Use of the fluorescent calcite marker calcein to label foraminiferal tests

We describe a novel application of the fluorescent compound calcein (Bis[N,N-bis(carboxymethyl)aminomethyl]fluorescein), which was used to fluorescently label foraminiferal calcite. Foraminifers that were incubated in a 10 mg L-1 solution of calcein and seawater precipitated normal-looking chambers during and after calcein incubation, which lasted up to three weeks. The survival rate, of specimens incubated in calcein was similar to that of control specimens; some specimens reproduced during or after calcein exposure. Thus, this calcein-tagging method is non-lethal. Chambers precipitated during calcein incubation fluoresced a yellow-green when viewed with epifluorescence or laser scanning confocal microscopy (470 nm excitation, 500 nm emission). When viewed alternatively with reflected light, chambers formed after calcein incubation were easily distinguished from calcein-marked chambers, because calcite precipitated after calcein exposure does not fluoresce. Fluorescence is retained through fixation and air drying, thus the signal can be viewed in archived specimens. The method was executed on specimens from 15 species collected from three habitats with diferent environmental conditions. Results indicate that calcein is incorporated by all 15 species. The method has a number of potential applications, including experiments aimed at identifying benthic foraminifers that are faithful recorders of paleoceanographic proxies, as well as field studies to assess locations and chronology of foraminiferal calcification.