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AME 87:167-183 (2021)  -  DOI: https://doi.org/10.3354/ame01977

Effects of nutrient enrichments on oligotrophic phytoplankton communities: a mesocosm experiment near Hawai‘i, USA

Daniela Böttjer-Wilson1,#, Angelicque E. White2,3,#,*, Karin M. Björkman2,3, Matthew J. Church4, Steve Poulos2,3, Eric Shimabukuro2,3, Yoshimi M. Rii5, Andrea Ludwig6, Klaus von Bröckel6, Ulf Riebesell6, Ricardo M. Letelier7, David M. Karl2,3

1Center for Teaching Excellence, University of Hawai‘i at Mānoa, Honolulu, Hawai‘i 96822, USA
2Department of Oceanography, School of Ocean and Earth Science and Technology, University of Hawai‘i at Mānoa, Honolulu, Hawai‘i 96822, USA
3Daniel K. Inouye Center for Microbial Oceanography: Research and Education, University of Hawai‘i at Mānoa, Honolulu, Hawai‘i 96822, USA
4Flathead Lake Biological Station, University of Montana, Polson, Montana 59860, USA
5Hawai‘i Institute of Marine Biology, University of Hawai‘i at Mānoa, Kaneohe, Hawai‘i 96744, USA
6GEOMAR Helmholtz Centre for Ocean Research Kiel, 24148 Kiel, Germany
7College of Earth, Ocean and Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97331, USA
#These authors contributed equally to this work
*Corresponding author:

ABSTRACT: A large-volume mesocosm-based nutrient perturbation experiment was conducted off the island of Hawai‘i, USA, to investigate the response of surface ocean phytoplankton communities to the addition of macronutrients, trace metals, and vitamins and to assess the feasibility of using mesocosms in the open ocean. Three free-drifting mesocosms (~60 m3) were deployed: one mesocosm served as a control (no nutrient amendments); a second (termed +P) was amended with nitrate (N), silicate (Si), phosphate (P), and a trace metal + vitamin mixture; and a third (termed -P) was amended with N, Si, and a trace metal + vitamin mixture but no P. These mesocosms were unreplicated due to logistical constraints and hence differences between treatments are qualitative. After 6 d, the largest response of the phytoplankton community was observed in the +P mesocosm, where chlorophyll a and 14C-based primary production were 2-3× greater than in the -P mesocosm and 4-6× greater than in the control. Comparison between mesocosm and ‘microcosm’ incubations (20 l) revealed differences in the magnitude and timing of production and marked differences in community structure with a reduced response of diatoms in microcosm treatments. Notably, we also observed pronounced declines in Prochlorococcus populations in all treatments, although these were greater in microcosms (up to 99%). Overall, this study confirmed the feasibility of deploying free-drifting mesocosms in the open ocean as a potentially powerful tool to investigate ecological impacts of nutrient perturbations and constitutes a valuable first step towards scaling plankton manipulation experiments.


KEY WORDS: Phytoplankton · Nutrient dynamics · Mesocosm · North Pacific Subtropical Gyre


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Cite this article as: Böttjer-Wilson D, White AE, Björkman KM, Church MJ and others (2021) Effects of nutrient enrichments on oligotrophic phytoplankton communities: a mesocosm experiment near Hawai‘i, USA. Aquat Microb Ecol 87:167-183. https://doi.org/10.3354/ame01977

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Published in AME Vol. 87. Online publication date: October 21, 2021
Print ISSN: 0948-3055; Online ISSN: 1616-1564
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