New Species of Sponges Found on the Pacific Seafloor

Plenaster craigi are tiny, newly discovered sponges that live on rock nodules targeted for deep-sea mining on the Pacific Ocean seafloor.

Thirteen thousand feet deep, on the cold, dark desert of the Pacific Ocean seafloor, scientists have discovered new sponges living on rock nodules targeted for deep-sea mining.

The tiny sponges, named Plenaster craigi partly for the multitude of stars that make up their backbones, belong in a genus of their own and are the most abundant organism found to date that live on the nodules.

“When I examined Plenaster for the first time, I was amazed by its unusual, simple skeleton,” said Swee-Cheng Lim, a sponge taxonomist from National University of Singapore and lead author of a paper on the discovery, published in the journal Systematics and Biodiversity.

The sponges were collected on two expeditions, in 2013 and 2015, led by Craig Smith, an oceanographer at the University of Hawaii, to the Clarion-Clipperton Zone (C.C.Z.), a chunk of the Pacific Ocean between Hawaii and Mexico that is the size of the continental United States. Dr. Lim, in collaboration with another research team led by Adrian Glover at the Natural History Museum in the United Kingdom, characterized and classified the sponges based on both their appearance and genetics.

“They’re living in a very food-limited environment,” Dr. Glover said. “It’s quite remarkable that they can survive.”

Stace Beaulieu, a deep-sea biological oceanographer at Woods Hole Oceanographic Institution, who was not involved in the study, said: “This is exciting because it is not only a new species but a new genus.” That is akin to discovering not just dogs, but a larger group that includes wolves, coyotes and jackals.

For small organisms in the C.C.Z. like Plenaster craigi, “pretty much everything collected is new,” said Diva Amon, a deep-sea biologist who also participated in Dr. Smith’s expeditions but was not involved in the study. Dr. Amon has reported several new species from the expeditions. But this discovery is “incredibly important,” she said. “This is one of the most abundant animals found living on the nodules and we didn’t even know it existed.”

In the last 40 years, over a hundred scientific expeditions have visited the C.C.Z. where metal-containing nodules lie half-buried on the seafloor. The nodules are lumps of rock that contain various metals including iron, copper, nickel, manganese and cobalt. “They range in size from golf balls to big potatoes,” says Mark Hannington, a marine geologist at Geomar Helmholtz Centre for Ocean Research Kiel in Germany. “Because they are loose, you can just scoop them up with a grater.”

The International Seabed Authority governs the seafloor outside of sovereign waters and has allocated 15 areas for exploration in the C.C.Z. to several companies affiliated with nations that include China, Japan, Singapore, Tonga and those in the European Union. A few dozen exploration licenses have been granted, but none for actual mining yet.

Plenaster craigi grow on the nodules and are vulnerable if mining for nodules commences. “We have collected a few hundreds of this sponge species and they were only found attached to the nodules,” Dr. Lim said.

“The C.C.Z. is a soft sediment habitat so the hard surfaces are limited,” Dr. Beaulieu said. While almost nothing is known of Plenaster craigi – what they eat, how they reproduce, where they are distributed – most sponge species, like corals, have to find hard surfaces to settle down on and grow while they are young, she said.

But the C.C.Z. is so vast, Dr. Glover believes that it is more likely large areas would be left undisturbed. The International Seabed Authority has already reserved wide swaths of seafloor for protection and commissioned large-scale exploration studies to establish life on the seafloor. “To get to the point where you can make informed decisions, you need to know what animals live there,” Dr. Glover said.

More pressing are the huge sediment plumes that mining activities will generate, says Ann Vanreusel, a marine biologist at Ghent University in Belgium. That’s where Plenaster craigi could prove to be useful as an indicator species because of its abundance, she says. “Every animal you collect from the seafloor seems to be a different species,” Dr. Vanreusel said. An organism that will clearly be disturbed from the plumes and abundant enough to count such as Plenaster craigi could help researchers figure out the effects of deep-sea mining and perhaps even the possibilities for recovery, she said.

“They can almost act like a canary,” Dr. Amon said.

But the key, Dr. Hannington said, is that deep-sea mining may not be economically viable. “Nobody has proved it can be done,” he said. Many details, like whether the metals can be extracted from the marine ore, still need to be worked out, he said. “If it turns out that marine mining is not economically feasible, all of the other problems go out the window.”

Dr. Glover’s team first noticed Plenaster craigi while on the 2013 expedition to the exploration area allocated to the United Kingdom. “For three years we were calling them sponge species A,” Dr. Glover said. Then in 2015, Dr. Lim participated in the second expedition to the area allocated to Singapore and began working with Dr. Glover to identify and classify the sponges. Now, Dr. Lim has begun work on a second sponge species growing on the nodules, while Dr. Glover is preparing an extensive study on deep sea mollusks.

The researchers are racing against time to study life on the seafloor while being limited not only by sample collection, but also a lack of scientists with the expertise to characterize and classify new species, Dr. Beaulieu said. “It takes a lot of time, one by one by one, to describe a new species,” she said, “and there are still so many to go.”