The merest sniff of an environmental problem can go straight to the heads of the soberest of science reporters and leave them mumbling jibberish about the imminent end of the world as we know it.
Today: acid drop in the ocean. It’s predicted that within this century our oceans will be more acidic than they have been in 55 million years – the time of the last major mass global extinctions. So what will it mean for the denizens of the deep and for ourselves? We’ll examine the results of the first full-scale study of how acidification affects marine ecosystems.
If only they had examined the results, we might have been spared the spectacle of the station’s flagship science programme twisting an elegant, important, yet preliminary, study into a ‘portent of doom’ and concluding that the world’s coral reefs are screwed unless we stop burning fossil fuels.
Many computer models and lab experiments have investigated how oceanic absorption of CO2 reduces the pH of the water, and the effect of such changes on various marine species. As pH declines, so too do levels of dissolved calcium carbonate, with which corals build their skeletons and molluscs build their shells. It is estimated that 40% of anthropogenic CO2 has been absorbed by the oceans, resulting in a decline in ocean pH of 0.1 over the last century, which corresponds to a 30% increase in hydrogen ions (pH is measured on a logarithmic scale). Models suggest that mean pH might drop by up to 0.5 by 2100.
Jason Hall-Spencer‘s research, published a week earlier in Nature (subscription required), is the first to explore the effects of so-called ocean acidification on an ecosystem scale. It focuses on a site in the Bay of Naples in the Mediterranean where CO2 bubbles through the water from volcanic vents in the seabed. While the mean pH of the oceans is about 8.2, around the vents it can be as low as 7.4.
By recording the species composition of reefs along a pH gradient, Hall-Spencer et al found that, the lower the pH, the more impoverished the reef flora and fauna:
Along gradients of normal pH (8.1–8.2) to lowered pH (mean 7.8–7.9, minimum 7.4–7.5), typical rocky shore communities with abundant calcareous organisms shifted to communities lacking scleractinian corals with significant reductions in sea urchin and coralline algal abundance. To our knowledge, this is the first ecosystem-scale validation of predictions that these important groups of organisms are susceptible to elevated amounts of pCO2. Sea-grass production was highest in an area at mean pH 7.6 (1,827 matm pCO2) where coralline algal biomass was significantly reduced and gastropod shells were dissolving due to periods of carbonate sub-saturation. The species populating the vent sites comprise a suite of organisms that are resilient to naturally high concentrations of pCO2 and indicate that ocean acidification may benefit highly invasive non-native algal species. Our results provide the first in situ insights into how shallow water marine communities might change when susceptible organisms are removed owing to ocean acidification.
a compelling demonstration of the usefulness of natural CO2 venting sites in assessing the long-term effects of ocean acidification on sea-floor ecosystems, an approach that undoubtedly needs to be further explored […] Our understanding of the processes that underlie its observed effects on ecosystems and biogeochemistry is still rudimentary, as is our ability to forecast its impacts. There is an urgent need to develop tools to assess and quantify such impacts across the entire range of biological responses, from subcellular regulation to ecosystem reorganization, and from short-term physiological acclimation to evolutionary adaptation.
For anyone after their next fix of ecotastrophe, however, a preliminary study can easily become a harbinger of disaster:
Quentin Cooper: So, Jason, if we’ve established that the ocean are becoming more acidic globally, and we’ve looked at these effects and seen that they have detrimental effects on sea creatures, and we also know the predictions are that we’re heading towards the same kind of conditions that we had 55 million years ago, at the time of the last mass extinctions, this all sounds like the key elements for a major portent of doom.
Hall-Spencer did not disagree:
Yes, it doesn’t look good for coral reefs, that’s for sure. Because even for relatively small drops in pH, the corals that we studied in the area dissolved really quickly at this site when we moved them in from outside the area. And so, I was a bit sceptical of some of the science that was coming out predicting these things, because they hadn’t tested it in the real world. But when you go to a place that has been acidified for thousands of years and see what’s been happening, it really does ring alarm bells.
Also in the studio was ocean biogeochemist Toby Tyrrell. He didn’t disagree either. Despite the programme’s promise to scrutinise the results, nobody thought to mention the fact that good reasons to doubt whether the experimental system is a representative model for future reductions in ocean pH had been raised by Riebesell in his Nature commentary:
But there are considerable differences between such systems and the situation arising from global-scale ocean acidification caused by rising atmospheric CO2.
For example, because the vent system effectively comprises an island of low pH, and because it occurs in shallow water, the site is subject to wildly fluctuating variations in pH. On very calm days the pH declines, but on very rough days it remains high. Those fluctuations could themselves be the cause of problems with organisms’ physiology rather than the low pH per se. It could hamper adaptation to low pH, which might otherwise be expected were conditions more constant. Adaptation might also be hindered by the fact that organisms will be migrating in and out of the vent system.
Fortunately there is scope for comparative work, because Hall-Spencer’s study site is not the only CO2 jacuzzi out there. Dive operator Bob Halstead provides pictures of a similar vent system in Papua New Guinea, where CO2 bubbles through what appears to be perfectly healthy coral reef. Of course, these pictures in themselves prove nothing. Indeed, Hall-Spencer told us:
I’ve got some pictures of corals that occur in the Mediterranean with bubbles going up straight past the colony. But when you measure the pH of the water, it’s not dramatically reduced because there’s only a few bubble streams.
He was nevertheless intrigued by Halstead’s example:
If those reefs are surviving low aragonite and low pH conditions then that is definitely cause for optimism about the world’s tropical coral reefs and would be an exciting scientific breakthrough. [But if] the pH is low there due to the CO2 bubbling, then that’s really important, and somebody should go and have a look, because that would refute what we’ve found […] We need to go out there and measure the chemistry of the water […] I’d love to check that out. If there are a lot of bubbles coming up, and there’s hard coral there, then it’s likely that my study is flawed.
As for the comparison with the state of the oceans 55 million years ago, it is true that the high-end projected rise in ocean pH within this century is in the same ball-park as that found during the Paleocene-Eocene Thermal Maximum (PETM), when many species were driven to extinction. But correlation and causation are, famously, not one and the same. The PETM extinctions cannot be attributed to the reductions in pH. It was also very hot at the time; the deep oceans were deprived of oxygen; and there was likely a reduction of deep sea turbulence. All of these factors have been implicated. It is not even known what triggered these various changes. The release of massive quantities of methane into the atmosphere as a result of volcanic activity over the space of a millennium is one possibility. And so is the ubiquitous asteroid impact. Intriguingly, the rate of carbon release (in the form of methane) into the atmosphere during the PETM was similar to the rate at which we are pumping it out today as CO2. But if we’re still emitting that much carbon in a hundred years, let alone 1000, we’ll eat our chuddies (which will be very dirty by then). And no, that’s not because the Environmentalists will have got their way, but because we will have found a new, improved alternatives for generating energy by then, despite the efforts of Environmentalists.
Anyway, the PETM is mentioned in neither Hall-Spencer’s paper nor Riebesell’s commentary. Hall-Spencer told us that the connection was Cooper’s own, in order to ‘prick people’s ears up.’
The agreement between the members of the Material World panel even extended to what needs to be done about the looming disaster:
QC: And if we are hearing those alarm bells, what do we do?
JHS: I think we need to use oil less quickly – so these price hikes are good in a way – and look towards wind, wave and tidal power.
QC: Any other suggestions to add, Toby, in terms of practical solutions? Because we’re already getting lots of people advising things along those lines and manage to ignore them. Is this something that people are going to pay more attention to?
TT: Yeah, unfortunately, in terms of avoiding ocean acidification consequences, we have to really look at curbing emissions. There have been some rather outlandish proposals such as taking the white cliffs of Dover and crumbling the chalk there – adding very large quantities of chalk to seawater to neutralise the acid, but really, they are not feasible to any practical degree, so I think we really need to look at stopping emitting CO2.
Less impractical than fiddling around with wind power and rationing energy? Now that’s impractical. Burn less fossil fuels and it’s gonna be harder to save the coral reefs if they really are in peril. Strangely, when we spoke to Hall-Spencer, he said that carbon capture was probably the most realistic option.
So what has happened here? How can a 15 minute feature on a dedicated science programme not only fail to consider problems with a study that have already been flagged up by an expert in the field, but also fail to scrutinise the results or even the politics of the scientists?
Coral biologists have long been pottering around working out how reefs work physiologically, ecologically and biochemically. Nice work if you can get it. Now, suddenly, they have a higher justification for their research. Coral biologists suddenly have an audience. When we suggested this to Hall-Spencer, he said:
I’m very pleased that it’s getting the attention it is, because it allows me to study something that I find fascinating and worrying. So I’m very glad that there’s this head of steam built up and that the funding is there.
He is also under the impression that when scientists get on the radio, they can can stop being scientists and let their hair down:
When you’re interviewed, you can give your own personal point of view, but when you publish a paper that goes up for rigorous peer review, then it’s got to have the caveats and everything else.
And they’re not even going to get challenged, apparently, even on BBC Radio 4. The result is that all the public gets to hear is the story without the caveats. It’s just too easy for all concerned to resort to trying to scare people into action. Much harder is to make your scare stories believable. It does, however, seem to work on opportunistic politicians and funding agencies. And that makes it all rather moreish.