About a quarter of the CO2 present in the atmosphere ends up in the oceans where it is transformed into carbonic acid (H2CO3). The increase in CO2 in the atmosphere therefore corresponds to a corresponding increase in that dissolved in sea water.
It has been estimated that between 1751 and 1994, the surface pH of ocean waters dropped from 8.25 to 8.14, with a corresponding increase in the concentration of H + ions. The Study: Ocean acidification effects on fish hearing, published on the Proceedings.
Biological sciences, said us: "Humans are rapidly changing the marine environment through a multitude of effects, including increased greenhouse gas emissions resulting in warmer and acidified oceans. Elevated CO2 conditions can cause sensory deficits and altered behaviors in marine organisms, either directly by affecting end organ sensitivity or due to likely alterations in brain chemistry.
Previous studies show that auditory-associated behaviors of larval and juvenile fishes can be affected by elevated CO2 (1000 µatm). Here, using auditory evoked potentials (AEP) and micro-computer tomography (microCT) we show that raising juvenile snapper, Chrysophyrs auratus, under predicted future CO2 conditions resulted in significant changes to their hearing ability.
Specifically, snapper raised under elevated CO2 conditions had a significant decrease in low frequency (less than 200 Hz) hearing sensitivity MicroCT demonstrated that these elevated CO2 snapper had sacculus otolith's that were s ignificantly larger and had fluctuating asymmetry, which likely explains the difference in hearing sensitivity.
We suggest that elevated CO2 conditions have a dual effect on hearing, directly effecting the sensitivity of the hearing end organs and altering previously described hearing induced behaviors. This is the first time that predicted future CO2 conditions have been empirically linked through modification of auditory anatomy to changes in fish hearing ability.
Given the widespread and well-documented impact of elevated CO2 on fish auditory anatomy, predictions of how fish life-history functions dependent on hearing may respond to climate change may need to be reassessed."