Concerning calculation methods and limitations of proxy-estimates of Proteins, Carbohydrates and Lipids in crustacean zooplankton from CHN analyses

The present comments resulted from a discussion I had with Dr. Riccardi about the validity of proxy estimates of protein, carbohydrate, and lipid in various zooplankton species of Northern Italian lakes (Riccardi & Mangoni 1999). For these estimates the authors used a calculation method proposed by Gnaiger & Bitterlich (1984; below referred to as G&B). The reason why I questioned the application of the unmodified G&B model to zooplankton was that carbohydrate in crustaceans is mostly present in form of chitin. The argumentation grow rapidly beyond a simple dispute about modes of calculation, leading to some more principle considerations about the limits of proxy estimates.