On Upwelling, Eutrophic Lakes, the Primitive Biosphere, and Biological Membranes

Abstract

Multivariate statistical techniques based on species abundance distributions allow the calculation of ecological distances between different spots in the sea. The distances can be compared to the geographic distance between the same points and to other distances calculated from the distribution of hydrographic properties. When ecological, geographic, and hydrographic fields are considered together, upwelling systems emerge as strong deformations. As an example, an analysis of two series of phytoplankton samples from the upwelling region of northwest Africa is presented and discussed.

Eutrophic lakes are similar to upwelling ecosystems in the sense that both kinds of systems are force‐fed with nutrients provided from neighboring areas or from deep layers. In both cases, externally supplied energy, derived from a large area, is dissipated locally. The energy maintains biological processes far from equilibrium and with enhanced activity. In the force‐fed systems gradients are steep, the ecological cycles are accelerated, and a fraction of the material circulates through external loops in the atmosphere (oxygen, nitrogen) or in the sediment (carbon, phosphate).

In all these situations, light and gravity define a dimension along which reducing power (in the form of reduced compounds) acquired in the photic zone is transferred downward, creating vertical gradients in redox potential. From this point of view, the marine or lacustrine ecosystem and the whole biosphere can be compared to a biological membrane, with the exception that the different forces in the membrane are at work within a more rigid physical matrix.

The input of external energy, in the form of water movement, is the most important driving force in pelagic ecosystems and this is reflected in the resulting distributions. The interpretation of the distributions has to be combined with the results of experimental work on plankton physiology in order to understand small scale patterns. Segregation of potential reactants (light, nutrients, cells) by stratification or their forced superposition by turbulent mixing controls pelagic life. Some expressions describing spatial structure in the concentration of species or other components of the ecosystem are proposed and discussed