Revisiting ocean acidification

I’m pretty busy this week, but if I can get readers to look at one article, it would be the very balanced one that appeared in The Economist on ocean acidification.

The article’s subtitle is “ocean acidification threatens the world’s oceans, but quantifying the risks is hard”, which is probably a fair statement given the current state of play in the research.  

It has always been suggested that there will likely to be winners and losers in the ocean from acidification, and this year some researchers have proposed that a meta-analysis of studies to date indicate that sea life may be more resilient than originally thought.  This has been immediately attacked by other researchers pointing out the complexity of the problem:  you have to look at how lower pH affects organisms at all stages of life, as well as warming ocean temperatures, and nutrient levels too.

There are still studies just coming out which have tried to work out more details as to different species’ responses.   Here are a few:

*  it’s still not looking great for the pteropods, one of the major fish foods of the cold oceans, although this study got some results a bit different from previous ones, and much uncertainty seems to remain.  (In fact, my general impression from reading  about this topic for a number of years now is that there is still a surprising lack of detailed knowledge about the detailed bio-chemistry of  sea creatures that build shells, in particular.) 

*  for the blue mussel, the effects on the larval stage are not good.

* on the other hand, for one species of clam, lower pH seemed to do no harm at all.

The problem with some of these studies must surely be how hard it is to accurately replicate the ocean environment in the lab for certain creatures, particularly if they don’t just float at one depth all day, as is the case (I seem to recall) with pteropods.

There has also been renewed comment about how widely the pH of ocean areas (particularly near the coast, I think) changes naturally in a short space of time.  The suggestion is that if creatures can survive that already, they are possibly resilient to forecast lowering of pH.  Yet, surely a significant drop of the  average pH a creature experiences during the day could be very important, even if the same creature spends part of its day/week at such a lower pH already.

Anyhow, as I said, The Economist article does a good job at explaining the current uncertainties, and suggests that it may well be coral reef studies that come up with the definitive proof that acidification will have major effects.  Here are the concluding paragraphs:

If reshaping food webs marginalises the pteropods, the salmon will have to adapt or die. But though the mesocosms may shed light on the fate of the pteropods, the outlook for the salmon will remain conjectural. Though EPOCA is ambitious, and expensive, the mesocosms are too small to contain fish, and the experiments far too short to show what sort of adaptation might be possible over many years, and what its costs might be.

This is one of the reasons why the fate of coral reefs may be more easily assessed than open-water ecosystems. The thing that provides structure in open-water ecosystems is the food-web, which is hard to observe and malleable. In reefs, the structure is big lumps of calcium carbonate on which things grow and around which they graze and hunt. Studies of Australia’s Great Barrier Reef show that levels of calcification are down, though it is not yet possible to say changes in chemistry are a reason for this. Current research comparing chemical data taken in the 1960s and 1970s with the situation today may clarify things.

But singling out the role of acidification will be hard. Ocean ecosystems are beset by changes in nutrient levels due to run off near the coasts and by overfishing, which plays havoc with food webs nearly everywhere. And the effects of global warming need to be included, too. Surface waters are expected to form more stable layers as the oceans warm, which will affect the availability of nutrients and, it is increasingly feared, of oxygen. Some, including Dr Riebesell, suspect that these physical and chemical effects of warming may prove a greater driver of productivity change in the ocean than altered pH. Wherever you look, there is always another other problem.

No reason for complacency, I say.