A geothermal-linked biological oasis in Yellowstone Lake, Yellowstone National Park, Wyoming D. LOVALVO, 1, * S. R. CLINGENPEEL, 2, * S. MCGINNIS, 3 R. E. MACUR, 2 J. D. VARLEY, 3 W. P. INSKEEP, 2 J. GLIME, 4 K. NEALSON 5 AND T. R. MCDERMOTT 2 1 Eastern Oceanics, West Redding, CT, USA 2 Thermal Biology Institute, Montana State University, Bozeman, MT, USA 3 Big Sky Institute, Montana State University, Bozeman, MT, USA 4 Department of Biological Sciences, Michigan Technological University, Houghton, MI, USA 5 Department of Earth Sciences, University of Southern California, Los Angeles, CA; and JC. Venter Institute, La Jolla, CA, USA ABSTRACT Hundreds of active and dormant geothermal vents have been located on the floor of Yellowstone Lake, although characterization of the associated biology (macro or micro) has been extremely limited. Herein, we describe an aquatic moss (Fontinalis) colony closely associated with vent emissions that considerably exceeded known temperature maxima for this plant. Vent waters were supersaturated with CO 2 , likely accommodating a CO 2 compensation point that would be expected to be quite elevated under these conditions. The moss was colo- nized by metazoa, including the crustaceans Hyalella and Gammarus, a segmented worm in the Lumbriculidae family, and a flatworm specimen tentatively identified as Polycelis. The presence of these invertebrates suggest a highly localized food chain that derives from the presence of geothermal inputs and thus is analogous to the deep marine vents that support significant biodiversity. Received 17 December 2009; accepted 5 April 2010 Corresponding authors: Timothy R. McDermott. Tel.: 406-994-2190; fax: 406-994-3933; e-mail: timmcder@ montana.edu; John D. Varley. Tel.: 406-994-2320; fax: 406-994-5122; e-mail: john.varley@montana.edu INTRODUCTION Yellowstone Lake contains hundreds of hydrothermal vents (Morgan et al., 2007) that contribute roughly 10% to the total geothermal venting activity in the Yellowstone geother- mal complex (Balistrieri et al., 2007). The lake bottom has been mapped three different times over the last 136 years, with vent exploration being the focus of work during the last quarter century. The majority of the Yellowstone Lake hydro- thermal vents have been documented using bathymetric and seismic approaches, and a submersible remote operating vehicle (ROV) (see Morgan et al., 2007, for comprehensive summary). The vents are primarily clustered in the northern half of the lake, spanning from the West Thumb to the Mary Bay regions, and all appear to be within the boundary of the current Yellowstone caldera (Morgan et al., 2007). Some vent activity has been located visually as gas bubbles or turbulence on the lake surface. Evidence of high output vents in the West Thumb area (Fig. S1) originally derived from observations of open ice during the winter, which sug- gested subsurface geothermal vent activity was maintaining water column temperatures above freezing. Subsequent ROV dives discovered a large vent cone and a rock outcrop shelf structure that emits large volumes of warm water and gas. Interestingly, this particular vent seemed unique relative to all other active vents thus far observed in the lake in that it is robustly colonized by plants. In all cases, the plants appeared very closely associated with vent emissions (http://www. tbi.montana.edu/media/Fontinalis_vent.html); i.e. only where water and gas venting activity was visually obvious. The occurrence of higher plants so closely associated with venting activity was of interest not only because of plant– temperature relationships, but also because of the relative depth and very low light conditions at this site. Also, while microbiological diversity and novelty associated with Yellow- stone’s diverse terrestrial geothermal features has been well documented (e.g., Brouns et al., 2005; Inskeep & McDer- mott, 2005; Reysenbach et al., 2005; Sheehan et al., 2005; Spear et al., 2005; Ward & Cohan, 2005; Young et al., 2005; Madigan et al., 2005), except for cursory visual descriptions *Both authors contributed equally. Ó 2010 Blackwell Publishing Ltd 327 Geobiology (2010), 8, 327–336 DOI: 10.1111/j.1472-4669.2010.00244.x