Introduction to ecosystems
Introduction to ecosystems

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Introduction to ecosystems

4.1.1 Investigating small organisms

In the next video you will be able to watch a marine scientist collecting plankton samples in a hi-tech way, but first listen to some background to the work as David Robinson talks to Penny Boreham about small organisms. Some of the planktonic organisms are single cells whereas others, such as the young stages of larger animals like crabs, are multicellular.

In the interview, you will also hear about an organism called ‘Tony’. Tony is found in a very unusual ecosystem – one that you may not have thought about before – and you will learn more about this in the video entitled ‘Investigating flagellates’.

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Investigating small organisms

DR. DAVID ROBINSON
I'm David Robinson, and I'm a biologist at The Open University. And in this series of clips, we're going down into the world of the small organism, organisms that normally we're not aware of. So when you look out to sea, you see masses and masses of water, and you're just not conscious of the huge number of organisms that are in only a small volume of that water. One of the most interesting things you do when you start out in biology by the sea is just take a net and sweep it through that water. And then take your net out and wash off everything that you've got in your net. And you find you've got a whole world in your bottle of tiny organisms. And it's a completely different area of study. Because they're small, you require very different techniques to study them. And because they're so small, and they're completely immersed in their environment, the environment has great influences on them that you might not suspect until you study them.
INTERVIEWER
You just said that different methods are needed for working with small organisms. What type of instruments or methods are needed?
DR. DAVID ROBINSON
Well, firstly, of course, there's microscopes in order to magnify them and see them. But I think some of the other methods are ways of collecting them. The sea clearly is very deep. Although the plankton don't go down to enormous depths, but they do have quite a vertical distribution. And if you want to sample at a particular depth, you have to be able to send your bottle down there, collect water at that depth, and then bring it back up without it getting contaminated at other levels. In the film, there's a very high tech way of doing it where you have computer-controlled bottles. In earlier days, you had a bottle that went down on the end of a string, and you sent a little lead messenger down which opened the bottle to take a sample, and then a second messenger to close it again, and then you dragged it up. And you've got your sample from a known depth. And that's effectively what they're doing with the whole series of one litre bottles arranged in a circle and a computer deciding when to open and close the lids. And of course, it's very important to get the depth right because plankton do move up and down in the water. And this vertical migration of some plankton takes place on a daily basis. And then also, you get sudden increases in population at a particular point as a result of tidal movement. So for example, a population of phytoplankton might be swept past your equipment by the tide going one way and then swept back again going the other way. And this will produce, for example, a pulse in a detector that picks up phytoplankton, or it will produce a sudden surge in the number of individuals that were trapped in your bottle.
INTERVIEWER
We saw the painstaking work that was being done on the organism familiarly known as Tony by the research scientist. He said it had taken relentless hours of patience to come to some of the conclusions he's come to. Has it been groundbreaking, what he's produced, the research he's produced, about Tony?
DR. DAVID ROBINSON
I think the research that he's produced about Tony is extremely interesting, particularly because of where his sample comes from. And you can see in the clip the big drill bits and they're drilling down into the ground. What they're looking for is a lair of rock called an aquifer - that can be rock, sand, gravel - that is able to absorb a lot of water. And if that water becomes organically contaminated, then it will have bacteria in it. And Tony is living off the bacteria in that water. That is a very, very unusual place to look for life and to look for communities. Because, of course, Tony depends upon there being lots of bacteria there to feed on. And if the bacteria population declines, then populations of Tonys decline. And Tonys are able to form cysts, which can resist quite a bit of drying, as well as keeping the organism alive during a period when there aren't many bacteria about. And I think this is of course quite a common thing, of single-cell organisms forming cysts. But it's in this very strange environment, deep in water-bearing rock, I think makes it so special.
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Dr Gabrielle Kennaway is trying to find out more about planktonic organisms within their ecosystems and she is using very sophisticated equipment to sample the plankton. She refers to the equipment as a CDT, an instrument for measuring conductivity, temperature and depth that is equipped with sampling bottle. She is particularly searching for phytoplankton, microscopic plant life. She will show you how phytoplankton can be detected in the water and she reveals a very interesting event.

Dr Paul Tett is interested in the behaviour of phytoplankton. He discusses the sources of energy in this aquatic ecosystem. Being small has advantages for phytoplankton and you should try and note the advantages that Dr Tett describes.

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Investigating phytoplankton

NARRATOR
Paul Tett is an ecologist who uses models from physics to shed light on the behaviour of oceanic plankton.
PAUL TETT
Understanding about the very small requires us to understand, first of all, the biology of the organisms, but also something about the physical nature of the environment in which they find themselves because we're dealing with a very different world at the level of the very small. The creatures that I'm studying are called plankton, and, in particular, the plant members of the plankton, the floating microscopic plants called phytoplankton. And you can see some of them there. These little plants are really microscopic, single cells. Each of them has some green chlorophyll and some red pigment. These colours are distinctive of different types of phytoplanktonic algae. So you would expect to find different coloured phytoplankton at different depths in the sea depending on the colour of the light that reaches them. They need light because they're plants. And they need light to grow. But in addition, they need things that I call nutrients, mineral nutrients. And these are salts or phosphates, and nitrate. The sort of thing that you'd find if you use Grow More fertiliser in the garden. The problem for phytoplankton is that they can very rarely get light and nutrients at the same time. Because light is at the surface of the sea and the nutrients are found deep down where organic matter decays in this cold water at the bottom of the sea.
NARRATOR
Being small does bring its compensations.
PAUL TETT
The advantages of being small, for phytoplankton, is that it helps them to get nutrients and it helps them to stay in the light. It helps them to get nutrients because a small creature has got a high ratio of surface area to volume. And it's the surface that governs the rate at which nutrient can be taken up. And it helps them to get light because small creatures sink very slowly in the sea water. And therefore, they can stay close to the surface of the sea. And the surface of the sea is where light is.
NARRATOR
These cultured phytoplankton are kept in the lab. They get optimal lighting and the ideal balance of nutrients. The sea is the dominant force in the life of the plankton. Their movement is dictated by motions of the water around them. Paul has modelled the forces that plankton experience. These vary from the smallest to the largest scale.
PAUL TETT
Plankton are carried around the ocean basins by currents. And one of the characteristic features of currents is that they form eddies and motions become irregular. And I can demonstrate that by pouring a little cream into my coffee cup. So first of all, I'll stir the coffee around to simulate the motion of water around the North Atlantic. And then I'll add the cream. And there it is forming swirls and eddies, which are characteristic of the largest scale of motion in the sea. On the smallest scale, the behaviour of water is dominated by the attraction between water molecules. This is called viscosity. It makes the water very sticky to small animals. It's as if they're living in honey rather than water. A consequence of the high viscosity at small scales is that microorganisms find it very difficult to get hold of particles from the water as perhaps will become apparent when I've buttered my toast and put some honey on it. Oh dear, and now, as is often the case, I've left a little smear of butter in the honey. So I better get that out. But it doesn't really want to come, does it? Let's try again. So for small organisms, it's as if they're wrapped in a jelly-like coat of this thick and viscous liquid. It's very hard for them to come into contact with other organisms or with their food. This is glycerine, a liquid which is much more viscous than water. And I'm using it to demonstrate the properties of water on the scale of small organisms. Now, what is remarkable about what I'll demonstrate is that I can reverse the effects of stirring in this liquid. You can't do that with water. When you've stirred your sugar into your teacup, you can't reassemble the sugar cube afterwards. So let's make this demonstration beginning by adding a few drops of this green glycerine. Now, I'm going to stir these drops. So as I go around, the drops elongate. And when I come back, they return, amazingly enough, to the original round shapes. There are strong implications of this for locomotion. Movement is completely reversible. A forward stroke, which drives the organism forward, is reversed by the backward stroke, which sucks the organism backwards. So these little creatures can't swim by moving their flagella up and down or forwards and backwards. Instead, they have to use a corkscrew like motion.
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