Water browning mediates predatory decimation of the Arctic fairy shrimp Branchinecta paludosa

Abstract

Summary Increased concentration of dissolved organic carbon (DOC) in northern watersheds is a concern. Such browning affects aquatic food webs and biodiversity in multiple ways, not least through increased attenuation of short‐wave UV radiation, which may facilitate establishment of new predators. We examined the effects of browning on occurrence of the predatory larvae of the phantom midge, Chaoborus nyblaei, and quantified their impact on the Arctic fairy shrimp Branchinecta paludosa in ponds in alpine southern Norway. The predator was present only above certain levels of DOC (here represented by total organic carbon, TOC). Comet assays revealed a 50‐fold higher DNA damage in the population inhabiting a clearwater pond (3.9 mg TOC L−1), compared to that from a brownwater site (10.5 mg TOC L−1). Laboratory experiments corroborated the key role of browning in protection against UV‐related DNA damage. Chaoborus nyblaei was a highly effective predator on B. paludosa, which suffered major population declines in ponds where the predator was present. Indeed, extinction of B. paludosa has been observed at lower altitudes of the surveyed area over the past decades, possibly in parallel with warming and increased vegetation cover, as inferred from analyses of Normalized Difference Vegetation Index (NDVI) for the surveyed area. These shifts could clearly have favoured establishment of C. nyblaei in the region. Our results point to climate‐induced cascading effects in alpine ponds, whereby increased warming and terrestrial C‐fixation cause increased catchment export of DOC, leading to increased browning of water and associated food‐web changes.

Water Browning Influences the Behavioral Effects of Ultraviolet Radiation on Zooplankton

“…The light regime also influences predator escape efficiency, mostly through visual predator avoidance (Brewer et al, 1999). In this case, water browning should decrease the chances of spotting a predator-or, vice versa, prey (Ranåker et al, 2012;Lindholm et al, 2016). In our experiments, D. magna individuals generally increased exploration activity with increasing DOM levels, suggesting that encounter rates with predators could increase.…”

Ozone depletion, ultraviolet radiation, climate change and prospects for a sustainable future

“…Species of aquatic and terrestrial organisms differ in their tolerances to UV radiation and these differences can lead to alterations in the composition and diversity of ecological communities under conditions of elevated UV radiation 31,32 . UV radiation also modifies herbivory and predator-prey interactions, which then alters trophic interactions, energy transfer, and the food webs in ecosystems 81 . Presently, ozone-driven changes in regional climate in the southern hemisphere are threatening the habitat and survival of a number of species.…”

Ecology of predator-induced morphological defense traits in Daphnia longispina (Cladocera, Arthropoda)

“…were observed. Chaoborus larvae may be rare in these ponds due to predation by large-bodied invertebrate predators, such as Dytiscidae, Odonata and predatory Corixidae/Notonectidae (Ranta 1982;Nyman et al 1985;Hädicke et al 2017), or due to UVR stress-which can be high in these shallow, clear-water ecosystems (Lindholm et al 2016). Interestingly, D. longispina never expressed neckteeth in water bodies with Corixidae/Notonectidae as the sole invertebrate predators, suggesting that only the presence of Chaoborus kairomone can induce neckteeth formation in this species.…”