Differences in biomass structure between oligotrophic and eutrophic marine ecosystems

Abstract

A normal trophic pyramid, with most living biomass comprised of plants, is widely assumed to represent marine ecosystems. Oligotrophic and eutrophic environments differ markedly in phytoplankton biomass, but, due to difficulties sampling and quantifying the small, non-plant organisms, it has been difficult to determine the relative plant and non-plant biomass. In eutrophic areas the chlorophyll α/protein ratio (Chl/Pr) of particulate matter, a relative index of phytoplankton to total biomass, approaches that of pure phytoplankton cultures, suggesting that plants constitute most of the biomass. In contrast, in oligotrophic areas the Chl/Pr ratio is low, indicating that most of the biomass consists of bacteria and zooplankton and that an inverted biomass pyramid better describes the system. Thus, ecosystem structure must be fundamentally different between eutrophic and oligotrophic areas.