Friday, 21 December 2012

9 - Collecting the creatures of the deep

When the ROV Isis  finds an interesting place on the seafloor, the sampling begins! Isis  is equipped with manipulator arms that can pick up samples to place them in boxes on the front of the vehicle, but as many deep-sea animals are very delicate, it is usually best to use the suction sampler (see image below). The suction sampler is like a vacuum cleaner, gently sucking up animals and sediment via a long tube. The animals can be deposited in any of five sealed rotatable chambers where they remain until the ROV is on board the ship again. As soon as the ROV is secured on deck and we are allowed near, all the biologists, armed with buckets, begin to move the animals and sediment samples to the sorting tables.

The suction sampler on ROV Isis  in use at E2.
The box in the background is attached to the ROV on swing arms and is used to hold samples

At the sorting tables, all samples are given individual numbers by Katrin Linse, so that we can keep track of what samples came from which place. One of each species of animal is preserved and safely stowed, so that, on our return, we can send them to taxonomic experts around the world for identification or if new to science, for description. All other samples are then divided up so that (hopefully) all scientists participating in this project get what they need to carry out their work. Sometimes different species go to different scientists. Or some species, like the yeti crabs, can also be shared – the legs to one person, digestive glands to another, gonads to someone else and so on. This means we make use of the entire sample and none of it is wasted. After all the large animals are sorted, the sediment that is left in the bottom of the buckets and chambers is sieved and then sorted under a microscope to find all the small animals that are difficult to see with the naked eye.

The samples are shared out because different scientists may analyse the samples in different ways as not everyone is studying the same thing. Below are explanations from each of the groups of scientists on board explaining how they analyse their samples and what they hope to understand from their work:

Katrin Linse (British Antarctic Survey) and Helena Wiklund (Natural History Museum, London)
Katrin looks at all the specimens collected to assess the overall biodiversity on a large scale. She wants to be able to describe the entire vent and off-vent assemblage of animals and answer questions such as which species lives where and with whom. Katrin and Helena also try to ascertain whether these animals are ‘specialist’ fauna (living only on the vents) or ‘background’ fauna, which come to the vent fields due to the greater availability of food (normally living in the general deep-sea waters of the Southern Ocean). Katrin and Helena also try to find the closest relatives of the animals we find by examining the DNA of each species. Also, looking into whether these animals have any special adaptations that allow them to live in these extreme environments. Helena has a special interest in polychaete worms and Katrin in molluscs.

Katrin with the first batch of samples on the sorting tables

Chong Chen (University of Oxford)
Chong is interested in snails! He is looking specifically at how species are connected with each other over distances of tens of metres to hundreds of kilometres. To do this he needs to compare the DNA of each snail collected, which he can get from small pieces of tissue taken from each specimen.

Leigh Marsh (University of Southampton)
Leigh primarily uses video footage to look at the spatial separation of animals around the vent habitats. In particular, she is interested in the yeti crab found at these vents. We have sampled crabs when abundant in hot areas close to the black-smoker chimneys and cooler areas further away. From this initial sampling, it has been found that females carrying eggs occur in the cooler areas further away from the hotter areas of the vent sites – it’s like a maternity ward for crabs! Leigh is also interested in examining how, when and where the yeti crabs reproduce to sustain their populations. That means, when samples are dished out, she measures the length of the carapace of each crab, identifies the sex of the crab and then removes the gonad tissue, which she then uses to assess the maturity stage.

The yeti crabs on the sorting table before being shared out to scientists

Clare Woulds (University of Leeds)
Clare uses the animal specimens to conduct experiments, which will help us to understand where the animals living close to vents derive their food and energy. For animals such as the brown snails that live on the vent chimneys, this involves placing them into aquaria filled with seawater from the site where they live. They are then kept at the temperature at which they normally live (in a high-tech fridge that she brought with her on the ship) for several days. The snails are unusual in that they have symbiotic microbes living in their tissues, and those microbes are able to harvest chemical energy from the mineral-rich hydrothermal vent fluid to make food (just as plants harvest sunlight to make food). She adds different chemical labels to the different aquaria, and these will allow her to see the uptake of different dissolved substances by the symbiotic microbes. Clare can then trace her chemical labels into the microbes’ DNA (and so figure out exactly which microbes take it up), and also, using cutting-edge microscope techniques, to be able to see exactly where the microbes are located in the animals.

Jane Heywood (British Antarctic Survey)
Chemosynthetic bacteria provide energy to deep-sea hydrothermal-vent ecosystems and support life. Many of these bacteria are found in symbiotic relationships with invertebrates such as the yeti crabs, brown snails and barnacles. Jane collects samples to examine the bacterial community from various tissues. For example, with the yeti crabs, she gives them a haircut, removing some of the hairs that grow from the underside of the shell. These hairs have many long chains of bacteria attached to them and Jane extracts their DNA and RNA and preserve samples for microscopy. Back on land genes will amplified from the DNA and sequence them to determine the diversity and community composition of these Kiwa-dwelling bacteria. Jane also performs similar analyses on bacteria associated with other hydrothermal vent fauna such as snails, barnacles and sea spiders and compare these to microbial communities in the surrounding environment; living on the rocks or free-living in the water. Assessing the microbial diversity and community structure will provide insights into the factors controlling these primary producers and the benefit, if any, that the animal gains from hosting these microbes.

Will Read and Chris Sweeting (University of Newcastle)
Chris and Will use a selection of animals for their food-web studies. Their primary goal is to figure out what these animals eat and how the energy sustaining life is transferred through the hydrothermal vent habitat. They start by removing various tissues (e.g. muscle, liver, gill) and freezing the samples at -81°C. The biological composition of the tissues will differ depending on their biological role, much like the way you see different percentages of fats, sugars and saturates written on food packaging. Taking different tissue samples will provide different types of information depending on the research question. The samples will then remain frozen until they get back to the lab in Newcastle where they dry the sample and process it for analysis. These data are used to figure out which animals are eating the bacteria at the base of the food chain as well as which animals are eating each other. We can also tell if the animal's diet changes with body size or spatial position within the hydrothermal vent habitat. The work links in with the research undertaken by the microbiologists and with those looking at the distribution of animals within the hydrothermal vent. By linking different aspects of the research together, it begins to provide a more holistic overview of the biological processes that occur at each location.

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