Caring for diving beetles boosts urban biodiversity

Diving beetles (Dytiscidae) maintain the balance of pond ecosystems. They feed on other aquatic organisms, such as mosquito larvae, and form part of the diet of larger animals, including fish, amphibians, and birds. Having such a crucial role in the food chain of ponds, they are a good indicator of biodiversity.

University of Helsinki researchers examined the number and species diversity of diving beetles in 20 ponds in the Helsinki Metropolitan Area. Over a six-year period, they found a decline in diving beetle numbers and species diversity, particularly in ponds isolated from each other or other water bodies. The study has recently been published in Freshwater Biology.

Ponds are losing their shared species

During six years of sampling, the researchers recorded 69 diving beetle species, representing 70% of all known species in the Uusimaa region. Ponds became more distinct from themselves year by year. This "uniqueness," however, is not always a good sign. Rather than gaining new species, the urban ponds have been losing their shared species.

"Urban habitats are usually more isolated than natural or semi-natural landscapes. They're also more prone to disturbance and recover more slowly than habitats in natural landscapes," says the lead author, Postdoctoral Researcher Wenfei Liao of University of Helsinki's Department of Geosciences and Geography.

She offers several recommendations to urban planners, city construction departments, and the public:

• Leave wetlands and ponds in their natural state. Habitat connections between ponds help species movement and reduce the negative effects of isolation.
• Avoid removing aquatic vegetation for pond cleanliness, as this may dramatically impair habitat quality for diving beetles. Sedges and bulrushes proliferating along pond edges provide shelter and habitats for diving beetles.
• Implement buffer zones with native plants in pond surroundings to mitigate runoff pollution and reduce the use of pesticides and fertilizers.
• Leave some ponds fishless. In ponds already having fish, monitor fish numbers, restricting them if necessary.
• Avoid dredging and construct pathways along pond edges to allow people access without disturbing vegetation.
• If possible, create a pond in your own garden and plant native plants. Do not let garden plants escape into the wild.
• Everyone can contribute by picking litter from water and pond edges.