The deep ocean has a subtle, unnerving quality. The real thing, not the Hollywood version with its glowing fish and razor-sharp teeth. It is cold, always dark, and almost devoid of the nutrients necessary for most life. You wouldn’t expect anyone to construct a house there, much less one that is thousands of square kilometers in size. Nevertheless, you would discover gardens if you could manage to descend 800 meters below the surface off the coast of Brazil. Massive, expansive gardens of sponges, filtering seawater while sitting in complete darkness, seemingly since the time of the dinosaurs.
Depending on who you ask, sponges are either the world’s most underappreciated creatures or evidence that evolution occasionally chooses radical simplicity. Not a brain. Not a muscle. without a digestive system. Just an old blueprint that hasn’t changed much over hundreds of millions of years, a body full of pores, and a few tiny flagella that force water through. Perhaps that’s precisely the reason they remain here.
Researchers from the University of New South Wales conducted a study that was recently published in the journal Microbiome and provides what may be the most comprehensive explanation of how these organisms manage. After analyzing Calyx sponges that were collected from depths of more than 800 meters, the team discovered something that fundamentally alters our understanding of deep-sea life. The sponges are not merely surviving in a passive manner. They have created, or rather inherited, a two-part microbial system that effectively addresses their waste and energy issues simultaneously.
Chemosynthesis is carried out by about 16% of the microbes that inhabit these sponges. They draw carbon dioxide from the surrounding water to create biomass by using the ammonia that the sponge generates as metabolic waste as fuel. It is essentially the same process as photosynthesis, but it is not dependent on light. Heterotrophs, or organisms that use organic matter as a source of energy, make up the remaining 84%. They have evolved to break down some of the hardest, most resistant substances that drift down from the surface in an area where organic matter is scarce: the cell walls of dead algae, which are inaccessible to most other organisms.
The clever thing is that the two approaches work well together, which is where it starts to feel more like engineering and less like biology. The chemosynthesizers are fed by the waste from the sponge. The indigestible debris that is falling from above is handled by the heterotrophs. Together, they produce biomass that sustains fish, brittle stars, and dozens of other creatures that congregate around these seafloor sponge gardens. The sponge is not merely enduring. It is creating an ecosystem for itself.
This has a deeper history that is worth mentioning. According to research that MIT scientists published earlier this year, sponges might have been the first animals on Earth. Sponge-like organisms existed long before the Cambrian explosion, which occurred about 540 million years ago when complex animal life abruptly diversified, according to chemical traces found in ancient rock. The timeline is further back according to an Uppsala University study. If that’s true, these animals have now survived every known mass extinction in geological history. Each and every one. That is not fortuitous. That’s a tactic.
Considering all of this, it’s amazing how much we still don’t know. On paper, the designation of deep-sea sponge grounds as vulnerable marine ecosystems by the UN is significant. However, as one of the UNSW researchers, Alessandro Garritano, put it simply, acknowledgment is insufficient. Seabed mining and deep-sea trawling are already endangering habitats that scientists haven’t even completely mapped, let alone comprehended. The rate at which industry is interested in the ocean floor and the rate at which science is attempting to catch up are at odds.
For its part, the sponge doesn’t seem to care. It has been doing this in the dark, without complaint, and without sunlight for an unfathomably long time. It’s important to pay attention to that.
