Norwegian Institute for Air Research
Netherlands Institute for Ecology
Tyndall Centre for Climate Change Research
Institute for Environmental Studies, Free University Amsterdam
University of Plymouth
Centre for Social and Economic Research on the Global Environment
Land-Ocean Interactions in the Coastal Zone
 


Nutrient Dynamics in European Water Systems

Case Study 3 - Alteration of coastal food webs by human activities

 
3.3 What you get
 
The capability of the BIOGEN model to simulate the Black Sea ecosystem functioning was demonstrated by running the model for the period 1985–1995. Reasonable agreement was observed between model predictions and data available for the central basin, both seasonally and in magnitude. As an example, vertical profiles of BIOGEN simulations and nutrients and chlorophyll a observations compared rather well for spring and summer periods (Figure 3.3(a)).
 
Figure 3.3(a). 1-D BIOGEN simulations in the open Black Sea water column. Observations recorded in (a) April 1997 and (b) July 1995. data (squares), model (line).
Figure 3.3(a). 1-D BIOGEN simulations in the open Black Sea water column. Observations recorded in (a) April 1997 and (b) July 1995. data (squares), model (line).
 

The BIOGEN model has further been used by Lancelot et al., (2002) to test the recent hypothesis of Gucu (2002) on the crucial role of overfishing rather than man-made eutrophication as being responsible for the successful development of gelatinous carnivores in the north-western Black Sea in the late 1980s–early 1990s.

The influence of the fisheries industry on the blooming of gelatinous carnivores was tested by running BIOGEN with the Danube nutrient loads of 1991 and changing the fishing coefficient. The latter was indirectly considered by modifying the mortality coefficient of copepods, where a lower value corresponds to a higher fish pressure.

Model simulations (Figure 3.3(b)) suggest, under conditions of well-balanced nutrient enrichment, a positive link between fishing pressure and gelatinous carnivores. A greater than two-fold increase of the biomass of both carnivorous gelatinous organisms is predicted for a doubling of fishing pressure.

 
Figure 3.3(b). Sensitivity of the 1991 BIOGEN predictions to fishing pressure obtained indirectly by changing copepod mortality to fish predation. (- - -), current 1991 prediction; (--), twofold decrease of copepod mortality by fish pressure (Lancelot et al., 2002) .
Figure 3.3(b). Sensitivity of the 1991 BIOGEN predictions to fishing pressure obtained indirectly by changing copepod mortality to fish predation. (- - -), current 1991 prediction; (--), twofold decrease of copepod mortality by fish pressure (Lancelot et al., 2002) .
Figure 3.3(b). Sensitivity of the 1991 BIOGEN predictions to fishing pressure obtained indirectly by changing copepod mortality to fish predation. (- - -), current 1991 prediction; (--), twofold decrease of copepod mortality by fish pressure (Lancelot et al., 2002) .
Figure 3.3(b). Sensitivity of the 1991 BIOGEN predictions to fishing pressure obtained indirectly by changing copepod mortality to fish predation. (– – –), current 1991 prediction; (——), twofold decrease of copepod mortality by fish pressure (Lancelot et al., 2002) .
 

This example clearly evidences the kinds of dramatic shifts that may result from man-made activity in a coastal ecosystems. Predictions on such features require the use of models that explicitly include the relevant ecological groups and processes.

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