By John Upton
Natural rock rafts are normally way too small for us humans to ride. But the fragments of lightweight pumice that form after waterlogged volcanoes explode are surfed around the world’s oceans by everything from algae and barnacles to nudibranchs and crabs.
Pumice, normally found in bathroom cabinets and beauty salons, is an extraordinary type of rock: It’s light enough to float on water. It forms when searing hot lava strikes water, which cools the material suddenly and freezes pockets of air inside. Following a marine eruption, ribbons of pumice can float all around an ocean, directed by currents and winds, until they eventually settle on far-flung shorelines. New Zealand’s Navy stumbled across 10,000 square miles of the stuff floating in the southern Pacific Ocean last month.
Research published in July revealed that extraordinarily diverse communities of wildlife quickly set their roots on these floating substrates, helping otherwise sedentary marine species travel great distances in short periods.
Scientists monitored pumice formed by a 2006 underwater volcanic eruption near the Pacific Islands nation of Tonga. They discovered more than 80 species using the floating rock as a raft, some of them hitchhiking a ride of more than 3,000 miles in less than nine months.
“The rafted community exhibits a variety of feeding strategies: photosynthetic, filter feeding, grazing and scavenging to predation, but with photosynthesising organisms and filter feeders most dominant,” the Australian researchers wrote in their paper, which was published in the online journal PloS ONE.
The pores that help the rock float also offered shelter for many of the species, the researchers found: “Vesicles and surface depressions offer protection from predation for obligate rafting organisms and for facultative species during initial growth.”
The Tongan pumice was still washing up on Australian beaches 20 months after the explosion, revealing that the wacky substance provides wildlife with more than just a means of jetting across an ocean: It can provide a mini-ecosystem with a seafaring home that lasts for years.