Energy Flow and Species Diversity in a Marine Phytoplankton Bloom

Abstract

MARGALEF¹ has attempted to predict the ways in which certain descriptive (but quantitative) properties of an ecosystem will change during the development of the ecosystem, or when the system is subjected to disturbance. Briefly, the hypothesis he uses states that the transition of an undisturbed ecosystem from a juvenile to a more mature condition is characterized by changes in the system such as the following: an increase in the amount of primary production; an increase in the total biomass; a decrease in the ratio of primary production to biomass; a greater efficiency of production; an increase in the species diversity; a decrease in the ratio of production to respiration; an increase in the importance of stratification and spatial organization. Some of these ideas have been criticized by Slobodkin² as lacking in empirical justification. The results of our field observations on the energy flow in a marine phytoplankton population³ lend support to the views of Margalef and of Odum⁴, but certain weaknesses in the hypothesis are exposed when an attempt is made to apply it to real data.