An integrate ecogenetic study of minimal ecosystemsThe microbial mats of Ebro Delta and the Camargue (Western Mediterranean)

Resumen

Microbial mats are vertically stratified microbial communities that develop in the physical-chemical microgradients established at the interfaces of water and solid substrates. They form laminated multilayered biofilms, which as a result of their metab- olism notably alter those microgradients. As highly diverse, physically and chemically active systems, microbial mats stabilize the sediment surface and prevent erosion of the surfaces where they are established. Lithified remains of microbial mats, known as stro- matolites, may be very old. In fact, the oldest known microfossils are stromatolites that date back from more than 3500 million years ago. Therefore, microbial mats are con- sidered to have constituted early ecosystems, probably the earliest ones. Although they now reach high degrees of complexity, during the Archean Eon they must have been very simple and thus fit well with the concept of a minimal ecosystem. Microorganisms in mats or in complex biofilms form coordinated functional communities that are much more efficient than mixed populations of floating planktonic organisms. Microbial mats resemble tissues formed by animals and plants in both their physiological cooperativity and in the extent to which they protect the “organism” from variations in environmental conditions, by a kind of homeostasis provided by the matrix or the boundaries of the mat. The survival value of this strategy in the milieu of the early Earth can be consid- ered the main clue to the resilience of life against adverse environmental conditions. Furthermore, the “invention” of the ecosystem has promoted recycling of the scarce and limited chemical elements on the surface of our planet, thus allowing the evolution of other, more diverse forms of life and the persistence of life as a planetary phenomenon.