1 Scientific RepoRts | 7: 15384 | DOI:10.1038/s41598-017-15507-1 www.nature.com/scientificreports stromatolites on the rise in peat- bound karstic wetlands Bernadette C. proemse 1,2 , Rolan S. eberhard 3 , Chris sharples 4 , John P. Bowman 5 , Karen Richards 3 , Michael Comfort 3 & Leon A. Barmuta 1 Stromatolites are the oldest evidence for life on Earth, but modern living examples are rare and predominantly occur in shallow marine or (hyper-) saline lacustrine environments, subject to exotic physico-chemical conditions. Here we report the discovery of living freshwater stromatolites in cool- temperate karstic wetlands in the Giblin River catchment of the UNESCO-listed Tasmanian Wilderness World Heritage Area, Australia. These stromatolites colonize the slopes of karstic spring mounds which create mildly alkaline (pH of 7.0-7.9) enclaves within an otherwise uniformly acidic organosol terrain. The freshwater emerging from the springs is Ca-HCO 3 dominated and water temperatures show no evidence of geothermal heating. Using 16 S rRNA gene clone library analysis we revealed that the bacterial community is dominated by Cyanobacteria, Alphaproteobacteria and an unusually high proportion of Chlorofexi, followed by Armatimonadetes and Planctomycetes, and is therefore unique compared to other living examples. Macroinvertebrates are sparse and snails in particular are disadvantaged by the development of debilitating accumulations of carbonate on their shells, corroborating evidence that stromatolites fourish under conditions where predation by metazoans is suppressed. Our fndings constitute a novel habitat for stromatolites because cool-temperate freshwater wetlands are not a conventional stromatolite niche, suggesting that stromatolites may be more common than previously thought. Stromatolites are a form of microbialite with repetitive, laminated structures of biologically (typically cyanobac- teria) mediated mineral precipitation 1,2 . Tese microbial accretions are the oldest evidence for life on Earth 2–6 and debates continue on whether they evolved frst on land or in the ocean 4,7–10 . Fossilized stromatolites and similar accretionary microbial mats have provided intriguing microbial archives for over a century 11,12 , revealing that microbialites were abundant in the shallow late-Archean and Proterozoic oceans, but declined with the emer- gence of multicellular life in the Cambrian 2,13 . Te evolution of grazing metazoans has therefore been suggested as a primary cause of stromatolite decline during the history of life on Earth. However, the role of metazoans in limiting stromatolite formation has been questioned 14,15 , and a living example for the co-occurrence of stromato- lites and benthic macroinvertebrates has recently been reported 16 . Evidence from gene sequencing also suggests that microbialites support diverse and distinct active eukaryotic communities which may infuence microbialite structure 17 . Modern living stromatolites are rare but occur in diverse habitats which are ofen subject to extreme con- ditions inhospitable to other life forms 1,12,18,19 . Well-known living examples are shallow marine stromato- lites in Hamelin Pool, Shark Bay, Western Australia 2–6 , and the shallow subtidal stromatolites in Highborne Cay, Bahamas 4,7–10 . Other occurrences include (hyper-) saline lacustrine environments such as Storr’s Lake, Bahamas 11,12 , a hyper-saline lake of the Kiritimati Atoll, Central Pacific 2,20 , high-altitude Lake Socompa, Argentina 14,15 , and supratidal pools along the coastline of South Africa 16,21 . However, stromatolites growing in low-salinity, low-temperature freshwaters have also been recognized at localities such as: Ruidera Pools Natural Park, Spain 22 , Pavilion Lake, British Columbia, Canada 23 , karst-water creeks in Germany and France 24,25 , cenote lakes in south-eastern mainland Australia 26 , and tufa depositing streams in SW Japan 27 . Te Giblin River catchment and certain others in south-west Tasmania, Australia, contain signifcant concen- trations of unusual wetlands comprising poorly drained, sparsely vegetated sandy to gravelly fats of variable size 1 School of Biological Sciences, University of Tasmania, Private Bag 55, Hobart, Tasmania, 7001, Australia. 2 Australian Centre for Research on Separation Science, University of Tasmania, Tasmania, 7001, Australia. 3 Department of Primary Industries, Parks, Water & Environment, GPO Box 44, Hobart, Tasmania, 7001, Australia. 4 Geography and Spatial Science, University of Tasmania, Private Bag 76, Hobart, Tasmania, 7001, Australia. 5 Tasmanian Institute of Agriculture, University of Tasmania, Private Bag 98, Hobart, Tasmania, 7001, Australia. Correspondence and requests for materials should be addressed to R.S.E. (email: Rolan.Eberhard@dpipwe.tas.gov.au) Received: 7 July 2017 Accepted: 27 October 2017 Published: xx xx xxxx OPEN