Deep-sea exploration has revealed the existence of ecosystems that are not powered by photosynthesis. For example, microorganisms that are able to metabolize hydrocarbons emitted from methane seeps form the basis of food webs that can comprise hundreds of animal species. Now, a study published in Proceedings of the National Academy of Sciences USA shows that some sea spiders (from the class Pycnogonida) harness the chemical energy of methane seeps by feeding on chemoautotrophic bacteria that live on their exoskeleton. During oceanographic expeditions off the coasts in California and Alaska, Dal Bó and colleagues collected specimens of three species of sea spiders known only from methane seeps. Through sequencing analyses and microscopic observations, they found abundant and diverse methanotrophic and methylotrophic bacteria living on the sea spider bodies. This association is more than skin deep: isotopic labelling experiments and subsequent single-cell imaging and analyses of digestive tissues showed that the sea spiders assimilate methane-derived carbon by consuming the methane-oxidizing bacteria. The presence of the bacteria also on the egg sacs carried by adult males suggests that these invertebrates pass on their microbial symbionts to their offspring. Beside putting sea spiders in the company of the hairy-chested yeti crab among the animals known to farm specialized bacteria on their own bodies, Dal Bó and colleagues’ discovery showcases how much there is still to discover about the life forms and ecosystems of the ocean depths.
Original reference: Proc. Natl Acad. Sci. USA 122, e2501422122 (2025)
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