How do Volcanoes affect Ocean Biodiversity?
Arguably, one of the most extreme environments to inhabit is one near a volcano. But what about when that volcano is underwater? Subduction zones in the deep sea are very seismically active and Jason Hall Spencer from Plymouth University has been looking at how subsea volcanoes affect the acidity of seawater and how this affects the species found nearby. He spoke with Robyn Williams from the Australian Broadcasting Corporation's science show at a recent conference in Canada.
Jason - I was first studying carbon dioxide vents near the mountain of Vesuvius, the famous one in Italy where the toe of the volcano is acidifying the water naturally because of high CO2 release. The very clear thing that we saw at that vent system was that as you go into the carbon dioxide bubbles, you get less and less types of organism that can survive that. CO2 is a stressor for animals. It's actually a fertiliser for some plants, so some plants there are growing really well. They're like lush grass beds and various types of algae that thrive but unfortunately, many of the animals that you would want to be there are disappearing. That was my last 4 years' work, but then it became clear that if we're going to make global predictions about the effects of CO2 on the oceans, we need to see if we can replicate our evidence for this problem from other parts of the planet. So, I've been going to these vent systems in Baja California, three volcanoes in Papua New Guinea, and other volcanic vents in Europe to see if we get the same effects and worryingly, we get exactly the same response: As CO2 goes up, biodiversity goes down. There are key organisms like sea urchins and coral and algae that just can't survive these conditions.
Robyn - These are vents underwater, presumably.
Jason - Yes. Sorry, it's like a Jacuzzi of bubbles underwater. They're very, very beautiful. When you roll over the back of the boat, start swimming through as a diver, it's exotic. It's very unusual, but it's not until you start looking carefully and counting organisms on the seabed that you realise something's amiss, something's not quite right.
Robyn - If they're there anyway, haven't they been pre-adapted to that sort of environment?
Jason - Yes, they probably have. There's organisms there, they're growing very, very well. What we're doing actually, our new Nature; Climate Change paper is all about transplant experiments we've done. Moving organisms that are from in this high CO2 world of the volcanic vent system outside into current day conditions. And what's interesting is they have actually upregulated their ability to calcify. They're able to lay down shell much faster than in the normal world that we see today.
Robyn - So they have adapted to that. What happens if the CO2 goes even higher than at the vents?
Jason - Well that is clearly problematic because then they die. The water becomes so corrosive that these organisms can't protect themselves. Unstressed organisms, ones with plenty of food, where the temperature doesn't get too high, they can actually protect themselves very often from corrosion. When you look at the CO2 vents in Papua New Guinea for example, there are corals there that are able to lay down skeletons and able to calcify despite the high CO2 levels that we expect in the coming decades. But the problem is, when you start swimming around in these high CO2 equivalents of the Great Barrier Reef, the numbers of species have gone through the floor. It's really crashed and that system is probably represents the least worst case scenario, because these volcanic vent systems in Papua New Guinea can be colonised by organisms from outside the vents. Now that clearly won't be possible when the whole global ocean is acidified. There won't be this recruitment from healthy populations outside. The Papua New Guinea reefs are the most diverse on Earth. They've got some strains of those corals that can survive. That's good news for coral reefs of course, but the bad news for people who like to see corals is the diversity has gone right down.
Robin - I see, and the whole point about survival is that the biodiversity needs to be complex. In other words, if you lose a great number of species, so the system then threatens to collapse.
Jason - Well that's right. Farmers typically like to reduce the biodiversity to the barest minimum because if you plough a field and grow crops, you make the system more efficient for producing food. You might think therefore that the seas will be better if we just simplified the whole thing, killed all these extra species that we don't want because we could get more food from it. Now that may be the case for some organisms that you can culture, but in Canada, here where this interview is taking place, the aquaculture industry is finding the waters are becoming too acidified for them to grow the oysters that they want to grow up into adults.
Robyn - Already that's happening?
Jason - Yeah, it's happening now. There's a quirk of oceanography that the coast on the northeast part of the Pacific is old water that originally sank in my part of the world, the North Atlantic, it sank down to the bottom of the deep sea, and it eventually wound its way round the Earth, and is upwelling here. It's coming to the surface here. So that's been accumulating carbon dioxide from the respiration of organisms all of that time. So it's already got CO2 loading naturally and we're adding in on top of that, from the atmosphere, extra CO2. That makes this water corrosive to things like oysters and so the oyster farmers here have got this double problem: upwelling, natural water that's high in CO2, which the oysters were able to cope with, but now, on top of that, that extra CO2 going in from above.
Robyn - How concerned are you that the CO2 increase is going to lead to a general problem? Because lots of people have said in the last few months that the adaptation that you mentioned, the fact that there can be some resilience in certain creatures, might be something that will obviate the whole thing?
Jason - Well I'm very encouraged that areas that are protected from stressors are actually more resilient as systems. So the more species you've got, the better they are to cope with things like acidification and that's why these marine protected areas that are being rolled out around the planet are such a good idea. I give them my full support because a resilient system buys you insurance against those chemical changes in the water that really, we can't do much about because the CO2 is already in the atmosphere. These areas are going to become acidified. You've got healthy sea grass beds for example - just by living there, they raise the pH of the water. Photosynthetic organisms raise the pH. That's got to be a good thing in the face of acidification, because calcifiers, things that build shells or skeletons continue to do so in the regions of sea grass beds. If you remove the sea grass beds, or if you abuse the habitats and lower their diversity then this natural solution to the problem can't happen.
Robyn - I was amazed to hear from the University of Queensland some research showing that mangrove swamps trees and sea grasses are 60 times more effective than even rainforests in mopping up CO2.
Jason - That's a good idea to look after them, isn't it? But they do the job for us. We're trying to pump carbon dioxide down below the seabed of the North Sea to lock it away because we're actually burning it and putting it in the atmosphere. That's got to be a good idea to stop doing that, to lock it up in perpetuity. But that's an engineering solution that's probably got its own inefficiencies, but if we can let nature do some of that work for us, that's sensible.