Would you give us some background on your education and early research?

I grew up in Sydney, Australia. From my earliest years, I had a fascination for nature and science in general. After a youth spent preoccupied with nature (from butterflies to reptiles), I completed an Honours degree at the University of Sydney, focusing in my last year on a series of invertebrates that housed symbiotic dinoflagellates. And so began my interest in plant-animal symbioses.

“Our work has identified climate warming as the number-one threat to coral reefs.”

After obtaining a scholarship, I did my Ph.D. with Professor Leonard Muscatine at the University of California at Los Angeles on the population dynamics of symbiotic dinoflagellates in sea anemones and corals. This led me to examine (with Professor Muscatine) samples from a curious event in the Caribbean. Little did I know that this phenomenon (coral bleaching) was to preoccupy me over much of my research career. I eventually returned home to take a lectureship at the University of Sydney (1991), moving to the University of Queensland in 2000 to take up the Foundation Chair in Marine Studies.

  What do you consider the main focus of your research?

I have spent the last 10 years focused on the impacts/changes that occur in coral reef communities as rapid changes to the environment occur. This work has sought to explain the linkages and drivers between changes at the physiological level and how they manifest themselves at successfully higher levels. I obtain particular pleasure when I can marry phenomena at these different levels of complexity. For example, some years ago, my research group (as well as colleagues elsewhere) deciphered the fundamental problems that corals and their dinoflagellate symbionts face as they become heat-stressed. The mechanism uncovered a key role for light in exacerbating the damage caused by heat. This insight suddenly explained why ecological studies were picking up the observation that corals were damaged during mass bleaching events on their upper sides or in areas of high light levels. These types of linkages between physiology and ecology (in this case) are powerful, as they allow you to reinforce one’s understandings from several different directions or disciplines.

In recent times, I have become increasingly interested in the complex behaviors of reef systems. For example, understanding the thermal threshold of corals to bleaching allowed us some predictive power when we wedded these to climate projections. From these data, we have been able to project trends (some of which we are already seeing) into the future. However, we have also been aware that these projections, although powerful, do not give credence to the important role that local variability (spatial and temporal) plays and will play in climate change. This has led me to initiate a large study on the southern Great Barrier Reef in which we are studying phenomena from dinoflagellates to sea birds, from storms to large-scale shifts in the East Australian Current. It is a massive project that involves NOAA and NASA, several universities, and a set of islands called the Capricorn-Bunker group. Ambitious though this may sound, I believe that these studies are critical if we are to understand the many challenges that we are likely to face as carbon dioxide concentrations continue to rise.

  A great deal of your papers focus on coral reef studies. What impact is global warming having on the world's coral reefs?

Coral reefs appear to be unusually sensitive to changes in ocean temperature and acidity. Unfortunately, the corals that Len Muscatine and I examined in the early 1980s were telling a highly significant story that few of us recognized at the time. Coral bleaching has been on the rise ever since—becoming more and more intense as the climate has warmed. Coral bleaching is a general response to stress—it happens when corals face conditions that are too warm or cold, or when there are toxins in the water such as herbicides or cyanide (used to catch aquarium fish in many developing nations). It represents a state in which the symbiosis (critical to the ability of corals to build coral reefs) between corals and their brown symbionts breaks down. The net effect is that the dinoflagellates depart, leaving the transparent coral tissue and gleaming white skeleton behind.

Professor Hoegh-Guldberg has the #5 paper on the 10-year list and the #14 paper on the 2-year list in the special topic of Coral Reef Ecology.

Our work has identified climate warming as the number-one threat to coral reefs. One has only to consider the impact of the global cycle of bleaching in 1997-1998, in which unusually warm weather worldwide plus some strange regional current patterns caused at least 16% of the world’s coral reefs to die. I think one needs to stop and consider that number. It might seem small until you consider that this is 16% of 400,000 km², or over 25,000 km² of coral reef! Sometimes this may be hard to imagine given the fact that we don’t visit or walk through coral reefs every day. But just imagine if we woke up one morning to discover that 16% of the world’s forests had died overnight.

Mass bleaching events such as these (which have continued since 1998) cause many of us to spend nights tossing and turning. Much of our research efforts consequently are focused on gaining better perspectives of how coral populations (and the hundreds of thousands of other dependent species) will fare when we warm the planet by a minimum of 2 degrees. These questions get us into areas such as the socio-economic ramifications of changes of this magnitude. For example, what happens to the estimated 100 million people that are dependent on coral reefs for food and other resources?

I believe that the writing is on the wall for coral reefs under climate change. Studies from the best laboratories project that coral reefs as we know them may largely disappear under rapid climate change. Two facts stand out. At 375 ppm carbon dioxide, we are at the highest levels in at least 1 million years (if not 20 million years). Secondly, the rates of change are almost two orders of magnitude faster than the faster rates of change seen in the last million years (outside short-lived spikes in the climate record such as the Younger Dryas event).

The latter is the key to understanding the problems faced by organisms under rapid human-driven climate change. When the earth warmed as it came out of the last ice age, global temperature changed by approximately 5-7 degrees over a period of about 10,000 years. This was so rapid that dramatic changes occurred to the distribution of almost every group of marine or terrestrial species. Many species went extinct. The issue we are now facing is that conditions are changing at approximately 50 to 100 times as fast.

Some paleontologists have confused the debate by saying that the current rates of change are nothing unusual and that the earth experienced change as rapid as that seen during the rare events like the Younger Dryas. Again, two facts stand out. Firstly, these events never took the earth above 300 ppm carbon dioxide and secondly, they were short-lived (in geological time) and returned to values similar to those prior to the event. These characteristics are fundamentally different to those involving the sustained increase of carbon dioxide to levels potentially as high as 600 ppm.

  How resilient are coral reef ecosystems?

Under normal circumstances, complex ecosystems like coral reefs are fairly resilient to disturbances that might push them away from equilibrium. Occasional storms and coastal flooding are examples of circumstances in which corals may be removed in great numbers from reef structures. Under natural conditions, coral populations and the myriad of other species have rebounded, usually over a couple of decades. This is due to the fact that components of healthy reefs such as grazing fish and invertebrates, and conditions such as low nutrient and sediment concentrations, keep fouling organisms like seaweeds at bay so that corals can recruit into the ecosystem. Over time, coral populations increase and reefs are restored following calamity.

Coral reefs are also ecologically complex—perhaps over a million species shelter within coral reefs. One of the consequences of this complexity is that ecological roles (e.g., grazing) may be performed by several groups of organisms on a coral reef with the next effect of adding insurance against the impact of losing one or another through natural perturbations. That is, if the numbers of one grazing species fall, another is there to step forward and fulfill the ecological function.

In more recent times, coral reefs have been beset with a multitude of impacts that have weakened their resilience. Overexploitation of fish has removed a significant component of the grazers from reef communities, leaving invertebrate grazers to hold the line. At the same time, water quality along most coastlines that have coral reefs has deteriorated, tipping the balance further in favor of non-coral organisms. And so on. The net effect of each of these changes is that we have significantly and drastically reduced the resilience of coral reefs such that recovery is taking longer and more and more reefs are not returning to their former high coral cover.

The resilience of coral reefs has a major role to play in the dynamics of coral reefs in a warmer, more acidic global ocean. One of the projections we are almost 100% certain of is that mass bleaching events will become increasingly frequent and severe, with mortality events such as the one in 1998 becoming much more commonplace. Recovery processes and hence factors that promote resilience consequently assume greater importance. This is why increasing rather than decreasing our efforts to reduce the stresses on coral reefs is crucial if we are to allow coral reefs any hope of being present in these much more disturbed worlds. These issues are a major focus of the recently formed Australian Research Council Centre for Excellence in Coral Reef Studies, which has provided a powerful network of research groups and laboratories focused on working out how we might boost the resilience of coral reefs under the challenging changes in the environment that they face.

  What can be done to protect coral reefs? Have any such programs been implemented, and if so, has progress been observed?

There are two basic strategies that must be put into place immediately if we are to have any reef ecosystem that resembles the coral-dominated reefs of today. Firstly, we must limit the rise in carbon dioxide to 500 ppm at the most. We know that anything higher than a 2-degree warming will lead to unsustainable rates of coral bleaching and mortality. Even then, we will be left with about 20% of the coral reefs we have today. We also know that the associated decrease in carbonate ions at 500 ppm carbon dioxide will also lead to corals being unable to form skeletons.

Secondly, we must increase our efforts to reduce the other stresses on coral reefs. If we continue to take away the "gardeners" (grazing fish and invertebrates) and the "pest-control officers" (mainly predatory fish) and persist in increasing the amount of sediments and nutrients that run off coastal areas into the waters surrounding coral reefs, their ability to bounce back will continue to erode. If this happens at the same time as the frequency and intensity of climate-related impacts like bleaching and mortality increase, we may see coral reefs like the Great Barrier Reef disappear into the annals of history.

That said, we are optimistic that emissions will be wrestled under control and that there is a lot we can do to increase resilience to allow coral reefs the best chances under this deepening crisis. This will involve a major global effort. The Coral Reef Targeted Research Project funded by the World Bank, Global Environment Facility and the University of Queensland is an example of the scale of the networks needed to begin to deal with this issue. With over 100 institutions and research laboratories worldwide, this project is bringing many minds to bear on the problems. I am hopeful that we will reverse the current deterioration of these wonderful and important ecosystems.

  Please tell us a little about your current projects, if you are free to do so.

I have a number of interesting directions and projects right now. The first is that we have been successful in producing the first EST (expressed sequence tag) libraries for Symbiodinium, the dinoflagellate that forms the all-important symbiosis with corals. We now have 1,360 different genes, whereas there were 13 known when we started. This is leading to a lot of activity in my laboratory aimed at finding and understanding how corals deal with stresses as broad as bacterial infection, thermal stress, and carbon limitation. It is fascinating to see the array of different genetic elements—this project has opened up our understanding of probably the most important organism on coral reefs. Out of this we are hoping to find genes that may explain why some corals are more tolerant to thermal stress.

The second direction we are putting effort into is understanding which elements of the carbonate balance on a coral reef are vulnerable to the problem of ocean acidification. In this regard, we are expanding previous excellent work on corals to organisms such as the developing stages of echinoderms and crustaceans, as well as asking questions about how bioerosion changes when you shift the concentration of carbonate ions. The latter could have major implications for existing reef structures as the rate of bioerosion (removal of carbonate by excavating organisms) is sensitive to seawater acidity.

The third major project going on in the laboratory is one focused on the spatial and temporal variability of climate impacts on coral reefs. This project involves people looking at a range of organisms from Symbiodinium to sea birds, and involves projects investigating the connectivity of reef systems, how one translates physiological vulnerability to the risk of mortality, and satellite projects with NOAA and NASA. This is a truly exciting and challenging project that will allow us to understand local and regional patterns. We are also interested in relating these sorts of changes to ecosystems to social and economic impacts. Coral reefs are very important worldwide in terms of supporting human societies through food and industries such as fisheries and tourism; many of these societies live in developing regions of the world. There is a direct linkage from ecosystem health to poverty. We are trying to understand how fundamental changes in the health of reef systems will affect these societies.

Professor Ove Hoegh-Guldberg, Ph.D.
Centre for Marine Studies
University of Queensland
Brisbane, Queensland, Australia

Related Links:
•	www.coralcoe.org.au
•	www.gefcoral.org
•	Coral Reef Ecology
All external sites will open in a new browser. The Thomson Corporation and esi-topics.com does not endorse external sites.

ESI Special Topics: November 2006 Citing URL: http://esi-topics.com/gwarm2006/interviews/OveHoegh-Guldberg.html