Deep-Sea Sponges Thrive in the Abyss Thanks to a Two-Pronged Microbial Strategy
A new study published in the journal Microbiome by researchers Alessandro N. Garritano and Torsten Thomas has revealed the remarkable survival strategies of deep-sea sponges of the genus Calyx, collected from a depth of 830 meters. The research identifies two distinct metabolic strategies employed by their symbiotic microbes, allowing the sponges to flourish in the dark, nutrient-starved conditions of the deep ocean.
Key Findings
The study analyzed Calyx species and found they host two types of microbial partners, each playing a critical role:
- Chemosynthesis (16% of microbial partners): These microbes use ammonia—a waste product from the sponge—as an energy source to fix carbon dioxide into biomass. This process is analogous to photosynthesis but requires no sunlight whatsoever.
- Heterotrophy (84% of microbial partners): These microbes produce enzymes that break down complex organic compounds, such as xylan and pectin, which are major components of algal cell walls. By converting otherwise indigestible, low-quality organic matter into nutrients the sponge can use, these microbes unlock a crucial food source.
"This dual strategy enables the sponges to thrive in deep-sea environments where light is absent and organic matter is scarce."
Background and Ecological Significance
By volume, approximately 95% of the ocean consists of permanently dark, cold deep sea. Deep-sea sponge gardens, which can cover thousands of square kilometers on the ocean floor, serve as habitats for other organisms and act as ecosystem engineers. Sponges are known to filter thousands of liters of water daily, releasing nutrients that support other marine life.
The sponge-microbe system functions as a biogeochemical reactor, recycling ammonia, carbon dioxide, and recalcitrant organic matter. The biomass generated by this process supports a broader community of organisms, including brittle stars and fish.
Threats and Conservation Status
The United Nations has classified deep-sea sponge gardens as Vulnerable Marine Ecosystems. The study notes that these ecosystems face significant threats from human activities, including deep-sea trawling and mining for rare metals. Recovery from such disturbances could potentially take centuries.
"The authors state that there is a need to understand the role of these ecosystems in the carbon cycle before they are damaged by human activities."