Deep-Sea Fish Found to Play Major Role in Ocean Carbon Cycle
A groundbreaking new study reveals that deep-dwelling fish contribute significantly to the ocean’s carbon cycle, excreting carbonate minerals at rates comparable to their shallow-water counterparts. This discovery validates existing global models and highlights the crucial, previously underestimated role of mesopelagic fish in regulating ocean chemistry.
The research, conducted by scientists at the University of Miami Rosenstiel School of Marine, Atmospheric, and Earth Science, focused on the blackbelly rosefish (Helicolenus dactylopterus), a species inhabiting depths of 350-430 meters (1,148-1,410 feet). The study aimed to determine if these deep-sea creatures form and excrete ichthyocarbonate – intestinal carbonate crucial for maintaining internal balance and influencing marine carbon cycling.
“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,” explained the study’s lead author. “This study is the first to confirm that they do and that the mechanisms and characteristics of ichthyocarbonate formation are remarkably consistent across depths.”
The ‘Chemical Engineers’ of the Deep
Researchers chose the blackbelly rosefish due to its unique physiological characteristics. Unlike many mesopelagic species, it lacks a swim bladder, allowing it to survive capture and laboratory acclimation. By maintaining specimens at 6 degrees Celsius – mirroring their natural habitat – the team observed the fish excreting approximately 5 milligrams of ichthyocarbonate per kilogram per hour, aligning with existing predictive models.
This finding is particularly significant given that mesopelagic fish account for up to 94 percent of global fish biomass. “This research fills a major gap in our understanding of ocean chemistry and carbon cycling,” stated a co-author and assistant professor. “With mesopelagic fish playing such a significant role, their contribution to carbonate flux – and how it might change with warming oceans – deserves greater attention.”
Key Findings Illuminate Ocean Carbon Dynamics
The study yielded several key insights:
- Deep-sea blackbelly rosefish produce carbonate at rates and compositions comparable to shallower fish, confirming that depth and pressure do not inhibit ichthyocarbonate formation.
- These results strengthen global estimates of fish-derived carbonate production, confirming that mesopelagic fish are substantial contributors to the ocean’s carbonate budget.
- Ichthyocarbonate composition remains consistent regardless of depth, influencing how and where it is stored or dissolved in the ocean.
“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 lead author added. “Mesopelagic fish aren’t just prey; they’re chemical engineers of the ocean.”
The research underscores the importance of ichthyocarbonate in the ocean carbon cycle, particularly considering the vast, largely unexplored biomass of the mesopelagic zone. .
Implications for Climate Modeling and Future Research
The authors believe these findings open new avenues for studying deep-sea carbon dynamics and could improve the accuracy of Earth system models – sophisticated computer simulations that integrate physical, chemical, and biological processes.
The study, titled “Osmoregulation by the gastro-intestinal tract of marine fish at depth – implications for the global carbon cycle,” was published on July 15, 2025, in the Journal of Experimental Biology. The research team included Martin Grosell, Bret Marek, Sarah Wells, Carolyn Pope, Cameron Sam, Rachael M. Heuer, and Amanda M. Oehlert, all affiliated with the University of Miami Rosenstiel School of Marine, Atmospheric, and Earth Science. Funding was provided by the National Science Foundation Chemical Oceanography Program and Earth Sciences Instrumentation and Facilities, alongside support from the University of Miami Rosenstiel School’s Departments of Marine Biology and Ecology and Marine Geosciences.
This research represents a critical step toward a more comprehensive understanding of the ocean’s role in regulating Earth’s climate and highlights the need for continued exploration of the deep sea.
