Three recent stories on the topic caught my eye, however, and two of them are potentially bad news for those who like to partake of a seafood buffet:
1. squid, including the type we routinely eat, seem to be adversely affected by increasing acidification (although the experiment in question did look at their growth at pH levels which won't be seen in the ocean for a hundred years or so);
2. the mechanism via which oysters suffer under low pH appears to be better understood:
They discovered that the tiny larvae undergo a dramatic growth spurt during their first 48 hours of life, forming new shell at a rate 10 times higher than they do when they are five days old.
3. To muddy the ocean acidification story further (almost a pun there), another recent study indicates the confusing situation regarding what is already doing well, and what's doing not so well, in the oceans, and the uncertainty as to what is causing the changes:This spurt is fuelled by nutrients packed into each larva's egg. As well as powering shell construction, the nutrients also fuel the development of feeding organs – vital for getting energy once the food source from the egg has been used up. But such high growth rates are difficult to sustain when seawater pH falls. That's because the carbonate ions normally used to build calcium carbonate shells instead react with the more acidic water, reducing the amount available for shell material.
The study, published in PLoS One found that different species react in different ways to changes in their environment. As carbon dioxide emissions dissolve in seawater they lower the pH of the oceans making them more acidic and more corrosive to shells.
Foraminifera and coccoliths, which are small shelled plankton and algae, appear to be surviving remarkably well in the more acidic conditions. But numbers of pteropods and bivalves – such as mussels, clams and oysters – are falling.
'Ecologically, some species are soaring, whilst others are crashing out of the system,' says Professor Jason Hall-Spencer, of Plymouth University, who co-authored the paper.
The scientists are unsure whether this drop in certain species is because of changing pH levels, or whether it is due to a combination of stress factors like warming, overfishing and eutrophication -which results from a build up of excess nutrients in water.