Abstract Citizen science is increasingly used to document biodiversity in urban ecosystems while simultaneously promoting public engagement with nature. However, how institutional coordination relates to participation levels and the resulting representation of urban biodiversity remains poorly understood, particularly in European cities. The City Nature Challenge is a global annual bioblitz that engages citizens in recording urban biodiversity through the iNaturalist platform. Using the first City Nature Challenge edition in Turin (north-western Italy) as a case study, we examined how coordination by a natural history museum influenced participation and biodiversity data collection within an urban context, and compared participation patterns across eight City Nature Challenge editions in Italy. During the 2025 event in Turin, 123 observers collected 4,085 observations representing 1,086 taxa (940 identified at species level), including 377 species newly recorded for the area, corresponding to a 20.8% increase in reported urban biodiversity on iNaturalist. Records included 55 species of conservation concern (5.8%) as well as non-native species typical of urban ecosystems (21.4%), and the first iNaturalist record of Agathidium laevigatum for the platform. Across Italy, City Nature Challenge editions coordinated by museums consistently showed higher participation levels than non-coordinated initiatives. Our results suggest that museum coordination is substantially associated with participation intensity and the composition of biodiversity records generated through urban citizen science. By potentially shaping how urban biodiversity is sampled and documented, institutional actors may play a key role in determining the ecological picture of cities emerging from citizen science initiatives.
Costantino et al. (Mon,) studied this question.