Giant sponge gardens discovered on seamounts in the Arctic deep sea
Sponges grow in large numbers and to impressive size on the peaks of
extinct underwater volcanoes

Date:
February 8, 2022
Source:
Max Planck Institute for Marine Microbiology
Summary:
Massive sponge gardens thrive on top of seamounts in the Central
Arctic Ocean, one of the most oligotrophic seas on Earth. They
appear to feed on the remnants of an extinct fauna. Microorganisms
support the sponges in exploiting this fluffy material as a source
of food and energy.



FULL STORY ========================================================================== Little food reaches the depths below the permanently ice-covered Arctic
Ocean, because light limits the productivity of algae. However, scientists
from Bremen, Bremerhaven and Kiel now discovered a surprisingly rich and densely populated ecosystem on the peaks of extinct underwater volcanoes, reporting their findings in the journal Nature Communications. These
hotspots of life were dominated by sponges, growing there in large
numbers and to impressive size.


========================================================================== "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," reports Antje Boetius, chief scientist 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 was able to
identify how sponges adapt to the most nutrient-poor environment. Morganti explains: "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." Living on the leftovers Sponges are considered to be one of the most
basal forms of animal life. They are nevertheless successful and abundant
in all oceans, from shallow tropical reefs to the arctic deep-sea. Many
sponges accommodate a complex community of microorganisms in a symbiotic relationship, which contributes to the health and nutrition of the
sponges by producing antibiotics, transferring nutrients and disposing
of excretions. This also 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 cooperated with
Anna de Kluijver, an expert from Utrecht University, and with the lab
of Gesine Mollenhauer at the Alfred Wegener Institute to identify the
food source, the growth and the age of the sponges. They learned that
thousands of years ago, substances seeping from the seabed's interior
were supporting a rich ecosystem, home to a variety of animals. When
they died out, their remnants remained. Now these form the base of this unexpected sponge garden.

Microbial analysis of the microorganisms supported the researchers'
hypothesis.

"The microbes have just the right toolbox for this habitat," explains Ute Hentschel from the GEOMAR Helmholtz Centre for Ocean Research in Kiel,
who carried out the microbiological analyses with her team. "The microbes
have the genes to digest refractory particulate and dissolved organic
matter and use it as a carbon and nitrogen source, as well as a number
of chemical energy sources available there." The scientists also showed
that the sponges act as ecosystem engineers: They produce spicules that
form a mat on which they crawl. This may further facilitate the local
settling of particles and biogenic materials. The sponge holobionts can
tap into this detrital matter, thus creating their own food trap.

Protecting requires understanding Langseth Ridge is an underwater mountain range not far from the North Pole that sits beneath the permanently
ice-covered water's surface. There, sponge biomass was comparable to that
of shallower sponge grounds with much higher nutrient input. "This is a
unique ecosystem. We have never seen anything like it before in the high Central Arctic. In the study area, primary productivity in the overlying
water provides less than one percent of the sponges' carbon demand.

Thus, this sponge garden may be a transient ecosystem, but it is rich
in species, including soft corals," says Antje Boetius.

The Arctic is one of the most affected regions by climate change. "Prior
to our study, no similar sponge ground has been identified in the
high Central Arctic, an area of the ice-covered ocean which remains understudied given the difficulties associated with observing and sampling
such ice- covered deep-sea ecosystems," Morganti stresses. The close cooperation of scientists from different institutions, including the Max
Planck Institute for Marine Microbiology, the Alfred Wegener Institute and GEOMAR, enabled a comprehensive understanding of this surprising hotspot
of life in the cold deep. "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," concludes Boetius.

========================================================================== Story Source: Materials provided by Max_Planck_Institute_for_Marine_Microbiology. Note: Content may be edited
for style and length.


========================================================================== Related Multimedia:
* Giant_sponge_gardens_discovered_in_the_Arctic_deep_sea ========================================================================== Journal Reference:
1. 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, A. Boetius. Giant sponge grounds of Central Arctic seamounts
are associated with extinct seep life. Nature Communications,
2022; 13 (1) DOI: 10.1038/s41467-022-28129-7 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220208113915.htm
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