The coming changes in ocean pH may well occur too rapidly for some marine species to adapt to and survive - warns Professor Lloyd Peck
The perceived big problem that past and predicted ocean acidification has for marine animals is that it makes extracting calcium carbonate from seawater to make skeletons more difficult. Many experiments have shown that exposure to reduced pH has negative consequences for most, if not all marine groups. The problems with the vast majority of studies is that they are perforce short-term and do not replicate the slower natural rates of change seen - and to come in the world's oceans.
They also do not allow for inter-generational adaptation responses. Therefore, our understanding of longer-term ecologically realistic effects is limited. In a recently published paper in the journal Global Change Biology
, a study lead by the British Antarctic Survey but including others from Great Britain, Singapore and Australia measured the size and composition of skeletons of four very different groups of animals across the globe. In all four groups - clams, predatory snails, sea urchins and lamp shells skeletons were smaller towards the poles and at lower temperatures. However, the best fit came when skeleton size was compared with the availability of calcium carbonate in seawater - which is also affected by temperature, salinity and pressure.
In one group, the clams, they need extra protection at high latitudes in Antarctica to protect them from being hit by icebergs. In this group their shells were thicker in Antarctica than elsewhere, which we might expect would buck the trend. But these clams change shape and become rounder in the cold polar waters, which keeps their skeletons as a smaller part of their total biomass, therefore staying within the trend of smaller skeletons in areas where calcium carbonate is less available.
The availability of calcium carbonate is measured as how saturated the seawater is and this varies across the globe. The lowest values on earth are in polar waters and these are similar to those predicted for temperate and tropical latitudes by the end of this century or in the early parts of next century. This work shows that for many groups over multi-generational evolutionary timescales, marine animals can adapt to reduced levels of calcium carbonate availability. It should, however, be noted that some groups such as lobsters and crabs with large crushing claws do not exist in Antarctica. And it may be that a greater difficulty in building calcium dense crushing structures limits these species.
The real question now is whether the coming changes in ocean pH will occur too rapidly for some or many groups to adapt to and cope. A further question is - will some of those that fail be in critical positions in the ecosystem, causing wider scale problems? In this respect, much depends on how fast each species reproduces and how many offspring it produces. These factors affect how quickly a beneficial genetic change can be made and how long it takes to spread through the population.
In terms of direct importance to human populations, some of the species studied here are eaten at some sites around the world. Urchins are eaten widely around the world for their roes. The clams are consumed in several tropical Asian sites such as Singapore, where they are known as mud clams. The snails studied here were whelks and the European species, the common dog whelk is eaten in the United Kingdom and several other countries across the European Union. But because such widely different groups were evaluated in the study, there is confidence that the response seen are widespread - which throws a spotlight on other groups consumed by humans including mussels, oysters, crabs and lobsters.Professor Lloyd Peck is principal investigator in marine science at the British Antarctic Survey Representatives of the four groups studied. Top left: predatory snail commonly called dogwhelk; top right: mud clam; bottom left: lamp shell; bottom right sea urchin.Three of the sites in the study of skeleton size. Left: tropical Australian beach; middle: New Zealand South Island shore; right: Antarctic Peninsula beach.
That's why in the fossil records, there are evolutions back and forth between molluscs having shells (like the nautilus) and without (like the octopus). It does not affect any life form's chances for survival.
Also the salinity, temperature and pH of the oceans are all tied and the levels of one cannot suddenly spike without causing them all to 'reset', as it were.
Evolution happens over millions of years, yet localised temperatures have swung wildly over periods of between 15,000 and 30,000 years each way.
The only possible conclusion being that life forms are reasonably unaffected by these changes, just as the polar bears have been unaffected by the constant freezing and defrosting in the Arctic that has happened hundreds of times within their existence there.
Doctor - UK
So many unknowns. How could the governments of the world be so stupid and so callous as to not act sooner in response to climate change? It all began when extremely the unpopular President Bush pulled out of the Kyoto protocol.
Bush sent a strong message to the world that said 'we see the dangers of climate change and understand that we are the world's number two polluter and contributor, however we are not going to do a single thing about it because our economy will suffer'.
How stupid and callous is that approach? Instead of showing leadership, America displayed arrogance and stupidity and a disregard for nature and the planet. We could now be the leaders of clean energy production and electric cars and could be leading on this issue, but instead you have immoral rich polluters spending millions to deceive people.
Robert - Worcester, USA
Ocean Acidification is now irreversible at least on timescales of tens of thousands of years. Even with stabilisation of atmospheric CO2 at 450 ppm, ocean acidification will have profound impacts (death and extinction) on many marine systems. Large and rapid reductions of global CO2 emissions are needed globally by at least 50 per cent by 2050.
Analysis of past events in the earth's geologic history suggest that chemical recovery (normal pH for life in the ocean) will take tens of thousands of years - while the recovery of ecosystem function and biological diversity (life as we know it) can take much longer. It could be millions of years.
Every day, 70 million tons of CO2 are released into earth's atmosphere. They remain in the atmosphere for thousands of years. Every day, 20 million tons of that CO2 are absorbed into the ocean, thereby increasing the overall acidity of the ocean. By 2100, Ocean acidity will increase another 150 to 200 per cent.
This is a dramatic change in the acidity of the oceans. And it has a serious impact on our ocean ecosystems; in particular, it has an impact on any species of calcifying organism that produces a calcium carbonate shell. These are changes that are occurring far too fast for the oceans to correct naturally.
Some 55 million years ago when we had an event like this (and that took over 10,000 years to occur), it took the oceans over 125,000 years to recover, just to get the chemistry back to normal. It took two to 10 million years for the organisms to re-evolve, to get back into a normal situation. So what we do over the next 100 years will have implications for ocean ecosystems from tens of thousands to millions of years. That's the implication of what we're doing to the oceans right now.
Larry Lawhorn, OT - Flagler Beach, Florida, USA