Faunal (Chironomidae, Cladocera) responses to post-Little Ice Age climate warming in the high Austrian Alps

Abstract

Present climate warming strongly affects limnological and ecological properties of lakes and may cause regime shifts that alter structure and function in the water bodies. Such effects are especially pronounced in climatologically extreme areas, e. g. at high altitudes. We examined a sediment core from Lake Oberer Landschitzsee, Austrian Alps, which spans the period from the Little Ice Age (LIA) to present. We investigated whether post-LIA climate warming altered aquatic invertebrate communities and limnological status in this sensitive high Alpine lake. Fossil Cladocera (Crustacea) and Chironomidae (Diptera) and organic matter in the core were analyzed. Chironomids were used to assess the lake's benthic quality (i. e. oxygen availability). An instrumental Alpine temperature record was used to assess whether changes in the biotic assemblages correspond to post-LIA temperature trends. The planktonic and macro- and microbenthic invertebrate communities exhibit almost complete and simultaneous species turnover after the LIA, from about AD 1850 onward, when Sergentia coracina-type replaced oxyphilous Micropsectra contracta-type as the dominant macrobenthic taxon, and phytophilous Acroperus harpae outcompeted Alona affinis and Alona quadrangularis in the microbenthos. These directional community shifts corresponded with a period of reduced benthic quality, higher sediment organic content, and progressive climate warming, superimposed on Alpine land-use changes, until the early twentieth century. Detected changes suggest increased productivity and lower benthic oxygen availability. Faunal shifts were even more pronounced during the late twentieth century, simultaneous with enhanced warming. A new planktonic Cladocera species, Bosmina longirostris, typically absent from high Alpine lakes, colonized the lake and gradually became dominant toward the core top. Results show that post-LIA climate warming, coupled with increasing benthic and planktonic production, substantially altered the limnological and ecological status of this remote Alpine lake. Observed faunal turnovers provide evidence that temperature-driven ecological thresholds, whether associated directly or indirectly with greater human activity, have been crossed. Species abundances and distributions have changed in response to post-LIA and late twentieth century climate warming. © 2012 Springer Science+Business Media B.V.