Arctic sponges have learned to feed on the remains of long-extinct worms

(ORDO NEWS) — Dense “sponge gardens” at the bottom of the Arctic Ocean thrive, slowly assimilating ancient organic matter – the remains of creatures that lived there thousands of years ago.

The ocean floor is not densely populated. The sunlight needed for photosynthesis does not penetrate there, there is little oxygen, and most of the organic matter that falls from the surface of the sea is eaten along the way.

It is especially deserted at the bottom of the Arctic Ocean, the central parts of which are covered with ice all year round. However, the Langset underwater ridge, located 350 kilometers from the pole, is densely covered with living sponges that thrive at a depth of 700-1000 meters.

Their community was discovered in 2016, and it was still unclear what all this biomass could eat. Usually sponges lead an attached lifestyle and filter food from water, which is too poor here.

In it, scientists from the Institute of Marine Biology of the Max Planck Society (Germany) present the results of the analysis of video footage and samples taken from the ocean floor during the 2016 expedition on the icebreaker Polarstern.

Arctic sponges have learned to feed on the remains of long extinct worms 2

The flat tops of the ridge turned out to be the most densely populated, more than half of the area of ​​\u200b\u200bwhich is covered by “sponge gardens”. There are orders of magnitude more of them than usual at the bottom in the central regions of the Arctic Ocean.

Most of these sponges belong to the species Geodia parva , G. hentscheli and Stelletta rhaphidiophora and, judging by the many small representatives, actively breed. “The analysis showed that sponges have microbial symbionts that allow them to use old organics,” says Teresa Morganti, one of the authors of the study. “It helps to survive on the remains of the former, now extinct inhabitants of the seabed.”

Arctic sponges have learned to feed on the remains of long extinct worms 3

Indeed, today this ridge is lifeless, although in the past geological activity remained there, and streams of water enriched with minerals, hydrogen sulfide or methane rose from under the bottom, which could feed ecosystems like “black smokers”.

Among them were pogonophora worms – ordinary inhabitants of the deep sea that live inside protective tubes made of chitin and limestone. Several thousand years ago, hydrothermal activity was interrupted, pogonophores died out, but a community of sponges flourished on the remains of their pipes.

Slowly moving, they raise the bottom sediment and filter the water, catching the remains of ancient organic matter from it. Isotope analysis confirmed that it serves as the main source of food for sponges.

The stable molecules of chitin are indigestible, so the nutrition of sponges depends on the material formed during the slow decomposition of this polymer, as well as under the action of microorganisms that live in abundance in the litter and the sponges themselves. These bacteria are capable of decomposing the chitin of long-dead worms, making it available to today’s sponges.

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