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APPEARANCES apart, they are no spongers. Tiny bacteria living inside sponges seem to be symbiotic and may have played a part in the drama that transformed Earth鈥檚 deep oceans 750 million years ago. This upheaval turned seas into the oxygen-rich haven for life so familiar to us today.
The discovery of the curious bacteria was an accident, says of the University of Maryland in Baltimore. He and his colleagues happened to notice microscopic phosphate granules spread throughout the tissue of three different species of Caribbean sponges they had in the lab. Living inside the sponges were bacteria that suck phosphorus out of seawater and precipitate it into granules. The team proposes how sponges and bacteria live in symbiosis to make the most of the phosphorus in the water for their own nutrition (PNAS, ). Phosphorus is a rare but essential nutrient for ocean life. Sponges need it to survive but can鈥檛 extract it from the water.
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Meanwhile, bacteria rely on the sponges to pump vast amounts of seawater over them so they can extract more phosphorus. So, Zhang says, the sponges and bacteria live in symbiosis.
That is interesting because sponges and many of the symbiotic bacteria that Zhang found in his samples have been around for hundreds of millions of years, since the early days of animal life on Earth. Around 750 million years ago the deep oceans were flooded with oxygen. This transformation was traditionally credited with driving the Cambrian explosion, the sudden flourishing of all the different types of animal shapes we know today (see 鈥�Sparks of life鈥�).
of the University of Cambridge and his colleagues proposed last year that early animals, specifically sponges, led to a surge in deep ocean oxygen, not the other way around.
They pointed out that sponges can survive on very low levels of oxygen and are great at pumping and filtering water. 鈥淚nvent something like a sponge [750 million years ago] and the world is their oyster. They have no competition. And now, for the first time water is being pumped and filtered,鈥� says Butterfield.
As the sponges pumped, they aerated the deep oceans with oxygen, he says. Phosphorus in the water would have reacted with that oxygen to form a hard phosphate precipitate, drastically reducing the amount of nutrients available to oxygen-consuming life forms, hence further boosting oxygen levels in the deep. Zhang and his colleagues鈥� study offers an interesting explanation for how the sponges and their symbiotic bacteria might have sequestered and regulated phosphate in the early ocean, says Butterfield.
鈥淚t has largely been thought that early animals evolved rather passively in response to physical and chemical changes on the early Earth,鈥� says Daniel Brady Mills of the University of Southern Denmark in Odense. 鈥淪tudies like this suggest that early animals could have actually exerted significant controls over Earth鈥檚 ancient chemistry.鈥�
聯Early animals could have actually exerted significant controls over Earth鈥檚 ancient chemistry聰
This article appeared in print under the headline 鈥淒id sponge microbiomes help aerate the oceans?鈥�