MEPS 450:275-280 (2012)  -  DOI: https://doi.org/10.3354/meps09513

ABSTRACT: The Coulter Counter, a common instrument used to enumerate phytoplankton, may over-estimate counts of particles <2.5 µm in equivalent spherical diameter (ESD) by an order of magnitude when samples are run at temperatures cooler than ambient laboratory conditions. This phenomenon is likely due to microbubbles generated as a colder sample warms. Evidence for this mechanism derives from the observation that increasing the relative fraction of organic-rich coastal water in warming samples results in increased amplification of small-particle counts due to the stabilization of microbubbles. Count amplification can be eliminated by ensuring there is no temperature difference between the diluent and the sample. Failing to correct for this error confounds analysis of marine phytoplankton size spectra, complicating a broad range of experiments from those measuring productivity to those used to develop ecosystem-based models.

KEY WORDS: Coulter Counter · Microbubbles · Temperature · Particle size · Picoplankton