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Density-dependent mortality in an oceanic copepod population

Nature volume 412, pages 638–641 (2001)Cite this article

Abstract

Planktonic copepods are primary consumers in the ocean and are perhaps the most numerous metazoans on earth. Secondary production by these zooplankton supports most food webs of the open sea, directly affecting pelagic fish populations and the biological pump of carbon into the deep ocean. Models of marine ecosystems are quite sensitive to the formulation of the term for zooplankton mortality1,2,3,4, although there are few data available to constrain mortality rates in such models. Here we present the first evidence for nonlinear, density-dependent mortality rates of open-ocean zooplankton. A high-frequency time series reveals that per capita mortality rates of eggs of Calanus finmarchicus Gunnerus are a function of the abundance of adult females and juveniles. The temporal dynamics of zooplankton populations can be influenced as much by time-dependent mortality rates as by variations in ‘bottom up’ forcing. The functional form and rates chosen for zooplankton mortality in ecosystem models can alter the balance of pelagic ecosystems1,2,3, modify elemental fluxes into the ocean's interior5, and modulate interannual variability in pelagic ecosystems6.

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Figure 1: Spring population growth of the copepod Calanus finmarchicus at ocean station M, in the Norwegian Sea (centred on 66° N, 2° E ).
Figure 2: Instantaneous rates of egg mortality (a) (me; d-1), birth (b) (b; d-1) and their difference (c) (b - me) at ocean station M, with estimated 95% confidence intervals (dotted lines).
Figure 3: Dependence of embryonic mortality rates on the abundance of Calanus finmarchicus adult females and juvenile stage C5 at ocean station M.

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Acknowledgements

We thank the late M. M. Mullin for his scientific insights, the captain and the crew as well as the scientists (X. Irigoien, U. Klenke, R. Head) on the vessel Polarfront for their support, and the Institute for Marine Research (Bergen, Norway), which provided logistical help. B. Niehoff provided egg-production rates, S. Jaklin and E. Mizdalski helped with analysing the samples and A. De Robertis generated bootstrap confidence intervals. This work was supported by funding from the European Commission through the TASC project and by the National Science Foundation and the National Oceanic and Atmospheric Administration through US GLOBEC (Global Ocean Ecosystem Dynamics).

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Author notes

  1. M. D. Ohman

    Present address: Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, 92093-0218, USA

Authors and Affiliations

  1. Station Zoologique, Villefranche-sur-Mer, 06230, France

    M. D. Ohman

  2. Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, D-27568, Germany

    H.-J. Hirche

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  1. M. D. Ohman
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  2. H.-J. Hirche
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Correspondence to M. D. Ohman.

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Ohman, M., Hirche, HJ. Density-dependent mortality in an oceanic copepod population. Nature 412, 638–641 (2001). https://doi.org/10.1038/35088068

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