Jet-Suspended, Calcite Ballasted Waterwarts
While studying the Cuatro Ciénegas microbialites, we noted planktonic populations of marble-sized colonies of blue-green algae developing at Escobedo’s Warm Spring, a sheltered, small, fast-flowing spring. There, cm-sized waterwarts were kept in suspension by the upwelling waters of a central 6-m deep well. Waterwarts were built by an Aphanothecelike unicellular cyanobacterium and supported a community of epiphytes that included filamentous cyanobacteria and diatoms, but were free of heterotrophic bacteria on the inside. Waterwarts contained orderly arrangements of mineral crystallites, made up of microcrystalline low-magnesium calcite, with high levels of Strontium and Sulfur. An analysis of the hydrological properties of the spring well and the waterwarts demonstrated that both, large colony size and the presence of controlled amounts of mineral ballast, are required to prevent the population from being washed out of the well. The mechanisms by which controlled nucleation of extracellular calcite is achieved remain to be explored.