The Use of Neutral Red and Evans Blue for Live-Dead Determinations of Marine Plankton (With Comments on the Use of Rotenone for Inhibition of Grazing)

Abstract

Modifications of the neutral red vital staining technique of Drgsel and co-workers to sort live and dead marine copepods have made possible live-dead determinations of most components of estuarine zooplankton. A stock solution of neutral red is added to a zooplankton sample to give a final concentration of 1:100,000. The length of the staining period vanes from one to six hours, depending on which taxa live-dead determinations are to be made. Calanoid copepods, their nauplii and polychaete larvae require the shortest staining period; barnacle nauplii and cyprids, and decapod zoeas require the longest time. Evans blue, which stains dead diatoms blue but dm not stain living ones, gives satisfactory results for live-dead determinations of most estuarine diatoms in final concentrations of 1:2000 to 1:400. The diatoms Biddulphia and Melosira, and the dinoflagellate Peridinium stained inconsistently with Evans blue, but live-dead determinations were successful using neutral red in a final concentration of 1:50,000. Grazing is a problem in plankton samples held for live-dead determinations of diatoms. This problem was reduced by using rotenone in a concentration of 2.5 pm to kill the calanoid copepod component of these samples.