How do diving beetle (Coleoptera: Dytiscidae) assemblages respond to water colour in urban ponds?

Urban land use changes can drive brownification by washing compounds such as dissolved organic matter and iron from terrestrial ecosystems into urban blue spaces. Such changes in the physicochemical properies of water can consequentially impact aquatic communities. Here, I present the results of how diving beetles, a family of aquatic insects, respond to water colour in 26 urban ponds in the Helsinki Metropolitan Area, Finland. My results showed that urbanisation did not have significant effects on water colour in urban ponds. Yet diving beetle assemblages in urban ponds were shaped by the colour of the pond water. Diving beetle assemblages responded to water colour differently in ponds with and without fish: in the presence of fish, diving beetle species richness and abundance exhibited significant positive correlations with increasing water colour, but in ponds without fish, the correlation was not significant. Although more species could be found in highly coloured water, some species, such as Hyphydrus ovatus and Hygrotus spp., tended to occur in clear water, indicating that some species are intolerant to brown water, despite the fact that brown water may provide dytiscids with prey refuges. This study emphasises the availability of heterogeneous habitats to meet the habitat requirements of aquatic invertebrates to support urban aquatic biodiversity.