Wet wall algal community response to in-field nutrient manipulation in the Great Smoky Mountains National Park, U.S.A.

Furey, Paula; Lowe, Rex; Johansen, Jeffrey

Subaerial algal assemblages, like those found on wet walls (moist vertical rock outcrops), are understudied communities and the factors that drive community dynamics in these environments are poorly understood. Due to the exposed and often vertical nature of these habitats, nutrients are predicted to be critical determinants of algal community structure. Through in-field experimental manipulations we measured the structural response of wet wall algal assemblages to nutrient manipulation at two altitudes in the Great Smoky Mountains National Park. Over a 10 week period, we misted five nutrient treatments (control [no-moisture, no-nutrients], no-nutrients [moisture-only], nitrogen, phosphorus, and both nitrogen and phosphorus) onto rock faces at six replicate wet wall areas at each altitude. We did not observe any differences in algal community structure or biomass (ash free dry mass) across treatments at either location. The algal communities at our higher elevation location were generally similar across all sites, and were dominated by cyanobacterial taxa with pigmented sheaths, such as . The diatoms present at this location were acid tolerant species, such as , reflecting the low pH levels and high acid precipitation levels of this area and altitude. In contrast, algal communities at our lower elevation location clustered by site. Two sites were dominated by mucilage-producing Cyanobacteria along with one diatom taxon. Two sites supported large populations of several raphid diatoms which may have been due to influences from soil associated with those sites. The remaining two sites separated out by the presence of particular green algal or cyanobacterial taxa, along with a mix of diatom taxa. This study demonstrated that wet walls are not as nitrogen or phosphorus limited as initially anticipated. Although not directly tested in this study, the clustering patterns and algal assemblages observed suggest that other factors, such as ultraviolet radiation, pH, moisture levels, or microhabitat differences, are influential in shaping wet wall, algal community structure. Our findings provide new understanding of wet wall algal ecology and provide insight into factors that potentially regulate algal community structure that will be helpful in the development of future studies.

Wet wall algal community response to in-field nutrient manipulation in the Great Smoky Mountains National Park, U.S.A.

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