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

• Published in: Marine Ecology Progress Series
• Main Authors: Schulz, Isabelle Katharina, Montresor, M, Klaas, C, Assmy, P, Wolzenburg, S, Gauns, M, Sarkar, A, Thiele, S, Wolf-Gladrow, D, Naqvi, W, Smetacek, V
• Other Authors: Biological and Environmental Sciences and Engineering (BESE) Division, Red Sea Research Center (RSRC), MARUM - Center for Marine Environmental Sciences, University of Bremen, 28359 Bremen, Germany, Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, 27570 Bremerhaven, Germany, Stazione Zoologica Anton Dohrn, 80121 Naples, Italy, Norwegian Polar Institute, Fram Centre, 9296 Tromsø, Norway, CSIR National Institute of Oceanography, 403 004 Goa, India, National Centre for Antarctic and Ocean Research, 403 804 Goa, India, Institute for Inorganic and Analytical Chemistry, Friedrich Schiller University, 07743 Jena, Germany, Max Planck Institute for Marine Microbiology, 28359 Bremen, Germany
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Inter-Research Science Center 2018
• Subjects: Antarctic; Protists; Fe-limitation; Si-limitation; Ecology-biogeochemistry relationship; Carbon:chlorophyll ratios; Ecosystem stability; Antarc*; Southern Ocean
• Online Access: http://hdl.handle.net/10754/628463; https://doi.org/10.3354/meps12685

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. We are indebted to the captain and crew of RV ‘Polarstern’ and the scientific team of LOHAFEX. The Council of Scientific and Industrial Research (CSIR), India and the Helmholtz Foundation, Germany, equally shared the costs of the experiment. This work was funded through the DFG ...