Coral reefs: Health, hazards and history

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A number of questions were raised. How does one gauge the spatial scales in both models and field studies that best permit one to understand particular systems? Given that multiple scales matter (e.g. one for dispersal, another for transmission), how can a hierarchical structure be sensibly integrated into models? When can spatially explicit models be replaced by appropriately parameterized nonspatial models? Can spatial disease models be used to help design field sampling programmes? These issues are likely to be central in future efforts to understand disease dynamics in natural populations. The final group faced a twofold mission. What is the relevance of genetics for epidemiology? Conversely, what are the evolutionary consequences of host-parasite interactions? Because these two short questions blithely span a daunting swathe of the biological sciences, this group made no pretence at being comprehensive, but instead focused on a set of general questions worthy of concerted

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attention. A sample of these is as follows. (I) Are there any novel epidemiological patterns that result from the existence of genetic variation? (2) Introducing genetics into ecological models, or ecology into evolutionary models, greatly increases the dimensionality of both; are there ways to ward off this proliferation of parameters, without losing the essence of the connection? (3) How can complexities of the immune system be incorporated into models of host-parasite coevolution, and are there useful parallels to be drawn with models in behavioral ecology (e.g. learning models in foraging theory)? (4) How is the evolution of virulence influenced by dynamical instability? Are there systemati differences between epidemics and endemic infections as evolutionary forces? Judging from this meeting, the field of wildlife disease epidemiology is in an exciting growth phase. It is likely that in coming years hostparasite interactions will increasingly emerge as playing a role in practi-

cally all areas of wildlife ecology and evolutionary biology, ranging from diet choice and reproductive behavior to population regulation, geographical range limitation and the determination of community structure. Some important directions of research in infectious disease epidemiology discussed in the meeting (e.g. the role of spatial dynamics in parasite persistence, the elucidation of indirect interactions in multispecies host-parasite assemblages) exemplify conceptual developments within the ecological sciences as a whole. The Newton meeting provided an invaluable function by crystallizing attention on many of the crucial empirical and theoretical questions which now face us. References 1 Anderson,

R.M. and May, KM., eds

(1982) Population Biology Diseases, Springer-Verlag

2 Anderson, Infectious Dynamics

of Infectious

R.M. and May, R.M. (1991) Diseases of Humans: and Control, Oxford

University

Press

CoralReefs: Health, Hazards andHistory TROPICAL CORAL REEFS cover barely 0.18% of the world’s oceans’. The great scientific interest they elicit might thus seem totally to outweigh their importance. Historically, much of this interest can be attributed to their striking biological richness. For example, the diversity of fishes on reefs is some two orders of magnitude higher than the oceans’ average2; at the level of Orders and Phyla, coral reefs are probably the most diverse ecosystem on the planet. Recently, the world’s attention has been focused on reefs for more pragmatic reasons: their role in a changing climate. The global phenomenon of coral bleaching (loss of symbiotic algae from tissues, often followed by colony death), recorded with increasing frequency since the 196Os, has been suggested as a harbinger of global warming3. Additionally, the fates of entire island nations may depend on the ability of reefs to keep pace with sea-level rise by growing upwards. Recent widespread reports of coral reef deterioration and death

Callum Roberts is at the Eastern Caribbean Center, University of the Virgin Islands, St Thomas, US Virgin Islands 00802, USA.

Callum M. Roberts have therefore sounded alarms in scientific circles and beyond. Proclamations of the impending demise of coral reefs are not new. In the 1960s massive outbreaks of the coral-eating crown-of-thorns starfish on the Australian Great Barrier Reef caused widespread prophecies of doom. Thirty years the later, the Great Barrier Reef and the crown-ofthorns are still there. To cut through the rhetoric and decide just how coral reefs really are faring in the 199Os, 125 reef scientists and managers gathered in Miami in June to examine the evidence at a conference entitled ‘Global Aspects of Coral Reefs: Health, Hazards and History’. In a welcome break from scientific norms, the organizers resurrected the original meaning of the word ‘colloquium’ and most of the meeting was centred around discussion of 62 preprinted case histories documenting the condition of the world’s reefs. To ,sharQen the minds of the participants, the final

two days of the five-day meeting were thrown open to press and public. The meeting sought answers to three critical questions: (1) are reefs worldwide in decline? (2) what are the major hazards to reefs? (3) how will global warming affect reefs? The geological record shows that reefs have survived through many changes of climate. Arthur Bloom (Cornell University, Ithaca, NY, USA) showed how, in the Holocene, reefs had experienced rates of sea-level rise an order of magnitude faster than those predicted for the coming 50 years. Ann Budd (University of Iowa, USA) noted that the two major periods of extinction in Caribbean reef corals since the closure of the Isthmus of Panama, 3.5 million years ago, did not coincide with periods of rapid climate change. Clive Wilkinson (Australian Institute of Marine Science) summed up the consensus among participants saying that ‘coral reefs will probably enjoy a little bit of climate change’! However, 425

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Bob Buddemeier (Kansas Geological Survey, USA) added that ‘for coral reefs, the major problem with climate change is that it is unlikely to be severe enough to eradicate humans’. It was this latter point which was to be the main concern of the meeting. Jeremy Woodley (University of the West Indies, Jamaica) made the important point that the services which reefs provide us with now should be the real focus of our discussion. Millions of people in developing countries (where 90% of reefs occur4) depend on them for their livelihoods. The health of reefs must therefore be measured in ecological rather than geological terms. Declining fisheries, falling biodiversity and eroding reef framework are measurable currencies that can have direct effects on the well-being of people. Interpreting the ecological changes that reefs have undergone in the brief period of our intimate acquaintante with them - a bare 40 or 50 years - is fraught with difficulty. In an ecosystem dominated by clonal organisms, often very long-lived, distinguishing short-term fluctuations from long-term trends is an important challenge. Here, the fledgling science of coral geochemistry promises to provide a powerful tool with which to reconstruct the conditions experienced by reef organisms over the past several hundreds to thousands of years. Thus, present-day conditions can be placed into a historical context. Recent studies suggest that sea-surface temperature, rainfall, sedimentation rates and salinity can be reconstructed from elements and compounds locked in annual growth bands of corals. Cores taken from large, living colonies and from

Table

I. The three

Hazard

most

important determined

hazards facing by participants

Sources

coral reefs and their at the meeting

main

effects,

as

Main effects

Overfishing

Direct: population declines; loss of fish diversity; habitat damage from destructive methods. Indirect: population increases in prey species (e.g. urchins) leading to bioerosion, reduced coral survival, algal overgrowth, etc.

Sedimentation

Land clearing, dredging, shipping activity (propwash)

Nutrient enrichment

Agriculture, Oclearing

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fossil colonies have been successfully used to generate records of past climate, such as the frequency and severity of El Nirio conditions in the Eastern Pacific5. A cautionary note was sounded at the meeting over use of geochemical sampling from coral cores. To what extent are our results biased by use of cores from very old colonies? Jim Bohnsack (National Marine Fisheries Service, Miami, USA) pointed out that the average fish lives only a few days. Can these Methuselahs of the coral world tell us much about the experience of the average coral? Terry Hughes (James Cook University, Australia) agreed, noting that the only coral colonies that had survived two decades of massive reef degradation at his north Jamaican study sites were of the species favoured for coring by geochemists. Would we have any idea that this decline had happened from analysis of their skeletons? Participants broke up into a series of regionally based groups to examine the status of reefs and the major hazards which affect them. Global coverage was nearly complete, with a few important omissions such as French Polynesia. Some groups swiftly reached agreement, others generated heated debate. However, after three days of discussion a list of 33 natural and human hazards to coral reefs had been drafted and their importance ranked. While the diversity of voting systems and selection criteria used to reach these conclusions fell far short of the methodological rigour we expect in science, the results can be considered robust in that they met with broad agreement.

sewage,

Reduced to corals reduced survival land

light penetration; energy cost from sediment clearance; settlement success and early of corals; reduced diversity.

Algal overgrowth of benthic organisms leading to loss of cover and diversity; reduced coral recruit settlement and survival.

1993

The overwhelming conclusion was that while some coral reefs remain in near-pristine condition, those close to centres of human population are undergoing serious declines. The three principal sources of this degradation are overfishing, sedimentation from land clearing and dredging, and nutrient enrichment causing eutrophication (Table 1). While the mix of causal agents varies from place to place, the results are similar: declining populations of fish and corals, overgrowth of reefs by algae, loss of diversity and erosion of the reef framework as rates of calcification fall. On a positive note, reefs in some areas are doing quite well. For example, 60% of Pacific coral reefs were considered to be in excellent condition. However, population pressure in the Pacific as a whole is relatively low compared with the IndoPacific centre of coral reef diversity in South East Asian seas. Here, degradation of reef habitats has been widespread, and accelerating habitat losses are set to have major impacts on global biodiversity. Similarly, reefs in the Caribbean have suffered badly in the last decade. Our database on reef condition, although large, cannot be considered unbiased. Jeremy Jackson (Smithsonian Tropical Research Institute, Panama) highlighted the predilection of reef ecologists to sample in attractive places, generally those with high diversity, coral cover and well developed reefs. Those present concluded that we need to increase the objectivity of our sampling to provide a firmer scientific basis for determining the direction of longterm trends in reef condition. Several exciting developments to improve the use of our current knowledge about reef condition were described. The International Centre for Living Aquatic Resource Management in the Philippines is about to begin the creation of a database on coral reefs based on a geographic information system (GIS) approach. In

Britain,

the

World

Conservation

Monitoring Centre plans to compile a World Atlas of Coral Reefs that would complement this approach. To provide information on patterns of biodiversity distribution, two other databases will be linked to these one for corals compiled by Charlie Veron (Australian Institute of Marine Science), the other for fishes compiled by a group from the IUCN Species Survival Commission. The meeting was divided over what to do to halt the decline of reefs. Some, like Bob Buddemeier,

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think that we already know enough about the causes of decline to do something about them, noting that ‘we have not as much science as we’d like but far more than we can use effectively’. Others felt that we know much too little. In one sense, by identifying the main sources of stress, we do already know enough. If we could only reduce sediment and nutrient runoff and levels of fishing, the outlook for reefs would be much better. However, in the real world this is not easy. As well as looking for ways of reducing levels of stress we need to determine the tolerance limits of the coral reef system and ways in which different stressors interact. The interaction of more than one source of stress represents perhaps the biggest threat to reefs. Many present at the meeting could document cases where reefs had recovered well from natural catastrophes such as hurricanes or extreme low tides. Add another stress, though, such as oil pollution or mass mortality of sea urchins, and recovery was halted or rapid decline ensued. It is here that our ignorance of reef processes is exposed most clearly. Research on the interacting

effects of stresses is now a major priority. Many people at the meeting emphasized that managers need to make decisions now about how to look after reefs based on the little we know. Communication between scientists and managers is still poor, with a few notable exceptions such as the Great Barrier Reef Marine Park Authority in Australia. The need to improve links between them was one of the key resolutions of the meeting. Scientists must take on research projects that address questions import ant to management of reefs, while managers must help scientists frame those questions in terms that will yield the greatest benefit. To provide a vehicle for turning words into action, the chairman of the organising committee, Bob Ginsburg (University of Miami, USA) called for the declaration of an International Year of the Reef, beginning in 1996 at the 8th International Coral Reef Symposium in Panama. He proposed that we start preparation for this event now by working to improve the database on trends in coral reef corn-munities, the continued development of worldwide reef monitoring networks and databases, and the

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closer collaboration of scientists and managers. Participants at the meeting left with a sense that they were taking part in the making of history. Charlie Veron summed up this feeling in saying that ‘future generations will either thank us or curse us for the outcome of this meeting. We either do it right now or we fail’. His feelings were echoed by those of Frank Talbot (Natural History Museum, Washington, USA) who stated that ‘it is inconceivable that we should leave reefs as damaged goods for the next generation’. However, unless reef scientists can take advantage of the catalyst this meeting provided, that is all that the next generation can expect. References 1 Smith, S.V. (1978) Nature 273, 225-226 2 McAllister, D.E., Schueler, F.W., Roberts, CM. and Hawkins, J.P. in Advances in Mapping the Diversity of Nature (Miller, R., ed.), Chapman & Hall (in press) 3 Glynn, P.W. (1991) Trends Ecol. Evol. 6, 175-179 4 Wells, SM., ed. (1988) Coral Reefs of the World(Vols l-3), IUCN/UNEP 5 Dunbar, R.B., Wellington, G.M., Colgan, M. and Glynn, P.W. (1987) Trans. Am. Geophys. Union 68, 1, 743

HowOldisAncient Woodland? PALAEOECOLOGY IS WIDE-RANGING and can encompass all branches of vegetation science. One of its most obvious applications is in the identification of past distributions and abundances of plant taxa, and the type and rate of change that has occurred in these communities and populations over time’-‘. Palaeoecological studies can therefore provide a means of viewing the history of present spatial distributions of vegetation. But what would seem a most obvious use of palaeoecology appears to have gone largely unheeded by plant ecologists; most ecological research still concentrates on what can be seen in the present with little regard for the past. The past is thus inferred from the present. But how much does our present-day vegetation and the processes that occur within it reflect processes and vegetation of the past?

Katherine Willis is at the Sub-dept of Quaternary Research, Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge, UK CB2 3EA. D 1993, Elscvter Science PuhI,she,i

Ltd ,“K)

Katherine J. Willis How have communities responded over time to external forces such as climatic change and anthropogenic disturbance? And how can the antiquity of the modern community be determined and integration of vegetation over long time periods be measured on a spatial scale? Antiquity and long-term vegetation dynamics must be relevant to basic ecological theory and in particular, to ideas on stability and flux in plant communities6. Without a palaeoecological

record,

we

can

only

infer

the

nature of processes operating on timescales greater than IO2 years by extrapolation from modern and recent historical data. This is unsatisfactory, at best. Recent palaeoecological work by D. Foster and colleagues8-10, on sites in New England, published in mainstream ecological literature, is a good

example of the value of palaeoecology to ecology. These papers demonstrate the important contribution that palaeoecology can make to ecological hypotheses and are written in such a way that palaeoecology and ecology are not seen as two distinct disciplines but rather as one entity. They focus on the scale of change, both temporal and spatial, that has occurred in Harvard Forest in the last 9500 years. The most striking feature that emerges from all three studies is the continuously changing nature of this woodland, be it naturally or anthropogenically induced, spatially or temporally. The spatial aspects (landscape, community, population) of these changes are demonstrated by using two palaeoecological sites of different size and thus contrasting pollen collecting source”. The larger site 427