Introduction

The purpose of this chapter is to assess the role of phytoplankton in the pelagic ecosystems and other aquatic habitats. The earliest suppositions to the effect that phytoplankton is the ‘grass’ of aquatic food chains and that the production of the ultimate beneficiaries (fish, birds and mammals) is linked to primary productivity are reviewed in the context of carbon dynamics and energy flow. The outcome has a bearing upon the long-standing problem of phytoplankton overabundance and related quality issues in enriched systems, its alleged role in detracting from ecosystem health and the approaches to its control.

The chapter begins with an overview of the energetics and flow of primary product through pelagic ecosystems, especially seeking a reappraisal of the relationship between biomass and production.

Material transfers and energy flow in pelagic systems

One of the essential components of ecological systems is the network of consumers that exploit the investment of primary producers in reduced organic carbon compounds. Some of these are re-invested in consumer biomass but much of the food intake is oxidised for the controlled release of the stored energy in support of activities (foraging, flight, reproduction) that contribute to the survival and genomic preservation of the consumer species in question. In thermodynamic terms, the food web serves to dissipate as heat that part of the solar energy flux that was photosynthetically incorporated into chemical bonds (see p.355).