Grazing of large-sized bacteria by sea-ice heterotrophic protists on the Mackenzie Shelf during the winter–spring transition

Abstract

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 50:25-38 (2007) - DOI: https://doi.org/10.3354/ame01155 Grazing of large-sized bacteria by sea-ice heterotrophic protists on the Mackenzie Shelf during the winter–spring transition Andrea Riedel1,2,*, Christine Michel2, Michel Gosselin1 1Institut des sciences de la mer (ISMER), Université du Québec à Rimouski, 310 allée des Ursulines, Rimouski, Québec G5L 3A1, Canada 2Fisheries and Oceans Canada, Freshwater Institute, 501 University Crescent, Winnipeg, Manitoba R3T 2N6, Canada *Email: andrea.niemi@dfo-mpo.gc.ca ABSTRACT: Heterotrophic bacterial dynamics were assessed in the sea ice and surface waters on the Mackenzie Shelf (Beaufort Sea), from 5 March to 3 May 2004. On 11 occasions, heterotrophic protist bacterivory was assessed from the disappearance of fluorescently labeled bacteria (FLB) in sea-ice samples collected from areas of high and low snow cover. Concurrently, sea-ice and surface water samples were analyzed for dissolved organic carbon (DOC), exopolymeric substances (EPS) and chlorophyll a concentrations, and protist and bacterial abundances. Total bacterial abundances were significantly higher in the sea ice than in surface waters. However, DOC concentrations and abundances of large (≥0.7 µm) bacteria were not significantly higher in the sea ice as compared to surface waters. This suggests that DOC was being released from the sea ice, potentially supporting the growth of large-sized bacteria at the ice–water interface. Heterotrophic protist (HP) bacterivory averaged 57% d–1 of large-sized bacterial abundances in the sea ice with ingestion rates averaging 768 and 441 bacteria HP–1 d–1, under high and low snow cover, respectively. High concentrations of EPS during the sea-ice algal bloom may have interfered with the grazing activities of heterotrophic protists as indicated by the significant negative correlations between ingestion rates and EPS-carbon concentrations under high (τ = –0.57, p < 0.05) and low (τ = –0.56, p < 0.05) snow cover. Bacterivory satisfied heterotrophic protist carbon requirements prior to, but not during, the sea-ice algal bloom, under high and low snow cover. EPS may have been an additional carbon source for the heterotrophs, especially during the sea-ice algal bloom period. This study provides evidence of an active heterotrophic microbial food web in first-year sea ice, prior to and during the sea-ice algal bloom. This study also highlights the significance of DOC and EPS as integral components of the microbial food web within the sea ice and surface waters of Arctic shelves. KEY WORDS: Bacteria · FLB · Grazing · DOC · EPS · Sea ice · Arctic Full text in pdf format PreviousNextCite this article as: Riedel A, Michel C, Gosselin M (2007) Grazing of large-sized bacteria by sea-ice heterotrophic protists on the Mackenzie Shelf during the winter–spring transition. Aquat Microb Ecol 50:25-38. https://doi.org/10.3354/ame01155 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 50, No. 1. Online publication date: December 12, 2007 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2007 Inter-Research.