Counting and sizing preserved Daphnia with the Optical Plankton Counter

Abstract

Monospecific samples of preserved Daphnia hyalina were counted and sized by the bench-top version of the Optical Plankton Counter (OPC) anti the results were compared to manual counts and size measurements. OPC and manual counts were in excellent agreement. Equivalent spherical diameters (ESD) provided by the OPC were slightly smaller than those calculated from microscopic measurements, but a constant correction of the ESD(OPC) by adding 80 μm resulted in good agreement between the sample means of ESD and biovolume for both methods. The OPC provides reliable counts and size distributions, which saves considerable time and effort in analyzing monospecific zooplankton samples.