We could just see the edge where it went back to regular water -- shiny water -- at night," Michael added, saying they could see the rock from every direction.
The pumice, which is filled with holes and cavities, floats like an iceberg does, with about 90% underwater and 10% above water, the pair explained.
When the pumice makes its way to the Great Barrier Reef, the sea life attached will travel too, potentially bringing diverse new colonies of barnacles, corals and more.
"This is a way for healthy, young corals to be rapidly introduced to the Great Barrier Reef," he said.
In 2016 and 2017, marine heat waves caused by climate change resulted in mass bleaching, which killed about half of the corals on the Great Barrier Reef, along with many others around the world.