Introduction

This chapter addresses the resource requirements for the assembly of photoautotrophic biomass. In addition to light and carbon, growth of phytoplankton consumes ‘nutrients’ and, equally, may often be constrained by their availability and fluxes. Put at the most basic level, every replication of a phytoplankton cell roundly demands the uptake and assimilation of a quota of (usually) inorganic nutrients similar to that in the mother cell, if her daughters are to have the similar composition. Ignoring skeletal biominerals for the moment, we may recall from Section 1.5.3 that, in addition to carbon, the living protoplast comprises at least 19 other elements. Some are needed in considerable abundance (hydrogen, oxygen, nitrogen), others in rather smaller amounts (phosphorus, sulphur, potassium, sodium, calcium, magnesium and chlorine), for the assembly and production of the organic matter of protoplasm. Others occur as vital traces in support of cellular metabolism (silicon, iron, manganese, molybdenum, copper, cobalt, zinc, boron, vanadium). However, it is less the amounts in which these elements are required that constrains growth than does the ease or otherwise with which they are obtained. It is the demand (D) relative to the supply (S) that is ultimately critical, bearing in mind that a measurable presence is not a measure of availability if the element in question is not both soluble and diffusible and, so, assimilable by cells.

There is a huge literature on this topic.