Castle Lake Projects

Bat presence and productivity in the Castle Lake basin: investigating distribution and trophic contributions from aquatic and terrestrial habitats.

Project summary:

This study investigates invertebrate based energy exchange between aquatic and terrestrial habitats in the Castle Lake Basin and the extent to which aquatic invertebrate production in Castle Lake subsidizes the Basin’s riparian and upland bat populations. Findings from this study will inform not only the understanding of complex food-web linkages between aquatic and terrestrial habitats and their significance for bats, but how those linkages relate to longer term patterns in forest management, disturbance regime, and climate for these species and the systems supporting them. The project is structured as a collaborative effort between the USFS and the UC Davis/ UNR Castle Lake Environmental Research and Education Program.

In 2007, the University of California, Davis (UCD) and the University of Nevada, Reno (UNR) embarked on a new partnership and research effort, designed to build on the existing Castle Lake long-term data set by mapping trophic pathways and subsidies between aquatic and terrestrial habitats in the Castle Lake basin, using a combination of direct measurement and both stable isotope and essential fatty acid food-web tracers. This study builds on information concerning aquatic and terrestrial invertebrate prey production and cross habitat subsidy collected during the first three years of the UCD/ UNR study. In addition, this study augments preliminary data on bat species presence and habitat use collected in the Castle Lake basin during the summer of 2007 as part of a USFS regional investigation of bat populations.

Findings from this study will support forest management and monitoring objectives detailed in the USFS Shasta-Trinity Land and Forest Management Plan both directly, by providing information on sensitive forest species, their foraging practices, and the food-web that supports them, and indirectly by linking those findings with a long-term dataset that can be used to model larger scale tends such as those associated with climate change. Additionally, this study furthers joint efforts by researchers from UCD and the UNR to refine a lake basin food-web model that can be applied to other sub-alpine lakes within the Upper Sacramento River Watershed.

Specific objectives:

  • To quantify invertebrate based energy pathways and flux between aquatic and terrestrial habitats in the Castle Lake Basin over the course of the Summer of 2008;
  • To identify the relative contributions of terrestrial and aquatic energy pathways and prey to bat forage using a combination of essential fatty acid and stable isotope biomarkers.


  • Aquatic origin prey dominates the forage of bat species in the Castle Lake basin, despite interspecific differences in habitat and prey preference, and significant terrestrial invertebrate production.
  • Essential fatty acid composition of bat wing punch tissue will reflect that of their aquatic or terrestrial invertebrate prey as identified using stable isotopes and essential fatty acid analysis.


Benthic Secondary production in a Mesotrophic Lake and its Implications for Terrestrial Consumer Energetics by Brownstein, Jacquelyn D., M.S., University of Nevada, Reno, 2010.