A thriving community of centuries-old sponges is devouring the fossils of an extinct ecosystem atop the peaks of an underwater mountain range near the North Pole, reports a new study.
The discovery of this stunning biological hotspot is a testament to the resilience of life in even the most inhospitable environments, like the dark and nutrient-poor slopes hidden under the Arctic sea ice. Given that human-driven climate change is warming this Northern region at least twice as fast as the rest of the planet, better knowledge of these surprisingly vibrant ecosystems “is essential for protecting and managing the unique diversity of these Arctic seas,” according to the study, which was published on Tuesday in Nature Communications.
Antje Boetius, the chief scientist of the expedition that discovered the sponge community and a co-author of the study, said her team was “jumping for joy” when an underwater camera returned the first footage of the sponge gardens to the research vessel.
“It was a ship full of deep sea biologists who have studied the Arctic for decades, but we couldn't have dreamed of finding such a hotspot ecosystem,” recalled Boetius, who is also the 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, in a call.
“We’ve planned for a long time to have a mission dedicated to the discovery of what lives on the Arctic seamounts,” she added. “They are a mystery. The first maps of the seamounts were made decades ago, but no one was ever able to go there with a camera or high-resolution methods. I always dreamed of such an expedition where we could just explore and find out what lives on the Arctic seamounts.”
Boetius and her colleagues were able to make good on this dream during a 2016 expedition on the German research icebreaker Polarstern, which deployed a camera and sonar platform called the the Ocean Floor Observation and Bathymetry System (OFOBS) that is specifically designed to probe the little-known world under the Arctic ice. The team spotted the flourishing sponge gardens on the summits of an extinct volcanic range called Langseth Ridge, about half a mile under the ocean surface.
Sponges are versatile creatures found all over the world; though they resemble plants, they are one of the most ancient animal families. The sponges at Langseth Ridge are extremely long-lived, averaging about 300 years of age, according to the team’s findings. What’s more, the biggest sponges observed in the gardens exceed 30 inches in length. This large size and old age suggest that they have been well-fed for centuries despite the lack of nutrients available on these seamounts.
To figure out what could be sustaining this ecosystem, study lead Teresa Morganti, a sponge expert from the Max Planck Institute for Marine Microbiology, examined the complex microbes within the tissues of the sponges. The results revealed that the animals are digesting the fossilized remains of an extinct ecosystem that lived on the seamounts thousands of years ago, when they were volcanically active.
These long-dead creatures included tube worms that left behind remnants of protein and chitin that can be processed by the bacterial communities that live inside the host sponges. “They have helpers, bacteria, that digest the material that they are sitting on,” explained Boetius. “That is really new. I've talked to many deep sea biologists and they have not heard of that before.”
“It makes sense,” she added, “because why would you not have this transition between a living and a dying, or dead, ecosystem that sponges may profit off of?”
To that point, these lush sponge communities may be transient, destined to eventually recede over centuries or millennia as they run out of fossil material to consume (though Boetius noted that sponges are exceptionally good at adapting to new biomes and finding novel food sources).
This unexpected ecosystem may also be threatened by the rapid disruptions that the Arctic is experiencing as the result of human-driven climate change. The sea ice that currently conceals and protects this secret sponge garden is swiftly declining, which could lead to more exploitative commercial activity, such as benthic trawling, in these polar reaches.
These emerging human pressures highlight the need to further explore and safeguard Arctic environments, so that we can better understand the incredible lifeforms that inhabit them.
“I'm glad we have these pictures and we can demonstrate that it's worthwhile protecting the habitat rather than just not caring,” said Boetius. “So for me, this has an extra importance.”
“Once you see the pictures of this teeming life, you might be more inclined to say, ‘okay, let's not just go into these untapped worlds. Let's first check out what is there and then make a plan or a policy for protecting them rather than destroying them,’” she concluded.