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

TLDR

Marine oligotrichous ciliates’ biomass has traditionally been estimated using theoretical carbon‑to‑volume ratios of 0.07–0.11 pg µm⁻³ derived from preserved cell volumes. The authors experimentally determined a carbon‑to‑volume conversion factor of 0.19 pg µm⁻³ for 2 % vol:vol Lugol‑preserved cultures of *Laboea strobila*, *Strombidium* spp., and *Strobilidium spiralis*. Because Lugol‑preserved cells are on average 76 % the volume of formalin‑preserved cells, the appropriate conversion for formalin is 0.14 pg µm⁻³, revealing that previous biomass estimates have been significantly underestimated.

Abstract

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.