Iron in the sea and in marine plankton

Abstract

Gran (1931, 1933) believes that the greater production of phytoplankton in coastal as compared with oceanic waters may be due to organic compounds of iron washed out from the land and in favour of this he has found a fair amount of experimental evidence. Agreeing well with Gran’s thesis was Harvey’s work on Nitzschia closterium (1933). The rate of growth of this diatom was much accelerated by enriching the cultures with small amounts of ferric ammonium citrate, ferric alum, or ferrous sulphate. A small piece of steel placed in the culture was also able to speed up growth. Both Gran and Harvey have found that soil extracts improve the growth of diatoms. Gran (1933) made a number of experiments with Waksman’s synthetic “ferri-ligno-proteid” which has the same biological and chemical reactions as have the essential components of humus and found it to have a marked effect on the growth of certain diatoms. Studies on the growth of Chlorella sp. by Hopkins (1930) in cultures containing added iron salts and a citrate in many different proportions showed that iron is effective physiologically only in the ionic form.