Study: No Evidence Ocean Acidification Harms Coral Reef Fish Behavior
Paper Reviewed: 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.
In an incredibly important and revealing paper published in the journal Nature, 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 a 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.”
Unfortunately, too many have been far too eager to jump to conclusions when it comes to estimating the impacts of ocean acidification.
And in this regard, 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.”
But how solid is this body of research?
Clark et al. note there are two important red flags that call the pessimistic ocean acidification projections of fish into question.
First, 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).
Second, they note that there are “substantial disparities [in published ocean acidification impacts] among studies and species, even when methodological approaches are similar.”
And so, to address these concerns, 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.”
In doing so, they replicated and built upon “some of the most prominent studies in this field to understand the diversity in behavioral responses within and across species.”
Furthermore, they raised the bar and enhanced the transparency of their work by fully documenting their methods and providing raw data to the public so that their work could be easily replicated by others.
And what did their work reveal?
Their study focused on three main research of ocean acidification research on fish: (1) chemical cues from predators, (2) activity levels and (3) behavioral lateralization.
With respect to chemical cues, Clark et al. “quantified the effects of elevated CO2 on predator cue avoidance across three consecutive years in 560 individuals from six species of pomacentrid coral reef fishes.”
Results of this segment of their analysis revealed that “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.”
Furthermore, 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.”
With respect to activity levels, Clark et al. note that prior studies indicate there is up to a 90-fold increase in activity in coral reef fishes exposed to end-of-century CO2 levels.
However, they report “most activity measurements (for example, distances moved) from coral reef fishes have not used video footage but have been made using direct manual observations” that are subjective in nature.
For their analysis, Clark et al. “filmed 582 individuals from six species across three years and quantified swimming activity in behavioral arenas using automated tracking software.”
The end result of this second focus was the observation that “fish exposed to high CO2 did not exhibit consistently elevated activity levels compared with conspecifics under control conditions.”
In contrast, they found that “activity levels were highly variable among individuals, increasing the risk of type-1 errors in experiments using small sample sizes, and possibly in large-sample experiments that rely on human observation rather than automated video analysis.”
Finally, with respect to behavioral lateralization, the researchers investigated this trait using 175 fishes across four species. Results indicated that there was no CO2 effect on population-level behavioral lateralization.
In commenting on their findings, Clark et al. state the obvious, 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.”
Consequently, they conclude that “on the basis of our findings on more than 900 wild and captive-reared individuals of six species across three years, we conclude that acclimation to end-of-century levels of CO2 does not meaningfully alter important behaviors of coral reef fishes.”
Therefore, they say “the catastrophic projections for fish sustainability based on CO2-induced behavioral impairments must be reassessed in light of our findings.”
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Andy Rowlands
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This ‘ocean acidification’ seriously annoys me. How can you measure the acidity, or increasing acidity, of something that is not an acid? The oceans are an alkaline.
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Monty
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One could measure the decreasing alkalinity.
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Andy Rowlands
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of course, and perhaps call it ‘ocean de-alkilinisation’, or some other concocted name. The important point however, is that for the oceans to become even the mildest acid, the pH would have to have a 20-fold decrease, passing through fresh water on the way. Unlikely in the extreme.
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Carbon Bigfoot
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I agree with you Andy as a drop from 8.2 to 8.1 pH is not acidification.
The other term Carbon Emissions are not Emissions they are by-products of the oxidation of hydrocarbons ( sometimes referred to as combustion ).
As long as we continue the inappropriate characterization of chemical terms we foster the continued ignorance of the faux scientists, media and the general public.
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Andy Rowlands
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I completely agree, like ‘fossil fuels’, they ain’t from dead dinosaurs.
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Squidly
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Most sea water around the world changes in pH by more than 0.3 pH every single 24hr period! .. some locations almost 0.5 pH !!!
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CD Marshall
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Unless I am completely wrong the pH of the oceans is based on volcanic activity and remains in the 8.1-8.3 baseline.
From a chemist (Pierre):
“CO2 reacts with water (H2O) to form carbonic acid (H2CO3). People think that increases in CO2 in the atmosphere will acidify the oceans and wreck havoc. Nothing can be further from the truth. It is the underwater volcanoes that spew calcium silicate (CaSiO3) on the ocean floor that control the acidity of the oceans. The ocean floor is littered with this product. Carbonic acid reacts with calcium silicate to give insoluble calcium carbonate (CaCO3). Carbonic acid then reacts with this calcium carbonate to give aqueous calcium bicarbonate (Ca(HCO3)2).
CaSiO3 + H2CO3 = CaCO3 + H2O + SiO2 (sand)
CaCO3 + H2CO3 = Ca(HCO3)2
Aqueous calcium bicarbonate has a natural pH of about 8.2 but runs from 8.1-8.3, slightly alkaline. The more carbonic acid you have, the more calcium silicate will react to neutralize it.”
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geran
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The oceans need constant supply of acid to counter the constant supply of alkalinity. CO2 is necessary to keep the alkalinity down. (Rain brings carbonic acid.) Dissolved CO2 is quickly sucked up by plant life, which serves the food chain for the oceans. The more CO2 the better.
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CD Marshall
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Oh and since over a million volcanoes are believed to be on the ocean floor with 100-500 thousand active or semi active at any given time, including the million plus years of previously heightened activity, I think its safe to say we’re in the clear of our oceans actually reaching neutral anytime soon.
I would be more worried about the assault on nuclear power though where they are claiming nuclear power plants are heating up the oceans.
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Matt
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One must be wary of scientists studying fish behaviour.
If you ignore the prominent driver related to breeding there are still the behaviours associated with change of light, tide cycle, and moon cycle. Without duplicating these variables you can have GIGO.
What I have never been able to figure out is how some species of fish with the weight of an atmosphere and water pressure on them can tune to barometric pressure.
Many fish species increase feeding activity with a falling barometer. Go figure!
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Jerry Krause
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Hi Matt,
Don’t you believe this is all an accident?
Have a good day, Jerry
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