A practical method for enumerating cysts of ciliates in natural marine sediments

Abstract

In order to determine the abundance of intact cysts of planktonic ciliates in natural sediments, we developed a new practical method using autofluorescence of the fixative glutar- aldehyde. After treatment with glutaraldehyde, the cyst walls fluoresced yellowish-green under blue excitation. The fluorescence was always clear in the intact cysts, while only part of the empty cysts was weakly fluorescent. This fluorescence made detection of the intact cysts easy among detrital materials, even for the cysts covered with detritus. It was also easy to distinguish the ciliate cysts morphologically from other organisms that also fluoresced in the treated sediments. This method was compared with the density gradient centrifugation technique, and the advantage of the former in frequent and routine investigations is discussed.