Publication Date

Spring 2010

Degree Type


Degree Name

Master of Science (MS)


Biological Sciences


John T. Boothby


Alexandrium, Elkhorn Slough, Flow cytometry, Fluorescent In Situ Hybridization

Subject Areas

Biology, Oceanography; Biology, Microbiology


This study describes the use of flow cytometry for the enumeration of the toxic marine dinoflagellate Alexandrium catenella in both estuarine samples from Elkhorn Slough, California and from sea water samples from inner Monterey Bay. Samples were subjected to a density-barrier sample enrichment technique employing percoll to separate debris from phytoplankton prior to sample fixation, labeling and analysis. Clarified, enriched preparations of phytoplankton were subjected to whole cell Fluorescent In Situ Hybridization (FISH) using a ribosomal DNA (rDNA) probe specific for the North American ribotype (NA1) of the dinoflagellate genus Alexandrium and analysis by flow cytometry. Flow cytometry was validated using epifluorescence microscopy on paired samples. Density-barrier sample enrichment and flow cytometry employing multi-parametric logical gating enabled detection Alexandrium catenella down to concentrations of 10 cells L-1.

Samples were taken semimonthly from 10 stations along the entire length of Elkhorn Slough and 1 station a mile offshore of the Moss Landing harbor entrance over a two year period from July 2006 to July 2008. In samples taken from the entrance to Elkhorn Slough, Alexandrium catenella was detected in low concentrations by flow cytometry and epifluorescence microscopy. In samples taken from the inland portions of Elkhorn Slough, rare occurrences of a few .A. catenella cells were detected by flow cytometry while no A. catenella was detected by epifluorescent microscopy