Trophic transfer of fatty acids in marine food webs

The research interests of my group are focused on the use of lipids and fatty acids (FA) as tools to study carbon flow and food web dynamics in the marine environment. FA are well suited to such studies because many dietary FA are incorporated into consumers with only minor modifications to structure, making FA useful as indicators or biomarkers of their source. Here, we propose to continue our ongoing work investigating the transfer of FA from prey to predators at low trophic levels by examining trophic transfer efficiencies of FA. This is a measure of the amount of FA deposited in a predator's tissue relative to the amount available in its diet, and we believe these will vary with consumer, concentration of FA and FA structure. Several FA, such as long chain omega-3 FA, are essential nutrients, required for growth and survival by all organisms. In the marine food web, the majority of these essential FA are synthesized only by phytoplankton; thus, it is particularly important to understand the efficiency with which such nutrients are transferred from diet to consumer. Trophic transfer efficiencies can also be incorporated into methods we are developing to estimate consumer diets by comparison of FA patterns, or profiles, in predator and prey. They are important in that application because they allow us to compensate for changes made to the diet FA profile by catabolism and other processes in the predator. We are proposing three specific objectives: 1) examine the influence of FA structure, dietary concentration, tissue and species on transfer efficiency of FA, using calanoid copepods (Calanus finmarchicus), Atlantic pollock (Pollachius virens) and Atlantic salmon (Salmo salar) as model species; 2) test the influence of trophic transfer efficiencies in our statistical models on the accuracy of diet estimates by conducting feeding studies with Atlantic salmon fed different diet mixtures; and 3) incorporate trophic transfer efficiencies of FA into our statistical models and apply to existing datasets from Baffin Island and the Bering Sea to estimate diets of Atlantic and Arctic cod (Gadus morhua and Boreogadus saida). These are ecosystems that are most susceptible to the effects of climate change and make good candidates to detect variation in carbon cycling over time. At larger scope, we will use trophic transfer efficiencies, combined with production levels of FA derived from remote sensing of phytoplankton, to estimate the essential FA budget of the ocean. Fundamentally, we believe that incorporation of these essential nutrients into mechanistic models will improve the accuracy of predictions of ecosystem properties and shifts, ultimately leading to better decision-making regarding management and conservation of our marine resources. Measurement of trophic transfer efficiencies of essential FA, as we have proposed here, is a necessary first step for their inclusion in such models.