Tracking ecological resilience: Patterns of community successions in the diatom records of Lake Towuti

Mariam K. Ageli, G. Doug Haffner and Paul Weidman, Great Lakes Institute for Environmental Research, University of Windsor, Windsor, ON, Canada, Paul B. Hamilton, Canadian Museum of Nature, Andrew J. Bramburger, Watershed Hydrology and Ecology Research Division, Environment and Climate Change Canada, ON, Canada, James M. Russell, Geological Sciences, Brown University, Providence, RI, Hendrik Vogel, Institute of Geological Sciences & Oeschger Center for Climate Change Research, University of Bern, Switzerland

Background/Question/Methods
The capacity for aquatic ecosystems to return to previous states over long timespans has become an increasingly important in a time of global change. We can study how aquatic ecosystems have responded to environmental changes over hundreds of thousands of years by analysing the diatom fossil records retrieved from deep sediment cores from ancient lakes. Recent studies from ancient Lake Towuti shows switches in state in the primary trophic level between planktonic stages, dominated by Aulacoseira, and benthic diatom stages dominated by Cymbopleura. Two planktonic states of over 10 ky each were separated by a benthic stage that persisted 3ky. In this study, we investigate whether these two planktonic diatom states represent a highly resilient community that was re-established after long periods of absence and perturbation. We are analyzing the diatom communities from two deep drilling cores retrieved from this lake to determine if the two planktonic states followed a similar pattern of assemblage. The Aulacosiera community was categorized into various forms through light microscopy and scanning electron microscopy. Frustules were counted using light microscopy to measure relative and absolute abundances.
Results/Conclusions
Over 8,000 diatom valves from both diatom stages have been counted in our preliminary dataset. The dominant planktonic taxa, Aulacoseira, which dominates over 90% of the valves analyzed, has been categorised into four taxa (A. granulata, A. pseudomuzzanensis, and two forms). Each form represents a combination of key morphological characteristics, including areolar size and distribution. All four taxa are present in both cores and follow a similar pattern of dominance and succession across during the planktonic maxima. The upper layers of each planktonic stage are dominated by forms characterised by smaller areolar structures (provisionally named as Aulacoseira towutiensis), dominating by 78.0% ± 5.3% in the upper ooze and 67.7% ± 10.9% in the lower ooze. Conversely, the bottom section of both oozes are dominated by forms characterised by larger areolar structures (currently classified as Aulacoseira pseudomuzzanensis), dominating by 68.2% ± 8.3% in the upper ooze. These results demonstrate that an aquatic community has the potential to return to a previous state of similar composition and relative abundances, even after longer periods of absence. Despite the perturbations that have occurred between the two planktonic states, this study shows that a community can also develop and succeed in a similar pattern, even when the period of time separating them is over thousands of years.