Ecology: Arctic sponge community feeds on extinct ecosystem

Dense collections of sponges discovered in the Central Arctic survive by feeding on the fossilized remains of an extinct community of animals, reports a study published in Nature Communications. These findings reveal a unique ecosystem in the Arctic, and the strategies used to exploit food sources in this understudied area.

The Central Arctic Ocean is one of the least explored ecosystems because it is covered with ice throughout the year. During an expedition to this region, Antje Boetius and her team of researchers discovered a large, previously unknown sponge community covering previously volcanic seamounts. They had built an Ocean Floor Observation Bathymetry System (a towed camera/sonar system) to survey under the ice in this highly inaccessible environment. The ice-covered region is extremely poor in nutrients, and the food sources supporting the large sponge community were unknown.

Using image analysis and tissue samples of the sponges, Teresa Morganti and colleagues were able to identify the sponges and to assess their age and their food sources. The sponges were on average 300 years old and found to house rich bacterial communities. They were located on the remains of a now-extinct animal community that relied on the previous volcanic activity of this site several thousand years ago. The authors suggest that the sponges use these fossilized remains as a food source, aided by the bacteria that use enzymes to break down the remains and supply nutrients to the sponge host.

The authors argue that due to the rapid decline of sea-ice cover, understanding these ecosystems is essential for protecting and managing the unique biodiversity of the Arctic.