Application 1:  Zooplankton growth and mortality rates during a spring bloom in a Norwegian fjord.

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Application 2:  Southern Ocean zooplankton growth and mortality rates in austral winter

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Zooplankton growth and mortality rates estimated from OPC measurements

Two echograms illustrate the vertical migration of euphausiids in aggregations from 2 am (upper) to 7 am (lower).  Their feeding on other zooplankton were estimated from OPC measurements

Link to: 

 

· GLOBEC OPC workshop website

 

· Download the report (Globec Report No.17)

Mathematical biomass spectrum theories

“A good deal of very nice mathematics has been developed describing population dynamics.  Unfortunately, for most organisms including zooplankton, the assumptions don’t fit well enough to make that mathematics useful without long lists of ad hoc adjustments.  For example, plankton animals in middle and high latitudes do not tend to unchanging (stable) age- or stage frequency distributions.  Thus, the classical calculations of population increase rates, which depend upon that stability … won’t work. …   Mortality is the most difficult.  Mortality rate variations are difficult to measure, so they become a row of free dials on the front of our models, one dial for each identified stage.  We simply turn them until the model output looks like our stage-abundance data. …”

— C. Miller (2004)

The developed biomass spectrum theories intend to integrate the mathematical models and in situ observations.

 

Basic theories (Zhou and Huntley 1997)

The propagation of biomass along the axis of individual body weight can be written as

                       

where t is the time, w is the body weight, g is the ensemble mean individual specific growth rate within the size class w, m is the ensemble mean population specific mortality rate within the size class w, and b(w, t) is the normalized biomass spectrum defined as the accumulative biomass within the size class interval (w-½Dw, w+½Dw) normalized by Dw. Here Dw represents an infinitesimal size class interval in the theory, or a finite size bin during sorting in field.

 

Applications

 

We can apply Equation (1) to study in situ individual growth and mortality rates.

 

Slope of a biomass spectrum (Zhou 2006)

The slope (¶ ln b/¶ ln w) of a biomass spectrum (b) is the inherent property of a community, which is determined by the community assimilation efficiency (h_n) and number of trophic levels (n), i.e.,

                       

                       

 

University of Massachusetts Boston

Department of Environment, Earth and Ocean Sciences