The relationship between alien crustaceans and pollution in Croatian large rivers: implications for biological monitoring.

Peracarid crustaceans contribute to the homogenization of macroinvertebrate communities as one of the most important group of aquatic invaders. This study investigated the relationship between alien peracarids and physical and chemical parameters indicative of nutrient and organic pollution, and their contribution to biocontamination of macroinvertebrate assemblages. The impact of alien macroinvertebrates, particularly alien peracarids, on selected biological metrics was examined. Sampling was conducted twice (2015 and 2016/2017) at 46 sites on four major rivers (Danube, Sava, Drava, Mura), accompanied with eight measurements of physical and chemical parameters. Invasive peracarids showed predominantly negative correlations with nutrient pollution, the strongest negative correlations with ammonia, nitrites and orthophosphates. Biocontamination of macroinvertebrate assemblages, calculated as family-level Site-specific Biocontamination Index, was mostly high and severe, whilst the abundance of alien Peracarida mainly determined the biocontamination class. Sites with higher densities of alien Peracarida had lower organic and nutrient pollution and higher biological metrics than sites with lower densities. Biological metrics showed a positive correlation with alien Peracarida densities, whilst their exclusion or exclusion of all alien macroinvertebrates species affected biological metric values. Invasive peracarids can be used as indicators of nutrient and organic pollution and should be included in the calculation of biological metrics for assessing ecological status. [ABSTRACT FROM AUTHOR]