Use of the abundance/biomass comparison method for detecting environmental stress: some considerations based on intertidal macrozoobenthos and bird communities

(I) The abundance/biomass comparison (ABC) method for detecting pollution effects was applied to data for macrozoobenthos taken from two intertidal areas: one virtually unpolluted (the Oosterschelde, Netherlands in 1981-84) and the other very polluted (the Westerschelde, Belgium in 1987). This method should be a sensitive indicator of natural physical and biological disturbance as well as of pollution-induced disturbance in both space and time. (2) Studies of macrozoobenthos from several study plots in the Oosterschelde indicated some environmental stress, related to a long tidal exposure time of the plot or to human disturbance (mussel fishing). Data from all other study plots showed an unstressed pattern. (3) Within one moderately stressed study plot in the Oosterschelde, density and biomass diversity remained fairly constant over about 4 years. (4) In the Westerschelde, the ABC method indicated an unstressed (unpolluted) situation in one and a moderately stressed (polluted) situation in two study plots. As there were few species (two to four), the method was not very reliable. (5) Applying the method to data for waders taken from the same study plots in the Oosterschelde revealed stress only in the plots with the shortest exposure time and the lowest available invertebrate biomass. This did not correspond with the patterns found for the macrozoobenthos. The amount of time available for feeding and the available biomass determine feeding conditions and are thus very important factors for waders. (6) An index is proposed for expressing the ABC method in values rather than in graphs. (7) It is argued that it is difficult to use this method in estuarine areas as an indicator of pollution because of the environmental stress typical for these areas. However. in general, it may be used to detect environmental stress