As Jurassic Park’s Dr. Ian Malcolm put it, “life, uh, finds a way,” and that truism appears to apply to three newfound species of sea spider that thrives in environments devoid of both sunlight and oxygen by farming the methane-eating microbes that coat the creatures’ shells.
These species of sea spider, each belonging to the genus Sericosura, live around methane seeps, areas of the ocean floor that release methane gas (CH4), in the deep ocean along the Pacific coast between Alaska and California. Due to the depths that these seeps are found, no sunlight is available, resulting in a lack of photosynthesizing plants or cyanobacteria; this, in turn, results in an environment largely devoid of oxygen, almost fully consumed by O2-eating bacteria by the time surface waters circulate to locations like California’s Del Mar seep, found 1,018 meters (3,340 feet) below the surface.
While most sea spiders “typically feed on slow, soft-bodied invertebrates with their piercing-sucking mouthparts,” members of the fangless Sericosura genus are only found in these “chemosynthetic habitats”—regions where life needs to utilize chemical compounds other than O2 or CO2 to survive—a curious factor that prompted researchers at Occidental College and the California Institute of Technology to determine how these seemingly out-of-place spiders live.
The exoskeletons of the tiny Sericosura spiders were found to be coated in a layer of bacteria that are known to use methane as an energy source—one of the main compounds escaping from the seeps—much in the way other life forms use either oxygen or carbon dioxide to sustain themselves. After feeding a form of methane that uses an alternate isotope of carbon (carbon-13) to the bacteria, they were able to track the modified CH4 to the spiders themselves, confirming that the creatures were consuming the microbes for food.
“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,” according to study lead Shana Goffredi, a professor at Occidental College in California. “This unique nutrition strategy has never been observed in sea spiders before.”
Instead of being picked up from the surrounding environment, these microbes appear to be passed down through the generations, from parent to offspring: the bacteria found on Sericosura’s egg sacks has been found to be identical to samples taken from their fathers, who carry the species’ unhatched young in sac-like bundles attached to their legs.
The researchers believe that the peculiar metabolic process used by these bacteria (Methylomonadaceae, Methylophagaceae and Methylophilaceae) may be reducing the amount of methane from the ocean floor that reaches the surface by consuming the powerful greenhouse gas before it can escape. Although Sericosura spiders are the first arthropods to host methane-eating microbes, certain species of tube worms and sponges have been found to be part of similar symbiotic relationships, prompting concern from the research team that disturbing the ocean floor might exacerbate the advance of global warming.
“You have to be very careful if you decide to use the seafloor for mining, for example,” Goffredi warned. “We don’t want to cause any kind of irreparable harm to very specific habitats that aren’t found anywhere else.”