High carbon dioxide levels in oceans affecting fish behavior

Posted Jan 18, 2012 by Lynn Herrmann
Increased carbon dioxide emissions caused by humans could be impacting brains and central nervous systems of sea fish, causing behavioral changes leading to serious consequences in their ability to survive, a new international report reveals.
Providing world-first evidence, a new report published in the journal Nature Climate Change found high CO2 levels in sea water interferes with fishes’ ability to smell, hear and evade predators.
Professor Phillip Munday with the ARC Centre of Excellence for Coral Reef Studies, who reported the findings, said in a news statement, “For several years our team have been testing the performance of baby coral fishes in sea water containing higher levels of dissolved CO2 – and it is now pretty clear that they sustain significant disruption to their central nervous system, which is likely to impair their chances of survival.”
The study, Near-future CO2 levels alter fish behavior by interfering with neurotransmitter function, by Munday and his colleagues began by observing the performance of baby clown and damsel fishes alongside predator fish in CO2-enriched water, and while predators were somewhat affected, the baby fish suffered high rates of attrition due to disruption of a key brain receptor.
“We’ve found that elevated CO2 in the oceans can directly interfere with fish neurotransmitter functions, which poses a direct and previously unknown threat to sea life,” Munday added.
The researchers then studied how fishes’ sense of hearing - used for locating and homing in on reefs at night, and avoiding them in the day - was affected. They found the fish were confused, did not avoid reef sounds during daylight. Munday said, “Being attracted to reefs during daylight would make them easy meat for predators.”
Schooling behavior of fish is also impacted by high CO2 levels, losing their natural ability to turn left or right, increasing their chance of being alone, also making them easy prey.
“All this led us to suspect it wasn’t simply damage to their individual senses that was going on – but rather, that higher levels of carbon dioxide were affecting their whole central nervous system,” Munday continued.
The brain receptor, GABA-A, is in most animals with brains, but the research team said the effects of elevated CO2 emissions are most likely experienced by animals in the water, as they normally have lower blood levels of CO2.
“We’ve now established it isn’t simply the acidification of the oceans that is causing disruption – as is the case with shellfish and plankton with chalky skeletons – but the actual dissolved CO2 itself is damaging the fishes’ nervous systems,” Munday said.
Humans are responsible for around 2.3 billion tonnes of CO2 emissions dissolving annually into the world's oceans, leading to changes in the waters' chemical environment.