Will high CO2 levels impact fish behaviour?
Carbon pollution has much greater impact than just climate change..
Will high CO2 detrimentally impact fish behaviour? was a fact-check asked on Metafact, a place to source the facts direct from experts. This expert answer originally published at metafact.io.
Professor Philip Munday, Professor of Marine Biology at James Cook University has answered this question: “Likely”
There are now many laboratory studies showing that elevated carbon dioxide (CO2) levels can affect the behaviour of some fish. Similar effects have also been observed in a range of invertebrates, including squid. Most of the studies conducted to date have focused on the larval and small juvenile stages because it is thought they should be more sensitive to altered environmental conditions than adults.
Elevated CO2 levels, around 1000 microatmospheres (equivalent to 1000 ppm) can alter a range of sensory and behavioural traits in fish, including response to olfactory cues, response to auditory cues, turning preference (lateralization), learning ability, boldness, activity and escape responses.
The experiments span a diversity of fish from coral reef fishes (most examples) to sticklebacks, European seabass, sharks, barramundi and salmon. These behavioural changes have been linked to higher mortality in larval fish exposed to elevated CO2 in the laboratory and then placed back on the reef under natural conditions.
However, not all species are equally affected, some appear to be much more sensitive to behavioural effects of elevated CO2 than others, and other species (e.g. cod and epaulette sharks) appear to suffer no adverse behavioural effects of exposure to high CO2 at all. Interestingly, however, the same larval cod that experience no adverse behavioural effects have much higher mortality when reared in elevated CO2 conditions. So, in this case, they are even more sensitive to high CO2, because it can directly increase mortality even if it doesn’t alter their behaviour.
As well as being species specific, recent studies have shown that the behavioral effects of high CO2 in fish can also be highly context specific. For example, new research has shown that fish from habitats where CO2 cycles on a daily basis, such as coral reefs, are less affected by higher CO2 levels when there is a daily cycle around the higher CO2 level compared to a stable high CO2. Therefore, it appears that CO2 cycles can mitigate, or even prevent, behavioural impairments at higher CO2 levels in some fish.
Other new research has shown that the history of the individuals can matter. For example, larval reef fishes exposed to a high-risk environment were unaffected by elevated CO2, whereas the behaviour of larval fish from a low-risk environment was altered by the same CO2 level.
New studies are also showing that sensory compensation and ecological complexity can help mitigate the behavioural effects of elevated CO2. While sensory impairments were detected in fish reared in high CO2, this did not affect their ability to catch prey in an ecological complex environment. This might help explain why the fish communities at natural CO2 seeps are not vastly different from fish communities on nearby reef that are not affected the CO2 seeps.
So, in summary, yes, high CO2 can alter fish behaviour, but not in all species, and there are other environmental factors that can either partially or fully mitigate these effects, at least under some circumstances. We also need to be aware of the CO2 levels used in previous experiment compared with likely end-points under more conservative CO2 emissions scenarios, such as the Paris Agreement. The reductions in CO2 emissions that need to be achieved to keep warming well below 2C would also mean that the threshold levels for the occurrence of behavioural effects of high CO2 in fish would not be reached.
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