Québec, QC, Canada

Correspondence: A Monier or C Lovejoy, Takuvik Joint International Laboratory, Centre National de la Recherche Scientifique (France, CNRS UMI 3376), Département de Biologie, Université Laval, Pavillon Charles-Eugene-Marchand, 1030, avenue de la médecine, Québec, QC, G1V 0A6 Canada. E-mail: a.monier@exeter.ac.uk or connie.lovejoy@bio.ulaval.ca

5Current address: Biosciences, College of Life and Environmental Sciences, University of Exeter, Exeter EX4 4QD, UK.

Received 10 June 2014; Revised 30 August 2014; Accepted 5 September 2014
Advance online publication 17 October 2014

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Abstract

Arctic Ocean microbial eukaryote phytoplankton form subsurface chlorophyll maximum (SCM), where much of the annual summer production occurs. This SCM is particularly persistent in the Western Arctic Ocean, which is strongly salinity stratified. The recent loss of multiyear sea ice and increased particulate-rich river discharge in the Arctic Ocean results in a greater volume of fresher water that may displace nutrient-rich saltier waters to deeper depths and decrease light penetration in areas affected by river discharge. Here, we surveyed microbial eukaryotic assemblages in the surface waters, and within and below the SCM. In most samples, we detected the pronounced SCM that usually occurs at the interface of the upper mixed layer and Pacific Summer Water (PSW). Poorly developed SCM was seen under two conditions, one above PSW and associated with a downwelling eddy, and the second in a region influenced by the Mackenzie River plume. Four phylogenetically distinct communities were identified: surface, pronounced SCM, weak SCM and a deeper community just below the SCM. Distance–decay relationships and phylogenetic structure suggested distinct ecological processes operating within these communities. In the pronounced SCM, picophytoplanktons were prevalent and community assembly was attributed to water mass history. In contrast, environmental filtering impacted the composition of the weak SCM communities, where heterotrophic Picozoa were more numerous. These results imply that displacement of Pacific waters to greater depth and increased terrigenous input may act as a control on SCM development and result in lower net summer primary production with a more heterotroph dominated eukaryotic microbial community.