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Aquatic Microbial Ecology

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AME 84:105-120 (2020)  -  DOI:

Multivariate control of heterotrophic bacterial abundance and zooplankton grazing in Labrador fjords (northeastern Canada)

Armelle-Galine Simo-Matchim1,*, Michel Gosselin2, Claude Belzile2

1Research and Collections, Canadian Museum of Nature, PO Box 3443, Station D, Ottawa, Ontario K1P 6P4, Canada
2Institut des sciences de la mer de Rimouski, Université du Québec à Rimouski, 310 Allée des Ursulines, Rimouski, Québec G5L 3A1, Canada
*Corresponding author:

ABSTRACT: This study was conducted in 4 Labrador fjords (Nachvak, Saglek, Okak, and Anaktalak) during the summers of 2007 and 2013, early fall 2010, and late fall 2009. Our results show that water temperature combined with the availability of nutrients and organic substrates are the main abiotic factors controlling the abundance of heterotrophic bacteria in Labrador fjords. Bacterivory also played a crucial role, with heterotrophic bacteria exerting a significant bottom-up control on the abundance of heterotrophic nanoflagellates (r = 0.35, p < 0.05) and ciliates (r = 0.70, p < 0.01). During summer 2013, the intrinsic phytoplankton growth rate varied between <0 and 0.64 d-1, with a mean value of 0.36 d-1. The herbivory rate was highly variable, ranging from 0.01 to 0.86 d-1, with a mean value of 0.31 d-1. Grazing mortality was 6-fold higher than phytoplankton growth rate. Mean phytoplankton growth and herbivory rates in Labrador fjords were comparable to the Barents and Bering seas. The intrinsic growth rate of total heterotrophic bacteria ranged between <0 and 0.68 d-1, with a mean value of 0.30 d-1. Bacterivory varied from 0.01 to 0.95 d-1, with a mean of 0.30 d-1. Mortality due to grazing was up to 2.3 times higher than total bacterial growth rate. This study improves our understanding of the factors influencing the dynamics of heterotrophic bacteria and indicates that herbivory and bacterivory exert substantial control on microbial communities in Labrador fjords.

KEY WORDS: Heterotrophic bacteria · Phytoplankton · Zooplankton · Growth · Grazing · Arctic · Canada · Labrador fjords

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Cite this article as: Simo-Matchim AG, Gosselin M, Belzile C (2020) Multivariate control of heterotrophic bacterial abundance and zooplankton grazing in Labrador fjords (northeastern Canada). Aquat Microb Ecol 84:105-120.

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