Elysia chlorotica, a bright green marine gastropod native to the eastern coast of North America, engages in one of nature's most extraordinary biological heists: kleptoplasty. As a juvenile, the sea slug feeds on the intertidal alga Vaucheria litorea. Rather than fully digesting its meal, Elysia chlorotica pierces the algal cell walls and selectively retains the functional photosynthetic plastids (chloroplasts) inside its own specialized digestive cells lining its gut.
Amazingly, these stolen organelles continue to fix carbon and produce energy through photosynthesis inside the animal for up to nine months without the slug needing further nourishment. For decades, scientists were baffled by how these chloroplasts survived so long inside a host organism without algal nuclear genes to repair damaged photosynthetic proteins, particularly the vulnerable Photosystem II complex. Early theories posited horizontal gene transfer between the alga and the slug's nucleus, though recent genomic sequencing suggests host-derived protective mechanisms and exceptionally stable algal proteins play a larger role than previously believed.
This solar-powered survival strategy allows Elysia chlorotica to survive harsh seasonal periods when food sources become scarce, serving as a unique living model for biological endosymbiosis and metabolic cellular integration.