The study by NOAA Fisheries scientists and partners specifically examined larval cod behavior, growth and composition of lipids – the fats needed for storing energy and building muscles – against increased ocean acidification.
According to NOAA “studies like this are important because most marine fish mortality occurs at the larval stage of development and the high-latitude oceans where Pacific cod and other important commercial fisheries occur are expected to be among the most vulnerable to ocean acidification.”
“Changing environmental conditions can impact species in multiple ways and not all life stages may respond in the same way,” said Tom Hurst, lead author of the paper, which was published online by Marine Environmental Research. “We wanted to explore this because it has implications for the sustainability of Pacific cod and other important fish stocks in Alaska.”
The behavioral study showed that four-to-five-week-old cod larvae, when exposed to elevated levels of carbon dioxide, moved more quickly to areas of higher light levels than those raised on carbon dioxide levels that presently exist in Alaska seawater. Scientists are just starting to explore the significance of that behavioral shift, which has also been observed in other fish.
In their second study, researchers looked at larval fish growth rates when exposed to elevated carbon dioxide and fed two different diets, one more lipid-rich than the other.
They found that regardless of diet, two-week-old larvae reared at elevated CO2 levels were smaller than those reared at current CO2 levels. They also found that by five weeks of age the fish exposed to elevated CO2 conditions seem to have recovered from their slow start.
The observed differences in growth rates are most likely due to the changing physiology of larvae as they develop. “It is possible that by the time they reach five weeks old cod larvae are able to acclimate to effects of elevated CO2”, Hurst noted.
Researchers also suggested that the faster growth of older larvae may be facilitated by behavior changes that stimulate more aggressive feeding.
The researcher team plans to use what has been learned from these studies and other ongoing research to develop computer models to better predict how ocean acidification may affect Pacific cod and pollock larval survival, recruitment and adult fish populations in the Bering Sea 20 to 100 years from now.
The laboratory studies were conducted as a joint effort of the Alaska Fisheries Science Center, the College of Earth, Ocean and Atmospheric Sciences, and the Cooperative Institute for Marine Resources Studies at Oregon State University.