Deep-Sea Fish Unveil New Insights into Earth's Carbon Cycle

A groundbreaking study conducted by researchers at the University of Miami's Rosenstiel School of Marine, Atmospheric, and Earth Science has revealed that mesopelagic fish, particularly the blackbelly rosefish (*Helicolenus dactylopterus*), play a significant role in the ocean's carbon cycle. This research, published on July 15, 2025, in the *Journal of Experimental Biology*, demonstrates that these deep-sea fish excrete carbonate minerals at rates comparable to their shallow-water counterparts, a finding that enhances our understanding of marine biogeochemical processes and challenges existing global carbon cycle models.

Historically, mesopelagic fish have been an overlooked component of oceanic chemistry, despite accounting for approximately 94% of the global fish biomass. The study's lead author, Dr. Martin Grosell, Chair of the Department of Marine Biology and Ecology at the University of Miami, emphasized the significance of these findings, stating that “mesopelagic fish aren't just prey; they're chemical engineers of the ocean.” The research was funded by the National Science Foundation Chemical Oceanography Program and aimed to fill crucial gaps in marine carbon cycling knowledge.

Using specimens of the blackbelly rosefish, which thrive at depths of 350 to 430 meters, the researchers maintained the fish in controlled conditions that replicated their natural habitat. They discovered that these fish excreted approximately 5 milligrams of ichthyocarbonate per kilogram per hour, aligning with predictions from thermal and metabolic scaling models. This finding indicates that the physiological processes responsible for carbonate production are consistent across varying ocean depths.

The implications of this research are profound. According to Dr. Amanda Oehlert, co-author and Assistant Professor in the Department of Marine Geosciences, understanding the contribution of mesopelagic fish to carbonate flux is vital, especially in light of ongoing ocean warming. The study suggests that as ocean temperatures rise, the dynamics of carbonate production by these fish could change significantly, potentially affecting global carbon budgets.

This research not only strengthens the existing models of fish-derived carbonate production but also emphasizes the importance of ichthyocarbonate in the ocean's carbon cycle. The study's findings could lead to new avenues for investigating deep-sea carbon dynamics and improving Earth system models that account for the interplay between physical, chemical, and biological processes in the ocean.

The study, titled "Osmoregulation by the gastro-intestinal tract of marine fish at depth—implications for the global carbon cycle," represents a significant step forward in marine biology and environmental science. As researchers continue to explore the depths of our oceans, the role of mesopelagic fish in regulating Earth's climate processes is becoming increasingly recognized, highlighting an urgent need for further investigation into this underexplored realm of marine life.