Deep Sea Corals

The Naked Scientists spoke to Dr Jason Hall-Spencer, University of Plymouth
23 April 2006

Interview with 

Dr Jason Hall-Spencer, University of Plymouth


Chris - Tell us about your research because you're looking at corals principally aren't you?

Jason - Yes, but I'm looking at deep sea corals. Previously people thought that corals only occurred in the tropics making great big coral reefs. But we've just discovered some really huge ones off the coastline of the UK.

Chris - I imagine a lot of people of thinking, myself included, what actually is coral?

Jason - It's related to an anemone but it's got a hard skeleton, like we've got a skeleton inside of us. These corals have got a hard chalky skeleton too. What's peculiar about them is that they've got stinging cells. They've got harpoons that inject their prey, and that's what they use to catch their prey.

Chris - But when you see this big chunk of coral reef, is all of that one massive alive organism or is this an ants' nest with lots of little things that co-operate to make one big colony home for themselves?

Jason - It's more like an ants' nest I suppose because each individual polyp, that is the individual anemones that make up the reef, make up a great big skeleton together. They are like ecosystem engineers because they make these reefs to catch their prey.

Chris - And how big is each of those polyps then?

Jason - Well each one is about the size of your thumb nail. But if you're the size of their prey, such as a little tiny flea, that's a large mouth ready to catch you and rip your head off.

Chris - So how did they evolve? Where did these polyps come from?

Jason - We think they came from things like Hydra. they've got lots of tentacles; they've all got stinging cells; and they're all related to things like jellyfish. These are sedentary jellyfish: jellyfish which live on the bottom and then form a skeleton.

Chris - So why's it significant that some live deep and some live shallow?

Jason - We didn't think that large reefs were formed in deep water. We thought that they had to be living in shallow water to catch enough light to feed their symbiotic bacteria that live in their skeletons. But it turns out that we've just been able to discover some large reefs of the coast of Ireland and Scotland and Norway, and that's very significant. You'd think that people would know the deep sea quite well but in fact there are large reefs there that no-one knew about until about five years ago.

Chris - Tell us a bit about that symbiotic relationship, in other words two organisms living side by side to mutual benefit.

Jason - Symbiosis is when two different unrelated organisms benefit each other. In the case of the corals in the tropics, there's an algae that lives inside its tissues that captures light and makes sugars. That benefits the corals themselves. The corals benefit the algae by being a highly armoured vehicle in which they can live.

Chris - Is it just a protection thing or does the coral do anything else for the algae?

Jason - The coral provides the algae with its waste products, which are nitrogenous. The algae would otherwise find this very hard to get hold of.

Chris - Because algae are plants aren't they.

Jason - Yes.

Chris - And when you go deep down in the ocean, what sort of depths are the corals you're looking at growing at?

Jason - Typically, the ones I'm looking at are a kilometre down.

Chris - That's a long way. How much light is there down there?

Jason - there's no light. We lowered some polystyrene cups down to that depth and they're crushed down to the size of a thimble, so there are huge pressures.

Chris - How do the corals withstand that kind of pressure?

Jason - It's because they don't have any air pockets in them. We have air pockets in us and so does a polystyrene cup. If I was lowered down on a rope to a kilometre depth, I'd implode. My skull would be crushed because I've got sinuses in there that are air pockets. But because there are no air pockets in a coral, it can withstand any depth.

Chris - If they can't get any light or have any algae, how do they get their energy? How are they metabolising?

Jason - Well the jury's still out on that actually. Lots of geologists think it's because they get their energy from methane seeps or from hydrocarbons that are coming out of the sea bed. I'm of the opinion that they live at depths where plankton comes down from the surface and concentrates into a thick soup. That could benefit the corals at depth.

Chris - A lot of people say that there are some interesting things lurking in the ocean depths that might benefit mankind in terms of medicine. Are there any examples you can think of for these corals, or is it relevant?

Jason - There's an intensive search on. The French in particular are looking for chemicals that can help with cancer in sponges that live in the deep water, but to my knowledge we haven't discovered that yet.

Chris - So why are these corals important?

Jason - They form habitats that are very important for the breeding, feeding and daily lives of fish. They form part of the life history of these deep sea fish populations. Unfortunately, these deep sea corals are very easily damaged if you tow fishing nets through them. The fish are attracted to the corals to feed and breed, but they also make the corals vulnerable to fishing equipment.

Chris - It's pretty deep a kilometre though. What kind of fish are knocking around a kilometre down?

Jason - There are all sorts. They've got unpleasant names like Black Scabbard Fish or Pudgy Cusk Eel. They're things that if you put them on your plate they look revolting. But what people do is that they fillet them, and then put them into school dinners in France for example. You wouldn't know if you bought it in a supermarket for example, that it was necessarily a deep sea fish.

Chris - Where are these reefs principally located? Around the UK?

Jason - It seems, although we don't really know because we haven't looked at most of the sea bed, that they're concentrated where the sea bed used to be glaciated in the past. So where icebergs trundled down the coast line of Europe, they scarred the sea bed with deep trenches and left behind lots of piles of stones that were scraped off the mountains. It seems that these piles of stones are in the way of strong ocean currents and: a) provide the corals with a substrate to live on; and b) the food that they need to survive.

Chris - Are they threatened then now that we're going out there with massive great nets and indiscriminately ploughing the sea bed?

Jason - Unfortunately yes, they are highly threatened at the moment. We've got to the stage where lots of the shallow water fish, for example cod, are much less abundant than they were in the past. So people are looking deeper and deeper to catch deeper fish populations. This is the frontier of new exploration. Places that haven't been touched since the last ice age are now being trawled through with heavy trawling gear.


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