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Int'l - Lodgers on manganese nodules: Sponges promote a high diversity

Sponges, which like to settle on the metallic nodules, also provide a home for many other animals

Polymetallic nodules and crusts cover many thousands of square kilometres of the world's deep-sea floor. They contain valuable metals and rare earth elements and are therefore of great economic interest. To date, there is no market-ready technology for deep-seabed mining. But it is already clear that interventions in the seabed have a massive and lasting impact on the areas affected. This is also confirmed by a study now published by Tanja Stratmann from the Max Planck Institute for Marine Microbiology in Bremen, Germany, and researchers from the Senckenberg am Meer Institute in Wilhelmshaven, Germany, and the Dutch research institute NIOZ.

In their study, Stratmann and her colleagues used data from a variety of existing surveys as well as deep seafloor imagery from two regions of the Pacific Ocean that are rich in manganese nodules. Using these data, they created a model of interactions in these regions.

"We discovered that stalked sponges are often attached to the polymetallic nodules," Stratmann explained. The sponges use the hard nodules amid the muddy deep-sea environment as the only available hard substrate. With their stalks, they anchor themselves to the nodule while their main body protrudes into the water to filter tiny particles from it. Moreover, the sponges themselves provide a habitat for other animals, such as small worms, crabs and clams. "Our models predict the following: If the nodules are removed, the sponges will also disappear, and with them the associated fauna," Stratmann added. "This reduces the number of animal species and links in the food web. Without the nodules, the food web in the deep sea becomes simpler and less divers."

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