At a Glance
- A new study provides the first direct proof that deep-dwelling mesopelagic fish produce and excrete significant amounts of carbonate minerals, known as ichthyocarbonate, into the ocean.
- Researchers used the blackbelly rosefish as a model species because it survives capture from deep waters, allowing for crucial laboratory observation of its physiological processes.
- The study found these deep-sea fish excrete carbonate at rates consistent with predictions for shallow-water species, confirming that pressure and cold do not inhibit this important function.
- These findings validate global climate models that had previously assumed, without evidence, that the vast biomass of mesopelagic fish contributed substantially to the ocean’s carbonate budget.
- Understanding this process is vital for accurately modeling the global carbon cycle and predicting how ocean chemistry might change in response to future climate warming.
Scientists have confirmed for the first time that deep-sea fish produce and excrete significant amounts of carbonate minerals. This finding validates their crucial role as “chemical engineers” in the ocean’s carbon cycle. The research, published in the Journal of Experimental Biology, addresses a significant knowledge gap regarding mesopelagic fish, which inhabit the ocean’s twilight zone and account for up to 94% of the world’s total fish biomass. These fish excrete stony, chalk-like particles called ichthyocarbonate as part of their osmoregulation process, a vital mechanism for balancing their internal salt levels in seawater.
To investigate this deep-sea process, researchers at the University of Miami Rosenstiel School of Marine, Atmospheric, and Earth Science studied the blackbelly rosefish, a species found at depths of 350 to 430 meters. Unlike most fragile, deep-dwelling fish, the blackbelly rosefish lacks a swim bladder and can survive the journey to a laboratory. In conditions mimicking their cold, deep-sea habitat, the fish were observed excreting carbonate at a rate of approximately 5 milligrams per kilogram per hour, a figure that aligns remarkably well with predictions based on fish from warmer, shallower waters.
“Mesopelagic fish live in deep, cold, high-pressure environments, and until now, it was unclear if they produced carbonate like shallow water fish do—or at what rate,” said Martin Grosell, lead author and chair of the Department of Marine Biology and Ecology at the Rosenstiel School, in a university press release. “These results offer strong support for global models of fish-derived carbonate production, which had assumed—but not verified—that mesopelagic species contribute at similar rates.” The study revealed that factors such as extreme pressure and low temperatures do not prevent the formation of these minerals.
The findings have significant implications for understanding global ocean chemistry and improving Earth system models, which are complex computer simulations of our planet’s climate. By confirming that the vast and mysterious population of mesopelagic fish is are major contributor to the ocean’s carbonate budget, this research opens new avenues for studying how deep-sea ecosystems influence the global carbon cycle and how they might be affected by a warming climate.
References
- Grosell, M., Marek, B., Walls, S., Pope, C., Cameron, S., Heuer, R. M., & Oehlert, A. M. (2025). Osmoregulation by the gastro-intestinal tract of marine fish at depth – implications for the global carbon cycle. Journal of Experimental Biology, 228(14). https://doi.org/10.1242/jeb.249834
- Udel, D. & University of Miami. (2025, July 25). Deep-sea fish confirmed as a significant source of ocean carbonate. Phys.Org; University of Miami. https://phys.org/news/2025-07-deep-sea-fish-significant-source.html
