Study finds warmer water affects the development of young fish more than acidification

For the world’s fish species, surviving climate change means growing up in oceans that are warmer and more acidic. How young fish cope with these new conditions will have a major impact on the distribution and abundance of global fish populations.

To investigate this issue, Professor Philip Munday and Dr. Sue-Ann Watson from the ARC Centre for Excellence for Coral Reef Studies led a team of researchers to find out what impact these conditions might have on the early life of the yellowtail kingfish – a large pelagic fish that is important to the commercial fishing industry as well as recreational fishers.

The team monitored the growth and development of baby fish – at larvae and juvenile stages – in water with higher temperature and acidity (conditions they are likely to experience in the future due to climate change).

In the warmer waters, twice as many baby fish did not survive compared with normal temperatures. However, in the more acidic waters, the growth and mortality of the young kingfish was not affected. Acidification did reduce the swimming performance of the young fish – however this varied between individual fish.

Researchers also found that young fish in the warmer water grew and developed faster, but that it was likely to be because of the constant food supplied to the fish in the experiment. In fact, constant food supply is unlikely to occur in nature (where food supplies are usually unreliable) which could mean that in the wild, even less young fish may survive in warmer conditions.

So what does this mean for the future of the yellowtail kingfish?

What we are likely to see in the future is that as ocean temperatures continue to warm, yellowtail kingfish populations will migrate to cooler waters to stay in their preferred temperature range. Over time, the distribution of the population will be different – less kingfish will remain in their warmer temperature range and populations will grow in their cooler temperature range. Similar fish species have already been documented moving closer to the North and South poles for this reason.

However, fish cannot migrate away from ocean acidification. The good news from the study is that acidification seems to have only limited effects on the young fish, as it did not affect their growth and mortality. Scientists did suggest that the reduced swimming performance of young fish could hamper their ability to escape predators, but since this effect varied a lot between individual fish, it is possible that over the long term, the species may be able to adapt.

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