Study Shows Ocean Acidification May Directly Harm Fish

Fossil fuel combustion, and with it the release of heat-trapping carbon dioxide (CO2), is still growing globally. Beyond climate change, this is also causing the world’s “other CO2 problem,” ocean acidification, i.e., the formation of carbonic acid when CO2 from the atmosphere enters seawater. Studies have already demonstrated a multitude of negative effects of elevated CO2 conditions for many groups of marine organisms such as corals, plankton, shellfish and sea urchins. To date, scientists have assumed marine fish were immune to ocean acidification.

However, in a new article published in the journal Nature Climate Change, researchers from Stony Brook University demonstrate that “the fish are okay” belief ignores an important knowledge gap – the possible effects of CO2 during the early development of fish eggs and larvae. Co-authors of the study, Christopher Gobler and Hannes Baumann, are professors at the Stony Brook University School of Marine and Atmospheric Science (SoMAS) and represent one of several international teams working on closing this gap.
 
Their present study is the first to show that elevated CO2 levels significantly decreased survival and growth rates in eggs and larvae of a fish. The researchers reared newly fertilized eggs of a common estuarine fish, the inland silverside (Menidia beryllina), under different CO2 levels predicted for future oceans (current: ~400 ppm, mid-century: ~600 ppm, end-of-century: ~1,000 ppm) and found that egg and larval stages of these fish were highly sensitive to CO2. On average, survival rates until one week post-hatch declined by more than 70 percent under elevated (1,000 ppm) compared to current day CO2 conditions. In addition, surviving larvae were 18 percent smaller in the high than in the low CO2 group.  The experiment was fully replicated and repeated five separate times, each revealing the same pattern.
 
“We knew from the study of other ocean animals, such as scallops and clams, that earliest life stages such as larvae are most sensitive to CO2 and thus targeted the same life stage during our investigation of fish,” said Professor Gobler.

The study thus joins a growing body of evidence, suggesting that fish will both directly and indirectly be affected by ocean acidification, which also includes the potential for decreasingly productive commercial fish stocks. 

“This study is a shot across the bow and shows that some important fish stocks may be eroded by high CO2 levels," Brad Warren, science director of Sustainable Fisheries Partnerships said. "And keep in mind, as estuarine fish, inland silversides are likely to be adapted to higher levels of CO2 than many fish found in the open ocean, where chemistry is much more stable. This suggests that many commercially harvested marine fish stocks may be vulnerable too. Pelagic spawners, such as albacore, bigeye, yellowfin, and bluefin tuna, whose larvae are not adapted to acidified waters, could be particularly vulnerable.”
 
However, the authors also caution that our understanding is still too limited for generalizations, since fish are a highly diverse group of animals, and species will likely react differently to increasing CO2 levels.
 
“In light of the broad implications of our findings, we believe that now is the time to comprehensively investigate fish early-life CO2 sensitivity, not just in one but in a wide range of species," Dr. Baumann said. "We also have to address the general potential of marine organisms to adapt to the CO2 levels projected for future oceans.”

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