Virioplankton dynamics and virally induced phytoplankton lysis versus microzooplankton grazing southeast of the Kerguelen (Southern Ocean)

• Published in: Deep Sea Research Part II: Topical Studies in Oceanography
• Main Authors: Brussaard, C. P. D., Timmermans, K. R., Uitz, J., Veldhuis, M. J. W.
• Other Authors: Royal Netherlands Institute for Sea Research (NIOZ), Institute for Biodiversity and Ecosystem Dynamics (IBED), University of Amsterdam Amsterdam (UvA), Laboratoire d'océanographie de Villefranche (LOV), Observatoire océanologique de Villefranche-sur-mer (OOVM), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2008
• Subjects: [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography; Austral; Kerguelen; Kerguelen Islands; Southern Ocean
• Online Access: https://hal.archives-ouvertes.fr/hal-03494362; https://doi.org/10.1016/j.dsr2.2007.12.034

Viral dynamics, community structure, and the impact of viruses on phytoplankton mortality in comparison with microzooplankton grazing were determined in the natural iron-fertilized waters southeast of the Kerguelen Islands, Southern Ocean, during the austral summer (January-February 2005). The study area was characterized by a phytoplankton bloom above the Kerguelen Plateau and the high-nutrient low-chlorophyll waters surrounding it. During the Kerguelen Ocean and Plateau compared Study (KEOPS), viral abundance was relatively high (1-19 x 10(7) mL(-1)) as compared to the few other studies in the Southern Ocean, significantly correlating with depth and system productivity. Viral abundance showed a strong positive relationship with the numerically dominant bacterial hosts, which in turn were correlated to phytoplankton biomass. In total, 13 different viral genome sizes were detected, with the lower-sized genomes 34 and 68 kb dominating at all stations. The viral community at the low chlorophyll C-transect grouped apart from the more productive transects A and B. Potential algal viruses were recorded for all stations, but only at very low intensities. Virally induced lysis of the smaller-sized (< 10 mu m) phytoplankton was a minor loss factor as compared to microzooplankton grazing (up to 6% and 45% of total < 30 mu m algal standing stock per day, respectively). Grazing was phytoplankton population-specific, but was in all cases able to keep the standing stock of the small-sized phytoplankton low (net growth rates between -0.2 and 0.2 d(-1)). Microzooplankton regenerated on average 1.1 pM Fed(-1) (present study), which represented approximately 30% of the total regeneration rate and at least 15% of the total biogenic Fe demand as calculated by [Sarthou, G., Vincent, D., Christaki, U., Obernosterer, L, Timmermans, K.R., Brussaard, C.P.D., 2008. The fate of biogenic iron during a phytoplankton bloom induced by natural fertilization: impact of copepod grazing. Deep-Sea Research II]. (C) 2008 Elsevier Ltd. All ...