New biocompatible tracer particles: use for estimation of microzooplankton grazing, digestion, and growth rates

Abstract

A new class of model food particles is introduced and compared to polystyrene beads and natural food. Made of carbohydrates or proteins, these particles closely resemble natural prey, and are characterised by constant and reproducible quality with respect to C:N ratio, size and effi- ciency of labelling. Uptake and digestibility by the heterotrophic dinoflagellate Oxyrrhis marina were tested and compared to conventional natural (the algae Synechocystis and Chlorella, FLB) and inert particles (carboxylated polystyrene microspheres and silicate particles). Our present data show that ingestion and digestion rates estimated for starch particles greenF and protein particles greenF were indistinguishable from those estimated for natural food of the same size, while ingestion rate and passage time of polystyrene and silicate spheres are up to 5 times lower. As we can provide unstained particles of a certain quality, it is possible to adapt the dinoflagellates to unlabelled parti- cles of the same quality for a longer time. Thus, our new biocompartible particles may be a useful, simple technique for studies where quasi-natural tracer particles of constant quality are needed. Applications are, for example, studies of zooplankton grazing, growth and reproduction of organisms or general models of the flux of particulate organic matter.