Scientists have found a tiny sponge that may be the most abundant and important marine organism on a vast stretch of the ocean floor, which companies and nations want to mine for valuable minerals.
by Todd Woody
A NEWLY DISCOVERED species of deep-sea sponge the size of a postage stamp may be one of the most plentiful forms of life on the Pacific Ocean floor – one that happens to live on polymetallic nodules containing minerals essential to making mobile phones and other products of modern life.
Less than a quarter-inch (5mm) wide, the recently discovered wispy white sponge, which has been preliminarily classified as an entirely new species and genus, lives on nodules that cover the seabed at depths of 13,000–16,000ft (4,000–5,000m). The nodules – potato-sized chunks, numbering in the millions – are rich in manganese with concentrations of nickel, iron, cobalt and other valuable metals. That makes them targets of mining corporations and nations that hold exploration rights over hundreds of thousands of square miles of the ocean floor in a vast stretch of the Pacific between Hawaii and Mexico called the Clarion-Clipperton Zone (CCZ).
“Despite over 100 cruises to the CCZ since the start of polymetallic nodule exploration in the late 1970s, it appears that one of the most abundant and potentially ecologically important nodule-dwelling species has been overlooked,” the researchers who discovered the sponge wrote in a paper published September 24 in the journal Systematics and Biodiversity.
The scientists from the National University of Singapore and the Natural History Museum in London found the sponge on expeditions in 2013 and 2015 to mining concessions held by two companies, UK Seabed Resources and Ocean Mineral Singapore.
The discovery, made through photos taken by remotely operated vehicles (ROVs) and nodules hauled up from the seafloor, underscores the challenges facing the International Seabed Authority. The United Nations-chartered organization is charged with writing regulations to permit mining while preserving the biodiversity of the deep sea beyond national jurisdiction.
“Fundamentally we don’t know the levels of biodiversity in the CCZ, we don’t know species ranges, we don’t know how populations are connected – we’re still very early in the game,” said Craig Smith, a deep-sea biologist at the University of Hawaii who led the expeditions. “Without knowing species ranges, it’s hard to predict what would constitute risk of extinction.
“We do know that the ecological systems are very susceptible to disturbance,” added Smith from Berlin, where he was attending a seabed authority workshop to design protected areas within mining concessions. “The mining disturbances will have a profound impact and the recovery timescales are very long.”
Smith has pioneered research into the biological diversity of the CCZ, and the scientists named the newly discovered sponge Plenaster craigi in his honor.
The significance of the sponge is not so much that it is a novel species – “more than 90 percent of the animals we bring up from the CCZ are new to science,” said Smith – but the fact of its apparent abundance. It lives on the nutrient-poor ocean floor where marine life tends to be rare if diverse, eking out an existence in never-ending darkness in frigid waters under extreme pressures. The researchers, however, found between four and 32 individual sponges per square meter (11 square ft) in the eastern Clarion-Clipperton Zone. In deep-sea terms, that’s as crowded as a Los Angeles freeway at rush hour.
Sponges lack digestive systems and feed on nutrients that they filter through their bodies. The researchers said that biology makes them a potential indicator species for the impacts of seabed mining, which would both remove their habitat and create plumes of sediment that would flow through the bodies of nearby sponges whose nodules are not collected.
Polymetallic nodules cover as much as 99 percent of the seafloor in some areas of the CCZ, according to the study. This is where miners want to mine – depending on the mineral content of those nodules – and also where scientists believe there are higher densities of sponges and other critters.
That’s because the nodules are essential habitat for sponges, anemones, corals and other marine life that attach themselves to the rocks or live on creatures that do. For instance, the ghost octopus, nicknamed Casper, which was discovered in 2016, lays its eggs on the stalks of dead sponges affixed to nodules.
“It’s a diverse fauna – 200 species of megafauna that you can see from ROVs,” said Smith. “About half of those species only live on nodules.”
So how did Plenaster craigi go undetected for so many years, even by its namesake? In short, the underwater cameras on which scientists rely to detect species on the seabed are not yet of a high-enough definition to allow researchers to identify animals as tiny as the sponge. Plus, the sheer number of new species being discovered on the seafloor – and a shortage of taxonomists and funding to describe and classify them – has created a backlog.
Instead, scientists use DNA sampling – a process known as DNA bar coding – to more quickly identify species. The technique, though, doesn’t reveal anything about an animal’s ecological role.
“We can make up a catalog of species based on their bar code, but until we describe them and study their ecology, it’s hard to know how important they are and what they are doing in the ecosystem or how they might respond to mining,” said Smith.
That’s problematic for efforts to draft regulations that will allow mining while avoiding an unacceptable loss of biodiversity in the deep ocean, according to the researchers.
“Knowledge of the taxonomy, species structure, biogeography and basic natural history of deep-sea animals is clearly essential for accurate assessment of the risk of species extinctions from large-scale mining,” they wrote in the paper.
Or as Adrian Glover, principal investigator for the Deep-Sea Research Group at the Natural History Museum, put it in a statement: “We were simply astonished to discover that the most abundant animal living on the metal-rich nodules was not only a new species, but from a new genus as well, despite the region being subject to many surveys in the past.
“It is clear that our taxonomic knowledge of the biodiversity in this region is still very limited,” he added.