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Hypothesis and Theory ARTICLE Provisionally accepted The full-text will be published soon. Notify me

Front. Mar. Sci. | doi: 10.3389/fmars.2019.00509

Growth limitation of marine fish by low iron availability in the open ocean

  • 1Catalan Institute for Research and Advance Studies (ICREA), Spain
  • 2Institut de Ciència i Tecnologia Ambientals (ICTA), Spain
  • 3UCLA Atmospheric and Oceanic Sciences, United States
  • 4Global Fishing Watch, United States

It is well-established that phytoplankton growth can be limited by the vanishingly low concentrations of dissolved iron found in large areas of the open ocean. However, the availability of iron is not typically considered an important factor in the ecology of marine animals, including fish. Here we compile observations to show that the iron contents of lower trophic level organisms in iron-limited regions can be an order of magnitude less than the iron contents of most fish. Although this shortfall could theoretically be overcome if iron assimilation rates were very high in fish, observations suggest this is not the case, consistent with the high recommended iron contents for mariculture feed. In addition, we highlight two occurrences among fish living in iron-poor regions that would conceivably be beneficial given iron scarcity: the absence of hemoglobin in Antarctic icefish, and the anadromous life history of salmon. Based on these multiple lines of evidence, we suggest that the iron content of lower trophic level organisms can be insufficient to support many fish species throughout their life cycles in iron-poor oceanic regions. We then use a global satellite-based estimate of fishing effort to show that relatively little fishing activity occurs in High Nitrate Low Chlorophyll (HNLC) regions, the most readily-identified iron-poor domains of the ocean, particularly when compared to satellite-based estimates of primary production and the observed mesozooplankton biomass in those waters. The low fishing effort is consistent with a low abundance of epipelagic fish in iron-limited regions, though other factors are likely to contribute as well. Our results imply that the importance of iron nutrition extends well beyond plankton and plays a role in the ecology of large marine animals.

Keywords: Iron limitation, fish, Fishing, global fishing watch, marine ecology, HNLC region, trophic transfer, Ecosystem stoichiometry, Trace metal

Received: 27 Nov 2018; Accepted: 05 Aug 2019.

Edited by:

Carol Robinson, University of East Anglia, United Kingdom

Reviewed by:

Rod W. Wilson, University of Exeter, United Kingdom
Peter Croot, National University of Ireland Galway, Ireland
Julian Blasco, Spanish National Research Council (CSIC), Spain  

Copyright: © 2019 Galbraith, Le Mezo, Bianchi and Kroodsma. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Prof. Eric D. Galbraith, Catalan Institute for Research and Advance Studies (ICREA), Barcelona, Spain, eric.d.galbraith@gmail.com