They don't bite prey — they graze bacteria. In the deep sea, sea spiders survive by harvesting methane-eating microbes.

Sericosura spiders are the first of their kind caught feeding on methane-fueled microbes.

Methane is a menace to Earth's climate, but to tiny spiders in the pitch-black depths of the ocean, it's fuel for life.

In a bizarre twist of nature, scientists have discovered three previously unknown species of sea spiders thriving around methane seeps off the U.S. West Coast.

Far from the sunlit world, these translucent, alien-like creatures survive not by hunting prey but by farming bacteria on their own exoskeletons. The microbes feast on methane leaking from the seafloor and, in return, produce sugars and fats, turning the spiders into living ecosystems that graze on their own microbial coats.

"Just like you would eat eggs for breakfast, the sea spider grazes the surface of its body, and it munches all those bacteria for nutrition," said Shana Goffredi, a professor at Occidental College in Los Angeles and the lead author of the study.

"This unique nutrition strategy has never been observed in sea spiders before."

Bacteria on the menu

Unlike their fang-wielding cousins that pierce and suck fluids from soft-bodied prey, these newly discovered Sericosura species appear to lack the tools to hunt. Instead, they feed by simply grazing the bacteria that coat their bodies — organisms that convert methane and oxygen into energy-rich nutrients.

"While the deep sea feels really far away, all organisms are interconnected. Even though they're small, these animals have a big impact in that environment," Goffredi said. "We can't ever hope to sustainably (use) the oceans if we don't really understand the oceans."

"More than a clever survival trick, this symbiotic relationship may help trap climate-warming methane before it escapes into the atmosphere. Though tiny, these spiders and their microbial hitchhikers could be unsung custodians of the carbon cycle in one of Earth's most extreme ecosystems."

And it all happens in total darkness

At depths where sunlight never penetrates, life thrives not through photosynthesis but chemosynthesis — an energy process driven by chemicals like methane. As dead marine matter sinks and decomposes, it releases methane through cracks in the seafloor, creating nutrient-rich zones where only the most uniquely adapted species can survive.

While the Sericosura spiders are the first of their kind caught feeding on methane-fueled microbes, they're not alone in their unusual diet. Other creatures, like tube worms and sponges, are also known to rely on similar microbial partners.

Given the deep ocean's critical role in trapping methane, Goffredi believes the same microbes found on these spiders could one day be harnessed to clean up contaminated water in other environments.

The newly identified Sericosura species are tiny — barely 1 centimeter long — and nearly transparent, which limits their ability to roam. In fact, the three species studied were each found in different regions off the coasts of Southern California and Alaska, suggesting that their populations are highly localized.

Survival wrapped in silk
Their reproductive process is just as strange as their diet. Because these spiders are so small, many of their organs are tucked into their legs. When mating, females eject hundreds of eggs from their kneecaps, which the males gather and carry around in sac-like bundles wrapped around their limbs, like bracelets.

Once the eggs hatch, a new cycle begins. Bacteria clinging to the father's body are passed to the baby spiders, giving them an instant, built-in food source.

"People tend to think of the deep sea as a kind of homogeneous ecosystem, but that's actually untrue. There's a lot of biodiversity by region and animals are very localized to specific habitats on the seafloor," Goffredi said.

"You have to be very careful if you decide to use the seafloor for mining, for example. We don't want to cause any kind of irreparable harm to very specific habitats that aren't found anywhere else."

The study has been published this week in Proceedings of the National Academy of Sciences.
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