UTS Science in Focus: Marine Microbes: The Ocean’s Lifeblood?


Facilitator: Thanks very much Peter and thank you all for coming. I should also thank the Faculty of Science for giving Justin and I the opportunity to tell you a little bit about our research this evening. Yeah, so letís get started. The ocean is arguably the earthís largest habitat. If youíve ever seen a satellite picture or earth from space, itís a blue plant. Thereís 70 per cent of ocean on our – excuse me, that was a bit fast. So if we look at the surface area of the planet, its 500 million square kilometres. If we consider the highest mountain and the deepest ocean trench – we already see some disparity there – and if we consider the average land elevation of 840 metres and the average ocean depth, we can do the maths pretty easily and know that the ocean forms the largest habitat for life on earth. To Australia, as an island continent, the oceanís very important. Our marine territory is larger than our land area. Itís relevant for most of us in Australia because we live so close to the coast.

Many Australians live within 50 kilometres and use those coasts for their recreational and other amenities. The ocean is incredibly valuable. The western rock lobster fishery, our largest fishery, is worth up to $350 million a year. You might also be interested to know that our recreational fishery is worth $2 billion dollars if it was sold. Tourism to the Great Barrier Reef contributes over $5 billion to our economy each year and in New South Wales the marine industry contributes $2 billion annually and itís important for jobs here in our local region. Marine microbes do the work in the ocean. Theyíre microscopic so not easily recognised but they constitute up to 90 percent of biomass, of living biomass, in the ocean. Thatís roughly equivalent to 240 billion elephants. You consider that in terms of size. What do they look like? Letís take a view – microscopically and zoom that. This is a cyanobacterium called a Prochlorococcus.

It typically grows in low nutrient water. It is – I should say there that itís the most abundant photosynthetic organism in the ocean. There are 10 to the power of 27 cells globally. Synechococcus is somewhat bigger cyanobacterium. It also photosynthesises and is more found in nutrient-rich waters. An Emiliana huxleyi is a coccolithophorids. Itís an organism that has these calcium carbonate scales, which makes it fairly distinctive when you see it in water. Iíll show you a picture of that a little later. This is a diatom example Fragilariopsis Antarctica. As the name implies itís a polar organism grown below 50 degrees south typically. Gymnodinium catenatum is a toxic dinoflagellate. These cells are somewhat larger, grow in coastal systems and can cause problems for aqua culture and shellfish industries.

Lastly, Iíve provided two examples of – I guess theyíre microbes and microscopic as single cells, but when they form these aggregations, here this is called a tuft and here a big colony, this is Trichodesmium and this is Phaeocystis and they are macroscopic, you can see those in the water. Collectively, these organisms are called Phytoplankton and theyíre responsible for photosynthesis in the ocean just as we would consider land plants here. We already know that there are rooted plants in the ocean called seagrasses and you might have also heard about kelp forests. But overwhelmingly, itís these small microbes that are responsible for most of the photosynthesis in the ocean. These phytoplankton can grow and form large accumulations that are observable from space. Here, this is a picture of Emiliana. As I explained earlier, it has these calcium carbonate scales, which are highly reflective.

This is the south coast of England and the bloom is almost as large as that whole land area. This is a toxic dinoflagellate, here blooming of the west coast of Tasmania and you can see it forms these what we call red tides. That can be harmful for other organisms growing in the vicinity. [PAUSE] What do they do? These microbes, these phytoplankton are basically providing food for the rest of the food web. So plankton a microscopic animals that consume phytoplankton and the zooplankton in turn are consumed by the higher food webs, the larger animals in the ocean. Typically, our most productive oceanographic systems are those in upwelling areas. Nutrients are brought to the surface of the ocean when prevailing winds, parallel to the coast in this case, cause water to actually move away from the coast and thatís replenished by deep ocean water. So thereís this circulation, this uplift of water that brings nutrients with it, phytoplankton have the opportunity to grow, they are consumed by zooplankton and they basically drive ocean production and produce lots of fish for our marine fisheries. Microbes are also critically important in the carbon cycle. They are basically converting dissolved carbon dioxide in the ocean together with nutrients into particulate organic carbon in the presence of sunlight.

In doing so they also produce oxygen. This oxygen is really critical for life on hearth. Humans wouldnít exist without oxygen. So itís the function of these microbes that are actually allowing us to inhabit the earth. This rate of conversion of dissolved or gaseous carbon dioxide into organic carbon is called productivity. The rate of carbon fixation is what we typically measure in the ocean. So weíll come back to that a little later. Each day more than a hundred million tonnes of carbon are fixed in this way by these autotrophic photosynthetic microbes. The organism that is the most abundant photosynthesiser in the ocean is responsible for 20 per cent of the oxygen in the earthís atmosphere, a really significant proportion. So just to summarise that or give you the comparison, the ocean is contributing about half of global photosynthesis. Itís fixing about 50 per cent of carbon dioxide on our planet annually. To show you than in a vertical perspective, here we have carbon dioxide, diffusing into the surface of the ocean. It is taken up by photosynthesisers in the presence of sunlight energy and in the presence of nutrients to form cells and these are then consumed by the food web.

Justin will talk further about the details hidden behind this box that end up being very important to the fate of that carbon in the ocean. But essentially, itís what happening here in the surface ocean that then determines what amount of organic carbon gets delivered further down into the ocean sediments. This is what we refer to as the biological pump. So the carbon dioxide in the surface is taken up by the food web and organisms then are dying. Theyíre reproducing and dying as part of their natural life cycles and they contribute then to the dead or decaying organic carbon, this particulate organic carbon in the ocean. Itís comprised of dead phytoplankton cells, zooplankton poo, which is these little oval dots and I guess the [tridal] remains of fish and other larger organisms. Essentially that is slowly sinking through the ocean and some of it reaches the ocean sediments and is buried there for millennia. I do want to mention that diatoms, these organisms I illustrated earlier, and coccolithophorids contribute to this vertical flux as we call it and actually may increase the ballast, the weight of this material, and may cause it to sink faster.

So it might matter if we have a change in composition of phytoplankton in the ocean and that may change the rate of sinking of this particulate carbon. Okay so yeah, looking at that in view, itís actually – this biological pump is a natural carbon sequestration mechanism. [PAUSE] So I guess in thinking about productivity and the link between these photosynthetic microbes and climate, we now have very good tools over large scales that can detect this productivity in the ocean. Thereís a satellite sensor called SeaWiFS that was basically optimised to capture signals from the ocean and was able to then quantify productivity quite accurately. Then we were able to link that to environmental factors. This is a seminal study published in nature several years ago that basically examined this productivity data on a global scale and did this over a decade and considered the links between productivity and climate.

Here in the upper plot itís describing the pattern of sea surface temperature. Sea surface temperature in red means itís hot, relatively, compared to blue which means itís cooler. In the middle plot, it shows you changes in this primary production, this productivity. This is nice because it actually – this third plot here – shows the change in productivity over the 10-year time period that they did this observation. The parts of the ocean in yellow indicate that with warming thereís a decrease in productivity. Okay, so a large part of the Pacific Ocean here in the middle, when thereís increased warming thereís a decrease in productivity. These observed decreases provide some indication of what will happen with future warming. I want to zoom in now on Australia. To do that I need to give you an oceanographic context. So weíre an island continent and unusual in the global ocean.

There are two warm tropical currents that move from north to south along both costs. Typically, in other continents we see the opposite pattern here on the west coast we see the currents move upwards, sorry, towards the north rather than towards the south. Because these currents bring warm nutrient-poor water, it really affects the oceanography in the region and the nutrient-poor water means that we donít necessarily have a lot of productivity, especially on our west coast, which would normally be a large area for upwelling. We know from long-term measurements at three of the longest time series stations in the southern hemisphere – theyíve been collecting data on ocean conditions from the 1940s – we know then from these long-term observations that ocean circulation is changing. East Australia currently forms part of the South Pacific gyre that is responding to changes in salt and temperature of the ocean and itís speeding up. Itís increasing itís southward transport. The speed of this current is faster in summer than it is in winter.

So as a result, weíre seeing changes in the temperature profiles in waters, particularly off Eastern Australia. Just to explain a little bit more about this current, it forms in the Coral Sea, it intensifies in Northern New South Wales and at Smokey Cape separates from the coast. Two-thirds of that flow moves across towards New Zealand and the examining southward flow forms what we call eddies and coastal fingers. They can move as far south as Tasmania. So these long-term data show as that the ocean is warming. Here Iíve shown temperature over the time period 1940 to 2010 for these three different locations. Rottnest Island is shown in red – this is the western station – shows, letís call it a one degree percentary increase in temperature if we just plotted that linearly over time that would be the average rise. Port Hacking, just south of Sydney, is showing a similar rise in temperature, but certainly our most southern station here at Maria Island off the east coast of Tasmania is showing the starkest increase in temperature indicative of more East Australia current water moving southward.

So now to link what these investigators found in the global ocean and examining the Australian situation, we did a similar study using the same optical sensor, satellite data. Over the same time period we did the same analysis at Maria Island. What we see here, shown in this plot, is a growth rate of the phytoplankton. So we take that as the difference in the amount of phytoplankton that might have occurred over a three-monthly period in the spring and we see that over this decade there has been a decline in the growth rate of those phytoplankton near Maria Island and also a decline in the total amount of biomass of those microbes. So it mirrors the global picture. Weíre seeing a decline in phytoplankton productivity and increase in sea surface temperature.

We know though that remote sensing only captures part of the story. Itís looking at the surface layer of the ocean typically and not able to capture any information at depth. So using other types of sensors that we put into the ocean we can actually look at – excuse me, sorry – we can actually look at patterns in the phytoplankton biomass with depth across large space scales. I guess here similarly we have red as high amounts of phytoplankton and blue as low amounts of phytoplankton. The first thing you might notice then is that we have this mid-range – at 40 metres, we have this maximum chlorophyll. Itís certainly not all clustered up here at the surface. The satellites then are typically only seeing something between zero and 20 metres. So thereís a large part of the picture that we still have yet to capture.

Just to explain what weíre using here, these are computer-guided underwater vehicles onto which we can put different instrumentation including sensors that measure the amount of phytoplankton in the water. This particular plot shows this transit of the glider from north to south in the Sydney region some years ago. So weíre measuring productivity in the ocean using oceanographic tools and Iím just showing you to estimate this rate of carbon fixation this is a typical plot showing the change in carbon fixed with light intensity. Iím summarising some data that was collected a couple of years ago on an oceanographic voyage by our group and it shows a sea surface temperature plot indicating that weíre in different water masses.

Itís a very variable region of the ocean off New South Wales. This red patch indicates the East Australia current, thereís a patch of really warm water relative to the other water next to it and we examined the productivity at three different stations indicative of those water masses. Here on the inner shelf coastal water we get four point six units of productivity here in the East Australia current or just at its edge we get one unit of productivity. But interestingly, when we were in the eddy, which is basically mixing water from great depth and bringing it to the surface providing nutrients for phytoplankton to grow in the surface, we have 14 units of productivity. So weíre seeing a massive contribution perhaps of the eddies in stimulating productivity in this region. [PAUSE] The other thing thatís happened in the ocean over this time period from 1940 to today has been a change in the amount of nutrients. If you remember itís not just the dissolved carbon dioxide in the seawater thatís driving productivity, these cells require nutrients and nitrogen and silicate are two major nutrients these guys need. So from 1940 to 2007 this data set sows that firstly the nitrogen availability hasnít necessarily changed but thereís been a huge decline in silicate.

Silicate is essential for these diatoms to grow. You remember I mentioned that theyíre important organisms that basically affect the way that that particular organic carbon sinks into the ocean. So really, from 1970 when we first started measuring silicate we see a potential for a great amount of decline in the potential for diatoms to grow. We think thereís two things that may be happening to drive that pattern, that decrease in silicate. The first is that silicate is introduced into the ocean through weathering of rocks that comes from our continental land run-off. So if thereís decreased rainfall across Eastern Australia then weíre likely to see decreased silicate into the ocean. So this may be indicative of a drying continent.

The second hypothesis weíre going out to test is that the East Australia current water is actually going to displace the water that exists on our continental shelf and it may contain low silicate and itís basically driving this pattern – more EAC water, less silicate. So our oceanographic work is really trying to answer this question. So to summarise then, we have a long-term increase in temperature, particularly on our east coast. We have long-term changes in nutrient availability and we have eddies that potentially affect productivity. So this gives us great interest in studying this part of the ocean. We are now blessed with a federally funded program to make more observations in the ocean. This is called the Integrated Marine Observing System and itís funded until 2013 and itís basically increased the number of instruments in the ocean by at least an order of magnitude. So the Port Hacking station, which forms one of the longest time series, as I mentioned, is based on a mooring now that basically is able to measure temperature at different depths in the ocean and a whole bunch of other oceanographic parameters that we can use to better understand the dynamics and productivity in that region.

In October of this year UTS together with other partners is going out into the ocean to investigate the EAC and the eddies it produces. Iím going to let Justin now take you from my macro scale into the micro scale and uncover the box. [PAUSE] Facilitator 2: So as Martinaís described, these phytoplankton, photosynthetic microbes are very important for carbon flux in our ocean and also controlling our food web. Iím going to talk to you about another bunch of microbes in the ocean, the bacteria, specifically the heterotrophic bacteria, which are the bacteria, which consume this carbon, which the phytoplankton produce. So as Martina showed us, the phytoplankton are at the base of the food web and they, along with the bottom parts of the food web, control this biological pump, which is essential for the oceanís carbon cycle. So how do the bacteria fit into all of this? So thereís two other parts to this story which we need to consider when we want to look at the importance of bacteria. One is when weíre considering phytoplankton photosynthesis, which Martina described earlier, not all of their photosynthesis ends up being turned into phytoplankton biomass.

In fact, a significant proportion of the photosynthesis is released back into the water column in the form of dissolved organic carbon. Now, this is one of the largest pools of carbon on earth so itís very important in that global carbon budget. But for a long time it was thought it was lost from the food web because these larger animals canít consume dissolved forms of carbon. So the big question was what happened to this carbon and how was it recycled? The second question is, what happens to all of this material thatís being exported in the biological pump? Is it all reaching the bottom of the ocean and are we getting a complete 100 per cent transfer of this carbon to the ocean sediments? So the answer to both of these questions lies in the activity of the bacteria in the ocean. So typically, when weíre swimming around at Bondi or somewhere like that we donít like to think that the water weíre swimming in is filled with microorganisms but in actual fact, every teaspoon of seawater contains around 10 million bacteria and 100 million viruses.

So every mouthful of water that youíre swallowing when you get dumped by a wave is filled with these guys. But luckily, most of them are quite benign so you donít have much to worry about. But just note the numbers here – very large numbers in such a small volume of water. If we go up to a larger volume, a slightly larger volume, a bucket of seawater, the number of microbes within this bucket of seawater equate to a higher number of organisms than the total number of humans that have ever lived on earth for the history of humankind. So thatís within this very small volume – again, a large number. If we now consider the diversity of these microbes – and weíll look at a litre of seawater in this case – recent estimates indicate that a single litre of seawater will contain 20,000 different bacterial species. This equates to double all of the species of bird, fish, mammal and reptile in Australia.

So as well as being abundant, theyíre very diverse and theyíre carrying out a number of different processes, which are important for the function of the ocean. So if we take a normal seawater sample and look at it under the microscope after scanning it with a DNA stain weíll typically see something like this. Weíll use an epifluorescence microscope that allows us to look at the DNA fluorescence of these organisms. So these bright dots correspond to individual bacterial cells with these smaller dots corresponding to viruses. Down here, we can see one of the phytoplankton cells like Martinaís been talking about. So this might look a lot like stars in the night sky if we look out at night but in actual fact, the total number of microbes in the ocean equate to more than 100 million times more than the stars in the visible universe. So again, thereís a lot of them. So the next question is what are they doing? Are they doing anything important or are they just the oceanís garbage and breaking down the dead fish and organic matter and keeping things clean? Or are they having a more important role? [PAUSE] So letís start off with their role in the food web.

So as I mentioned, thereís this big pool of dissolved organic carbon and heterotrophic bacteria are able to assimilate this carbon very efficiently. So we see a large percentage of photosynthesis is actually directly rooted through into the bacteria. Now, this needs to find itís way back into the food web so that Nemo can get some access to this carbon. The way this happens is thereís another group of microscope zooplankton which graze upon these heterotrophic bacteria and these are then grazed upon by the larger plankton. So we can see that eventually this carbon gets back into the higher food web. This is whatís known as a microbial loop. So we can this integrates the role of bacteria into the ocean food web. What does this all mean for carbon cycling? Well, one of the first things we need to consider is that during these processes these organisms are respiring. So theyíre returning carbon dioxide back into the water and this can in some cases make its way back into the atmosphere.

So letís look at that in the role of the biological pump. So Martina discussed the biological pump and its important role in carbon flux in the ocean. We have our sinking poo and dead animals and if we zoom in one of these we can see that these particles, which are often referred to as marine snow particles because we have this constant flux of these small white particles in the ocean, so here we can see a zoomed in image of the marine snow particle. These particles are really rich in organic carbon, which is a good growth element for bacteria. So if we look further under a microscope, and again staying with the DNA stain, weíll see something that looks like this with each of these blue dots corresponding to a bacterium. You can see that these particles become very heavily colonised by bacteria as they sink through the ocean. These bacteria use enzymes to break down this particular carbon and then they consume it, which actively returns the carbon to the food web. It also leads to respiration on these particles and we have high levels of bacterial respiration occurring, which is returning carbon dioxide back into the water.

So what we get, instead of having this clean flux of particulate organic carbon to the sea floor, we get respiration returning carbon dioxide and this actively short circuits the biological pump. So you can see that all of the good work that they phytoplankton perform is stopped by some of these activities of the bacteria. So this indicates that we must consider the role of bacteria in the ocean carbon pump cycle. So as Martina suggested, we get influx of carbon dioxide into the ocean, but we also get an efflux out from respiration within the food web and we now know that we really need to consider the role of these very abundant microorganisms in respiration leading to the increased flux in carbon dioxide. So what you can see is we get a balance between ocean photosynthesis and respiration. This can change depending on parts of the ocean and the microbial communities and this ultimately influences whether the ocean is a source or a sink for carbon dioxide in different regions.

[PAUSE] So how do we go about studying these organisms? Well, typically, oceanographers go out on research voyages on big ships and we take samples across large distances across scales of kilometres or hundreds of kilometres. Weíll take samples in these types of bottles, which will often give us a water sample of around five to 10 litres. As Martina suggested, we can also now use satellite imaging technology to look at the distributions of some of the photosynthetic microbes. So here we can see an image of the phytoplankton off the south-eastern coast of Australia and we can see that we get these fairly patchy distributions of phytoplankton. But these are very grand scales and if we think about the life of an individual microbe, theyíre not really going to care much about whatís happening across these very large distances. So some of my research is trying to look into what happens at the scale of the individual microbes and how this could also be important for chemical cycling in the ocean. So the scale of interests for an individual cell in the ocean is going to be on the order of a fraction of an individual drop of seawater. So much smaller scales.

What does life look like for a bacteria in this kind of environment? What we have here is an artistís impression of the world experienced by a marine bacteria. One of the things that stand out from this is itís not a uniform homogenous environment, which is often thought of in traditional oceanographic theory, that things below scales of a few metres are homogenous. What we can see is that thereís a number of ecological processes that drive patchiness in resources. So we have a zooplankton leaving an amino acid-rich trail of excretion behind it. We have a phytoplankton cell here and, as I mentioned, they release a large part of their photosynthesis back into the water as dissolved carbon and this can lead to a plume of dissolved carbon around individual phytoplankton cells. Here we see a phytoplankton cell which has been infected by a virus and has now burst apart releasing all of the organic material within this particle, within this cell, into the water column and this pulse release of chemicals.

Here we see one of these sinking marine snow particles, which has been colonised by bacteria and are breaking it down with their enzymes and thereís actually a leeching of organic material into the trail behind this sinking particle. So we get these hot spots of chemicals in the water column, both in particulate and dissolved form, and itís possible that bacteria can use behavioural foraging responses to take advantage of these patches in the same way as larger organisms might take advantage of patches in terrestrial environments. But to study these types of processes we need to consider this disconnection between these oceanographic sampling processes and the ecology of these microbes. So as I mentioned, we take these large volume samples but 10 litre volumes arenít going to allow us to look at processes occurring within individual drops of seawater. So using these types of processes to look at these dynamics in the ocean isnít matching. So one of the things we did was designed our own micro scale sampling devices and here we can see one of these, which simply composed of an array of 100 syringes which have been modified to each take in 50 microliter volume.

So these are taking in volumes, which are more like an individual drop of water, and we deploy this in the water column and itís spring-loaded so we can take this sample at any depth and then look at the special distributions of bacteria across these small scales. So as I showed earlier, across these scales of tens to hundreds of kilometres we can see these patchy distributions driven by large-scale oceanographic phenomenon. But what happens when we look at the very small scales? What we see is we also find these very patchy distributions of bacteria but note the scale in this plot, itís now millimetres. So weíre looking at very small scales and we start to get these hotspots of bacterial abundance indicating that they may be showing some of the behaviour that we saw in the artistís impression. If we then look at the relative amounts of metabolically active bacteria in the sample and we can see that thereís also hotspots in bacterial activity. So here we can see the relative numbers of active bacteria and we get these hotspots where we might expect to find increased carbon uptake rates and respiration rates indicating that thereís these micro scale processes which could play an important role in the chemical cycling.

So whatís driving these patters we observe in the environment? One potential mechanism behind these patterns is the behavioural response or the chemotactic response which allows cells to respond to these chemicals. So again, weíre faced with the challenge of studying processes at very small scales. In this case we want to look at the behaviour of the organisms but these are occurring across very small distances and short timeframes. So we used a relatively new technique called microfluidics to try to look at some of the behaviours of these microbes within a patchy seascape. So microfluidics involves creating these very small chips into which we can put complex channels and structures and what we can see here is a microfluidic channel. This is on the stage of a microscope. So here we can see the objective lens on the microscope so you can see the small size of these structures. Hereís a schematic diagram of the microfluidic channel that weíve been using.

To give you an idea of the dimensions, this is about two centimetres long, three millimetres wide and 50 micrometres deep. The two main points of this channel is that we have these inlet points, one at the back here where we can inject the bacteria into the channel and the second inlet point here, which is connected to this 100-micrometre wide micro injector. With this we inject our band of organic substrates to simulate these types of micro scale patches we might see in the environment. We then use video microscopy to track the swimming paths of individual bacteria with the objective to see whether they are able to respond to these micro scale patches and obtain higher exposure to the organic carbon. So we performed a series of experiments using this setup. Some of the data Iíll show you today is with the marine bacteria pseudo-autonomous haloplanktis and we looked at its behavioural response to patches of dissolved organic carbon and in this case it was the products of phytoplankton species. So as I mentioned earlier, a lot of these micro scale patches are associated with phytoplankton in the ocean.

What we can see here is across one of our microfluidic channels and here we can see the band that we inject of the dissolved organic carbon and we can visualise that by adding a fluorescent stain to the patch. Then what we want to do is look at the behavioural response of the bacteria, which we measure with video microscopy and image analysis techniques, and here we can see the swimming paths of individual bacteria within our channel. So each one of these little white lines corresponds to the swimming track of an individual bacteria. We see within a very short time we saw this within a few seconds, we get this really strong accumulation of bacteria in the middle of the channel corresponding with this patch of nutrients indicating that they can both sense and then direct their movement in response to this high food patch for them.

This accumulation of cells persisted for several minutes until the nutrients were taken up or diffused out and we can see that after 20 to 25 minutes we get back to a more homogenous distribution of the bacteria. So what does this type of swimming and foraging behaviour give the bacteria in terms of an advantage in the food that they may receive? So we – to look into this, we compared the distribution of the bacteria in these experiments to the distribution of the nutrients as they diffused out and then compared that to the distribution of a population of randomly distributed nonmotile bacteria to calculate the gain in nutrient exposure. We found that for the marine bacteria corresponding to this blue line they received a gain of around three-fold in their exposure and uptake of the carbon source indicating that this type of foraging response would provide them with a competitive advantage over other bacteria in the water column. Here we can see, interestingly, we performed the same experiment with E.coli, the stomach bacteria and we see that it performs a lot more poorly than the marine bacteria indicating that the marine bacteria are well adapted to take advantage of these ephemeral small-scale events in the ocean.

What does this mean for carbon cycling? Well we can expect to see accelerated carbon cycling rates at the base of the food web. [PAUSE] So what does this mean for the microbial food web in the ocean? As I described earlier, these bacteria are eaten by micro zooplankton, which is important for shifting this carbon into Nemo. So if we get these patches of bacteria occurring in the ocean, how do their predators respond? So we performed the same experiment using the microfluidic channel. But in this case we had a patch of the heterotrophic bacteria and we looked at one of their grazers or their predators, a flagellate called [Neobodadesignas unclear] and looked at their foraging response and once again found that they concentrated their swimming behaviour corresponding with the position of the bacterial patch. The bacteria form a patch in response to the dissolved substrates and then their predators follow them in and increase their grazing rates upon them by increasing their grazing efficiency within this localised patch of food. This could eventually lead to an accelerated transfer of carbon through the base of the food web. So in the same way that these larger organisms, these dolphins are responding to a patch in prey resource, so thereís this localised patch of food and theyíre concentrating their foraging behaviour to take advantage of this patch we can see that microbes use the same types of behaviours in the ocean.

So what does all this mean for the carbon cycle? Well you can see that these micro scale processes influence the activity and behaviour of bacteria in the ocean and by actively taking advantage of these patches, it might influence carbon turnover rates. This could ultimately have an effect on bulk carbon flux rates in the ocean and influence the ocean carbon cycle. So that means that processes occurring across these very small scales could ultimately have an influence on the processes which influence our climate. So Iíve described some of the potential effects that microbes could have on our climate and on the important chemical cycles for our climate but if we predict that there might be climate change in the next few years, what are some of the potential effects of this on the microbes themselves? So as Martina described earlier, thereís evidence that increased water temperatures can decrease phytoplankton photosynthesis.

So this will obviously have an effect on the biological pump. But this can be compounded by the fact that increased water temperatures also increase the bacterial activity and respiration rates. So itís been suggested and shown in some experiments that this increase in bacterial respiration associated with increased temperature may weaken the biological pump and weíll find that we get a shift in this balance between photosynthesis and respiration in the balance of respiration. What this means is that more CO2 could be released from parts of the ocean than are absorbed and we get this positive feedback effect where atmospheric CO2 levels could be increased further. Another predicted effect of future climate change on the marine microbes is we might expect to find more nasty bacteria having more significant effects in our ocean environments. So one case is cholera, which is a disease which has affected people, particularly in third world countries and over the last several decades has been responsible for the deaths of tens of thousands of people.

A vibrio cholera is associated with the marine bacteria vibrio cholera, which is an aquatic bacteria and the growth of this bacteria has been shown to be increased in higher temperatures. Additionally, if we get increased water sea level in low lying regions such as Bangladesh, we might expect to see bigger influxes of the water into environments where there are people living and we could expect to see increases in cholera outbreaks due to these effects of climate change. So just to sum up, marine microbes are the most abundant and diverse organisms in the ocean. They are responsible for around 50 per cent of global photosynthesis. So for us this means on average half of every breath of oxygen we breathe in is derived from the activity of these guys. They form the foundation of ocean productivity, which has an influence on marine fisheries yields, and this is obviously important for the human population because we gain more than 15 per cent of our protein in our diet from fish.

Microbes are also important for driving the important chemical cycles in the ocean which can ultimately mediate our climate. So as weíve described today, Martina showed that microbes can be influenced by large-scale processes across oceanographic provinces and across regions of hundreds of kilometres but we can also see that microbes are influenced by processes occurring more at the scale of the organisms themselves. Weíve also seen that microbes can influence climate and may also be influenced by climate change and this indicates that there may be unforeseen feedback effects if we get a climate change scenario. This is some of the research which is being conducted at our group here at UTS C3 where weíre looking at different components of this to try to get a handle on how climate change may influence some of these processes.

So with that, Iíll thank you for your attention and Martina and I will be happy to take any questions..