Clark, T.D., Raby, G.D.,
Roche, D.G., Binning, S.A.,
Speers-Roesch, B., Jutfelt, F.
and Sundin, J.
2020
Ocean acidification
does not impair
the behavior of
coral reef fishes.
Nature 577: 370-375.
NOTE:
Clark et al. (2020) write that "establishing a robust and independently replicated database of the effects of ocean acidification on fishes is essential to gain reliable understanding of the consequences of climate change on marine ecosystems." Such a database, they add, is critical "before drawing broad conclusions and implementing management measures."
Clark et al. note that "a number of highly publicized studies have reported detrimental effects of elevated CO2 levels on the sensory systems and behaviors of fishes, with coral reef fishes appearing to be the most sensitive despite experiencing large daily and seasonal fluctuations in nature (for example, 100-1,300 µatm)."
Such projected detrimental effects include "alterations in olfaction, hearing, vision, learning, behavioral lateralization, activity levels, boldness, anxiety and susceptibility to predation," which have led to "dire predictions for fish populations and marine ecosystems."
SUMMARY:
Clark et al. state that "in contrast to previous studies on the same and closely related species, we found no consistent detrimental effects of end-of-century CO2 levels on the avoidance of predator chemical cues, activity levels or behavioral lateralization."
They conclude that "on the basis of our findings on more than 900 wild and captive-reared individuals of 6 species across 3 years, we conclude that acclimation to end-of-century levels of CO2 does not meaningfully alter important behaviors of coral reef fishes."
"The catastrophic projections for fish sustainability based on CO2-induced behavioral impairments must be reassessed in light of our findings."
DETAILS:
How solid was the prior research?
Clark et al. note there were two important red flags:
(1)
Fish are well-known for having robust acid-base regulatory systems that help them maintain tissue pH, even under extreme partial pressure levels of CO2 (pCO2) that exceed end-of-century pCO2 forecasts by 15 times (i.e., 15,000 µatm).
(2)
There are "substantial disparities [in published ocean acidification impacts] among studies and species, even when methodological approaches are similar."
The team of seven scientists "commenced a three-year research program in 2014 to quantify the effects of end-of-century ocean acidification on the sensory and behavioral ecology of coral reef fishes."
And what did their work reveal?
"None of the coral reef fishes that we examined exhibited attraction to predator cues when acclimated to high CO2 levels, in contrast to previous reports on the same and other species."
They used statistical procedures to compare their data with prior datasets and found that "the [negative] results reported previously for coral reef fishes are highly improbable (probability of 0 out of 10,000)...show[ing] no evidence of CO2 effects on chemical cue avoidance."
For their analysis, Clark et al. "filmed 582 individuals from 6 species across 3 years and quantified swimming activity in behavioral arenas using automated tracking software."
The end result was the observation that "fish exposed to high CO2 did not exhibit consistently elevated activity levels compared with conspecifics under control conditions."