Abstract
Although alkaline Hunter’s Hot Springs in southeastern Oregon has been studied extensively for over 40 years, most of these studies and the subsequent publications were before the advent of molecular methods. However, there are many field observations and laboratory experiments that reveal the major aspects of the phototrophic species composition within various physical and chemical gradients of these springs. Relatively constant temperature boundaries demark the upper boundary of the unicellular cyanobacterium, Synechococcus at 73–74 °C (the world-wide upper limit for photosynthesis), and 68–70 °C the upper limit for Chloroflexus. The upper limit for the cover of the filamentous cyanobacterium, Geitlerinema (Oscillatoria) is at 54–55 °C, and the in situ lower limit at 47–48 °C for all three of these phototrophs due to the upper temperature limit for the grazing ostracod, Thermopsis. The in situ upper limit for the cyanobacteria Pleurocapsa and Calothrix is at ~47–48 °C, which are more grazer-resistant and grazer dependent. All of these demarcations are easily visible in the field. In addition, there is a biosulfide production in some sections of the springs that have a large impact on the microbiology. Most of the temperature and chemical limits have been explained by field and laboratory experiments.
Highlights
Hunter’s Hot Springs, alkaline springs, with several sources in 16 ha (42.44088 °N, 120.36907 °W)are located 3.2 km north of Lakeview, Oregon
It has been shown that in some cases the upper limit of some species is determined by temperature
The lower limit of the massive distribution of Synechococcus is limited by Geitlerinema, and that of Geitlerinema and Synechococcus/Chloroflexus by the ostracods
Summary
Hunter’s Hot Springs, alkaline springs, with several sources in 16 ha (42.44088 °N, 120.36907 °W). In a few newly established springs at Hunter’s, no ostracods were present, in which case, the G. terebriformis mat extended to temperatures below about 30 °C, it tapered out visibly with a lower suboptimal temperature below about 35 °C (Figure 12). In one spring (“Fenceline”) where the G. terebriformis cover was absent, the ostracods fed and truncated the Synechococcus/Chloroflexus mat at about 47 °C, the normal upper temperature limit for the animals [20]. These animals made feeding, swimming sorties to higher temperatures, but became comatose and closed their carapaces in a short time with increasing temperature. ~48 °C by ostracod grazing, revealing dark patches of Pleurocapsa/Calothrix in ostracod zone below 47–48 °C
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