We are analyzing bongo-net samples to assess planktonic foraminifera ecology and seasonality off Peru. Samples are analyzed in Petri dishes with water. Presence of protoplasm is notorious and we use this to tell between living and dead individuals. Also, as stated in the literature, we don´t stain the sample so we can observe the natural color of (sub)species. However, this is not helpful when looking at small individuals. It is hard to recognize their protoplasm.
Would you recommend to stain a subsample containing the small individuals after the piciking? Or is it a better way to overcome this difficulty?
Thanks in advance
That's a tough situation--if you use a stain, you lose the natural color, but with cytoplasm being the same refractive index as water, it's difficult to tell if the cells are alive or dead.
Are you using bright field microscopy? Have you tried dark field or phase contrast? You could also play around with other stains, like Lugol's iodine, which stains nuclei of living cells.
An alternative to Rose Bengal may be staining using CellTracker Green or Sudan Black B - see references by Berhard below:
Bernhard, J.M., 1988. Postmortem vital staining in benthic foraminifera; duration and importance in population and distributional studies. The Journal of Foraminiferal Research, 18(2), pp.143-146.
Bernhard, J.M., Ostermann, D.R., Williams, D.S. and Blanks, J.K., 2006. Comparison of two methods to identify live benthic foraminifera: A test between Rose Bengal and CellTracker Green with implications for stable isotope paleoreconstructions. Paleoceanography, 21(4).
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