An assessment of sample processing methods for stable isotope analyses of coastal foodwebs

Abstract

[Abstract] The relative abundance of the light and heavy forms of stable isotopes of Carbon and Nitrogen is commonly used in the research of marine food webs. Dehydration of samples is needed for C and N isotopic analysis, and in those organisms with inorganic carbonate structures acidification with hydrochloric acid is also needed for sample preparation. There is not a consensus about the methodology appropriate for sample processing. In the present study, the effects of different sample processing methods in the relative abundance of stable isotopes of C and N in the different trophic compartments of a coastal food web are evaluated. The final purpose is to define an adequate methodology to be used in the construction of whole food webs. The results obtained after acidification show a decrease in carbon values for sedimentary organic matter, suspended particulate organic matter, plankton and invertebrates with carbonated structures, and a variable response for nitrogen values. According to our results we recommend sampling acidification for carbon analysis in compartments in which variations of this element were observed. For nitrogen analysis acidification should not be done. Different treatments of dehydration studied provoked significant differences only in nitrogen values, thereby freeze-drying seems the most adequate method. Muscle tissue should be used in invertebrate with carbonated structures whenever body sizes make it possible.