The measurement of productivity and growth rates

Abstract

As we are discussing a group of small single-celled organisms floating free in surface waters the measurement of growth rates arid nutrient fluxes presents some special problems. The enclosure of the water sample in a chamber or bottle encloses a fragment of the whole planktonic food chain so that any measurement of the flux of oxygen, carbon or nutrients is a measure of community processes including both autotrophs and heterotrophs. Any attempt to measure growth by increases in cell number must account for the possible presence of grazing organisms and other mortality terms. In many experiments attempts have been made to eliminate all but the photo synthetic fluxes of oxygen and carbon by excluding the grazing animals and confining the phytoplankton in bottles. There is a long history of photosynthesis measurements in limnology and oceanography as such measurements have been made for years under the guise of productivity measurements.