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Elevated Levels of CO2 Cause Additional Stress on Marine Life

11 June 2012

SPAIN and CHILE - An international study led by the National Research Council (CSIC) and the Pontifical Catholic University of Chile has made it known how elevated levels of carbon dioxide (CO2) exacerbate the stress of low levels of oxygen (O2) in the ocean.

This work, carried out along the Chilean coast and published in the journal Biogeoscience, focuses on defining the water column in which the conjunction of these parameters limits the ability to maintain the presence of marine organisms.

The oceans have absorbed about 25 per cent of CO2 emitted by humans, altering the chemistry of the seas and oceans. This has provoked a progressive acidification of the water, which constitutes a threat to calcifying organisms (corals and calcifying plankton). However, the CO2 also affects the efficiency of marine aerobic respiration, which depends on the relationship between the levels of CO2 and O2 in water.

"This work emphasizes that not only hypoxia (low O2 ), creates breathing problems, but high levels of CO2 are also a threat to the marine aerobic respiration process. Thus, the thickness of the water column which houses breathing problems and could be even greater if we consider the predictions of increased CO2 in the oceans, the tendency is to continue increasing," explained CSIC researcher Eva Mayol, the Mediterranean Institute for Advanced Study.

The results of this study revealed that due to the combined effect of low concentrations of O2 and high CO2, respiration is compromised between 200 and 400 meters deep, while the biocalcification continues to be involved in almost all water column, except in the surface waters in small plots in the 600 meters.

"Viewed in this way, acidification not only brings with it problems of calcification in calcareous organisms, but also a threat to the process of respiration in aerobic organisms. Thus, high levels of CO2 acts as a hinge, connecting two major challenges, breathing and biocalcification," said CSIC researcher Carlos Duarte, the Mediterranean Institute for Advanced Study.

The study warns that if CO2 continues to increase, and the superficial layers of the ocean reached critical levels, aerobic marine life that lives mainly in these waters, could be strongly affected in the process of breathing and affect major agencies for fishing industry.

The CSIC and the Pontificia Universidad Catolica de Chile are members of the International Global Change Laboratory (LINCGlobal). This organisation facilitates the interaction between Latin American and Spanish researchers in order to understand, predict and develop strategies to respond to the impact of global change on marine and terrestrial ecosystems of the Southern Cone of South America and the Iberian Peninsula.

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