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Ecosystem Modelling

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Ecosystem Modelling Animation

 Highlights

A. Ecosystem changes on the Scotian Shelf: bottom-up or top-down?

Alain F. Vézina and Benoit Casault
Bedford Institute of Oceanography, Dartmouth, N.S., Canada.

This poster represents highlights from two papers: Casault et al 2003. Can. Data Rep. Hydrogr. Oc. Sci. 164. and DFO Ecosystem Status Report 2003/004. [Available from the CSAS]

Decadal Changes on the Scotian Shelf:
Satelite view of the Scotian Shelf
Bottom-Up:

Ocean climate affecting primary production and then the whole ecosystem.


Click on the image above for a larger view.

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Top-down:

Changes at the top of the food web: (e.g. fishing) cascade down through the whole ecosystem

Groundfish
Lower groundfish

Pelagics
Higher pelagics

Zooplankton
Lower zooplankton

Phytoplankton
Higher phytoplankton

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Can ecosystem modelling help us understand the respective roles of these forces?

Input: ocean climateClimate

Input: mortality to higher predators

Predators

Model: plankton ecosystem

Ecosystem

Output: Simulations that can be compared to observations Simulations vs observations

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Simulations for 3 areas of the Scotian shelf:
Simulations in 3 areas of the Scotia Shelf
Mixed layer depth (climate)Western Scotian Shelf mixed layerCentral Scotian Shelf mixed layerEastern Scotian Shelf mixed layer

Mixed layer shallower during the 90s

Nutrients (bottom-up control)Western Scotian Shelf NutrientsCentral Scotian Shelf NutrientsEastern Scotian Shelf Nutrients

Nutrients decreasing in the 90s

Phytoplankton (primary production)Western Scotian Shelf Primary ProductionCentral Scotian Shelf Primary ProductionEastern Scotian Shelf Primary Production

Phytoplankton staying the same or increasing slightly.
Earlier blooms on the Eastern and Western Shelves.

Zooplankton (secondary production)Western Scotian Shelf Secondary ProductionCentral Scotian Shelf Secondary ProductionEastern Scotian Shelf Secondary Production

Zooplankton decreasing during the 90s.

The scorecard:

How well is the model doing?

  Chl NO3 Zooplankton Timing Bloom
Eastern Shelf ++
~
++		 --
 
--		 --
 
--		 ++
~
++
Central Shelf ++
++		 --
--		 -- ~
 
~
Western Shelf ++
~		 -
-		 - +
~

Symbols marked in red are obs bottle. Others are obs CPR.

 

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Trends:

Trends in the data can be largely explained by bottom-up effects:

  • Stronger stratification leads to lower production, decreased zooplankton and earlier spring blooms. Overall the effect on phytoplankton biomass is slight to positive.
  • Zooplankton is more sensitive to ocean climate than phytoplankton biomass, complicating the interpretation of ocean color for changes in ocean productivity.
  • Top down effects help improve the match between and observations for seasonal patterns, e.g. increase summer phytoplankton.
  • Simulations point to regional differences in the ecosystem response to changes in ocean climate: Measurements on one part of the Scotian shelf may not necessarily be extrapolated to another.
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B. Simulations of plankton dynamics: the APDM model

Alain F. Vézina, Markus Pahlow, Benoit Casault and Heidi Maass
Bedford Institute of Oceanography, Dartmouth, N.S., Canada.

Big model:
Model testing and refinement:
Models/data intercomparison:
Optimization - cost function:
Small model:
AZMP Station 2 interannual variability:
AZMP Station 2 Integrated Chl:
   
 
  Last Updated : 2007-02-07 Important Notices