Are They Really Rocks?

In contrast with other parts of Shark Bay, Hamelin Pool, situated at the bay’s southern extremity, appears bleak and lifeless. Because of a high evaporation rate, these tepid shallows are twice as salty as normal seawater. What appear to be dull-gray rocks fringe the water’s edge. Closer examination, however, reveals that these “rocks” are actually stromatolites, the product of colonies of one-celled microorganisms called cyanobacteria or blue-green algas. About three billion of them occupy every ten square feet [1 sq m]!

These hardy microbes mix sticky mucus with materials extracted from seawater to form a cement, which they add layer by layer to their rocklike home. The process is exceptionally slow. Indeed, by the time it grows to a height of one foot [30 cm], a stromatolite may be nearly 1,000 years old!

Hamelin Pool contains the most abundant and diverse marine stromatolites in the world. What is more, it is one of the last stromatolite strongholds to be found anywhere.

[Picture on page 16, 17]

Billions of tiny organisms build stromatolites