Abstract
Lorica volume, carbon, nitrogen, and ATP content were measured in nine species of tintinnid ciliates spanning a size range of two orders of magnitude. Tintinnid carbon was linearly related to both lorica volume and ATP content. The mean C:ATP ratio was 65. Tintinnid ATP as a percentage of total ATP in the <153 μm fraction averaged 7% over an annual cycle in Narragansett Bay. It is concluded that ATP is a useful indicator of living phytoplankton carbon in pre-screened, small-volume samples during periods of moderate to high phytoplankton biomass, but that protozoan microzooplankton interference is significant when phytoplankton standing stocks are low.
