Name: UTS科學聚焦。海洋微生物，海洋的命脈？海洋的命脈？ (UTS Science in Focus: Marine Microbes: The Ocean's Lifeblood?)
Uploaded: 2021-01-14T05:01:40.000Z
Duration: 44 min 29 s
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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.

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UTS科學聚焦。海洋微生物，海洋的命脈？海洋的命脈？ (UTS Science in Focus: Marine Microbes: The Ocean's Lifeblood?)

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climate

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