What lies at the bottom of the ocean? For many, it’s a dark and mysterious place, full of creatures we know little about. But sometimes, discoveries shed light on these mysteries. A new study has done just that, focusing on an unusual deep ocean dweller who likes to eat Sargassum.
Bathyopsurus nybelini , an isopod living nearly 3.7 miles (6,100 meters) deep beneath the ocean's surface, has a very unique diet: it feeds on Sargassum algae that sinks down from the ocean’s surface.
The study, led by Johanna Weston, a hadal ecologist at Woods Hole Oceanographic Institution ( WHOI ), reveals just how connected the surface of our oceans is to the deep sea.
Let's find out what makes this discovery so fascinating and important.
Sargassum in the deep ocean
In the summer of 2022, a group of researchers set out on an adventure with Alvin , a human-occupied submersible, to explore the Puerto Rico Trench and the Mid-Cayman Spreading Center in the Caribbean Sea.
Thanks to Alvin's recent upgrades, including better deep-diving abilities and high-res image capturing, this journey became a reality.
While exploring the ocean depths, the team observed something unexpected: an isopod swimming upside down and away from the seafloor, clutching a frond of Sargassum algae as long as its own body.
At these depths -- between 5,001 and 6,284 meters -- Alvin filmed 32 individual isopods and collected two samples for further study.
According to Weston, “It was exciting to see this beautiful animal actively interacting with Sargassum, deep in the ocean. This isopod is so rarely seen; only a handful of specimens were collected during the groundbreaking 1948 Deep Sea Swedish Expedition.”
Unexpected food source
Sargassum is a type of brown algae typically found floating on the ocean's surface, forming dense mats that stretch for miles. In the sunlit zone, it thrives, photosynthesizing like any other plant.
However, when Sargassum dies or detaches from its floating mats, it begins a slow, downward journey into the dark abyss.
That’s where Bathyopsurus nybelini comes in. This deep-sea isopod seems to wait patiently, adapted to find and feast on this sunken source of nutrients.
“This isopod illustrates that an animal in a dark and high-pressure environment at the bottom of the seafloor has evolved multiple adaptations to feed on algae that grow in a sunlit ecosystem," explains Mackenzie Gerringer, a deep-ocean physiologist at SUNY Geneseo and co-lead author of the study.
It’s an unlikely meal, but one that provides essential nourishment.
Isopods and deep ocean Sargassum
Why is this discovery such a big deal? For one, Bathyopsurus nybelini has developed unique adaptations to survive in an environment where most creatures would struggle to find food.
It uses a specialized swimming stroke, moving upside down and backward with large paddle-like legs, to carry Sargassum fronds off the seafloor. This might be a clever strategy to avoid predators by lifting its food into the water column.
But the adaptations don’t stop there. This isopod has mouthparts that are serrated and ideal for tearing and consuming the tough, fibrous Sargassum.
Inside its gut, it harbors bacteria that help break down the algae’s complex polysaccharides -- molecules that are notoriously difficult to digest.
“Life everywhere, even in the deepest depths of the sea, is inexorably connected to the microorganisms around it,” says Logan Peoples, an aquatic microbial ecologist at Flathead Lake Biological Station .
Web of life from surface to seafloor
The presence of Sargassum at such deep depths has bigger implications for how we understand ocean ecology. This study highlights the close connection between the surface ocean and the deep sea.
When Sargassum sinks, it plays a role in carbon cycling and storage, which affects global climate patterns.
We’re already seeing significant ecological and economic impacts on coastal communities due to changes in how much Sargassum is found in the tropical Atlantic and Caribbean Sea.
Researchers are eager to figure out just how much Sargassum makes it to the seafloor and how its arrival varies with the seasons and long-term environmental changes.
Understanding these dynamics could help us predict how deep ocean communities respond to shifting environmental conditions.
Why does this matter?
The discovery of Bathyopsurus nybelini feeding on Sargassum also highlights the importance of advanced technologies in deep-sea exploration.
Alvin, the submersible that made this observation possible, was recently certified to dive to depths of 6,500 meters.
This achievement opens new doors for marine research and underscores the significance of developing new tools and techniques to explore and study the ocean’s most remote regions.
As Anna Michel, Chief Scientist for the National Deep Submergence Facility , noted, "The discovery described in this paper was possible due to its new deeper diving capabilities, which is very exciting for the Alvin team."
Deep-sea ecosystems and human impact
Why should we care about an isopod munching on seaweed at the bottom of the ocean? Well, it all comes down to how connected our planet’s ecosystems are.
As human activities change ocean conditions -- from climate change to pollution -- it’s really important to understand how surface processes link to deep ocean ecosystems.
Every discovery, like that of Bathyopsurus nybelini , reminds us that even the most extreme environments on Earth are part of a larger, interconnected web of life.
The more we learn, the better equipped we are to protect these ecosystems and manage the impacts of our actions.
Impact of Sargassum on the deep ocean
This study is just the beginning. Scientists plan to continue investigating how Sargassum and other surface-derived materials affect life in the deep sea.
More research is needed to understand the seasonal and long-term changes in the abundance of Sargassum and its impact on deep-ocean food webs.
As we explore further, new discoveries will undoubtedly reshape our understanding of these hidden ecosystems.
As Weston puts it, “We’re excited to share its amazing story of adaptation and this important reminder that habitats and organisms on our planet are deeply and intricately connected.”
The ocean is vast, and there is so much more to uncover. So, what other secrets lie in the deep, dark waters? Only time, curiosity, and continued exploration will tell.
The full study was published in the journal Proceedings of the Royal Society B: Biological Sciences .
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