They may look like a cross between a gigantic cauliflower and a rock, but stromatolites are incredibly important – they’re the first evidence of life on Earth.
Stromatolites – Greek for ‘layered rock’ – are microbial reefs created by cyanobacteria (formerly known as blue-green algae).
Stromatolite deposits are formed by sediment trapping and binding, and/or by precipitation activities of the microbial communities (Awramik 1976). The microbes are active on the surface layer of the stromatolites, while the underlying build-up is a lithified remnant of former microbial surface communities, that could be interpreted as a trace-fossil.
These deposits built up very slowly: a single 1m structure may be 2,000 to 3,000 years old. But the tiny microbes that make up modern stromatolites are similar to organism that existed 3.5 billion years ago! Consider that the Earth itself has been around for 4.5 billion years, and that Homo sapiens have only been on Earth for 195,000 years.(1)
What’s more, stromatolites are the reason why we’re alive today! Before cyanobacteria, the air was only 1% oxygen. Then, for 2 billion years, our photosynthesising stromatolites pumped oxygen into the oceans (like underwater trees, before trees existed). When the oceans’ waters were saturated, oxygen was released into the air, and with around 20% of oxygen in the air, life was able to flourish and evolve.(2)
Even today you can see stromatolites ‘fizzing’ underwater, releasing oxygen.
Where do Stromatolites live?
Living stromatolites are no longer widely distributed. There are only two well-developed marine stromatolites areas in the world: in the Bahamas and at Hamelin Pool in the Shark Bay area of Western Australia. Hamelin Pool is home to the most extensive living stromatolite system in the world: the organisms thrive in the area’s hypersaline water, which is twice as saline as normal seawater.
Australia’s marine stromatolites are protected: they're part of the Hamelin Pool Marine Nature Reserve, which lies within the UNESCO World Heritage listed Shark Bay. The adjacent Hamelin Station Reserve, is now owned by Bush Heritage Australia.
Hamlin Pool is perfect for stromatolites because it’s hypersaline. It’s hypersaline because sea grass forms a ‘barrier’ between Hamlin Pool and the rest of the ocean, preventing ocean circulation, which would dilute the super-salty water.(3) But, sea grass meadows are being damaged by the runoff caused by floods, and extreme temperature events. Climate change is likely to lead to more frequent tropical storms and more frequent flooding events in the area,(4) threatening the stromatolites of Hamlin Pool.
Human interference is another threat. To protect the delicate structures, visitors are restricted to the boardwalk. From here they may be underwhelmed: stromatolites look a little like cow pats from that vista. But, as our Science Fellow and stromatolite expert Dr. Erica Suosaari says “underwater, the shapes, the sizes and the different mat surfaces are overwhelming in their variety…you feel like you’re in you in a Precambrian world!”.
What's Bush Heritage doing?
On the border of Hamelin Pool lies Hamelin Station, a 202,00 ha property that Bush Heritage purchased in 2015. Hamelin Station was once a pastoral property running sheep and goats. We’ve since removed stock and have begun a process of restoration and revegetation. These land management practices will help to lessen the damage of runoff events in the future.
We’ve also employed Dr. Erica Suosaari as a Science Fellow. Erica is a global expert on stromatolites, and recently finished her PhD on the ‘provinces’ of stromatolites in Hamelin Pool. She's excited to continue spending ‘countless hours underwater’ working to understand these ‘seemingly unassuming structures, and to help unlock information about early Earth.’