RELATING C-N RATIOS IN ZOOPLANKTON FOOD AND FECAL PELLETS USING A BIOCHEMICAL-MODEL

A model is developed which predicts faecal pellet C:N ratio by considering how carbon and nitrogen in food items are distributed between various biochemical compounds (proteins, carbohydrates, lipids), and then how these compounds are assimilated within the zooplankton gut. The model successfully reproduced the generally observed trend that pellet C:N ratios are greater than those of the food from which they are derived. The model is superior to simpler models based on elements rather than specific compounds because it has the potential to reproduce the wide variability in average carbon assimilation efficiency which occurs among foods of different types. The model was, however, derived from a very limited quantity of data. The work highlighted the need for more data on the biochemical composition of marine organisms, and how various biochemical fractions are assimilated by zooplankton, in order to provide realistic predictions of how C:N ratios in pellets relate to those in food.