Contribution by Bundesanstalt für Gewässerkunde (BfG), Koblenz 
- Federal Institute of Hydrology - 
Biological long-term study (sublittoral macrozoobenthos) of the German North Sea 
estuaries 
Objectives 
The BfG contribution to GOOS is aimed at the description and assessment of the current 
status of macrozoobenthos in the sublittoral area of the German North Sea estuaries (rivers 
Ems, Jade, Weser, Elbe, Eider), the description and assessment of temporal stock 
developments, and an improved description and assessment of the potential impacts of 
dredging and disposal measures on the macrozoobenthos. 
Present scientific knowledge 
River estuaries with their individual sizes, lengths, and characteristics, are habitats with a large 
variety of biotopes. They constitute connecting links and transitions between marine and 
limnetic habitats. 
High nutrient levels and water currents account for a high biological turnover, but suspended 
and colloidal particles may also impair light conditions, thus affecting plant growth, and may 
even clog the delicate gills of some animals. Fluctuating salinities due to tides and freshwater 
runoff are making high physiological demands on organisms and may exceed the freshwater 
tolerance of some marine species. Only genuine brackish-water species have developed 
specializations for this habitat. These biota have been subjected to intensive exploitation and 
modification by man, fundamentally changing the characteristics of ecosystems, causing the 
extinction of species, reduction of population densities and biocoenosis effects. Because of 
these changes, the brackish-water zones of rivers are considered to be ecologically very 
vulnerable habitats. Lasting impacts have been the result of dyking, which was begun over 
1000 years ago, morphological changes to riverbeds to facilitate shipping, and the 
deterioration of water quality due to inputs from various sources. 
After the conclusion of international treaties, instructions for the management of dredged 
materials in coastal areas (HABAK-WSV) were developed for the area of responsibility of the 
Federal Waterways and Shipping Administration. It is the purpose of these instructions to 
gather information allowing an assessment of the potential ecological effects of dredged 
materials. Natural sediment transports in the coastal zone due to tidal influences lead to 
considerable sediment deposition in the navigation channels of the main ports. The routine 
maintenance of these channels includes dredging to guarantee their navigable depth. About 30 
-50 million cubic meters of material are dredged annually from the navigable waterways of 
the German North Sea. To assess potential effects it is necessary to have a profound 
knowledge of the abundance of sublittoral macrozoobenthos in the area. The main questions 
arising are: How stable is the inventory of species (introduction or loss of species), and where 
are the distribution limits of certain species, e.g. of Red-List endangered species like the 
crustacean Corophium lacustre, the sponge Halichondria panicea, the ragworm Sabellaria 
spinulosa, or the amphipod Gammarus salinus, a brackish-water species? The problem lies 
mainly in the spatial heterogeneity and temporal variability of the sublittoral benthic 
communities. 
Monitoring of macrozoobenthos stocks in the estuaries focuses primarily on the identification 
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