Atlantic cod larvae vulnerable to ocean acidification

December 14th, 2011 by Leibniz Institute of Marine Sciences

Fish stocks are not only threatened by over-fishing.

An international research group led by the Leibniz Institute of Marine Sciences (IFM-GEOMAR) has found evidence for potentially harmful effects the increasing acidification of the oceans may have on larvae of commercially important fish species such as cod.

The study, ‘Severe tissue damage in Atlantic cod larvae under increasing ocean acidification‘, was published in the internationally renowned journal Nature Climate Change.

While it is common knowledge that commercial fish stocks are globally threatened by over-fishing, this study shows that they may also be vulnerable to previously underestimated factors of climate change.

The accumulation of carbon dioxide in the atmosphere, mainly due to the burning of fossil fuels, will lower the pH of the oceans, a process termed “ocean acidification”.

In the past, scientists have primarily focused on calcifying organisms, which are believed to be particularly at risk due to the dissolution of their calcium carbonate structures.

The recent study by an international research group led by the Leibniz Institute of Marine Sciences (IFM-GEOMAR) shows that commercial fish species may also be threatened by increasing acidification.

“Test series showed that the larval stages of cod is especially vulnerable to changes in the pH-value,” Andrea Frommel, lead author of the study, said.

Andrea Frommel measuring pH values in mesocosms to determine impact on Atlantic cod larvae (click image to expand - ©IFM - GEOMAR)

Frommel and her colleagues from Germany, Norway and Great Britain exposed Atlantic cod offspring to three different carbon dioxide concentrations: today’s concentration (380 µatm/ 380 parts per million), the expected concentration for the end of the next century (1800 µatm / 1800 ppm) and an extreme concentration that may be reached in coastal areas in the future (4200 µatm) to examine the influence of ocean acidification.

Andrea Frommel said “fish were considered to be relatively robust to changes in pH because of the fact that they are good acid base regulators but our research found damage to cod larvae raised at 1800 µatm/ ppm which is already found in several places today.”

“We are already seeing much higher concentrations of CO2 in the Baltic Sea. Concentrations of 2300 µatm are measured routinely.  This is mainly due to the fact that the Baltic Sea has little mixing, so the C02 absorbed by the ocean and respired by organisms is not replenished with oxygen-rich water from elsewhere.”

“This phenomenon could occur in any place with little exchange and high biological activity, such as in fjords where the Atlantic cod used in the study spawn. As the water is cold, it has the potential to hold more dissolved gases,” she said.

“The CO2 levels will certainly not reach 4200 µatm globally any time soon, but locally, these concentrations are possible and could occur faster than we think,” she adds.

In order to mimic natural conditions for the cod larvae, the experiment was carried out in large open-air mesocosms in Bergen, Norway.

Atlantic cod, Gadus morhua, larva (click image to expand ©Andrea Frommel)

The larval development was monitored for a time span of seven weeks after hatching.

Tissue damage with possible lethal consequences was documented in a range of vital organs in the larvae.

“During this critical stage many structural alterations take place in the larvae, requiring a large amount of energy. As larvae hatch without functional gills, the main site for effective acid-base regulation, the mechanisms to cope with a low pH environment are particularly costly. Therefore, they may not have the energy needed for development available making them more prone to damage,” Frommel said.

“This study shows that the increasing acidification of the oceans has the potential to reduce larval survival in marine fish. As the larval stage is the bottleneck to recruitment in commercial mass-spawning fish, ocean acidification must be considered as another anthropogenic stressor in future stock analysis of already exploited fish,” she said.

Funding was provided through the European Community’s Seventh Framework Programme (FP7) ‘European Project on Ocean Acidification’ (EPOCA), the European Marie Curie Initial Training NetworkCalcification of Marine Organisms’ (CalMarO) and the project by German Ministry for Education and Research (BMBF) ‘Biological Impacts of Ocean ACIDification’ (BIOACID).


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