Aquatic Sciences Meeting, Albuquerque 2001

CS37 Zooplankton

Date: Tuesday, February 13, 2001, Time: 10:30:00 AM

Location: Aztec

Hirche, H, J, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, GERMANY, hhirche@awi-brmerhaven.de

Ohman, M, D, Scripps Institution of Oceanography, La Jolla, CA, USA, mohman@ucsd.edu

NONLINEAR, DENSITY-DEPENDENT DYNAMICS OF AN OCEANIC COPEPOD POPULATION

Using inverse methods, we solved for instantaneous egg mortality rates of Calanus finmarchicus at ocean weather station M in the Norwegian Sea. Zooplankton sampling and several types of experimental work were carried out daily for 80 days as part of the TASC study in spring-early summer 1997. We used daily egg recruitment rates, development times, and detailed population stage structure information from this high-frequency time series to solve for time-dependent birth and egg death rates. Our estimation procedure is derived from a delay-differential equation, and corrects for N1 mortality explicitly in estimating egg mortality rates. Surprisingly, the onset of rapid population growth of C. finmarchicus in spring appears to be governed more by a decline in the death rate than by an increase in the birth rate. Egg mortality rates are strongly density-dependent, apparently governed by egg cannibalism. This density-dependent mortality introduces a nonlinear term into population dynamics equations, an effect about which there has been much speculation but virtually no evidence for open ocean zooplankton.

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Aquatic Sciences Meeting, Albuquerque 2001

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