Robyn Williams: Now to those coccoliths and their friends. Why should you care? Well, their absence would take your breath away. I am with Professor Gustaaf Hallegraeff in Hobart.

Many people think that our oxygen comes mainly from forests, they are the lungs of our city, but in fact the forests absorb almost as much oxygen as they give out. Where do our breaths come from?

Gustaaf Hallegraeff: A lot of people in the street don't really know or respect the microscopic plankton algae of the world oceans, and in fact every second breath of oxygen that we take comes from the microscopic algae in the oceans. The second breath of air comes from the higher plants on the land.

Robyn Williams: They exude oxygen, and that just fills the atmosphere in general, does it?

Gustaaf Hallegraeff: That's right, and of course these organisms were here way before the land plants. These organisms evolved already 3.5 billion years ago, and the land plants are relative newcomers, they only turned up about 400 million years ago. So a lot of the oxygen that actually accumulated in our atmosphere first came from the marine microscopic algae.

Robyn Williams: These microscopic creatures, the algae, as you say, they come and go in vast populations, some are okay, and some are very harmful. I remember going over the mountains and I could see Jervis Bay which had gone the most incredible greenish colour, and it was almost glowing, and sometimes we have red blooms. These are not good.

Gustaaf Hallegraeff: Yes, I am well familiar with that Jervis Bay algal bloom, in 1999 or something. Basically overnight it coloured Jervis Bay a milky green. The local people really had never seen anything, and initially they blamed effluent from the local milk factories. This in fact was a completely natural event, it's just a single-celled species that found itself in the right environmental conditions of temperature and nutrients. These organisms can divide sometimes 5 to 10 times per day, so you just need a week of favourable conditions and the whole bay turns milky white.

So this particular organism, a coccolithophorid, was in fact a good species. So it does a lot of photosynthesis, so it takes carbon dioxide from the atmosphere, so it clears out the greenhouse gases, and in exchange it gives us land animals oxygen. So this was a good species. A week later the organism was gone and there really were no harmful effects of that particular organism.

But yes, there are other algal species that can cause us harm. For listeners that live in Sydney, were in Sydney in November last year, there were about 13 beaches, including the famous Bondi Beach, suddenly on a blue Monday it just was coloured like blood, and people looked at it in amazement. You know, where did that come from, what is it?

So these are organisms that I've been working on for more than 40 years of my life. So that again was a relatively harmless species. The only harm it really did cause was people on that day in Sydney could not go in the water. If they would have done so, they would have probably developed maybe some skin rashes. The surfers liked it, they had their wetsuits on and that organism was in fact bioluminescent at night, and the surfers loved that.

Robyn Williams: They didn't look as if they were covered in blood though, did they, all the red stuff?

Gustaaf Hallegraeff: No, no, it just drips off. So that was a borderline what we call harmful algal bloom, but there are other species of algae that can cause devastating harmful impacts on human society. There are some species that exude chemicals in the water and can kill fish. And whereas wild fish stocks can deal with that somehow, they sense that there is something in the water that irritates their gills and actually swim away. For example, we are aware that whole herring migrations sometimes change their regular path to avoid such an algal bloom.

When an algal bloom like that, a fish-killing algal bloom enters a major aquaculture area, and that happened in 1996 in Port Lincoln where they had just established a big tuna aquaculture operation, that basically overnight killed $45 million worth of cultured tuna. So we need to understand these phenomena, we need to have monitoring programs in place to…

Robyn Williams: That's in South Australia.

Gustaaf Hallegraeff: That's in South Australia, yes. We need to have monitoring programs in place, and come up with all kinds of mitigation strategies. Like the first thing, if you are operating a fish farm, and we are running fish farms here in Tasmania, you have at least one person on staff that almost every day takes a water sample to see what's in there. If you see such a harmful algal bloom develop, then you start to be on the alert.

You watch for concentrations to rise, then the first thing is to stop feeding the fish so that the fish are less active, stay on the bottom in the cages, they are not coming into contact with the algae. When it gets worse you tow away cages. That happened in Port Lincoln in South Australia. You had an incident like that in Tasmania in 2003. And then if it gets worse then you really need to do much more drastic things. I'm working with some Korean scientists where we learned that there are special clays that actually mop up all of these toxic chemicals, and at least gives the fish an immediate relief.

Robyn Williams: These are clays, like in the soil?

Gustaaf Hallegraeff: Yes, naturally derived soil kind of clay…

Robyn Williams: You'd need an awful lot of soil, wouldn't you?

Gustaaf Hallegraeff: Yes, but you just sprinkle it on the surface of the water and it gives the fish an immediate relief. So in Korea they have annually recurrent algal blooms in a major aquaculture area and over time they learned that this is the only way that they can deal with it. Otherwise they have to move that whole aquaculture to another location.

Robyn Williams: How much does it cost Tasmania, the harm that's done by not being able to manage these blooms properly?

Gustaaf Hallegraeff: I started to develop this expertise when I was still in Europe, and in Europe and also North America and Japan we have known of these phenomena for a long time. And in fact the very first record of a really harmful algal bloom that potentially could kill people dates back to Captain Vancouver. When he landed in what is now called Vancouver in 1793, some of his crew jumped the ship, ate a meal of blue mussels, and five of those people actually died from a phenomenon that we now have coined paralytic shellfish poison.

So these microscopic algae, just like there are berries in the forest that can be toxic, mushrooms that are toxic to human beings and we learn not to eat them, so there are particular algal species that produce chemicals that have completely natural functions for the microscopic algae but they have toxic impacts higher up the food chain.

So Captain Vancouver was very intrigued at what was going on and tried to communicate with the local native Indian tribes, and these Indian tribes made it clear to him, 'You stupid Europeans, don't you know that when the water is bioluminescent you don't eat shellfish?' So that was really the very first known algal bloom monitoring program.

And over time Western society has caught up on this knowledge that the native Indians already had, we do it through all kind of fancy technologies, we now use molecular probes to test for different species in the water. If a species is present that potentially has a harmful impact, we start to test all of the seafood products for toxins. And according to the toxin levels in seafood, we close particular fisheries.

We had such a problem most recently in November 2012 in Tasmania, and in fact we were caught out somewhat. Even though we had a monitoring program in place, the plankton communities in the east coast of Tasmania, that is a climate change hotspot, so the whole marine ecosystem is changing, this is an organism that is called a dinoflagellate, Alexandrium tamarense. We had seen it as early as 1982. It was always a very low concentration so we didn't worry about it, and a lot of our monitoring effort had been focused on other areas where we had different species that were causing problems, like the Huon River and D'Entrecasteaux Channel. So that's left that whole east coast of Tasmania basically uncovered by any monitoring programs. And suddenly there was an algal bloom there, and unfortunately it escaped our initial monitoring, so some mussels were exported to Japan, and these people have much better monitoring programs than we have and they picked up the toxins. And that is not looking good…

Robyn Williams: No, no. I actually heard it cost you about $12 million.

Gustaaf Hallegraeff: Correct. The first thing that happened, that led to a global recall, not just of Tasmanian shellfish, it led to a global recall of all Australian shellfish. That is how international markets respond. We call this the halo effect, or the public court system. And then we still are assessing the impact of that incident. Then we had to close in Tasmania the harvest of mussels, oysters, scallops. There was some concern of abalone, they appeared to be only minorly contaminated.

But the biggest cost actually was we found that the digestive system of lobsters was contaminated. And it was just before the Christmas season. So there was a lot of discussion, what are we going to do about the lobsters? It would have been possible, for example, still to market the lobsters but as a tail only with all of the digestive system removed. But the industry itself, and I can understand where they are coming from, decided that would devalue their product and they didn't want to go there. So also a lot of lobster fisheries were closed, that has cost Tasmania at least $12 million.

Robyn Williams: Going back to what you were saying before about how so many of these algae and other creatures in the ocean absorb carbon dioxide, they have also fairly robust shells, even though they are tiny. What happens when the acidity level of the ocean goes up? Will they be affected, and will they therefore not be able to absorb as much CO 2 from the atmosphere as before?

Gustaaf Hallegraeff: Climate change has many different aspects to it. One of them, indeed, you get increased carbon dioxide in the atmosphere, and that actually stimulates photosynthesis. So we do an enormous amount of work where we now grow an enormous amount of different Australian microscopic algal species in all climate change scenarios, and actually the good news is that most microscopic algae will actually grow better. They do photosynthesis better. So they grow faster and they will keep taking more carbon dioxide out of the atmosphere.

However, there has been some concern expressed, I should correctly refer to, that some species that produce calcareous shells, like the coccolithophorids, that they could potentially be more vulnerable to corrosion by the seawater becoming more acidic. Indeed some early experiments that were done on the northern hemisphere showed this potential effect.

So we have been repeating this work, and it appears that there is an enormous variability, that even within one species of coccolithophorid there are different genetic strains living in different parts of the world that have different sensitivity. So the only thing that we have been able to demonstrate is that an organism like coccolithophorids, they will not ever become extinct. They have been here for so long, they are so successful, they have such genetic diversity, they can deal with it. They've seen it all. So I still can sleep at night.

Robyn Williams: Breathing deeply, and every second breath coming from these creatures.

Gustaaf Hallegraeff: Correct.

Robyn Williams: The deeply breathing Professor Gustaaf Hallegraeff from the University of Tasmania, where they have just spent the week discussing climate and oceans and warming with CSIRO. And breathing, no doubt.