OOS 25-4 - Historical data from heroic age explorers provides context for interpreting present-day diatom biodiversity

Background/Question/Methods
The Nimrod Expedition to the South Pole, Antarctica, (1907-1909) was led by Sir Ernest Shackelton. During their stay preparing for the journey at Cape Royds in the Ross Sea Region, James Murray collected numerous microbial mat samples from the nearby small lakes and ponds. The pioneering team of W. West and G.S. West identified 30 taxa of diatoms from 8 genera, and described 8 new species. Diatoms are single-celled algae found in nearly every aquatic habitat. Their silica (SiO2) walls are one of the features that make them useful as environmental tools in a number of fields, including paleoclimatology, ecology, and paleontology. The usefulness of diatoms is especially true in Antarctica given the limited instrumental records. Thus, this first investigation of diatoms has greatly influenced understanding of microbial biodiversity in the coastal regions of Antarctic. For example, Cape Royds serves as the type locality for 1/6th of the continental diatom flora. Based on historical analysis of the journals of several expedition members to understand their exploration of Cape Royds, we relocated and resampled specific ponds to document any changes that may have occurred.

Results/Conclusions
While the diatom community was stable in several ponds on Cape Royds, in Pony Lake a major shift occurred from dominance by Luticola muticopsis, a specialist for ornithogenic soils, to Craspedostauros laevissimus, which is found elsewhere in the Ross Sea region, including the McMurdo Dry Valleys. We used a metacommunity simulation package to model community assembly dynamics for diatoms in Pony Lake. Diatom habitat preferences were based on observed diatom occurrences and the measured pond habitat characteristics. Transfer functions suggest a significant decrease in silica concentrations in Pony Lake, not other lakes. Ponds are susceptible to a drastic change in local habitat as occurred in Pony Lake and the observed shift in the diatom community is not directly linked to the presence of humans. This study illustrates the value of historical analyses and museum collections in understanding changing conditions in remote locations. Furthermore, the identification of the types of community assembly dynamics that exert the largest controls over microbial biodiversity in Antarctica may be useful in supporting decisions about policy and conservation.