Giant Sponge Gardens Discovered on Seamounts in the Arctic Deep Sea

Giant sponge gardens

Little food gets to the depths below the perpetually ice-covered Arctic Ocean since light limits the productivity of algae. Researchers from Bremen, Bremerhaven, and Kiel found a surprisingly abundant and densely populated ecosystem on the tops of extinct underwater volcanoes. These hubs of life were dominated by sponge gardens, growing there in large numbers and to an impressive size. They reported their discoveries in the journal Nature Communications.

” Thriving over extinct volcanic seamounts of the Langseth Ridge, we found enormous sponge gardens but did not know what they were subsisting,” reports Antje Boetius, chief researcher of the expedition, head of the Research Group for Deep-Sea Ecology and Technology at the Max Planck Institute for Marine Microbiology, and director of the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research.

Using samples from the mission, first-author Teresa Morganti, sponge expert from the Max Planck Institute for Marine Microbiology in Bremen, determined how sponges adapt to the most nutrient-poor environment.

Morganti clarifies: “Our evaluation showed that the sponges have microbial symbionts that can utilize old organic matter. This allows them to feed on the remnants of previous, currently extinct inhabitants of the seamounts, such as the tubes of worms composed of protein and chitin and other trapped detritus.”

Surviving on the leftovers

Sponges are considered one of the most basal forms of animal life. Nevertheless, they are successful and bountiful in all oceans, from shallow tropical reefs to the arctic deep sea.

Numerous sponges accommodate an intricate community of microorganisms in a symbiotic relationship. This adds to the health and nutrition of the sponges by making antibiotics, transferring nutrients, and getting rid of excretions. This additionally goes for Geodia-sponges, which dominated the community on the Arctic seamounts.

The unity of sponge and associated microbes is called a sponge holobiont. Teresa Morganti worked together with Anna de Kluijver, an expert from Utrecht University, and with the laboratory of Gesine Mollenhauer at the Alfred Wegener Institute to identify the food source, the growth, and the age of the sponges.

They found out that thousands of years ago, substances permeating the seabed’s interior were sustaining a rich ecosystem, home to various animals. When they died out, their remains stayed. Currently, these form the base of this unexpected sponge garden.

Microbial analysis of the microorganisms supported the researchers’ hypothesis. “The microbes have simply the appropriate toolbox for this habitat,” describes Ute Hentschel from the GEOMAR Helmholtz Centre for Ocean Research in Kiel. Hentschel conducted the microbiological evaluations with her group. “The microbes have the genes to digest refractory particulate and dissolved organic matter and utilize it as a carbon and nitrogen source, as well as several chemical energy sources available there.”

The scientists likewise revealed that the sponges work as ecosystem engineers: They generate spicules that form a mat on which they creep. This might further facilitate the local settling of particles and biogenic materials. The sponge holobionts can use this detrital matter, thus producing their food trap.

Protecting needs understanding

Langseth Ridge is an underwater range of mountains not far from the North Pole that rests underneath the perpetually ice-covered water’s surface. There, sponge biomass was comparable to shallower sponge grounds with much greater nutrient input. “This is an exceptional ecosystem. We have never seen anything like it before in the high Central Arctic. In the study area, primary productivity in the overlying water supplies less than one percent of the sponges’ carbon demand. Therefore, this sponge garden may be a transient ecosystem, yet it is rich in species, including soft corals,” says Antje Boetius.

The Arctic is among the most impacted regions by climate change. “Prior to our research, no similar sponge ground has been found in the high Central Arctic, an area of the ice-covered ocean. This area remains understudied caused the challenges associated with observing and sampling such ice-covered deep-sea ecosystems,” Morganti stresses.

The close collaboration of researchers from different institutions, including limit Planck Institute for Marine Microbiology, the Alfred Wegener Institute, and GEOMAR, allowed an extensive understanding of this shocking hotspot of life in the cold deep. “With sea-ice cover quickly decreasing and the ocean environment changing, a better understanding of hotspot ecosystems is important for protecting and managing the distinct variety of these Arctic seas under pressure,” concludes Boetius.

Read the original article on Scitech Daily.

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Reference: “Giant sponge grounds of Central Arctic seamounts are associated with extinct seep life” by T. M. Morganti, B. M. Slaby, A. de Kluijver, K. Busch, U. Hentschel, J. J. Middelburg, H. Grotheer, G. Mollenhauer, J. Dannheim, H. T. Rapp, A. Purser and A. Boetius, 8 February 2022, Nature Communications.
DOI: 10.1038/s41467-022-28129-7