The potential use of behavioural bioassays as a first-tier approach for screening urban soil biodiversity: a pilot study

Soil health represents a key component of urban ecosystems and a priority for achieving the European Union’s climate neutrality and biodiversity restoration goals. Changes in edaphic diversity are the first indicators of soil health, but require long investigation times. Therefore, rapid, multi-level, and low-impact diagnostic tools are required. Behavioural bioassays, including avoidance and disaggregation tests, serve as rapid and ecologically relevant indicators for identifying soils subject to population decline. However, the metrics of in situ biodiversity loss and the laboratory-based ecotoxicological responses are not aligned. This pilot study investigates the potential use of the behavioural endpoints as screening indicators of biodiversity in invertebrate and bacterial communities in three urban soils. Multi-species bioassays were employed using model organisms with contrasting morpho-ecological traits, i.e. soft-body (earthworms) and hard-body (collembolans, and terrestrial isopods), to evaluate soil quality gradients. The behavioural results were then compared with ecological biodiversity data concerning the soil fauna and microbial communities. The behavioural responses of model organisms consistently aligned with reductions in invertebrate biodiversity, indicating habitat population decline. These changes, however, did not emerge from microbial analysis, suggesting that links between organismal responses and microbial diversity are yet to be investigated. The results support the use of behavioural bioassays, in combination with faunal diversity assessments, as an effective first-tier screening tool for urban soil health evaluation. This multi-level framework enhances the resolution and efficiency of soil quality monitoring and supports targeted management interventions in degraded urban environments, as well as in peri-urban, agricultural, and other human-impacted landscapes.