Global warming, ocean acidification, and KO’d crayfish

What do global warming, ocean acidification, and KO’d crayfish have in common? Carbon dioxide.

A forthcoming paper by Biewbower and Cooper caught my eye because it incidentally supports a contention in the last paper I co-authored on crustacean nociception (Puri & Faulkes 2010). We couldn’t find any evidence that crustaceans responded to acids.

The new paper isn’t actually interested in acids; it’s all about what carbon dioxide does to crayfish. The first question is, can crayfish detect changes in carbon dioxide concentrations at all?

The authors ran crayfish through a Y-maze: one arm with high CO₂ concentrations, and one without. The higher the carbon dioxide concentrations, the more the crayfish tended to avoid that end of the maze, suggesting that yes, the crayfish can detect carbon dioxide in water. They also found that when placed in a pool containing high levels of carbon dioxide, crayfish would leave the water to cross in the air to a chamber with lower levels.

Another possible interpretation is that the crayfish aren’t detecting carbon dioxide in these experiments, but a lack of oxygen. It could also be low pH. When you ramp up the concentration of carbon dioxide in water, create carbonic acid. This is why burning fossil fuels is leading to ocean acidification. Crayfish could have avoided the end of the maze because they detected the low oxygen or low pH rather than the carbon dioxide specifically.

Consequently, they created two control conditions in addition to regular water. First, they created a low-oxygen water by bubbling nitrogen through it. Crayfish did not discriminate between the nitrogen laden water and the regular water. Second, they made one end of the Y maze with normal CO₂ concentrations, but acidic pH; about 4.85.

And the crayfish walked right into it.

No difference between the regular water and the acidic. So their study supports ours: decapod crustaceans seem to be mostly ignorant of changes in pH.

Another interpretation might be that the animals are responding to low oxygen; to control for that, the authors also had a control condition with very high nitrogen concentrations in the water, which lowered oxygen, and again, the crayfish didn’t distinguish between that and regular water.

Bierbower and Cooper also found that at high concentrations, carbon dioxide does a number on the crayfish, effectively putting them out of action stopping their heart and ventilation (“breathing,” more or less).

Why are crayfish repelled by high levels of carbon dioxide? Not clear. Bierbower and Cooper suggest that high levels of carbon dioxide might be a cue that an environment is toxic. That said, these are swamp crayfish (Procambarus clarkii), and they probably have a pretty high tolerance for low quality water. It would be interesting to see if crayfish that favour highly oxygenated streams might be more sensitive to carbon dioxide concentrations.

While very interesting to me because of its relevance to a story I’ve been working on (crustacean nociception), this paper might have limited interest to others. Both the introduction and discussion are very general, and don’t convey a strong sense of where this fits into a broader research picture.

References

Bierbower, S., & Cooper, R. (2010). The effects of acute carbon dioxide on behavior and physiology in Procambarus clarkii. Journal of Experimental Zoology Part A: Ecological Genetics and Physiology DOI: 10.1002/jez.620

Puri S, Faulkes Z. 2010. Do decapod crustaceans have nociceptors for extreme pH? PLoS ONE 5(4): e10244. doi: 10.1371/journal.pone.0010244