Scientists in Australia have discovered that elevated carbon dioxide levels make it difficult for fish to recognise one another and form groups with familiar individuals.
Like humans, fish prefer to group with individuals with whom they are familiar, rather than strangers. This protects them from predators and provides them with faster social learning, all of which bolsters survival rates.
But it now turns out that climate change may threaten this behaviour. Scientists at the ARC Centre of Excellence for Coral Reef Studies at James Cook University, Australia have discovered that high carbon dioxide levels – such as those anticipated by climate change models – can hinder the schooling behaviour of fish.
In their investigation, the researchers reared fish under high carbon dioxide levels (similar to those projected for 2011 by IPCC models). Individual fish where then placed between two schools of fish: one of familiar fish and the other made up of strangers. Fish raised under normal conditions consistently chose the familiar school, while fish reared under elevated CO2 levels showed no preference for either the unfamiliar or familiar school.
The researchers believe that carbon dioxide interferes with the functioning of neuroreceptors in the fish brains. Higher carbon dioxide levels change the concentration of ions (electrically charged atoms and molecules) in the fishes’ blood, altering the way that the neuroreceptors work. This impairs basic senses, such as sight and smell, which are vital for recognition in fish.
These results could have serious implications for tropical fish, whose habitat is already threatened by climate change. “Familiarity is an important trait for defence, particularly in a predator-rich environment like a coral reef,” says lead investigator Lauren Nadler.
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