Coral Reefs and Climate Change

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00:00:06.04 Hello, my name is Nancy Knowlton
00:00:08.05 and I work at the Smithsonian's National Museum of Natural History.
00:00:11.06 And today I'd like to talk to you about climate change,
00:00:13.11 and in particular, the effect of climate change on coral reefs.
00:00:17.05 Now, it's important when thinking about climate change
00:00:20.22 and coral reefs to recognize that climate change is not the only thing
00:00:24.13 that's happening to coral reefs today,
00:00:25.26 there is a coral reef crisis, it's both local and global,
00:00:30.00 and it's caused by a variety of things in addition to climate change.
00:00:33.21 And essentially, if you want to think about it,
00:00:35.22 as what we're doing to planet earth or "planet ocean", as I like to think about it,
00:00:40.23 we're doing a huge experiment where we're putting things into the system
00:00:44.24 and then we're taking things out of the system as well.
00:00:47.19 So, on the input side, we're putting in nutrients, toxic materials, sediments,
00:00:52.16 and invasive species and carbon dioxide,
00:00:55.12 which is of course the root cause of climate change.
00:00:57.22 And then of course on the output side, we're taking out anything big.
00:01:00.22 So, climate change has to be viewed for coral reefs
00:01:03.28 as part of a complex assemblage of threats that coral reefs face.
00:01:08.26 And it's important to recognize that and we'll get back to this in terms of its implications
00:01:14.18 for what to do about climate change towards the end of the talk.
00:01:18.03 Now, as I say, this is a global problem that coral reefs are facing
00:01:24.07 and have been facing for quite awhile and before we get into the nitty-gritty of climate change,
00:01:28.09 I'd like to give you a sense of the scale of the threats that coral reefs face.
00:01:32.20 This photograph was taken when I was a student in 1975,
00:01:37.00 quite a long time ago at this point,
00:01:38.23 but at the time, the corals looked absolutely beautiful,
00:01:41.08 almost everything you can see in this picture,
00:01:44.10 the heads of coral right here, or all the branching corals,
00:01:47.22 all through here, another bushy-like coral down here,
00:01:52.00 all of that was living coral, and about 70 percent of the bottom
00:01:55.08 was covered with living coral back in 1975.
00:01:58.11 Unfortunately, those reefs are essentially now gone.
00:02:01.22 And they've been replaced by seaweed reefs, primarily,
00:02:05.00 and if this were just a story of Jamaica,
00:02:07.10 and Discovery Bay, that would be one thing,
00:02:09.24 but it, as I said, it's a global problem and as a consequence,
00:02:13.24 recent estimates suggest that about one third of all reef-building corals
00:02:18.01 are now at risk of extinction.
00:02:19.22 And as I mentioned before and I'd like to emphasize again,
00:02:23.01 this is not just climate, but a combination of climate change and local impacts
00:02:28.01 such as over-fishing and pollution and invasive species in some places.
00:02:32.24 So, why does this matter, why do we actually care about coral reefs
00:02:36.21 in the context of climate change?
00:02:38.20 Well, first of all, they're home to millions of species.
00:02:41.08 How many millions we don't actually know
00:02:43.13 but millions, large numbers. In fact, coral reefs are really the most diverse environment that we have in the ocean.
00:02:51.12 And some of them grow on corals, like you saw in the previous slides,
00:02:56.00 some of them wander around,
00:02:57.01 such as these beautiful crabs that you see in parts of the Pacific Ocean
00:03:00.26 and make coral reefs their home.
00:03:02.29 Now, coral reefs are also very important to us as people
00:03:06.02 economically, they provide food, they are the source of,
00:03:10.09 support tourism, because people come to coral reefs
00:03:13.19 to snorkel and dive on them.
00:03:15.24 The biodiversity itself is important in the context of biopharmaceuticals
00:03:19.22 and other products and the reefs themselves provide protection to shorelines
00:03:24.01 against big waves from storms or even earthquakes,
00:03:27.14 as in the context of tsunamis.
00:03:30.06 Now, it's interesting to note that this value of coral reefs
00:03:34.23 often is one in which actually, just having a healthy reef there
00:03:39.29 is the biggest part of the value, the non-extractive uses often dominate
00:03:44.17 the value of coral reefs.
00:03:46.02 And globally, the numbers we're talking about are big,
00:03:48.14 29.8 billion dollars is a recent estimate of how much coral reefs are worth to people
00:03:54.15 around the world every single year.
00:03:56.19 So, global warming is a consequence of carbon dioxide in the atmosphere.
00:04:04.04 And the reason coral reef biologists care about global warming
00:04:07.21 is because of the relationship between global warming
00:04:10.03 and something that's called coral bleaching.
00:04:12.03 Now, you see here, a picture that was taken in Panama
00:04:16.00 in September of 2010.
00:04:19.01 And you can see that all the corals, practically everything you see there,
00:04:22.24 is bone white. That is, they're bleached.
00:04:26.00 And this what people mean by coral bleaching.
00:04:29.08 And 2010 in the Caribbean was a particularly severe example
00:04:33.22 but we've had a number of severe examples of coral bleaching over the last couple of decades.
00:04:38.14 Now, the reason people care about coral bleaching,
00:04:41.19 coral reef biologists in particular care, but the public at large,
00:04:45.19 does care as well, is because the corals often die
00:04:50.28 if the bleaching is severe.
00:04:52.21 And this is a picture taken of the Great Barrier Reef during a major bleaching event.
00:04:57.09 And most of the corals you see here, these big white corals,
00:05:00.00 which you see scattered all the way out into the distance,
00:05:02.11 all of these are bleached and a number of the brownish ones in here are actually dead.
00:05:06.15 And during the 1998 El Nino in the Indian Ocean, for example,
00:05:11.04 about 80 percent of the corals bleached and about 20 percent of them died.
00:05:14.25 So, we're talking about major, major sources of mortality
00:05:17.21 and in this context, it's also very important to remember that corals grow slowly,
00:05:21.20 they grow rather like trees, only about a half an inch per year,
00:05:25.06 so that means it takes a long, long time for reefs to recover after one of these major bleaching events.
00:05:30.27 Now, what is bleaching?
00:05:33.19 It's essentially a breakdown in the symbiosis,
00:05:37.00 the positive relationship between the coral animal
00:05:40.02 and tiny, one-celled algae that live in its tissues.
00:05:43.26 And here you see on the top a picture of a coral,
00:05:48.14 this is one coral here, it's actually a somewhat unusual coral
00:05:52.21 in the sense that it's a single coral polyp, as it's called, with a mouth in the center,
00:05:57.08 and what you can see here is the skeleton,
00:06:00.09 which is white, in the center,
00:06:02.01 and then this filmy circle around that white skeleton,
00:06:07.08 is actually the living tissue of the coral.
00:06:09.20 So, the coral in this picture is still alive.
00:06:12.07 But because there's been a breakdown in the relationship between the corals
00:06:16.20 and their symbiotic algae,
00:06:18.26 you can actually see right through the tissues.
00:06:20.27 It's as if we as people, suddenly our muscles all became transparent
00:06:25.24 and you could look right through our skin and our muscles
00:06:29.06 and could see our skeletons walking abound and that's what you've got going on here,
00:06:32.11 And here's another example, a little bit farther away,
00:06:34.15 and you can see a mixture of healthy, or reasonably healthy, coral,
00:06:38.15 parts of the coral colony, which have a normal coloration,
00:06:41.08 and then these white parts which are still alive,
00:06:43.28 but you're seeing right through the tissue, into the skeleton, which is why it looks bleached.
00:06:48.22 Now, the biggest problem with respect to climate change
00:06:53.26 and bleaching is that corals are very, very sensitive
00:06:56.25 to even relatively small increases in temperature.
00:06:59.22 So, here you see the temperature record from about the year 1000
00:07:05.22 into the present and then projected into the future
00:07:08.28 based on computer models.
00:07:10.21 Now, the biggest problem is that bleaching tends to occur
00:07:13.28 when temperatures are about one degree centigrade
00:07:17.04 above the normal seasonal maximum.
00:07:19.11 So, here, you see this dotted line, which is what you can think of as the bleaching threshold,
00:07:24.04 where bleaching occurs.
00:07:25.04 And what you can see very clearly here,
00:07:27.16 and which is the reason coral reef biologists are so worried about global climate change
00:07:31.25 is that the projections for the future, relatively quickly,
00:07:35.18 by the middle of this century, have temperatures way above the bleaching threshold,
00:07:40.04 suggesting that bleaching and massive mortality of corals
00:07:43.13 could become a regular event, say by 2050.
00:07:47.15 Now, there's also secondary effects that are associated with bleaching
00:07:52.04 because bleaching, even if the coral doesn't die right away,
00:07:54.14 it's a very stressful, stressful condition.
00:07:58.07 And often what happens is that corals might survive the bleaching per se,
00:08:01.12 but then they succumb to various kinds of disease,
00:08:04.05 so you see two kinds of disease here,
00:08:05.29 white band disease affecting this coral here,
00:08:08.16 and then black band disease. Here you see the coral that's dead,
00:08:13.00 and then this advancing front of black band disease
00:08:16.19 moving down and killing the coral progressively.
00:08:19.12 And these kinds of diseases become much more common after corals on a reef have bleached.
00:08:24.15 And now, unfortunately, warming oceans are not the only problem
00:08:30.01 with respect to climate change.
00:08:32.03 And that's because the same carbon dioxide that's causing global warming
00:08:36.07 is also dissolving into the ocean and making the ocean more acidic.
00:08:40.18 And this is called ocean acidification.
00:08:42.16 Sometimes we call it the other CO2 problem or global warming's evil twin.
00:08:47.02 And this is, in the long term, perhaps as serious or even more serious
00:08:51.04 than the effects of rising temperatures on coral.
00:08:53.28 So, here you see a chart which shows essentially the suitability
00:08:58.02 of ocean chemistry for coral reef growth
00:09:00.15 and back in the 1700's, these red areas, those are all areas where coral reef, corals are expected to grow easily,
00:09:08.20 and then as you move through the present and into the future,
00:09:12.26 you arrive at a world where conditions for coral reef growth
00:09:16.16 are very poor throughout much of the tropics where corals grow.
00:09:21.28 And so, the projections for the future, in terms of relationship between ocean acidification
00:09:26.28 and coral reefs are arguably even more serious
00:09:30.02 than they are for global warming.
00:09:32.00 Now, why is this? Essentially because when corals grow in acidic water,
00:09:36.25 they find it much, much harder to grow their skeletons
00:09:39.21 and so, here you see an experiment that was done, this is a healthy coral,
00:09:45.12 and then it was put in water, acidic water, like what we might see by the end of the century,
00:09:50.06 and you can see that the entire colony has lost its skeleton,
00:09:55.05 and so these individual components of the coral colony, the polyps,
00:09:59.23 have completely dissolved away their skeleton
00:10:02.26 and they're growing as individual sea anemone-like structures
00:10:06.11 and actually, scientists were somewhat surprised by this result,
00:10:09.22 in the sense that the corals themselves, the coral did survive, it didn't die outright.
00:10:14.19 But the problem here is that these things have no skeleton,
00:10:18.03 they can't build reefs, you can't have a Great Barrier Reef made of soft, squishy things like sea anemones,
00:10:23.25 and so, with ocean acidification, we're likely to lose that three-dimensional complexity,
00:10:28.13 which makes it possible for reefs to be the home for these millions of species that I mentioned at the beginning.
00:10:33.21 Now, initially when these photographs were published in a scientific paper,
00:10:38.14 they were called scenarios for the future, but since that paper was published,
00:10:42.04 we've actually found places in the world which naturally mimic
00:10:46.17 what we might be heading to globally in these small places where carbon dioxide
00:10:51.07 is actually bubbling out of the sea floor, almost like champagne.
00:10:54.18 And what that causes is a local change in the chemistry of the ocean,
00:10:58.26 and so you can essentially have a mini-experiment that replicates what we're likely to see
00:11:03.24 say, by the end of this century.
00:11:06.11 And when you look at these natural carbon dioxide seeps,
00:11:10.26 where ocean chemistry is changed through this champagne-like process,
00:11:14.26 what you find is away from the seeps,
00:11:16.28 the reefs look like healthy, normal reefs, but as you get closer and closer
00:11:20.19 to the those champagne bubbles, then you move first into a world
00:11:24.22 where many of the corals, particularly the branching, the more delicate corals,
00:11:29.06 like those shown here, drop off and all you find are these big, massive corals in place
00:11:34.08 and eventually, really close to the seeps,
00:11:36.03 in places where, say, it would be equivalent to about a thousand parts per million
00:11:42.02 in terms of concentrations of carbon dioxide in the atmosphere,
00:11:46.20 you lose coral reefs altogether.
00:11:48.08 So, we know both from experiments in the lab and actually observations in the real world
00:11:52.23 where we've got mini examples of extreme ocean acidification
00:11:56.23 that coral reefs and high concentrations of carbon dioxide in the atmosphere
00:12:00.12 are really, they just don't go together.
00:12:02.18 And in this context, it's important to remember that the carbon dioxide that we are releasing today
00:12:08.13 stays in the atmosphere for a very long time, centuries,
00:12:11.09 because it takes a long time for it to sort of cycle out of the atmosphere,
00:12:14.22 and as a consequence everything we're doing today, the effects have a very long lag,
00:12:20.11 and it takes a long time for the atmosphere to repair itself in the context of carbon dioxide.
00:12:25.14 So, these are, it's very, the sooner we do something about the carbon dioxide problem, the better.
00:12:31.07 Now, what can we do now?
00:12:34.10 Now, obviously in the long term, we have to deal with the carbon dioxide problem,
00:12:39.05 but in the short term, it's important to remember what I started off with,
00:12:42.16 which is that the coral reef crisis that we're facing is both a local problem
00:12:46.05 and a global problem. And so, you've got a lot of things in addition to carbon dioxide,
00:12:51.12 you have carbon dioxide here, but you have all these other things that are going on,
00:12:54.23 taking the nutrients in the water, for example, or the overfishing, taking anything big out of there,
00:13:01.17 so now, those are something that we can about now.
00:13:03.14 And why is that problem? Because anything we can do to reduce local stresses
00:13:09.02 helps make coral reefs more resilient.
00:13:13.16 That is, if you have an extreme bleaching event
00:13:15.17 and a lot of coral mortality, the corals that survive are better able to bounce back
00:13:21.00 and regrow into a healthy reef if locally the conditions are favorable for coral growth.
00:13:27.04 And so, in terms of what we can do now, there's actually a lot we can do now
00:13:31.16 on the short term and the local scale.
00:13:33.27 And it basically boils down to two primary things we need to do.
00:13:37.10 We need to control fishing pressure
00:13:39.10 so that coral reefs don't get covered with seaweeds,
00:13:42.25 what happens is when you have a lot of, when you take fish out of the system,
00:13:46.27 you take a lot of the seaweed eating fish out of the system,
00:13:49.17 and then the corals tend to be smothered by seaweeds,
00:13:52.23 and then you can improve water quality, which, bad water quality
00:13:56.17 both kills corals directly and also, again, favors the growth of seaweeds.
00:14:00.08 Now, this isn't actually rocket science, we know how to do this,
00:14:03.08 this is pretty easy to do in the science sense of things
00:14:06.18 and we know how to do it, and one of the most important ways that we can do this
00:14:12.14 is through the placement of marine protected areas.
00:14:17.00 These essentially create more resilient reefs
00:14:20.20 by reducing local stressors.
00:14:22.11 And in Australia, we have kind of a gold standard, if you will,
00:14:25.19 for protection on the Great Barrier Reef
00:14:29.10 where more than 33 percent of the entire area of the Great Barrier Reef
00:14:32.22 is in no-take status, that means that you're not allowed to take any fish out at all.
00:14:37.13 And so this is a kind of gold standard for which we would hope to aim
00:14:43.16 around reefs around the world.
00:14:45.07 And the United States, we also have four mega-protected areas
00:14:48.14 that occur in US waters, both in the northwest Hawaiian islands, shown here,
00:14:52.13 and also in a couple of other places through the Pacific,
00:14:55.09 including the Northern Line Islands here.
00:14:57.10 So, we've set up protected areas to produce more resilient reefs in some places
00:15:03.15 but a lot more needs to be done
00:15:04.29 and then some things aren't actually directly improved by marine protected areas alone,
00:15:12.19 for example, water quality, which typically involves managing how we use the land
00:15:17.06 because things on the land ultimately wash into the ocean.
00:15:20.10 So, to conclude, there are things we can do.
00:15:26.03 We want to reverse this trajectory
00:15:28.13 of reefs going, cascading downward; we want to get to the point
00:15:32.15 where reefs are starting to recover.
00:15:34.14 So, in the short term, in the local scale,
00:15:36.15 control fishing and improve water quality, but we are going to have to do something
00:15:40.17 on the longer term and global scale,
00:15:42.04 which is harder to do, this is rocket science,
00:15:44.13 we're going to have to figure out how to reduce carbon dioxide emissions,
00:15:48.04 and move to an economy which is less carbon intensive
00:15:51.17 and then in that kind of intervening period,
00:15:54.07 we're also going to have to work very hard to prevent extinctions
00:15:57.18 while we learn to transition to a lower-carbon kind of economy.
00:16:03.29 And this actually, this part, really is rocket science.
00:16:06.24 Thanks very much.
00:16:08.12

This Talk

Speaker: Nancy Knowlton

Audience:

General Public
Educators of H. School / Intro Undergrad
Student
Educators of Adv. Undergrad / Grad
Researcher
Educators

Recorded: January 2012

Talk Overview

Dr. Knowlton has spent over 30 years studying coral reefs. In her talk, she describes the devastating effects of increasing ocean temperature and acidification, both due to increased atmospheric CO2 levels, on coral reefs around the world. She explains that short term, local action and long term, global efforts are needed to halt the coral reef crisis.

Speaker Bio

Nancy Knowlton

Nancy Knowlton received her undergraduate degree from Harvard University and her PhD from the University of California, Berkeley. She was a professor at Yale University before moving to the Smithsonian Tropical Research Institute in Panama and later joining the Scripps Institute of Oceanography at UC San Diego. Currently, she is the Sant Chair in Marine… Continue Reading