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.