Stream habitat or water quality - what influences stronger fish and macrozoobenthos biodiversity?

The data obtained within the framework of a survey of macrozoobenthos and fish communities in Czech streams of the Danube and Elbe river basins were evaluated with respect to the relation between biodiversity and level of water (organic pollution) and/or physical habitat quality (heterogeneity, substrate, riparian vegetation, canalisation). The diversity of macrozoobenthos species was the highest at the water quality corresponding to betamesosaprobity (saprobiological index SI ≈ 2,0) and oligosaprobity (SI ≈ 1,0) in lowland and highland streams respectively, declining both towards lower and higher saprobic (≈ trophic) levels. The response of macrozoobenthos to habitat quality deterioration was less considerable with rising degradation in highland streams than in lowland ones. Fish assemblage followed a similar trend, namely: the highest biodiversity in betamezosaprobity in both lowland and highland streams. In comparison with the assemblage of benthic macroinvertebrates, fish community response was more pronounced both regarding water quality and habitat degradation. Both fish and macrozoobenthos biodiversity were influenced more by water quality than by physical habitat degradation.