More than 800 meters below the surface off Brazil's coast, where eternal darkness reigns and food is nearly impossible to find, vast gardens of deep-sea sponges are thriving in conditions that would kill most life on Earth. UNSW researchers have just revealed how these ancient creatures pull off this seemingly impossible feat—through an intricate partnership with microbes that turns waste into survival.
Published in the journal Microbiome, the groundbreaking study examined Calyx sponges collected from the Atlantic Ocean's abyssal depths and discovered something elegant: the sponge's microbial partners employ two complementary survival strategies to keep their host alive. Some microbes generate energy through chemosynthesis, harnessing ammonia produced by the sponge itself—essentially photosynthesis without sunlight. Others specialize in breaking down the toughest compounds hidden in the cell walls of dead algae that slowly sink down from the sunlit surface waters far above.
"Our study shows that sponges and their microbial partners are complex, biogeochemical reactors," explains researcher Alessandro Garritano, who led the work at UNSW. The implications ripple outward through the entire ecosystem. The biomass created by this remarkable partnership doesn't stay locked within the sponge—it feeds brittle stars, fish, and a cascade of other organisms clinging to the dark seafloor, proving that even in the ocean's most barren regions, life finds a way to build community.
These sponge gardens have puzzled scientists for years. How could anything persist across enormous stretches of seafloor in such relentlessly harsh conditions—cold, permanently dark, and starved of nutrients? The answer, it turns out, lies in microbes that have evolved to do the seemingly impossible: extract nutrition from the scraps that fall from above. The sponges themselves play host to these microbial engineers, creating what amounts to a living factory that continuously converts waste into sustenance.
The research also underscores how much remains unknown about deep-sea life. As human activities intensify—from deep-sea trawling to seabed mining—these fragile ecosystems face mounting pressure from industries that have only recently developed the technology to reach them. The United Nations has recognized deep-sea sponge grounds as vulnerable marine ecosystems, a designation meant to signal their ecological importance. Yet recognition, as Garritano warns, is far from sufficient protection.
"Recognition alone isn't enough to protect these delicate creatures and the ecosystems they help to create," he says. Many deep-sea sponge communities remain poorly understood and largely unprotected, even as industrial activity creeps deeper into the abyss. The new research provides critical insight into why these ecosystems matter not just for the strange and wonderful creatures that inhabit them, but for the larger ocean nutrient cycles that influence life across the entire planet. Understanding how deep-sea sponges and their microbial partners function is the first step toward defending them—before we lose worlds we're only now beginning to comprehend.