Zooplankton biomasses in estuaries are often high and represent an important food source for fish, like theendangered Delta Smelt. Human interferences (nitrates from crops, freshwater flow alteration, invasive species introduction…) have altered the structure of the San Francisco Estuary (SFE) ecosystem. We use stable isotope analysis to improve our knowledge of the planktonic food web in the SFE and gain insights into its evolution over the past decades. Every living thing has a specific isotopic signature. For example, in the plankton we study exists Carbon 13 and Carbon 12. Carbon 13 is different only because it has one extra neutron, and it is the rarer of the two in each species because it is harder to move around through chemical processes, as it is heavier. We can observe a "signature" unique for every plankton species, which is a ratio of the heavier isotope over the lighter isotope. The "signature" is created by the organisms (usually plants in the form of detritus, algae, etc.) ingested by the creature. By using these known ratios of certain plant species, and combining the isotope analysis of multiple isotopes (Nitrogen, Carbon, Sulfur, etc.), we can observe both the types of food a species of zooplankton is feeding on (where the organic material was derived), as well as what trophic level the species feeds in. By using this information, we can eventually draw a more accurate food web for the SFE. These test results, that I helped collect, will not be available before my internship has finished. Therefore, we have also been examining the effect of Formalin preservation vs. Frozen preservation (the chosen method of preserving species before Stable Isotope Analysis). Since many of our historical samples that we are looking at are over 30 years old, they have been preserved in Formalin. We are interested in seeing if this method of preserving the zooplankton will affect our Isotope Analysis. Our results showed there were only small differences in the carbon isotopic composition of frozen and formalin preserved samples we tested, validating the use of our historical samples. Nitrogen isotope results were not as clear (additional experiments in progress to confirm this) but taxon-specific correction factors could be determined and applied to historical samples as the impact of formalin preservation often appeared constant over time.


Biodiversity | Marine Biology | Other Biochemistry, Biophysics, and Structural Biology


Julien Moderan

Lab site

Romberg Tiburon Center for Environmental Studies (RTC)

Funding Acknowledgement

This material is based upon work supported by the S.D. Bechtel, Jr. Foundation and by the National Science Foundation under Grant No. 0952013 and Grant No. 0934931. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the S.D. Bechtel, Jr. Foundation or the National Science Foundation. This project has also been made possible with support of the National Marine Sanctuary Foundation. The STAR program is administered by the Cal Poly Center for Excellence in Science and Mathematics Education (CESaME) on behalf of the California State University (CSU).



URL: https://digitalcommons.calpoly.edu/star/134


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