BIOMASS DISTRIBUTION IN MARINE PLANKTONIC COMMUNITIES

Patterns in primary production and carbon export from the euphotic zon e suggest that the relative contribution of planktonic heterotrophs to community biomass should decline along gradients of phytoplankton bio mass 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 bi omass (H:A ratio) is not constant in marine plankton communities but r ather tends to decline with increasing phytoplankton biomass and prima ry production. Our results show that the plankton of unproductive regi ons are characterized by very high relative heterotrophic biomasses re sulting in inverted biomass pyramids, whereas the plankton of producti ve areas are characterized by a smaller contribution of heterotrophs t o community biomass and a normal biomass pyramid with a broad autotrop hic 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 stru cture of the community could be explained by the changes in the biomas s-specific rates of phytoplankton production that seem to occur from u ltraoligotrophic 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 b iomass in open ocean to resource control in upwelling and coastal area s.