An experimentally determined carbon : volume ratio for marine “oligotrichous” ciliates from estuarine and coastal waters

The biomass of marine “oligotri chous” ciliates has often been estimated by measuring the cell volume of preserved samples and converting to units of carbon based on theoretical carbon: volume (C: vol) ratios of 0.07–0.11 pg µ m −3 . Using laboratory cultures of several strains of Laboea strobila , Strombidium spp., and Strobilidium spiralis , we experimentally derived a C: vol conversion factor of 0.19 pg µ m −3 for cells preserved with 2% vol : vol Lugol’s iodine. Cell volume estimates of Lugol’s‐preserved cells averaged 76% of cell volume estimates of Formalin‐preserved cells. Hence a C : vol ratio of 0.14 pg µ m −3 applies to Formalin‐preserved cells. Our study indicates that the biomass of oligotrichous ciliates in marine systems has been significantly underestimated by the use of inappropriate C: vol ratios.