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

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.