Coral reefs and climate change

Mark Spalding from the Conservation Science Laboratory explains how coral reefs are being affected by climate change...
25 July 2014

Interview with 

Mark Spalding, Conservation Science Laboratory, University of Cambridge


Coral reefs all over the world are being affected by climate change. Mark Spalding Elkhorn coralfrom the Conservation Science Laboratory explains how and why to Chris Smith...

Mark -   So, I work for an organisation called the Nature Conservancy.  They're not well-known in the UK and our mission is to look after the lands and waters which all life depends.  That's what we're setting out to do and we're an organisation that works around the world, 35 countries in the sea and on land.  My work is focused very much on marine habitats.  I guess my passion for the sea started probably at pretty early age actually.  I was, I think 11 when I first dived on a coral reef and I don't think I ever really looked back.

Chris -   Why are coral reefs important?  Why do we regard them as really important for conservation?

Mark -   So many ways.  So, coral reefs are these wonderful rain forests of the sea we talk about.  They're mega diverse habitats that are built many of the tropics where they kind of circle the land and they're highly productive.  So, they're wonderfully important for many people who rely on it for fish.  They also actually produce many other benefits - so, they protect our many coasts from the impact of waves and many tropical countries of course, you've got hurricanes and things that threaten coasts.  So, that's tremendously important.  Someone asked the question earlier about some of the chemicals and cosmetics, and products that we might get from the sea.  Well, coral reefs have been seen as - because of their immense diversity, it's potentially really important sites for providing new pharmaceuticals and new compounds that we might use in all sorts of ways.  Already, products from coral reef animals are being used in some drugs for cancer, and in sunscreens as well actually strangely enough, and there's much more to be found.

Chris -   Tell us about the sunscreens.  I'm intrigued.  You rub bits of coral onto you?

Mark -   No, it would be pretty painful I think.  No, but corals are actually dependent on light, which is why we get them in bright sunlit waters and because they're dependent on light, they're also subjected to quite a lot of UV light which just as it can with us, can cause problems for the coral.  So, they've developed some mechanisms to defend themselves from UV light which we've then been able to utilise.

Chris -   But how do they rub it on?

Mark -   A lot of these things, we look to nature for the inspiration and then the scientists then work with compounds that we're finding in nature to build the properties that we might want.

Chris -   Why are coral reefs regarded as threatened?

Mark -   Well, if you look at the reefs of the world, they're spread out in a soft of belt around the tropics.  They've adapted to live in an environment which is pretty stable year-round, fairly stable temperatures, and they have adapted to that extremely well.  What's happening now is that we're starting to see already slight increases in the world's temperatures and the sea water temperatures as well.  And it turns out that corals are extremely vulnerable even to the smallest changes in temperatures.  So, an increase above the normal maximum of a degree or two for a few weeks will cause a stress response in corals.

Chris -   Do we know why they're so sensitive?

Mark -   Only that they've seem to have adapted.  We don't know enough to be quite honest, but they seem to have adapted to this sort of lovely year-round Jamaica kind of temperature and can't cope with a bit more.  They have a very complex relationship inside their body tissues with an algae, which uses sunlight to generate energy which the corals use.  They're almost photosynthetic as organisms.  When they get too hot, the algae become expelled.  The coral go white and we call it bleaching.  At that point, they're starving.  They're still alive, but they're not getting any food anymore.  If it continues for even just a few weeks, the corals will perish.  At that point, the reef looks pretty dead.  They can come back of course once the temperatures cool down, but those corals are dead.

Chris -   What is the scale of the problem if you look around the world at the reefs we've been monitoring?

Mark -   People first noticed coral bleaching probably 20 years ago, but there was no extreme events.  And then in 1998, we had an El Niño year which is a Pacific Ocean climatic phenomenon and an oceanographic phenomenon, but it essentially drove warm waters around the world.  It was the most extreme el Niño we'd had.  I happened to be doing an expedition at the time in the Seychelles, looking at the coral reefs across the Seychelles, hoping to have this wonderful time diving on the world's most pristine coral reefs.

Chris -   A holiday.

Mark -   Yeah.  There was a good report at the end of it! That's the difference.  It was wonderful.  We were on a yacht, sailing down the Seychelles.  But as we got there, we saw that the corals were all bleaching and it was actually really depressing to do a 2,000km transect through the Seychelles Islands and watch the coral reefs in the Seychelles die.  And as we came back, we heard the news from the entire Western Indian Ocean, that it was the Maldives, the Seychelles, the Chagos Islands, and so on, huge areas of coral reefs had all, 90% of the coral reefs had died that year.

Chris -   That's a new thing.  do we think this is a worsening trend or do we just think there've been blips like this in the past and that this is just another one and it will get better.

Mark -   No one had seen anything on the scale of what happened in 1998 and it is increasing more frequently and more extensive.  There hasn't been anything to parallel '98, but unfortunately, omens are pretty poor for next year.  It looks like there's another big el Niño brewing, so it looks like we'll see another of these events.  The real concern from the scientists is that corals are not going to have enough time for the evolutionary adaptation that they might need.  And as temperatures warm up, these events might become more frequent.  And so, they won't be able to recover in between these events.  So, it's a very worrying time for coral reefs.

Chris -   Can we do anything about it?

Mark -   We're not sure.  There seems to be some evidence that corals themselves are doing something about it that the corals that come back are a little bit more robust.  My organisation is doing some pretty interesting stuff in the Caribbean coral reefs where we're trying to grow and we've got nurseries, just like you might see plant nurseries with tens of thousands of corals being grown up underwater.  And we are selecting them for the resistance to bleaching and we're starting to plant them out on the coral reefs of the Caribbean.  So, we're trying but really, we're pretty worried about the state of coral reefs worldwide.

Chris -   But the benefit is, they don't wake you up at night, do they, your corals in your nursery?

Mark -   Yes.

Chris -   Any questions so far for Mark?

Emily -   I'm Emily and I was wondering how poisonous coral stings are.

Mark -   Emily, great question.  Well corals, if you look up closer to coral, it's made up of lots of little, small organisms living in a colony and those small organisms, just like sea anemones, they're exactly the same group of animals of sea anemones.  They have, all of them, the capacity to sting, they have a little special adaptation in nematocysts which enables them to sting.  Now, most corals couldn't sting a person or you wouldn't feel it.  There's a few corals that do sting and it's a little bit like a nettle sting.  Not that bad, but a few people are allergic to it and some people are found that the more they get stung, the worst their reaction is.  But generally, not that bad.

Chris -   Anything else?  Georgia, what have you got?

Georgia -   I have a question about that.  In Finding Nemo, the clown fish swims around...

Chris -   That well known documentary, yeah!

Georgia -   The clown fish swims around the coral and it gives him more of an immunity to stings, but it's the other way around for humans.

Mark -   The observation is exactly right.  It's an anemone of course that the clown fish lives in, but as I said, they're related to corals.  And yes, they do seem to develop an immunity to the stings which other fish don't have.  And I believe it's something that builds in on the mucus on the surface of the skin of the clown fish.  If you take a clown fish out of an anemone for long enough, it will lose its immunity and if it goes into the anemone, it will be stung and it will be eaten.  So, when a clown fish meets an anemone, it spends a bit of time adapting and just touching the edge of the anemone until it develops its immunity.

Chris -   Is that like sort of graded drinking where you get a few minor hangovers but you build up a tolerance?

Mark -   A little bit like that, building up a tolerance.

Chris -   Any other questions?

Georgia -   We also have a question from Twitter.  Oren Jello wants to know where coral reefs can go.  What stops them from growing everywhere?

Mark -   That's a really good question too.  Climate change is already on us and I think we need to get that clear.  So, as temperatures are warming up, a lot of species are already changing their distribution.  We see that in UK waters.  I'm sure you've seen it with the birds.  So, we're already seeing that and corals are moving too.  But as you move out from the tropics, you get a slightly different sort of a climate because you get much more seasonality outside of the tropics.  So, I said to you at the beginning, corals are adapted to this lovely, sort of wall to wall Jamaican type temperature year-round.  As you move out of the tropics, you get cold winters and that's quite tough.  Corals don't like the cold either.  So, they've kind of adapted to this.  So, it's not a given that corals can migrate further north or south out of the tropics.  But we are seeing some movements in those directions.

Chris -   Lloyd.

Lloyd -   It's really interesting, but if you look at animals that live in stable temperature environments, so the two places in the sea where the temperatures are very stable are in the tropics and the poles.  Animals living there have very small abilities to survive when the temperatures warm up.  So, there's been a fair bit of experimentation looking at those temperatures they can survive with and they're literaturally maybe a couple of degrees over their normal temperatures.  They start to die.  But if you look in-between where the temperatures are variable in the sea, in the temperate latitudes, the cold temperate latitudes, warm temperate latitudes, they have maybe 6 to 10-degree buffer over the top of what they normally see that they can survive.  And it looks like it's this exposure to variability of temperature in the environment that gives animals the capacity to survive a warming environment that isn't there when they live in very stable conditions like the tropics or in the poles.

Mark -   So, you're seeing that in the Antarctic as well, are you?

Lloyd -   Absolutely and there's been 2 or 3 pieces of work published on the same groups of animals from the poles to the tropics.  And the polar and tropical animals both have the same limit in terms of their ability to cope with the warming and the ones in-between have a much, much higher ability to cope with the warming there.


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