The Reef Builders: An Interview with Nancy Knowlton

From the class Anthozoa in the phylum Cnidaria, corals are among the oldest and most primitive animals—the first ancestors appeared in the Cambrian period 570 million years ago. Closely related to sea anemones, whose basic polyp structure they share, corals have no brain and only a very rudimentary nervous system, yet they have collectively built some of the most imposing structures on earth. After visiting the Cocos Islands, Charles Darwin remarked in his journal that “such formations surely rank high among the wonderful formations of the world. We feel surprise when travellers tell us of the vast dimensions of the Pyramids and other great ruins, but how utterly insignificant are the greatest of these when compared to the mountains of stone accumulated by the agency of various minute and tender animals!” The reef builders, or hermatypic corals (also known as stony corals) constitute about a thousand different species, but the structures they build are estimated to be home to somewhere between one and nine million marine species. That makes these brainless, sessile cnidarians some of the most critical organisms in the web of life. Yet coral reefs the world over are collapsing under the strains induced by human activity.

Dr. Nancy Knowlton, Sant Chair of Marine Science at the Smithsonian Institution, has been studying corals for over thirty years, and her research has aided in the realization that traditional estimates of marine diversity must be scaled up by a factor of ten. Knowlton is also a scientific advisor to the Hyperbolic Crochet Coral Reef Project by the Institute For Figuring. IFF director Margaret Wertheim interviewed Knowlton in April in New York.

Cabinet: The year 2008 has been declared the International Year of the Reef. Why now?


Nancy Knowlton: Because the situation with coral reefs is verging on catastrophic. In the last three decades, we have lost about eighty percent of all the reefs in the Caribbean, and we now know that the reefs in the Pacific are also highly threatened. Even places like the Great Barrier Reef, which we used to think of as healthy, are now experiencing significant mortality.

How much of the world is covered in reef? 


Only about 0.1 percent in total area. It’s quite small. Nothing like the percentage cover of tropical rainforests, with which reefs are often compared in terms of 
biodiversity.

Have coral reefs historically been an important part of the world’s ecology?

Reefs have been on the planet for as long as we’ve had complex life. The organisms that build reefs are very primitive creatures: they have only a one-ended digestive tract—the same opening serves both for ingestion and elimination—and they have only two types of tissues, so they are much simpler than people, worms, or clams. Reefs themselves go back hundreds of millions of years. Scleractinian corals, which is what we have today, date back to the Triassic period about 230 million years ago; more primitive ancestors, the tabulate and rugose corals, were widespread during the Ordovican era some 450 million years ago. If you look at the history of reef growth over geological time, it increases and decreases depending on physical conditions. Right now, we’re in a period of relatively robust reef development.

So reefs should be pretty prosperous now. Why then are they under such threat?

Unfortunately, a lot of human activity has a negative impact on reefs. The removal of fish that eat seaweed, for example, is particularly detrimental because the biggest competitors corals have are seaweeds. Seaweeds grow about ten times faster than coral, so in order for a reef to persist, you need things that are constantly eating seaweed—keeping them back like a lawnmower. Parrot-fish, for example, act as these lawnmowers, as do various types of sea urchins. If you don’t have lawnmowers on the reefs, you effectively wind up with grass. Certain types of land use also result in a lot of nutrients, sediments, and toxic material washing into the ocean, which is very bad for reefs. And then we are putting carbon dioxide into the atmosphere. Over the long term, this is really the biggest threat. Global warming is hard on reefs because they depend on a very delicate relationship with single-celled algae called zooxanthellae. Zooxanthellae live near their thermal maximum, so if the temperature rises one degree centigrade over normal maximum levels, it cripples their ability to photosynthesize. Corals depend on these photosynthetic partners in order to grow quickly. Even a very slight rise in temperature can cause a phenomenon called “coral bleaching,” which is the breakdown of this relationship—the corals evict the algae and, unless conditions improve relatively quickly, the corals starve to death.

Over the long term, an even bigger problem is the effect that carbon dioxide has on the acidity of seawater. As more carbon dioxide gets dissolved, the ocean becomes more acidic. Just as your mother told you to not to drink lots of Coca-Cola because it tends to dissolve your teeth, similarly if you have an ocean that’s too acidic, it will either dissolve skeletons or make it very difficult for organisms to form new skeletons. Current projections for the increase in the concentration of atmospheric carbon dioxide indicate that we are not only going to have a world which is too warm for coral reefs; we are going to have world which is too acidic 
for coral reefs.

Given the inherent delicacy of reefs and the dramatic changes in the environment over hundreds of millions of years, how come they weren’t wiped out long ago?

Actually during earth’s history when it has been very hot, or during periods of high ocean acidity, there wasn’t much reef development either. But some fraction of diversity survives these major extinction events and when conditions become more favorable, reef development returns. Phylogenetic studies show that corals as a group survived the great Permian-Triassic extinction event 251 million years ago when around ninety-six percent of all marine species died out, but they probably did so through soft-bodied species that lacked calcified skeletons.

So they can bounce back from quite small remnants?

Yes they can, but we’re talking about a timeframe of millions of years, which is not the timeframe people usually care much about. We humans evolved in the conditions that have been prevailing over the last thirty thousand years, and we are radically changing those conditions. We are creating climates for other living organisms that are very different from those we evolved under, and it’s not likely we are going to be very happy with these changes.

In your lifetime, you’ve seen quite dramatic changes in some of the reefs you’ve been studying. Tell us about that from a personal perspective.

I started studying coral reefs in the mid-1970s, and at the time I was working on the north coast of Jamaica in a place called Discovery Bay. Those reefs were the epicenter of scientific study. Back then, the percentage of coral cover was about seventy percent. Since then that percentage has gone to less than five percent. Much of the change occurred over a three- to four-year period. So we essentially witnessed the collapse of these reefs. Before this happened, none of us worried about the long-term survival of these reefs. We knew they were over-fished, but we didn’t make a connection between this kind of human pressure and the vulnerability of reefs to survive other kinds of changes. What happened was that those reefs suffered major damage from hurricanes, and then a disease wiped out essentially all of an important species of sea urchin, which was really the last remaining lawnmower on the reef. There were other changes as well, including rising temperature events. All these things combined resulted in a catastrophic collapse—not just in Jamaica but across the entire Caribbean, where we have lost around eighty percent of the living coral in just three decades.

Is it conceivable that we are facing the disappearance of coral reefs?

Oh, definitely! It’s very depressing when you watch these extraordinarily beautiful and complex ecosystems literally vanish before your eyes in the course of your professional career. But I think it’s important to recognize that there are still healthy, beautiful reefs on the planet. They tend to be in remote places such as the Northern Line Islands in the Kiribati Republic, and those reefs show a lot more resilience to, say, bleaching events. We need to think about management strategies that increase resilience, and the best way to do that is to decrease fishing pressure and improve water quality. If we don’t create conditions for that kind of resilience, then what happens is you have one event like a hurricane, another event like an unusually warm water year, and each time the reef shrinks, it doesn’t recover from that lowered state, and eventually you wind up with no reef at all.

One of the facts I am most fond of is that we human beings share twenty-five percent of our DNA with lettuce. Lettuce is a plant; corals are animals. How much of our DNA do we share with corals? 


I have no idea, but it’s going to be higher than twenty-five percent. Most of the diversity on the planet is in fact bacteria. If you look at the Tree of Life as this huge wild bush, then lettuce, people, and corals are in fact all on one tiny little twig that is just one part of the overall tree. That is why we share such a surprising amount of DNA with lettuce, and even more with corals.

Coral reefs are sometimes called the rainforests of the ocean, but tropical rainforests cover a significant percentage of our planet’s landmass. How can something so small as reefs be so important?

Because they are so diverse. They probably have somewhere between one to nine million species, although we don’t know the full figure. It’s certainly a good deal higher than we understood until recently. Reefs also provide crucially important amounts of protein to people living in developing countries near the coast. And they provide shoreline protection because they function as giant walls; if you get a big storm or a tsunami, they shelter the coastlines from the full impact of these huge waves. Reefs are also immensely important economically for the tourist industries of many developing countries. Over the longer term, reefs have the potential to provide important bio-pharmaceutical products as well. 


What is being done or could be done to reverse these destructive trends? 


We’re seeing a lot of movement on the climate change issue. Not nearly enough, but at least it is movement. The first step toward solving a problem is recognizing that there is a problem, and I think we are getting there. The next step is doing something about it. The issue we really need to address urgently is carbon dioxide emissions—not just because of global warming but also because, as I said, of ocean acidification. At the moment, carbon dioxide concentration in the atmosphere is about 380 parts per million (ppm). About a quarter of all human-generated carbon dioxide winds up being dissolved in the oceans where it reacts with water to form carbonic acid. The effect is to decrease the concentration of carbonate ions in the water, which are what corals use to build their skeletons, and which all shell-building organisms need.

A recent study in Science looked at what happens as oceans become more acidic. Experimental studies show that once you get levels of atmospheric carbon dioxide approaching 480 ppm, then carbonate ion concentration drops to a point where coral accretion effectively stops. Most models suggest the levels will get to at least 500 ppm and possibly much more. That’s going to be disastrous for reefs because even if coral organisms could adapt to higher temperatures (we don’t know whether they can, but maybe it’s possible), they can’t possibly adapt quickly to basic changes in chemistry. We really need to think about not just reducing carbon dioxide emissions, but how we can remove carbon dioxide from the atmosphere.

People are notoriously willing to postpone doing hard things until they absolutely have no choice. The irony is that in many cases we will postpone doing things because we think it will be hard, and they are hard in some ways, but in many ways they are actually good for our economy. There are lots of win-win, or green solutions which help make the world a better place for coral reefs, and are also better for people economically.

Given that we are heading into the era of nine billion people rather than six billion, is it realistic to think we can reduce carbon dioxide emissions sufficiently to save coral reefs?

It’s not just population growth; that’s part of the problem. It’s also consumption. Per capita consumption is a very big issue. It is not an easy situation by any means, but if we wait another twenty to thirty years it will be lost. If we really start to recognize the seriousness and do something quickly, I think there is a chance. Reefs are going to go downhill, that’s certain, but it’s a question of how degraded they will become, and we can make a big difference if we act now.

Recently there has been quite a lot of attention given to new technological methods to re-grow reefs—building metal frames under the water and attaching electric currents to them, and so on. Do you see those technological solutions as a way forward?

The metal frames are interesting because they act as a catalyst to get coral growth started. The electric current helps stimulate the process. But once the frame has been covered in a thin layer of coral, the current can’t flow any more so you’re back to whatever environmental conditions pertain. I don’t want to write off technological solutions, but they have real limits. There is also a lot of research going on in the field of reef restoration, where people hand-seed depleted areas of reefs with little pieces of baby coral. This is good because we do need to know how to restore reefs, and in some places you can see forests of coral that have been hand-planted. But it is important to remember that reef restoration tends to be too expensive to implement on a global scale. And more importantly, you can’t restore anything if you don’t get rid of the conditions that were responsible for the reefs’ vanishing in the first place. You can install all the electrical frames you’d like, but if you still have over-fishing and poor water quality, you are not going to wind up with a coral reef.