American Scientist

May-June 2007

Volume: 95 Number: 3

The brilliant colors of the Cargill salt ponds fringing San Francisco Bay are created by a complex ecosystem. Water from the bay is pumped in, then shuttled from pond to pond as it evaporates to leave behind solid salt, a process that takes about five years. The increasingly salty brine hosts a succession of life forms, so the color of the pond can indicate the concentration of its salts. Low to mid-salinity ponds appear deep green; the color lightens, then shifts to oranges and reds as rising salinity favors salt-loving algae, brine shrimp and microorganisms. As Shiladitya DasSarma explains in "Extreme Microbes," the biology of haloarchaea, which lend purple and scarlet tints to hypersaline waters, holds clues to life in many forbidding environments. Similar organisms can endure the lack of oxygen, near-complete desiccation, high-energy solar radiation and extremes of temperature and pH. (Cover image by Robert Campbell Photography/Chamois Moon.)