Cod damaged by ocean acidification
12 December 2011
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.