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MEPS 601:77-95 (2018)  -  DOI: https://doi.org/10.3354/meps12685

Remarkable structural resistance of a nanoflagellate-dominated plankton community to iron fertilization during the Southern Ocean experiment LOHAFEX

Isabelle Schulz1,2,3, Marina Montresor4, Christine Klaas1, Philipp Assmy1,2,5, Sina Wolzenburg1, Mangesh Gauns6, Amit Sarkar6,7, Stefan Thiele8,9, Dieter Wolf-Gladrow1, Wajih Naqvi6, Victor Smetacek1,6,*

1Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, 27570 Bremerhaven, Germany
2MARUM - Center for Marine Environmental Sciences, University of Bremen, 28359 Bremen, Germany
3Biological and Environmental Science and Engineering Division, Red Sea Research Center, King Abdullah University of Science and Technology, 23955-6900 Thuwal, Kingdom of Saudi Arabia
4Stazione Zoologica Anton Dohrn, 80121 Naples, Italy
5Norwegian Polar Institute, Fram Centre, 9296 Tromsø, Norway
6CSIR National Institute of Oceanography, 403 004 Goa, India
7National Centre for Antarctic and Ocean Research, 403 804 Goa, India
8Max Planck Institute for Marine Microbiology, 28359 Bremen, Germany
9Institute for Inorganic and Analytical Chemistry, Friedrich Schiller University, 07743 Jena, Germany
*Corresponding author:

ABSTRACT: The genesis of phytoplankton blooms and the fate of their biomass in iron-limited, high-nutrient-low-chlorophyll regions can be studied under natural conditions with ocean iron fertilization (OIF) experiments. The Indo-German OIF experiment LOHAFEX was carried out over 40 d in late summer 2009 within the cold core of a mesoscale eddy in the productive south-west Atlantic sector of the Southern Ocean. Silicate concentrations were very low, and phytoplankton biomass was dominated by autotrophic nanoflagellates (ANF) in the size range 3-10 µm. As in all previous OIF experiments, the phytoplankton responded to iron fertilization by increasing the maximum quantum yield (Fv/Fm) and cellular chlorophyll levels. Within 3 wk, chlorophyll levels tripled and ANF biomass doubled. With the exception of some diatoms and dinoflagellates, the biomass levels of all other groups of the phyto- and protozooplankton (heterotrophic nanoflagellates, dinoflagellates and ciliates) remained remarkably stable throughout the experiment both inside and outside the fertilized patch. We attribute the unusually high biomass attained and maintained by ANF to the absence of their grazers, the salps, and to constraints on protozooplankton grazers by heavy predation exerted by the large copepod stock. The resistance to change of the ecosystem structure over 38 d after fertilization, indicated by homogeneity at regional and temporal scales, suggests that it was locked into a stable, mature state that had evolved in the course of the seasonal cycle. The LOHAFEX bloom provides a case study of a resistant/robust dynamic equilibrium between auto- and heterotrophic ecosystem components resulting in low vertical flux both inside and outside the patch despite high biomass levels.


KEY WORDS: Antarctic · Protists · Fe-limitation · Si-limitation · Ecology-biogeochemistry relationship · Carbon:chlorophyll ratios · Ecosystem stability


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Cite this article as: Schulz I, Montresor M, Klaas C, Assmy P and others (2018) Remarkable structural resistance of a nanoflagellate-dominated plankton community to iron fertilization during the Southern Ocean experiment LOHAFEX. Mar Ecol Prog Ser 601:77-95. https://doi.org/10.3354/meps12685

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