Scientists have discovered three new species of a sea spider that live off bacteria feeding on methane — a rare survival tactic seen deep in the ocean off the U.S. West Coast. These tiny creatures, each about the size of a fingernail, were found near underwater areas called methane seeps, where gas seeps out of cracks in the ocean floor.
The findings were published this week in the Proceedings of the National Academy of Sciences. The research team, led by Shana Goffredi of Occidental College in California, identified the new sea spider species, all part of the Sericosura genus, and found that these creatures rely heavily on bacteria that grow directly on their outer shells.
Instead of hunting for food, the sea spiders seem to scrape the bacteria from their own bodies to eat. This marks the first time scientists have seen this type of behavior in sea spiders.
Microbe partnership offers energy and protection
The relationship between the sea spiders and the bacteria is unusual but effective. The bacteria, which feed on methane, create energy-rich nutrients like sugars and fats that benefit the sea spiders. In exchange, the spiders offer a safe surface for the bacteria to grow.
These methane seeps are found at great depths, where sunlight doesn’t reach, so bacteria there must rely on chemical energy instead of light. Marine biologist Nicole Dubilier, who was not involved in the study, called the partnership “a perfect zone” for both organisms, noting that even if most of the bacteria are eaten, the survivors can continue reproducing.
Unlike other sea spiders, which typically use fang-like parts to catch soft prey like jellyfish, these newly found species lack such features. In laboratory settings, researchers observed them feeding on the bacteria growing on their own bodies, confirming their unusual feeding method.
Chemical analysis of their tissues backed this up, showing that the bacteria weren’t just living on the spiders but were also serving as a primary food source.
Reproductive behavior may offer clues for microbiome research
Beyond feeding habits, the study revealed striking reproductive behavior. Females release hundreds of eggs from joints in their legs, which the males gather into pouches and carry. Once the eggs hatch, the young sea spiders appear to collect bacteria from the males’ bodies, starting the microbial relationship early in life.
Scientists say this discovery could offer insights into how helpful bacteria are passed from one generation to the next — a process that also happens in humans, such as the transfer of gut bacteria from mothers to newborns.
Researchers believe this deep-sea discovery may also have environmental value. The methane-eating microbes not only support sea life but may help limit the amount of methane — a powerful greenhouse gas — from entering the atmosphere. Understanding how these microbes work could lead to future ways of reducing ocean pollution.
Goffredi noted that while people often think of the deep sea as one uniform environment, it actually contains a wide range of ecosystems, each with its own unique species.