Invasive ecosystem engineers and biotic indices: giving a wrong impression of water quality improvement?

by A. Zaijko (KUCORPI)

DSC_3903 Benthic component of an ecosystem is considered in ecological status assessment of the key European Directives. Most of the metrics proposed for the benthic quality assessment are biodiversity based. Their robustness and applicability are widely discussed in many recent studies. However an impact of invasive alien species on biotic indices and environmental quality assessments has been largely overlooked by researchers so far. In the current study we assessed Benthic Quality Index (BQI) in a coastal ecosystem, highly affected by invasive ecosystem engineer – the zebra mussel Dreissena polymorpha. The results of this study indicated that several important characteristics of the indicator (including its responsiveness, sensitiveness, predictability, accuracy) could be compromised due to the impact of IAS present in an ecosystem.
100_1969 Zebra mussel ability of modifying benthic habitats and forming local patches of elevated biological diversity may bias the results of benthic quality assessment. The calculated BQI values were significantly higher in the presence of zebra mussel with evident outliers in samples with particularly high zebra mussel abundances.Therefore we found that BQI determined in our study was artificially elevated providing false signal of the ecological status improvement. Based on the results presented, we suggested data correction framework that has been tested on the current dataset and proved to be effective minimizing zebra mussel impact on BQI assessment. Our experience could be applied for other coastal ecosystems invaded by the zebra mussel or any other aquatic invasive species with resembling biological traits and bioinvasion impacts.
If not considered in the course of the assessment, any species richness-based index may reflect IAS impact rather than anthropogenic pressure effect. Proper adjustments of ecological status assessment are desirable for the ecosystems strongly affected by IAS.

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Citation: Zaiko A., Daunys D. “Invasive ecosystem engineers and biotic indices: Giving a wrong impression of water quality improvement?.” Ecological Indicators 52 (2015): 292-299.