PML scientist Dr David Lowe is part of a team which exposes ocean acidification risk to cod hatchlings.
Ocean acidification, caused by increasing atmospheric concentrations of carbon dioxide (CO2) is one of the most critical anthropogenic threats to marine life, with the potential to disturb shell and skeleton building; the acid-base balance; blood circulation; respiration; the nervous system and reproduction and growth.
There is a growing body of research that has looked at how individual species or habitats might be affected but observations on fish have shown that they are relatively robust to changes in the pH of the water in which they swim; it is thought that they are able to buffer the effects, in the kidneys and especially across the gills. But larval fish do not fully form their gills until many days after hatching. Although some research has revealed that larval fish, mostly tropical, non-commercial species, may suffer impacts on their behaviour and on their balancing organs – the otoliths, no studies have looked at the impacts on the larvae of mass-spawning commercial species.
Dr Lowe, working with colleagues in Germany and Norway has helped to find evidence that larval cod are severely impacted by rising concentrations of CO2 in seawater through a series of experiments carried out in near natural conditions in large containers, called mesocosms, in a Norwegian fiord, close to where cod are known to spawn. (Nature Climate Change 11.12.11) Using delicate microscopical techniques and careful examination David Lowe found severe to lethal tissue damage in many of the larval cods’ internal organs, including eyes, liver, kidney, pancreas and gut. Interestingly large numbers of bacteria were observed in the gut, perhaps indicating a reduced immune response, leaving the fish open to disease.
The histological damage is described as ‘regressive changes that terminate in functional impairment or loss of the organ and involve deposits, architectural and structural alterations, degeneration, atrophy and necrosis’. In short the study demonstrates widespread tissue damage as a result of ocean acidification during a critical life-stage of a commercially important fish. Coupled with the fact that many cod populations spawn in areas that are likely to be particularly impacted by future ocean acidification, the implications for an important food fish are of concern.