Applicability of the vital dyes neutral red and fluorescein diacetate to differentiate between alive and dead non-copepod zooplankton

It is a common practice for planktonologists to use neutral red (NR) staining to identify viable copepods in marine zooplankton. A new fluorescent dye, fluorescein diacetate (FDA), has also been successfully applied to Copepoda. Meanwhile, almost nothing is known about if NR- and FDA-based viability assays are applicable to many other zooplankton taxa. In this study, efficiencies of NR and FDA staining were evaluated and compared for different taxa and developmental stages of the Black Sea non-copepod zooplankton. Both the dyes were shown to stain well larvae of polychaetes, gastropods and bivalves, rotifers, fish eggs, barnacle nauplii, decapod zoeae, and the heterotrophic dinoflagellate Noctiluca sсintillans. Dominant species of Cladocera (Pleopis polyphemoides, Evadne spinifera, Pseudevadne tergestina) were stained efficiently with FDA only. Some taxa had sufficient statistics of positive staining only with one of the dyes, NR (e.g. appendicularians and chaetognaths) or FDA (e.g. barnacle cyprids). Correspondingly, more data are demanded to fill the gaps in the target taxa. The dyes proved to be taxa-specific and hence, their reliable application should be based on their target groups.