A warm acid bath is not good for fish larvae

In a recent research article in the Journal of Experimental Biology (JEB), researchers used the larvae and juveniles of European sea bass to study effects of ocean acidification and warming over two generations of the fish. Studying the effects of acidification is important because the pH of oceans has already decreased by 0.1 pH units, which actually means a 30% increase in acidity. As ocean acidification and warming occur concurrently, it obviously makes sense to include warming in such studies. As for fish, the first author of the research article, Sarah Howald from the Alfred Wegener Institute for Polar and Marine Research (AWI), Germany, comments on the results in a section of the journal called Inside JEB. In her comments, she explains that “Fish had been thought to be less vulnerable to ocean acidification due to well-developed acid-base regulation systems”. More recently, however, researchers have discovered that fish larvae may be more sensitive than previously believed. In the current study, the researchers were particularly interested in how subsequent generations would respond. They therefore conducted a long-term study (5.5 years), in which the experimental treatment consisted of rearing newly hatched fish larvae in acidified conditions (and the appropriate control), corresponding to those that the IPCC predicts will be a reality in 120 years. When these fish reached maturity and spawned, this second generation of fish larvae was transferred again to acidified conditions and to combinations with cooler or warmer water. It turned out that larvae in a combination of acidified and warmer water were smaller when they metamorphosed into juvenile fish than the larvae that developed in other experimental treatments. However, as juveniles, the growth of these fish was actually accelerated. According to Inside JEB “…the team isn’t sure whether the warmth was accelerating the fish’s growth or whether the acidity failed to impair the growing juveniles”. The team also warns that faster growth comes at a risk of possible food deficiency.

Sources:
Howald, S. et al. 2022. Effects of ocean acidification over successive generations decrease resilience of larval European sea bass to ocean acidification and warming but juveniles could benefit from higher temperatures in the NE Atlantic. J. Exp. Biol. 225 (9): jeb243802. https://doi.org/10.1242/jeb.243802
Kathryn, K. 2022. Ocean acidification impacts fish larvae but warming could compensate juveniles. Inside JEB. J. Exp. Biol. 225 (9): jeb244420. https://doi.org/10.1242/jeb.244420