The Application of Lipid Trophic Markers to Track the Diet History of Thysanoessa rashii in the Bering Sea

Abstract

As a component of the Bering Ecosystem Study (BEST) program, a suite of lipid trophic markers is being examined and validated as markers of the dietary history and trophic transfer of carbon of the euphausiid Thysanoessa rashii. Animals were collected by MOCNESS in the Bering Sea during the summer of 2008. Individual tows were split with a subset of krill immediately frozen until lipid analysis and others used for shipboard feeding experiments. Experimental feedings included various diets (i.e. in-situ seston and seston supplemented with protists, and ice algae) to compare with the field collected animals. All samples were analyzed for total lipid, major lipid classes, and individual lipid trophic markers. The lipid contents in T. rashii were up to 35 % of dry weight with a dominance of phospholipids (> 38% of total lipid). Although phospolipids usually considered to be structural lipids, its absolute quantities were elevated with total lipid content. Triacylglycerols appeared as the major storage lipid class, while wax esters were only present as a minor component. The relative abundances of fatty acid useful as trophic markers (including 189 and 7 and 20:53) were slightly increased after feeding compared to the composition of seston or food additions. Results of these short term feeding experiments suggest that selected lipid markers may reflect rapid changes in diet. Moreover, some of lipid markers (such as sterols) may provide information on a long-term feeding history. Lipid profiles which encompass a suite of lipids may be useful to track changes in the diet history of Bering Sea euphausiids.