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

• Published in: Freshwater Biology
• Main Authors: Lindholm, Markus, Wolf, Raoul, Finstad, Anders, Hessen, Dag O.
• Other Authors: Norges Forskningsråd
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2016
• Subjects: Arctic; Browning; Norway
• Online Access: http://dx.doi.org/10.1111/fwb.12712; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Ffwb.12712; https://onlinelibrary.wiley.com/doi/pdf/10.1111/fwb.12712

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.