Habitat deterioration despite protection: long-term declines of littoral area of fishponds in Czech nature reserves

Fishponds play a key role in current pondscapes in many developed countries. Their littoral areas, supporting multiple ecosystem functions including the maintenance of aquatic and riparian biodiversity, have been adversely affected by the move shift towards more intensive aquaculture and widespread eutrophication in the middle 20th century. To counteract these changes, many fishponds received some protection, but its long-term efficiency has not been studied. Here we focus on the role of conservation status in protecting the area of littoral areas of fishponds in Czechia between the years 1950 and 2019. We found that the conservation status of these fishponds did not prevent habitat deterioration in most of the fishponds, especially during the second half of the 20th century. Moreover, we detected no significant effects of the reserve establishment year, fishpond area and conservation target on the littoral areas. This suggests that the conservation measures are insufficient across fishpond reserve types. We attribute the negative trends to persisting high fish stocks, especially of common carp, and eutrophication resulting from additional feeding, pond manuring, and ongoing nutrient inputs from the pond catchments. Sediment dredging and high grazing pressure by waterfowl in some reserves can further aggravate the situation. We conclude that effective protection of the littoral areas requires a paradigm shift towards less intensive fish stock management, more frequent summer drainage, and effective reduction of all nutrient inputs to increase the water quality. Such measures can help recover the littoral areas and the associated biota. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=54 SRC="FIGDIR/small/473897v1_ufig1.gif" ALT="Figure 1"> View larger version (27K): org.highwire.dtl.DTLVardef@8e9b31org.highwire.dtl.DTLVardef@6ecaf9org.highwire.dtl.DTLVardef@1cfaefdorg.highwire.dtl.DTLVardef@1e9952f_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LILittoral vegetation in ponds supports high biodiversity but often lacks protection. C_LIO_LIWe evaluated long-term changes in the littoral areas of fishponds in Czechia. C_LIO_LIThe areas decreased markedly in both protected and unprotected ponds since 1950. C_LIO_LIReserve duration, fishpond area and conservation target did not affect the trends. C_LIO_LIChanges in fishpond management are recommended for littoral area recovery. C_LI