On an underwater mountain in the Arctic Ocean lives a community of sponges with a ghoulish secret. With little to eat in the nutrient-poor water, the sponges survive by digesting the remains of long-dead animals that once inhabited the seamount peaks where the sponges now live. And they’ve been feasting on their extinct neighbors’ corpses for centuries.

Scientists recently discovered these macabre creatures on the Langseth Ridge, part of a former volcanic seamount in the Central Arctic, at depths of 1,640 to 1,969 feet (500 to 600 meters) where temperatures hover just above freezing. In those icy depths, researchers found thousands of sponges covering an area measuring 5.8 square miles (15 square kilometers).

The scientists used a camera and sensor network called the Ocean Floor Observation and Bathymetry System to capture video, still images and other data from the sponge community; they also collected samples of the sponges and their environment using a remotely operated diving robot called “Nereid Under-Ice,” according to a study published in the journal Nature Communications.

Not only were there thousands of sponges clustered on the seamount peaks, many of them had grown quite large, reaching up to 3 feet (1 m) in diameter, said lead study author Teresa Morganti, a postdoctoral researcher at the Max Planck Institute for Marine Microbiology in Bremen, Germany. And many of the sponges were actively reproducing, showing “substantial budding,” the scientists wrote in the study.

Under the sponges, the researchers found a dense biomass made mostly of tubes left behind by marine worms that died out when the seamount’s volcanic activity ceased about 2,000 to 3,000 years ago, and sponge tracks over the fossil mats showed where the sponges had foraged before settling down atop the preserved remains. Many individual sponges were at least 300 years old, and they hosted diverse microorganisms. Bacteria in the phylum Chloroflexi likely played an important part in degrading the fossilized tubeworms and releasing dissolved organic matter that kept the sponges well-fed, the study authors reported.

Source: Azerbaijan State News Agency