Long‐term monitoring reveals decreasing water beetle diversity, loss of specialists and community shifts over the past 28 years

1. Lentic freshwater organisms are influenced by a multitude of factors,
including geomorphology, hydrology, anthropogenic impacts and climate change.
Organisms that depend on patchy resources such as water beetles may also be sensitive
to anthropogenic habitat degradation, like pollution, eutrophication, water level or man-
agement alteration.
2. To assess composition and ecological trends in the water beetle communities of
Central Europe, we sampled water beetles (Dytiscidae, Haliplidae, Noteridae) in 33 water
bodies in Southern Germany from 1991 to 2018. We used manual, time-standardised
capture during three periods: between 1991 and 1995, 2007 and 2008, and 2017
and 2018.
3. During the 28-year survey period, we captured a total of 81 species. We found
annual declines in both species number (ca −1%) and abundance (ca −2%). Also, com-
munity composition showed significant changes over time. The significant impact of pH
on the community composition suggests that the recorded changes through time partly
reflect natural succession processes. However, a pronounced decline of beetle species
belonging to the moor-related beetle associations indicated that Central European water
beetles are also threatened by non-successional factors, including desiccation, increased
nitrogen input and/or mineralisation, and the loss of specific habitats. This trend to phys-
iographical homogenisation resulted in corresponding community composition shifts.
4. To effectively protect endangered species, conservation strategies need to be aimed
at regularly creating new water bodies with mineralic bottom substratum, and mainte-
nance of moor water bodies that represent late successional stages.