AUSTRALIAN FRONTIERS OF SCIENCE, 2008

The Shine Dome, Canberra, 21-22 February

Session 6: Discussion

Question: I was just wondering what the extent of some of these species' adaptation is to changing environmental conditions, and whether the extent of adaptation or niche differentiation would give you some uncertainty in terms of the interpretation of past sea surface temperatures.

Leanne Armand: These diatoms are very specific to where they like to live. Anyone who tries to culture these things finds that if you take anything that is related to sea-ice out of the sea-ice and put them into even a 2°C temperature to culture them, they die. They just don't like it. In fact, the vulnerability of the diatoms, at least in terms of temperature or taking them out of their environment, is rather catastrophic. So in the future, as I heard someone else say, it is not so much the climate change in the oceans in terms of the ecosystems that are currently there, it is the ecosystem around Antarctica that is going to be probably the worst hit, and may not survive. This is the question we want to know the answer to: will it actually survive? The palaeontological record will say yes, it does survive, because obviously there are niches somewhere on Antarctica that these specific organisms can retreat back to at some point, being then able, when the ice increases at another point when it is very cold, to take over again. The Antarctic diatom community is so regional that it is not even linked to what is going on up in the Arctic. They are a group of organisms that are unique to this environment.

In terms of the sea surface temperature, what happens when you take one of the eurythermal species, one that is in that open ocean zone and can live between 2° and 10°C, is that their morphology slightly changes. They still look exactly the same, but what you will find is that Fragilariopsis kerguelensis species, for example, will get shorter. It looks exactly the same, the pattern is the same, but it is smaller. And as it gets into the zone where it really loves to take off and be very prolific, it is actually quite long and large. But it is exactly the same diatom. You can still tell. There is no distinct morphological change in that point.

The estimates are only as good as the models and the data that you put in in the first place. We have a huge global dataset with the French, and whenever we get an opportunity we take a sea-floor sample and marry it up with the current conditions above – and we use regulated datasets that we source the information from. At the moment the sea surface temperature is down to a ± 1°C error. The sea-ice is a different story!

Question: Temperature is one of the factors expressed in the environment, but how about salinity or pH? Can you extract some information from diatoms for that?

Leanne Armand: Salinity does not appear to affect diatoms much at all, at least in the Southern Ocean area. As to the pH, there are a lot of people playing around with cultures – unfortunately, they are not Southern Ocean diatoms – with changes in pH or even changes in how much CO2 is in the water, et cetera: double times, triple times. At the moment the diatoms don't appear to be terribly upset by it. I imagine that there are some physiological responses, though, that are affected, although that is not my expertise, but they still seem to just chug along quite happily (at this stage).

Question: You showed the fluorescence experiments and the disparity between the species that were 'doing their thing' versus the ones whose abundance was observed. Since their life cycle is so short, why aren't they in some sort of equilibrium?

Leanne Armand: That is what our expectation was. We are really just as surprised to see the huge disparities between what we saw currently fluorescing and the relative abundance. You have got to take into account that we have taken a bucket of water, with the fluorescent marker, and put it into an incubator of that sea-water temperature, just for that 24-hour period, with the natural light cycle et cetera. Maybe sometimes the diatoms just go into shock and won't do anything. It all comes down to playing around. That is the first time we have actually gone out and tested that fluorescent marker in the sea, versus testing it just in the laboratory cultures.

Question: Normally when one does one's research project, one doesn't expose oneself to any sort of peril. But I think I heard you say you were on these boats for a month at a time in these waters, which I imagine are not exactly tropical. Can you say something about what it is like to do your work – what your experiences are like on the boats, and what the sea conditions are like, what the weather is like?

Leanne Armand: What are sea conditions like, in the Southern Ocean? I could talk about this for hours!

It is difficult, there is no doubt about it. The first thing is that you have got to be super-organised. You have to know your methodology down to the last button. You take everything with you on the ship – if you have forgotten something, that's it, your experiment is finished. So first of all you have got to be super-prepared and have that worked out.

People get seasick, obviously, myself included. So a lot of the times you will even do quite basic things that you would think, 'I would never have to do that' – you actually get a piece of paper and write down your methodology in big, bright, bold letters, like, 'Step 1, 2, 3,' because occasionally the seas are so rough that you have to just keep going, regardless of your state or the state of the boat or whatever. Virtually, you are on automatic pilot to a certain degree to do some of the work. That's not all the time, and there will be times when the seas are so rough that no-one's allowed outside, bad luck for your experiment if you wanted to take a sample here or whatever. So a lot of the time you are dependent on the conditions while you are at sea.

A six weeks' cruise is usually what it is when we do this sort of biogeochemistry-type series study or whatever. And of course there are a lot of competing interests. So it is a highly organised event.

Question: I have a question about your use of the diatoms there, or your observation that because of the bloom on that island a diatom morphed into a different shape and started breaking off. Have you observed those smaller pieces in cores and stuff, and what are the implications?

Leanne Armand: No. The implication there is that that particular soft form is so thinly silicified (because, essentially, there is no silica left in the water) that we think it has actually got an evolutionary tactic. There are two tactics when you are a diatom and suddenly your nutrients run out. You can make a spore, such as I have referred to earlier, where there is a very heavily silicified little organism, and you're so heavy that you are just going to drop out to the water. When you are on the plateau, where it is 500 metres deep, that is a good strategy. Go down to the sea-floor and wait till conditions are better, and maybe the current and the tides will flip you back up into the nice nutrient conditions. If you are a diatom in the open ocean, where your sea-floor is 4000 metres below, that's a bad strategy, because you're not ever going to get back up again.

Suppose you're a diatom that wants to hang around. You may want to hang around but get out of the light, because you don't want to photosynthesise and you don't want to form anything; you just want to get out of that light zone and hang around where maybe the waters that are upwelling underneath are richer in the nutrients that you are after. Or you may want to hang around in that zone at the top but not want to do anything; you just want to s-u-r-v-i-v-e. And I think that is basically what that little funny form is doing, because if you want to then make use of those good conditions that come back, if you are a diatom that is not a spore, you can start doing your thing straight away. But a spore that gets thrown back up has to break out of his spore and then he has to start doing things, he has already lost the advantage of the good conditions over the one that has just been hanging around looking very sick.

I think that is basically what we found here. No-one had actually ever observed that before, and I hunted high and low for people who did culture studies, to find out, 'What do you think of this? Has anyone seen this?' and no-one had except one guy at Monash who said to me, 'Oh, it just looks like one of my very, very sick cultures that's about to die.' That put us onto the idea that this is quite possibly, in this particular area, a survival strategy for when the tides come through and bring up a new lot of nutrient-rich water to keep that bloom going.

Question (cont.): So that is never preserved, then, in the detritus?

Leanne Armand: It is not preserved. The only thing I would see is a change in the heavy form coming down, and then perhaps no heavy form afterwards. So you would probably have a break in heavy forms, and that is probably what we are going to see.

Question: Given that you have seen single species change form to become unrecognisable, how confident are you that when you go down and collect your core samples that you are not seeing one species in different forms, and not four to five different species?

Leanne Armand: Experience tells me that what we actually get in the cores is always the heavily silicified diatoms. The other thing you have to consider is that if you are a diatom going 4000 metres down, if you're not heavily silicified anyway you are going to dissolve on the way down. The record that we have, in fact, of the sediments is of all the species that are consistently making this heavy form.

Heavy forms can be two things. First, you don't want to get chomped by a zooplankton, so you make something really tough and crusty, and they'll avoid you. Or you can put lots of barbs or spines on you, again another thing to escape. Or you do what the other ones that make spores do, a resting stage – that is then a very heavily silicified shell that will send you down, and that will preserve very well.

So what we are seeing in the cores are really the heavily preserved species. Our story is really based on those ones. Of course, when you get onto plateaus or around the continental margin, the bloom is so dense – you may have heard of 'marine snow' – that it just comes out in one go, gloop! And you have got that one layer. That is what those laminations are around the Antarctic continent: they are the whole bloom, basically, just falling out.

Question: With respect to climate change, there has been a lot of controversy about the use of biomass as fuels, for example the American corn. Given the massive abundance of these organisms, is it feasible to harvest them for use as feedstocks for fuels for human consumption?

Leanne Armand: I have never been asked anything like that. Is it feasible? I guess it is. Certainly if you put a 50-mesh net out, you can fill it up pretty quickly. As to whether they are actually edible, I don't reckon they would be great, because they are made of silica. If you ate silica, I reckon your teeth would wear down. I don't know. Really, I don't have the answer to that.

Malcolm McCulloch: There is lots of interest in putting iron in the oceans to get other organisms, the phytoplankton, to bloom. That is part of the basis of the experiment around Kerguelen, because there was a natural source of iron from that island. But doing these biomanipulations has lots of uncertainties, for example in how you affect other species. There is a fair bit of controversy in scientific circles, or amongst the experts, as to whether such a manipulation of our environment is appropriate – particularly when, as Leanne has so well shown, we don't know in any sort of detail what is going on.

Leanne Armand: That is the bottom line. There may have been 200 years of studying diatoms, if you like, but that first 100 years was just describing them. We have wonderful books describing them in great detail, but we still know nothing, really, about their physiology, their life cycles, who is represented by this kind of chemical regime and that chemical regime. Going out and studying the zone where they were naturally iron-fertilised provided an insight in itself, because yes, we could say that there was a certain community that subsisted on that availability of iron, and certainly once you got out of that area where the iron was input, you just got your classic diatom that was just hanging around in the water trying to survive.

I don't think that iron fertilisation is the answer, because it depletes other nutrients in the water which are used by other organisms, or it produces such a shock bloom that you disrupt what is going on anyway in terms of that ecosystem. So I don't think the answer for that lies quite there.

But in terms of feeding the population, certainly aquaculture uses cultured diatoms to feed fish or other organisms. That certainly happens now. But I don't know about going out and getting them and packaging them up. People use them as face packs for the mud, I know that.

Question: I have a question about the diversity. You say that diatoms are quite diverse. On the other hand, they do not seem to be very adaptive, which suggests that speciation is not occurring very much. To me that seems like a kind of paradox. Can you comment on that?

Leanne Armand: They seem to have had a very early explosion; just after the Cretaceous period they just went crazy. After that time, once the periodicity of interglacial cycles came in – the warms and the colds – that is when they started to be quite diverse in terms of where they were occurring. For the Antarctic diatoms, I know that they go back to a Miocene-type period where we can say, 'This species has a lineage back to then, and we haven't found it anywhere else.' So in terms of their evolution, I think yes, you are quite right, the speciation happened a long time ago. Genetic studies in terms of understanding diatoms are only just starting, and I think there are something like four Southern Ocean diatoms understood genetically at this point in time.

So that is another point in my going out to Antarctica soon, that we are trying to get everyone on board – geneticists, biochemists, everybody, as much as we can. If we are going to go and do this once in one area, we want to try and target every possible science that is available to understand what is going on and get the maximum amount of information – just so we can benchmark this area, at least. It is so hard to study the Southern Ocean and Antarctica, in some respects, because there is just too much of it to cover. So we are trying to be selective in terms of picking areas.

Sorry, I diverged there. You said 'speciation' and, in terms of their evolution, 'diversity'. The diversity just happened a long time ago, and they have been quite regular in that sense.

Question: Just to help answer the earlier question about biofuels, and whether diatoms can be used or not: there was a paper published in Nature, just before Christmas, on that exact same topic. There is an individual who wants to culture some phytoplankton in the North Sea and has been talking about putting it on the stock market so that he can sell it as biofuel.

Leanne Armand: He might have a bit of a problem with predators as well. If he makes something that is quite tasty to the zooplankton, he is going to have a hard time stopping them. For that matter, bacteria and viruses like diatoms as well, and there is some evidence that there is a lot of symbiosis going on, in terms of the stickiness in certain ribbon-forming diatoms. Bacteria and viruses like to hang on to that lovely sticky stuff, and perhaps give the diatom back some sort of missing mineral or element or whatever so that they survive. Anyway, that will be curious. (I wouldn't be investing.)

Malcolm McCulloch: Just as a plug: if you go to the Academy website you will see that there is an article on iron fertilisation, and you can catch up on that if you want to do so. It's at www.science.org.au/nova/106/106box01.htm.