Excretion of organic matter by marine phytoplankton: Do healthy cells do it?1

Abstract

It is widely accepted that marine phytoplankton lose appreciable photoassimilated carbon into seawater as organic compounds; the phenomenon is usually referred to as excretion. Two lines of evidence for excretion are found in the literature: measurements in field studies of “organic 14 C” in productivity experiments and the appearance of organic matter in laboratory culture filtrates. Laboratory experiments and a literature review lead to the suggestion that the evidence for excretion is marred by two procedural artifacts, inadequate assessment of control blanks in the 14 C field measurements and the results of cultural shock in laboratory studies. Evidence of extensive excretion by phytoplankton is not good.