Investigating Food Webs

A few people asked me to explain further about what I’m doing here, what Michelle and Sarah are working on and why.  I thought I’d show some more of our day to day sampling activities.

I don’t know about you but I thought I knew about food webs.

Food webs describe the relationship between animals and plants, their dependency upon one another and the interaction between species.

There is an apex predator, let’s say the orca.

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Food web from Enciclopedia visual de la Antarctica

The orca eats a leopard seal, which has eaten a penguin. The penguin has been eating squid, which ate fish, which were eating krill for their dinner.

Humans also eat the squid and the fish which have been eating krill.

Krill are the tiny creatures breeding in such huge numbers that they support the whole system, even gigantic whales eat krill and plankton.

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Large Krill. Should have put something for scale.

But it doesn’t stop – or start there. Krill eat phytoplankton (plankton which photosynthesise) as well as zooplankton (microscopic animals which eat phytoplankton) if there is less phytoplankton there will be less krill. Less krill and the whole system will be affected.

So it is these tiny microscopic organisms that live in the sea the soil and even the air – I have just discovered that there is aeroplankton – which are underpinning the more visable systems involving orcas and penguins.

We know that the world is warming, predictions are that it will be +1.5 to 4°C by the end of the century.

The most dramatic changes have been seen in the Arctic and Antarctic regions, these areas have seen polar heat waves of +20°-30°C in recent years.

This rise in temperature has obvious and immediate consequences on areas suitable for life, and for animals and plants living in the polar regions. The loss of sea ice causes problems for seals which breed on it and the changing temperature and acidity of the sea cause krill to move from their usual locations in the sea.

Scientists know quite a lot about changing rain patterns, temperatures, and melting ice They are able to make predictions about how these factors will affect larger animals in the Arctic and Antarctic, the animals which are being affected by climate change but which are able to change their behaviour, they can adapt. Whales can move to areas where food is more plentiful, seals can change their breeding behaviour.

The area where less is known is how the changing temperatures will affect the microbial communities underpinning these whole food web systems. All the tiny plant and animal life in the soil, sea and air, how will those species be affected by changes in temperature? Will they be able to adapt, and if so how quickly?

The food webs that I have been investigating with Michelle and Sarah are not the models which include orcas and sea lions and squid, we are looking at communities on a very small level, a microscopic world including diatoms, bacteria, and zooplankton where the big guys are crawling invertebrates, little shrimp-like (to my eyes, I have been asked to point out that they are nothing like shrimps) jumping creatures called springtails about 1mm long.

To study a range of communities like these you could set up lab experiments creating artificial habitats at different temperatures but the beauty of finding a place like Deception Island is that the landscape is a natural laboratory.

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very hot patches in the sand and sea

Because the island is an active volcano there are areas with very localised hot spots meaning that you can test the exact same environment but at different temperatures.

We have been testing moss carpets, fresh water, and intertidal locations.

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Patch 3 in a moss carpet. Using the slide quadrate to cut a rectangular plug.

We are trying to find out, as Sarah says; Who is there and what is their activity?

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Three sites at Fumarole Bay marked by stakes and bouys

Here on Fumarole Beach for instance is an area of sediment or sand which is covered by the tide twice a day.

We have used probes to measure the temperature just under the surface and found a natural gradient from 5°C to 35°C so now we can collect our samples.

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We set up 4 sites covering the gradient and hammer in metal stakes to mark them over the next few days. Each stake has a data logger attached and buried just under the sand, this will record the temperature of the site every 15 mins for 72 hours.

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Setting up five patches at an intertidal site on Pendulum Beach

(In actual fact some of the sites got much hotter than we had expected, up to nearly 100°C and our loggers exploded and melted. Luckily we had some very clever people at the base who were able to remodel the circuit boards and extract the data from the chips. This is what I’ve really enjoyed about field work, you can never guess what might happen next.)

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Minidot Logger with expertly tied string

Using a machine called a multimeter with multiple probes we record:

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Using the multi meter in fresh water in the lava fields above Crater Lake

conductivity – how easily electricity passes through the water – telling us how much mineral content there is, the pH – acidity, and oxygen levels, at five patches marked by flags on each site.

We collect a 5cm round core of the earth or sand at each patch at each site, this will be carefully sieved and inspected to unearth all the invertebrates living there.

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Collecting core samples at Stone Throw Ridge

Sarah does a water chemistry test at each site to see if there are any other variables such as very high iron content, these could be as a result of the difference in temperature or they could have an effect on other things we are measuring.

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Water chemistry. Injecting Zinc Chloride into water.

Every single sample is packed into tubes and bagged and logged, labeled with Michelle’s system that I totally understood by the last day of our expedition.

At the moss carpets we use a quadrate to cut away an exact rectangle of moss and in the sites with sediment we use the same quadrate to carefully toothbrush the surface of rocks into a tube.

In these samples we are collecting the green stuff. Chlorophyll.

Some of the samples will be mulched down and then have their chlorophyll exploded in ethanol. This will go into a spectrophotometer which will determine the greenness and therefore how much photosynthesis is going on in that patch.

The other half of the ‘rock scrape’ samples are going to be looked at for diatoms. Diatoms are single celled photosynthesising organisms which to me look quite similar to snowflakes, I’m looking forward to discovering more about them and seeing the ones we have found on Deception Island.

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Moss carpet at Stone Throw Ridge

We haven’t been processing all these samples in our Antarctic Lab, other than doing a LOT of filtering. When everything arrives back in England the samples will be processed in Michelle’s lab and hopefully I will be able to go and see.

Our igloo lab on Deception Island

I’m writing this from Hesperides. We have just been through the Beagle Chanel, entering from the Atlantic side and are now in the Pacific rounding the West of the islands in order to go back into the Estrecho de Magallanes. It suddenly got very rough at lunch and everyone sloshed around with their soup bowls and lurched dangerously about brandishing the incredibly pointy and sharp knives they have on this ship.

I wish Poirot could come aboard, it would be such fun.