The McMurdo Dry Valleys of the Transantarctic Mountains host perennial microbial mats in ephemeral glacier meltwater streams that flow during austral summers. Stream microbial mat biomass primarily consists of filamentous cyanobacteria with diverse diatom communities. Microbial mats are fundamental to the Dry Valleys ecosystem as they are the primary regulators of nutrient cycling in the landscape, however, can they be scoured by high flows and grow slowly. In longer streams that have more variable flow duration during summer, diatom communities are mostly composed of larger species that are highly silicified, whereas smaller lightly silicified species are found in shorter streams with more consistent flow durations. We tested microbial mat community response to different hydrologic regimes by transplanting mat patches between short (consistent flow) and long (variable flow) streams. Transplanted mat patches were surveyed over the last two austral summers to evaluate how mat communities respond to changing flow and water quality. We hypothesized that competitive interactions will result in the turnover of diatom and bacterial communities. Whereby differences in community structure influences the adhesion of mats to substrata, and thus their interannual persistence.
Results/Conclusions
During the following summer a high proportion of mats that had been transplanted into short streams were scoured away. While mats that had been transplanted into longer streams initially retained higher coverage. Later that summer, mats in short streams began to regrow, while mats in longer streams did not exhibit much change. The second summer following the transplant we observed significant regrowth of mats that were moved into short streams. However, mat biomass was lost in patches transplanted into long streams. We generally found that epipelic mats (growing on sediment) were more resistant to being transplanted into long streams compared with epilithic mats (growing on rocks). Our findings emphasize that the interannual persistence of microbial mats under intermittent flow depends on the community structure of mats and how they adhere to the substrate under variable flow.