Biomass distribution in marine planktonic communities

TLDR

Patterns in primary production and carbon export suggest that heterotrophic biomass relative to autotrophs declines with increasing phytoplankton biomass, a shift that may be driven by changes in phytoplankton production rates across oligotrophic to eutrophic gradients, though other factors could also contribute. Using an extensive literature data survey, the authors test whether the heterotroph‑to‑autotroph biomass ratio decreases with higher phytoplankton biomass and primary production. The study finds that unproductive regions have inverted biomass pyramids with high heterotrophic biomass, while productive regions display normal pyramids with lower heterotroph contribution; open‑ocean communities also support more upper‑layer heterotrophic biomass than coastal ones, indicating a shift from consumer to resource control of primary production across marine environments.

Abstract

Patterns in primary production and carbon export from the euphotic zone suggest that the relative contribution of planktonic heterotrophs to community biomass should decline along gradients of phytoplankton biomass and primary production. Here, we use an extensive literature data survey to test the hypothesis that the ratio of total heterotrophic (bacteria + protozoa + mesozooplankton) biomass to total autotrophic biomass (H : A ratio) is not constant in marine plankton communities but rather tends to decline with increasing phytoplankton biomass and primary production. Our results show that the plankton of unproductive regions are characterized by very high relative heterotrophic biomasses resulting in inverted biomass pyramids, whereas the plankton of productive areas are characterized by a smaller contribution of heterotrophs to community biomass and a normal biomass pyramid with a broad autotrophic base. Moreover, open‐ocean communities support significantly more heterotrophic biomass in the upper layers than do coastal communities for a given autotrophic biomass. These differences in the biomass structure of the community could be explained by the changes in the biomass‐specific rates of phytoplankton production that seem to occur from ultraoligotrophic to eutrophic marine regions, but other factors could also generate them. The patterns described suggest a rather systematic shift from consumer control of primary production and phytoplankton biomass in open ocean to resource control in upwelling and coastal areas.