Several studies have shown that climate changes over the latter part of the 20th century affected the phenology and population dynamics of single species. However, the key limitation to forecasting the effects of changing climate on ecosystems lies in understanding how it will affect interactions among species. Climate change may cause dramatic perturbations to food webs if interacting species respond differently to shifting environmental conditions. We investigated the effects of climate on physical and biological lake processes, using a historical dataset of over 40 years from Lake Washington, USA. The phytoplankton spring bloom advanced roughly in parallel to stratification onset and in 2002 it occurred about 20 days earlier than it did in 1962. Among the zooplankton species, the timing of spring peaks in the rotifer Keratella advanced strongly, whereas Leptodiaptomus and Daphnia showed slight or no changes. These changes have generated a growing time-lag between the spring phytoplankton peak and zooplankton peak, which is especially critical for the keystone herbivore Daphnia. A long-term decline in Daphnia populations is associated with an expanding temporal mismatch with the spring diatom bloom, which has severe consequences for resource flow to upper trophic levels.
An Austrian by birth, Monika Winder received her M.Sc. in Biology from the University of Innsbruck. She then moved to Switzerland where she completed her Ph.D. in 2002 in Natural Science from the ETH in Zuerich. She worked in the Department of Limnology at the EAWAG and studied mechanisms regulating the occurrence, behavior, and life history of alpine zooplankton. She continued her research with a Swiss/Austrian Post-doctoral Fellowship at the University of Washington with Daniel Schindler. She is currently a post-doctoral researcher in the School of Aquatic & Fisheries Sciences, working on the impact of climate change on lake ecosystems.
Fisheries acoustics studies the distribution, abundance, habitat use, and ecology of fish species within ecosystems. Acoustic surveys are appealing assessment techniques since large volumes of water can be rapidly sampled at high spatial and temporal resolutions. One of the main challenges with acoustic data is to discriminate and identify fish species in mixed aggregations. The conventional use of trawl catch data to interpret acoustic samples has several limitations, including species-specific selectivity and catch efficiency of the fishing gear, the resolution and paucity of net samples, and interpolation in non-sampled areas. To investigate the potential for acoustic target discrimination and classification, I use numerical models of echo backscatter combined with in situ measurements to characterize the acoustic properties of co-occurring forage fish species in the North Pacific. I explore several discrimination metrics based on these single target characteristics. One of the most promising techniques to classify species is the use of backscatter differences between pairs of carrier frequencies. Constraints of the method are identified and recommendations to maximize acoustic detection and discrimination are made. I will also identify possible future steps in the ongoing efforts to develop acoustic discrimination techniques.
Stephane received his B.Sc. and M.Sc. at the University of Montreal in Quebec, Canada. He was working in freshwater ecology and fish bioenergetics and at the same time toying with acoustics to monitor fish diel movements within lakes. He made the switch to marine ecology for his Ph.D. with Dr. George Rose at the Memorial University of Newfoundland. There he worked on the acoustic properties and shoaling behavior of Atlantic redfish (Sebastes spp.). After completion of his Ph.D. in 2001, he moved to the School of Aquatic & Fishery Science as a research associate with Dr. John Horne. He is currently working on the acoustic characterization and discrimination of Alaska forage fish species.