Deep-Sea Isopods Live Over Five Years Sans Food

Deep-sea isopods, giant crustaceans that inhabit the cold, dark depths of the ocean, can survive for more than five years without food thanks to a combination of anatomical and genetic adaptations, according to a new study published in Cell.

The findings focus on two species, Bathynomus doederleini, found about 300 metres below the sea surface, and Bathynomus jamesi, found at depths of around 900 metres, Reuters reports.

The deep sea is a harsh environment where food is scarce and arrives only occasionally as dead organic matter drifting down from above.

“It is a world of perpetual night and crushing pressure, yet life finds a way,” said Jianhai Xiang, a crustacean biologist at the Institute of Oceanology of the Chinese Academy of Sciences and one of the study's authors.

Researchers found that deep-sea isopods survive long periods without food through a combination of a huge stomach, an extremely low metabolism and the activity of a gene involved in controlling energy production.

These bottom-dwelling scavengers have flattened, segmented bodies, 14 jointed legs and a hard exoskeleton. Some species grow to more than half a metre in length. Like pill bugs found on land, they can curl into a ball for protection.

According to lead author Jianbo Yuan, a professor at the Institute of Oceanology, deep-sea isopods have a clever “earn more, spend less” survival strategy.

In the deeper-dwelling species, the stomach occupies about two-thirds of the body cavity, allowing the animals to store large amounts of food when it becomes available.

Yuan compared the stomach to a “food warehouse” that slowly releases energy while the body runs on “standby mode”.

With drastically lower metabolism, slower digestion and highly efficient nutrient use, Yuan said, "they can make that one meal last for years."

Researchers also found that microbes living in the isopods’ stomachs may contribute to their survival. In the deeper-dwelling species, bacteria called Chlamydiae were linked to fat storage, potentially providing the animals with a slow-release source of energy while giving the bacteria a stable environment.

“This is a win-win,” Yuan said.

The study also identified a gene called ND1 that appears to have originated in a symbiotic bacterium before becoming part of the isopod's own genome through a process known as horizontal gene transfer.

Yuan said the isopod appears to have “borrowed” or “hijacked” a bacterial gene that helps control energy production.

“This is surprising because bacteria and animals are very different, and such transfers are extremely rare,” Yuan said. “The gene gives the isopod an extra tool to fine-tune its energy use, especially when it needs to slow down.”

Because deep-sea isopods are difficult to study alive, researchers tested the ND1 gene in zebrafish, nematode worms and human cells. The gene increased metabolism under normal temperatures but helped conserve energy and extend survival during starvation under cold conditions.

Yuan said ND1 functions like a metabolic switch, increasing or reducing energy use depending on environmental conditions.

Study co-author Kahou Chu, professor emeritus at the Chinese University of Hong Kong, said horizontal gene transfer can provide organisms with a faster route to acquiring new traits than ordinary inheritance, helping some species out-compete others in extreme environments.

Xiang described the deep sea as “Earth’s largest living space” and said the unusual adaptations of its inhabitants could provide ideas for medicine, robotics and conservation.

Understanding how animals survive severe food shortages can also help researchers think about resilience in a changing planet, including food-web disruptions and climate change, Xiang said.