A Changing Paradigm of Pelagic Food Webs

The paper catalogues the development of knowledge that has increasingly challenged the conventional understanding (the paradigm) that the predominant pathway of energy flow in pelagic systems is founded on the primary production of phytoplankton, its consumption by herbivorous zooplankton and, in turn, the feeding of larger carnivorous animals, including fish of commercial value. Aquatic food webs are now recognised to be more diverse in their carbon sources, more complex in structure and more versatile in their function. Adjacent terrestrial catchments supply nutrients and, crucially, dissolved inorganic carbon, dissolved organic carbon and particulate organic carbon. Pivotal roles in the processing of autochthonous organic carbon are often fulfilled by pelagic microbes and bacterivorous nanoplankton and microplankton. Mesozooplankton consumes algae directly if sufficiently concentrated but is itself a limiting resource to pelagic fish, which either must be specially adapted to gather sufficient zooplankton or must switch to benthic or littoral foods. Opportunistic feeding by such fish, though primarily nourished in the inshore, continues to control abundant zooplankton. Mobility and dietary electivity of adult fish integrate the pelagic food web into that of the benthos. Except in very large lakes and in the open ocean, the influence of benthic food webs influences the flow of carbon within the pelagic and beyond, serving to invalidate the traditional paradigm of trophic relationships and demanding formulation of another. The flows of matter and energy … result from a simple composition of the activity of individuals and of species R. Margalef, 1997. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)