Fatty acids as biomarkers of plankton trophic structure in Table Rock Lake, Missouri

Recently, fatty acid profiles have been used as an alternative to stable isotopes for measuring trophic linkages in freshwater food webs.  An advantage of fatty acids is that many different compounds can be resolved and most of these are conserved, providing a “signature” of different food resources in consumers.  We examined the fatty acid profiles of phytoplankton and zooplankton in a Missouri reservoir.  During April, June, and August 2008, we collected phytoplankton and common zooplankton taxa from two depths (6 m and 12 m) at each of two sites on Table Rock Lake.  Following extraction and concentration of fatty acids, gas chromatography allowed the separation and measurement of linoleic acid, α-linoleic acid, arachidonic acid, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA).  Preliminary analysis of phytoplankton EPA:DHA ratios showed no significant differences between months or between depths, and sites (mean EPA:DHA = 2.0).  June samples of algal composition indicated a discernible difference between depths, with chrysophytes dominant at 6 meters and diatoms (Fragillaria) at 12 meters.  We expect further analysis of the fatty acids to allow us to match the vertically-migrating zooplankton with depth of their primary food resources.