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Giant sponge gardens found deep in the Arctic Ocean

Since light limits the productivity of algae, few nutrients reach the depths of the permanently ice-covered Arctic Ocean. However, a team of scientists led by the Max Plank Institute for Marine Microbiology has recently discovered surprisingly rich and densely populated ecosystems on the peaks of extinct underwater volcanoes in the Arctic, consisting of giant sponge gardens.

“Thriving on top of extinct volcanic seamounts of the Langseth Ridge we found massive sponge gardens, but did not know what they were feeding on,” said the chief scientist of the expedition Antje Boetius, an expert in Deep-Sea Ecology and Technology at the Max Planck Institute.

By analyzing samples collected during the expedition, the scientists discovered that the sponge gardens adapted to their nutrient-poor environment by accommodating complex communities of microorganisms in symbiotic relationships, and forming so-called “sponge holobionts.” These microbial symbionts contribute to the health and nutrition of the sponges by producing antibiotics, transferring nutrients, and disposing of excretions. 

According to the researchers, thousands of years ago, substances seeping from the interior of the seabed were supporting a rich ecosystem, home to a large diversity of animals. When they died, their remnants remained, forming the food base of the current sponge population.

“Our analysis revealed that the sponges have microbial symbionts that are able to use old organic matter. This allows them to feed on the remnants of former, now extinct inhabitants of the seamounts, such as the tubes of worms composed of protein and chitin and other trapped detritus,” explained study first author Teresa Morganti, a marine scientist at the Max Planck Institute. 

In addition, the sponges seem to act as ecosystem engineers, producing spicules that form a mat on which they crawl, and which traps particles and biogenic materials. The symbiotic microbes can digest refractory particulate and dissolved organic matter and use it as a carbon and nitrogen source. Thus, with the help of their symbionts, the sponges can tap into this detrital matter, utilizing it as a food source.

Since the Arctic is one of the most affected regions by climate change, these sponge communities are in need of immediate protection.

“With sea-ice cover rapidly declining and the ocean environment changing, a better knowledge of hotspot ecosystems is essential for protecting and managing the unique diversity of these Arctic seas under pressure,” concluded Professor Boetius. 

The study is published in the journal Nature Communications.

By Andrei Ionescu, Staff Writer

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