Benthic microbial mats in the glacial-fed meltwater streams are hotspots of priamry productivity in the McMurdo Dry Valleys (MDV), Antarctica. Benthic diatoms are common in these mats and the 45 priamrily endemic taxa represent the most diverse group of eukaryotes in the MDV. In this harsh polar desert, the streams are thermally dynamic with large diel fluctuations in water temperature, ranging from 4-15 deg C. Stream temperature may play a role in determining the growth rates and survival of the benthic diatoms. We investigated the physiological growth rate response of diatoms to temperatures that reflect maximum diel stream temperatures to understand species-specific adaptations to their environment. We established unialgal cultures of four diatom taxa from MDV mats and determined their growth rates under three temperature conditions. The diatom taxa investigated were isolates of Psammothidium papilio (Antarctic endemic), Hantzschia abundans (widespread), Hantzschia amphioxys (widespread), and Hantzschia amphioxys fo. muelleri (South Victoria Land endemic). Growth rates estimated as the rate of increase in the measured in vivo chlorophyll a fluorescence content of culture tubes over time.
We hypothesized that Antarctic endemic diatom species would illustrate psychrophilic behavior and grow faster at colder temperatures, and that their intrinsic growth rates would vary by temperature. We found that Hantzschia amphioxys fo. muelleri (South Victoria Land endemic) grew faster than the other taxa and thrived at higher temperatures. Hantzschia amphioxys exhibited a maximum growth rate at the intermediate temperature. In contrast,