Evaluation of double formalin—Lugol's fixation in assessing number and biomass of ciliates: an example of estimations at mesoscale in NE Atlantic

Ciliated protozoa are potential grazers of primary and bacterial production and act as intermediaries between picoplankton and copepods and other large suspension feeders. Accurate determination of ciliate abundance and feeding mode is crucial in oceanic carbon budget estimations. However, the impact of different fixatives on the abundance and cell volume of ciliates has been investigated in only a few studies using either laboratory cultures or natural populations. Lugol's solution and formalin are the most commonly used fixatives for the preservation of ciliates samples. In the present study, the aim was to compare 0.4% Lugol's solution and 2% borated-formalin fixation and evaluate the need of counting duplicate samples each using a different fixative. For this, a large number of samples ( n=110) from the NE Atlantic was analyzed in the frame of POMME program (Multidisciplinary Mesoscale Ocean Program). We established a statistically significant relationship ( p