Abstract
Blue infrastructure is an important component of urban green infrastructure, due to its capacity for water cycle regulation and soil formation, as well as supporting unique biodiversity. Urban ponds, as part of urban blue, can harbour a diverse assemblage of aquatic macroinvertebrates. As yet, it is not clear how urbanisation affects macroinvertebrate diversity. In this study, we focus on diving beetles (Dytiscidae) in the Helsinki Metropolitan Area, Finland, to investigate how urbanisation affects their diversity, as well as the effects of margin steepness and the presence or absence of fish on urban dytiscids. We sampled dytiscids using 1-L activity traps in 14 fishless ponds and 11 ponds with fish, at ten sites. We applied generalised linear mixed models (GLMM) and non-metric multidimensional scaling (NMDS) to analyse the effects on dytiscid assemblages. We found that urbanisation had a negative effect on species richness but not on abundance. Steepness of pond margins and the presence or absence of predatory fish, affected both species richness and abundance: dytiscids prefer ponds with gently sloping margins; they have 80% higher species richness and are 79% more abundant in fishless ponds, and medium to large-sized dytiscid species are more capable of coexisting with fish. Urban wetlands can support a diversity of dytiscids at the regional level, and the presence of ponds without predatory fish is beneficial for maintaining dytiscid diversity. We recommend maintaining a diverse range of ponds and wetland habitats for the maintenance of aquatic biodiversity in urban regions.
Highlights
Interest in green infrastructure—networks of vegetated land surfaces—has increased with growing awareness of the broad range of benefits they provide for residents of urban regions, as perceived through the concepts of Ecosystem Services (Nesshover et al 2017) and Nature-Based Solutions (Eggermont et al 2015; Tzoulas et al 2007)
We found that both urbanisation and pond characteristics had an effect on dytiscid species richness, while abundance was only affected by the pond characteristics
Our study suggests that dytiscids seek shelter in shallower margins to avoid fish, because the effect of margin steepness on dytiscid species richness is stronger in ponds with fish (Fig. 2c) than ponds without fish (Fig. 2d)
Summary
Interest in green infrastructure—networks of vegetated land surfaces—has increased with growing awareness of the broad range of benefits they provide for residents of urban regions, as perceived through the concepts of Ecosystem Services (Nesshover et al 2017) and Nature-Based Solutions (Eggermont et al 2015; Tzoulas et al 2007). Many of the benefits provided by green infrastructure are associated with hydrology, such as the storage, purification and controlled release of water (Eggermont et al 2015), as a consequence of which blue infrastructure elements, such as water bodies, channels and wetland habitats, are important components of urban green infrastructure (Vierikko and Niemela 2016). Hamer and Parris 2011; Murray et al 2013; Wahlroos et al 2015; Hill et al 2017) Such habitats, are prone to the consequences of urbanisation, such as increasing extent of impermeable surfaces, loss of connectivity and the loss and fragmentation of habitats (Concepcion et al 2015). Intrinsic environmental factors of urban wetland habitats can reduce the diversity of their communities of aquatic organisms. Pond margins with steep slopes can be a challenge for mature larvae trying to access suitable habitats for pupation
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