A recent study has revealed that rising carbon dioxide (CO₂)-driven changes in ocean chemistry are impairing the sense of smell in fish, with wide-ranging implications for marine ecosystems and food chains.
Researchers exposed juvenile marine-fish species to elevated CO₂ concentrations expected later this century and observed that the fish required up to 42 percent closer proximity to an odour source in order to detect it compared with those in current CO₂ conditions. The effect was linked to changes in the olfactory system and altered gene expression in neural-processing regions responsible for smell.
In behavioural tests, fish exposed to higher CO₂ levels failed to respond to predator cues, avoided less effectively and displayed muted escape reactions. One lead researcher noted that although the olfactory receptors themselves appeared unaffected, the neural pathways processing smell signals in the brain were disrupted.
The findings raise concern for survival behaviours that rely on scent — such as detecting predators, locating food, navigating to spawning grounds and recognizing habitat cues. Scientists warn that if fish cannot detect threats or key environmental signals, population-level impacts may follow: higher predation, reduced reproductive success and impaired migration.
Experts say the study underscores how indirect consequences of human-driven CO₂ emissions — beyond warming — are quietly altering marine life. Ocean acidification and chemical changes in seawater are not only affecting shell-forming organisms, but also sensory systems of vertebrates in ways that may destabilize marine ecosystems.
Although full ecosystem-scale effects remain uncertain, the research calls for greater attention to how sensory impairment in marine species under climate-stress conditions could affect fisheries, conservation strategies and food security.
