The swimming kinematics of larval Atlantic cod, Gadus morhua L., are resilient to elevated seawater pCO2

Kinematics of swimming behavior of larval Atlantic cod, aged 12 and 27 days post-hatch (dph) and cultured under three pCO2 conditions (control-370, medium-1800, and high-4200 µatm) from March to May 2010, were extracted from swim path recordings obtained using silhouette video photography. The swim paths were analyzed for swim duration, distance and speed, stop duration, and horizontal and vertical turn angles to determine whether elevated seawater pCO2-at beyond near-future ocean acidification levels-affects the swimming kinematics of Atlantic cod larvae. There were no significant differences in most of the variables tested: the swimming kinematics of Atlantic cod larvae at 12 and 27 dph were highly resilient to extremely elevated pCO2 levels. Nonetheless, cod larvae cultured at the highest pCO2 concentration displayed vertical turn angles that were more restricted (median turn angle, 15°) than larvae in the control (19°) and medium (19°) treatments at 12 dph (but not at 27 dph). Significant reduction in the stop duration of cod larvae from the high treatment (median stop duration, 0.28 s) was also observed compared to the larvae from the control group (0.32 s) at 27 dph (but not at 12 dph). The functional and ecological significance of these subtle differences are unclear and, therefore, require further investigation in order to determine whether they are ecologically relevant or spurious.

Differential impacts of elevated CO2 and acidosis on the energy budget of gill and liver cells from Atlantic cod

Ocean acidification impacts fish and other marine species through increased seawater PCO2 levels (hypercapnia). Knowledge of the physiological mechanisms mediating effects in various tissues of fish is incomplete. Here we tested the effects of extracellular hypercapnia and acidosis on energy metabolism of gill and liver cells of Atlantic cod. Exposure media mimicked blood conditions in vivo, either during normo- or hypercapnia and at control or acidic extracellular pH (pHe). We determined metabolic rate and energy expenditure for protein biosynthesis, Na+/K+-ATPase and H+-ATPase and considered nutrition status by measurements of metabolic rate and protein biosynthesis in media with and without free amino acids (FAA). Addition of FAA stimulated hepatic but not branchial oxygen consumption. Normo- and hypercapnic acidosis as well as hypercapnia at control pHe depressed metabolic stimulation of hepatocytes. In gill cells, acidosis depressed respiration independent of PCO2 and FAA levels. For both cell types, depressed respiration was not correlated with the same reduction in energy allocated to protein biosynthesis or Na+/K+-ATPase. Hepatic energy expenditure for protein synthesis and Na+/K+- ATPase was even elevated at acidic compared to control pHe suggesting increased costs for ion regulation and cel- lular reorganization. Hypercapnia at control pHe strongly reduced oxygen demand of branchial Na+/K+-ATPase with a similar trend for H+-ATPase. We conclude that extracellular acidosis triggers metabolic depression in gill and metabolically stimulated liver cells. Additionally, hypercapnia itself seems to limit capacities for metabolic usage of amino acids in liver cells while it decreases the use and costs of ion regulatory ATPases in gill cells.

Effects of ocean acidification on the calcification of otoliths of larval Atlantic cod Gadus morhua

The growth and development of the aragonitic CaCO3 otoliths of teleost fish could be vulnerable to processes resulting from ocean acidification. The potential effects of an increase in atmospheric CO2 on the calcification of the otoliths were investigated by rearing Atlantic cod Gadus morhua L. larvae in 3 pCO2 concentrations-control (370 µatm), medium (1800 µatm) and high (4200 µatm)-from March to May 2010. Increased otolith growth was observed in 7 to 46 d post hatch (dph) cod larvae at elevated pCO2 concentrations. The sagittae and lapilli were usually largest in the high pCO2 treatment followed by the medium and control treatments. The greatest difference in mean otolith surface area (normalized to fish length) was for sagittae at 11 dph, with medium and high treatments being 46 and 43% larger than the control group, respectively. There was no significant pCO2 effect on the shape of the otoliths nor were there any trends in the fluctuating asymmetry, defined as the difference between the right and left sides, in relation to the increase in otolith growth from elevated pCO2.

Seawater carbonate chemistry and severe tissue damage in Atlantic cod larvae under increasing ocean acidification, 2012

Ocean acidification, caused by increasing atmospheric concentrations of CO2, is one of the most critical anthropogenicthreats to marine life. Changes in seawater carbonate chemistry have the potential to disturb calcification, acid-base regulation, blood circulation and respiration, as well as the nervous system of marine organisms, leading to long-term effects such as reduced growth rates and reproduction. In teleost fishes, early life-history stages are particularly vulnerable as they lack specialized internal pH regulatory mechanisms. So far, impacts of relevant CO2concentrations on larval fish have been found in behaviour and otolith size, mainly in tropical, non-commercial species. Here we show detrimental effects of ocean acidification on the development of a mass-spawning fish species of high commercial importance. We reared Atlantic cod larvae at three levels of CO2, (1) present day, (2) end of next century and (3) an extreme, coastal upwelling scenario, in a long-term ( 2.5 1/2 months) mesocosm experiment. Exposure to CO2 resulted in severe to lethal tissue damage in many internal organs, with the degree of damage increasing with CO2 concentration. As larval survival is the bottleneck to recruitment, ocean acidification has the potential to act as an additional source of natural mortality, affecting populations of already exploited fish stocks.

Egg and early larval stages of Baltic cod, Gadus morhua duirng ocean acidification experiments, 2012

The accumulation of carbon dioxide in the atmosphere will lower the pH in ocean waters, a process termed ocean acidification (OA). Despite its potentially detrimental effects on calcifying organisms, experimental studies on the possible impacts on fish remain scarce. While adults will most likely remain relatively unaffected by changes in seawater pH, early life-history stages are potentially more sensitive, due to the lack of gills with specialized ion-regulatory mechanisms. We tested the effects of OA on growth and development of embryos and larvae of eastern Baltic cod, the commercially most important fish stock in the Baltic Sea. Cod were reared from newly fertilized eggs to early non-feeding larvae in 5 different experiments looking at a range of response variables to OA, as well as the combined effect of CO2 and temperature. No effect on hatching, survival, development, and otolith size was found at any stage in the development of Baltic cod. Field data show that in the Bornholm Basin, the main spawning site of eastern Baltic cod, in situ levels of pCO2are already at levels of 1,100 µatm with a pH of 7.2, mainly due to high eutrophication supporting microbial activity and permanent stratification with little water exchange. Our data show that the eggs and early larval stages of Baltic cod seem to be robust to even high levels of OA (3,200 µatm), indicating an adaptational response to CO2.