Fossil-eating sponges found on the Arctic seabed.

The U.K.’s National History Museum celebrates the unexpected discovery of Arctic sponges that feed on 3,000-year-old fossils:

The fossilised remains of an ancient ecosystem have provided an unlikely food source for the marine life, providing sustenance in an area of the ocean where vital nutrients are hard to come by.

The co-author of the first study on this unusual ecosystem, Professor Antje Boetius, says, ‘This is a unique ecosystem, and we have never seen anything like it before in the high central Arctic.

‘Primary productivity in the overlying water provides less than one percent of the sponges’ carbon demand, with fossil matter contributing a significant part of the remaining amount. Thus, this sponge garden may be a transient ecosystem, but it is rich in species, including soft corals.’

While scientists now have a better understanding of this ecosystem, there are likely to be many others which haven’t been discovered and would need protection from future climate change.

Aside from hydrothermal vents, other underwater communities can form around dead whales, sunken wood and cold seeps. The latter are where hydrocarbons, primarily methane, seep out of the Earth’s crust as a result of tectonic activity. Microorganisms can take advantage of this to release energy through reactions involving these compounds, producing carbonates as a byproduct.

Over time, this allows organisms which feed on these microbes to arrive and survive, followed by other animals including predators. This creates areas that are significantly more diverse than the surrounding ocean, with one study describing them as ‘oases’ of the Arctic.

However, the seeps are dependent on the continued release of hydrocarbons. As the underground reservoirs that feed them run dry, organisms with the highest energy demands begin to die out, until eventually nothing is left.

The carbonates released by seep microbes over their lifetime precipitate as rock, which is left behind when the seep disappears. This can provide a surface for animals like corals and sponges to grow on following the end of the seep.

However, it now appears that the remains of seep ecosystems can provide food for the communities which replace them.

Over time, a range of species, including one previously unknown to science, established the densest community of sponges found anywhere in the Arctic. However, when the site was discovered by researchers, they were unsure as to how such a community could survive in nutrient-poor waters.

Analysis of samples taken from the site subsequently revealed that the sponges have a mixed diet to obtain the carbon they need to grow, including the fossils of both polychaete worm tubes and bivalves.

‘The main limit to how far and deep the sponges can spread is their supply of food,’ [Museum sponge scientist Dr. Ana Riesgo Gil] explains. ‘Sponges primarily live by filtering food, such as plankton or bacteria, from the water, but they also make use of other sources. Some sponges are carnivorous and have adapted to trap and consume prey.

‘While the species composition and size of the sponges at the Langseth Ridge site are not particularly unusual, what they feed on is. This paper is very interesting because it shows that sponges can feed off refractory dissolved organic matter, which as far as I’m aware isn’t something that we previously knew they could do.’

You can read more of Boetius’ sponge study here, in Nature Communications.