An adult bigfin reef squid, one of the types of squid used in the study.
Photo: Blake Spady

Rising CO2 levels aren’t just dissolving coral reefs. They might be causing squid to act all kinds of weird.

That, at least, is the takeaway of a new laboratory experiment published in the journal Global Change Biology, which shows how elevated CO2 levels can affect the predatory behavior of two tentacled hunters, the pygmy squid and bigfin reef squid. While the experiment has some important caveats, it offers a reminder that the ecological fallout of changing ocean chemistry will be complex, and probably, weirder than we can imagine.

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While many studies have documented the harmful effects of rising CO2 (and a corresponding uptick in ocean acidity) on corals and mollusks, far fewer have looked at how these changes affects animal behavior.

“Most [behavioral studies] have focused on fish, however more recently, the effects of elevated CO2 has been demonstrated on less active invertebrates such as snails,” lead study author Blake Spady from the ARC Centre of Excellence for Coral Reef Studies told Earther in an email. “This raised the question as to whether highly active invertebrates, such as squid, were similarly affected.”

So, Spady and his colleagues did what any good scientists would: they dumped a bunch of squid in aquaria, pumped the water full of CO2 to mimic future ocean conditions under high carbon emissions scenarios, gave the little squirts some live prey, and watched what happened.

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Both types of squid were affected pretty dramatically.

Pygmy squid were about 20 percent less likely to attack prey in the high-CO2 treatments. Both pygmy and bigfin reef squid took longer to initiate their attacks when subjected to higher CO2 levels, and both “displayed more conspicuous body patterns during the attack,” according to Spady.

An adult bigfin reef squid.
Photo: Blake Spady

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Nobody’s sure why these changes occurred, or whether they’ll persist long term (the experiments only lasted five and 28 days for the pygmy and bigfin reef squid, respectively). Spady noted that previous research in fish and mollusks has shown how elevated CO2 can affect certain neurotransmitters impacting behavior, adding that they plan to investigate this in squid in the future.

It also isn’t clear if the effects will be the same in the wild. While tank squid managed to catch the same number of prey despite slower attacks, “in the wild, with increased variables it is possible that the changes in behavior seen here could give prey a greater chance of escape,” Spady said.

Zoe Doubleday, a cephalopod ecologist at the University of Adelaide who wasn’t involved with the study, cautioned that the lab conditions used in studies like this are “highly simplistic,” and that conclusions drawn from the field and lab can be quite different.

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For instance, “we find that snails are thriving in acidic conditions at natural CO2 vents, when all lab-based studies suggest that snails shouldn’t even be able to live at these vents,” Doubleday told Earther in an email. “We suggest they are able to thrive because CO2 increases their food supply (algae).”

Doubleday thought it was interesting that the two species showed somewhat different responses to elevated CO2. “There are over 800 [cephalopod] species and this suggests that the effect of [ocean acidification] on cephalopods could vary from species to species,” she said.

Clearly, a lot more research is needed. But it’s probably in our best interests to figure out what’s in store for cephalopods in the Anthropocene. After all, once they conquer the oceans, we’ll want them on our side.

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