Mud, Marine Snow and Coral Reefs

The survival of coral reefs requires integrated watershed-based management activities and marine conservation

Eric Wolanski, Robert Richmond, Laurence McCook and Hugh Sweatman

oral reefs are the most diverse of mine tailings on them, fishing with ex- metabolites from which the corals de- Call marine ecosystems, and they plosives and cyanide, and land recla- rive much of their energy. (Corals con- are rivaled in biodiversity by few ter- mation. Reefs that experience such in- struct their hard habitat the way mol- restrial ecosystems. They support peo- sults often die; those that deteriorate lusks grow their shells, by accreting ple directly and indirectly by building but survive cannot recover to their calcium carbonate.) The main function- islands and atolls. They protect shore- original health as long as the distur- al components of a coral reef ecosys- lines from coastal erosion, support fish- bances continue. In other countries the tem include the hard corals, coralline eries of economic and cultural value, disturbances are more chronic than algae, filamentous and fleshy algae, provide diving-related tourism and acute. Reefs are assaulted by muddy blue-green algae (cyanobacteria), and serve as habitats for organisms that runoff, nutrients and pesticides from a host of invertebrates and fishes. produce natural products of biomed- adjacent river catchments, overfishing Coralline algae are essential to a ical interest. They are also museums of and global-warming effects. These dis- healthy reef because they cement reef the planet’s natural wealth and places turbances affect the key parameters structures and contain chemicals that of incredible natural beauty. permitting reef resilience: water and induce metamorphosis in coral planula Despite their recognized biological, substratum quality. As a result, corals larvae. Filamentous and fleshy algae economic and aesthetic value, coral fail to reproduce successfully, and the can be very abundant; indeed, the reefs are being destroyed at an alarm- coral larvae arriving from more pris- most telltale sign of a degraded coral ing rate throughout the world. Some tine reefs are unable to settle and thrive reef is the replacement of corals by al- countries have seen 50 percent of their on substrata covered by mud, cyano- gae (Figure 2). coral reefs destroyed by human activi- bacteria or fleshy algae. Coral popula- Three genera of corals dominate Pa- ties in the past 15 years. Some human tions thus fail to recover or reestablish cific reefs: Acropora, Porites and Pocillo- influences are acute—for example, themselves. pora. Acropora corals are the most spec- mining reefs for limestone, dumping Can science help save coral reefs? tacular; they are also framework Despite much talk about managing builders, providing habitat for a vari- Eric Wolanski received his Ph.D. in environmental coral reefs, the potential role of science ety of fishes and other reef organisms. engineering from the Johns Hopkins University in is limited. But it is important: Scientists They include the table, elkhorn, 1972. He is a leading scientist at the Australian can demonstrate the key processes con- staghorn and fast-growing branching Institute of Marine Science, where he studies trop- trolling the health of coral reefs and species. Porites corals include boulder ical coastal oceanography and its biological impli- how human activities damage them. or massive corals. Pocillopora corals in- cations for mangroves and coral reefs. Robert Rich- Then, we can hope, land-use managers clude both coarsely and finely branch- mond received his Ph.D. in biology from the State and marine-resources managers will be ing species, widely distributed across University of New York at Stony Brook in 1983. He is a professor of marine biology at the Universi- able to modify human behavior to re- the Pacific and into the Red Sea. ty of Guam Marine Laboratory. His research inter- duce or reverse damage to coral reefs. Natural disturbances—including ests include sublethal stresses on coral reefs. Lau- Toward this end we have developed a hurricanes (tropical cyclones or ty- rence McCook received his Ph.D. in biology from large-scale model for illuminating reef phoons), river floods (Figure 4), earth- Dalhousie University in 1992; he is a research sci- degradation and predicting the impact quakes and lava flows—have affected entist specializing in the ecology of algae and reef of future human activity. coral reefs for millions of years; they are degradation at the Australian Institute of Marine typically acute and have short-lived ef- Science, working with the Cooperative Research The Coral Reef Ecosystem fects. Reef areas away from human in- Centre for the Great Barrier Reef World Heritage The ecological functioning of a coral fluences often recover within a few Area. Hugh Sweatman received his Ph.D. from reef relies on the symbiotic association years if water and substratum quality Macquarie University in 1985; he is a research scientist at the Australian Institute of Marine Sci- between corals and dinoflagellate algae remain high. Acute, natural distur- ence where he leads the long-term reef-monitoring (zooxanthellae). In this system, the di- bances thus help maintain diversity on program. Address for Wolanski: AIMS, PMB No. noflagellates reside as symbionts with- coral reefs by knocking back dominant 3, Townsville MC, Qld. 4810, Australia. E-mail: in the cells of the coral host; the sym- species and allowing less competitive [email protected] bionts take in nutrients and produce species to reestablish themselves. © 2003 Sigma Xi, The Scientific Research Society. Reproduction with permission only. Contact [email protected]. 44 American Scientist, Volume 91 Figure 1. Healthy coral reefs such as this section of Australia’s Great Barrier Reef not only are aesthetic treasures but also possess the greatest biodiversity of any aquatic ecosystem. In particular, reefs in which various species of the fast-growing, branching Acropora corals dominate provide habitat for a spectacular array of life both large and small. Despite the recognized value of reefs, worldwide they have been degraded dra- matically over the past several decades owing to anthropogenic effects, and little has been done to halt their decline. A large part of the prob- lem has been a lack of tools that would allow land- and marine-resource managers to estimate the relative benefits to reef health of various regulatory actions. The authors have developed a model that permits managers to estimate the effects on reefs of regulating various human activities. (Except where noted, photographs by the authors.)

The synergistic and cumulative effects hesive bridges of exopolymer (mucus). suspension readily attaches to the of human disturbances superimposed The aggregates resemble snowflakes sticky marine snow, forming muddy over natural disturbances make recov- and hence are called “marine snow” marine snow. The clay particles act as ery less likely and, in some cases, result (Figure 5). ballast that makes the flocs settle onto in stable states dominated by algae. Human activities on land often re- coral reefs. Muddy marine snow flocs sult in increased nutrient concentra- settle fast, typically at a speed of about Marine Snow tions in coastal coral reef waters, which 5 centimeters per minute—about 1,000 The water around coral reefs some- enhances the growth of algae. In turn, times faster than individual mud parti- times looks clear, but it can contain a increased nutrients also result in an in- cles settle. The settled muddy marine variety of suspended matter, starting creased prevalence of marine snow. In snow has detrimental or even lethal ef- with inorganic particles such as resus- the nutrient-enriched coastal waters of fects on small coral reef organisms. pended calcareous material, fecal ma- Guam and the Great Barrier Reef, ma- Corals and reef organisms such as terial, organic detrital particles, and rine snow flocs can exceed several cen- barnacles are able to clean themselves mucus secreted by plankton, algae and timeters in diameter. Wave-exposed of small settling flocs as long as the silt bacteria. Corals themselves secrete mu- waters have smaller flocs than do more content remains low—less than 0.5 mil- cus to cleanse their colony surfaces and sheltered areas. ligrams per square centimeter. At high as a metabolic by-product. This mucus Marine snow is almost neutrally siltation levels (4 to 5 milligrams per prevents corals from becoming clogged buoyant and can remain in suspension square centimeter) or when flocs are with sediment particles and also for hours in turbulent reef waters. large (particles 200 to 2,000 micrometers shields against desiccation if they are Near-shore waters, however, may con- in diameter), the coral polyps initially exposed to air at low tide. Particles in tain additional suspended fine clay exude thick layers of mucus and die af- suspension in water are rapidly aggre- particles, rich in nutrients and detritus ter less than one hour of exposure—a gated by flocculation as well as by ad- derived from land runoff. This mud in short time compared with the rate of © 2003 Sigma Xi, The Scientific Research Society. Reproduction with permission only. Contact [email protected]. 2003 January–February 45 natural marine snow deposition on coral reefs. Katharina Fabricius, at the Australian Institute of Marine Science, found, from laboratory experiments, that settling muddy marine snow flocs are far more hazardous to young than to older corals; the mortality rate is 10 times greater for young coral recruits (newly established animals) than for adult corals. Coral recruits typically die after 43 hours of exposure to muddy marine snow, a threshold that is rou- tinely exceeded in nutrient-enriched coastal waters of the Great Barrier Reef but not in areas farther offshore. The presence of muddy marine snow on coral is often short-lived, resulting from Figure 2. Most coral-reef decline, including this example at Palau, is tied in subtle but pre- a river flood or from resuspension by dictable ways to sediment-laden runoff from human activities within adjacent watersheds. Such wind-generated waves in a storm. The runoff may not initiate the decline of a reef; more often, in fact, it prevents a reef from recovering settled muddy marine snow, having from an acute shock such as a tropical cyclone. The effects are multiple. First, coral larvae, which done its dirty work, is consumed by may have drifted from a distant healthy reef, are unable to colonize because the reef has become plankton and reef organisms, or flushed covered in a muddy algal mat. Second, those larvae that do establish a foothold may be smoth- out by waves and currents. It usually ered by newly deposited mud. Third, and at least as significant, the prevalence of herbivorous leaves no “smoking gun,” just a de- fish, which feed on the fleshy algae that damage coral larvae, is inversely proportional to water graded reef. turbidity. In much the same way that regular mowing maintains a fast-growing suburban lawn, Pollutants, including pesticides, herbivorous fish control filamentous algae and enable coral growth. A reef with adult corals but no recruitment of juveniles is in reality dead, but just doesn’t know it yet. heavy metals and hydrocarbons, also degrade coastal reefs. They can inter- fere with the chemically sensitive 10°S processes of reproduction and recruitment in corals and other reef organisms, such as synchronization of spawning, egg-sperm interactions, fer- Cape Grenville tilization, embryological development, larval settlement, larval metamorphosis and acquisition of symbiotic zooxanthellae by young corals following Princess Charlotte Bay recruitment. Figure 3. Model area included 261 reefs in several zones (black type) of Australia’s Great Bar- 15°S Cooktown/Lizard Island rier Reef. Coral cover on 48 of these reefs has been monitored annually for more than a decade and shows great variability in time and space. This variability is characterized by a ma- Cairns jor decrease in coral cover following acute disturbances, such as a tropical cyclone or a river flood, and slow recovery thereafter. For in- Innisfail stance, tropical cyclone Ivor in 1990 affected the coral cover on all the outer shelf reefs in Townsville the Cooktown/Lizard Island sector; 10 years later, the coral had recovered to cover more Cape Upstart than 50 percent of the reef surface. Inshore Whitsunday reefs in the Cairns sector recovered slowly after 20°S losing coral cover through the combined ef- Pompey fects of bleaching, an infestion of coral-eating crown-of-thorns starfish and tropical cyclone Rona in 1999. Among midshelf reefs near Townsville, Rib Reef is dominated by fast- Swain growing tabulate Acropora corals. The reef cov- 0 100 200 300 400 500 er was severely reduced by starfish infestation Capricorn in the 1980s. Recovery was reversed by tropical kilometers Bunker cyclone Justin in 1997 and by another outbreak of starfish. Coral cover declined sharply on two 145°E 150°E midshelf reefs in the Whitsunday sector in 1997 as a result of tropical cyclone Justin. © 2003 Sigma Xi, The Scientific Research Society. Reproduction 46 American Scientist, Volume 91 with permission only. Contact [email protected]. 050100150 200

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Figure 4. Muddy plume of the Burdekin Riv- er during a river flood, in the Great Barrier Reef near Townsville, can be seen in this oblique aerial photograph. The plume at this location spans 5 kilometers in width and is made readily visible by its high turbidity. Both the entrained mud and reduced salinity can cause acute damage to coral reefs. The map (above) shows the salinity distribution in a 400-kilometer-long section of the Great Barrier Reef for the 1991 river flood, predicted by Brian King using a three-dimensional hydrodynamic model. (By contrast, during times of normal river outflow, no reductions in salinity would be evident.) The model uses historical data on daily river discharges, as well as wind speed and direction data, to calculate the movement of river flood plumes from 1969 onwards. The Toll mental degradation can also result from with marine and reef issues. In Aus- If, through increased muddiness or pol- overexploitation of populations of her- tralia, about four agencies deal with lution, a single link in the coral repro- bivorous fishes, such as parrotfish and land-based issues and two with reefs ductive chain is broken, the system cas- surgeonfish, which feed on fleshy al- (not counting fishing). It is as if land cades toward eventual demise. One gae. In overfished systems, fleshy algae and sea were not interconnected hundred percent successful fertilization can overgrow corals and prevent coral ecosystems. This disconnect between followed by 0 percent recruitment has larvae from recruiting. watershed-based activities and marine the same outcome as 100 percent fertil- Human activity will continue to in- conservation has resulted in serious en- ization failure. Therefore many reefs crease. As a result, coral reefs will in- vironmental degradation throughout near human population centers simply creasingly degrade—as long as human the world. do not recover from disturbances. Less activities on land and in coral reef wa- Science can help save coral reefs by attractive Porites and Pocillopora corals ters continue to be managed indepen- providing land- and marine-resource replace the habitat-building Acropora dently. In both developing and devel- managers with accurate and adequate corals, and, quite often, the benthos be- oped countries, including Australia, data on key threats and the synergisms comes covered by fleshy algae, sponges the U.S., Japan and the French overseas involved, specific indicators of reef re- and worms. This in turn causes a shift territories, different government agen- silience, as well as science-based mod- in resident fish populations. Environ- cies deal with land-based issues and els to predict the impact of various de- © 2003 Sigma Xi, The Scientific Research Society. Reproduction with permission only. Contact [email protected]. 2003 January–February 47 Figure 5. Marine snow flocs such as the one at left—photographed by Katharina Fabricius in reefal waters of Palau, Micronesia—may reach 30 centimeters in length but are typically smaller—0.5 to 5 millimeters in size. Flocs are formed by colonies of phytoplankton, fecal pellets, mucus secreted by bacteria and plankton, macroscopic aggregates of Thalassiosira nana, large diatoms, dinoflagellates and tintinnid ciliates, as well as a variety of other plankton and their remains. Additional mucus is produced by diatoms and microbes that colonize the nutrient-rich clay particles derived from erosion in river catchments. Mud readily aggregates on marine snow because it is sticky, forming muddy marine snow flocs, shown spanning 0.8 millimeters in the photograph at right. The mud acts as ballast, forcing the marine snow to settle on the corals, which they smother, particularly the juvenile recruits. cisions about land use and reef fish- in a 400-kilometer-long swath that ex- ganisms in the upper northeast reef eries on reef health. We have devel- tends from Lizard Island in the north to slope. Reefs for the program were cho- oped such a mathematical model for the Whitsunday Islands in the south. sen from three shelf positions (inshore, the Great Barrier Reef, for which exten- We wished to model the region believed midshelf and outer shelf) at six lati- sive physical and biological data are to be most susceptible to anthropogenic tudes, four of which fall within the available. impacts from land runoff (Figure 4). model domain. Coastal reefs are the Data to develop the model came from most affected by runoff but are not Modeling Reef Health the Long-term Monitoring Program at monitored because of poor visibility Australia’s Great Barrier Reef stretches the Australian Institute of Marine Sci- and the presence of crocodiles. The data along 2,600 kilometers of the east coast ence, which has surveyed 48 reefs an- on algal and coral cover (Figures 6 and 9) of Australia from 25 S to 10 S. The do- nually since 1992 for assemblages of reef present evidence of large changes in the main of our model comprises 261 reefs fishes and communities of benthic or- reefs over time in each region; the changes vary among regions. The data 100 show a strong linear relationship be- Fitzroy tween the abundance of herbivorous Island Low fish and water visibility (Figure 7)—as Isles might be expected, since the fish keep Havannah algae populations down—and this ob- Green Island Island 80 (16049) servation is central to the formulation of a reef-health model. The model uses algal cover as a North proxy measure of reef health. The eco- Michaelmas Chicken Davies Direction Island logical components of the model include hard corals in two age groups, 60 Martin John Myrmidon (14123) Brewer juvenile and adult, together with algae Dip and herbivorous fish. Corals and fleshy algae compete for space, and herbivo- Agincourt St. Crispin rous fish consume algae. Reef distur- No. 1 Hastings Mackay Rib Figure 6. Algal cover, which displaces corals, 40 serves in the model as a parameter for the algae (model), percent health of the Great Barrier Reef. Its distribu- Opal (2) Lizard tion has been monitored yearly since 1992 for No Name Island the 48 reefs. This scatter plot of observed and Carter predicted algal cover suggests that the model has promise. The outlier points (red) are reefs 20 infested with the coral-eating crown-of-thorns starfish, Acanthaster planci. Such infestations are not incorporated into the model because the ecology of the starfish is insufficiently understood—in particular the ability of the starfish to migrate within a reef and between 0 0 20 40 60 80 100 reefs. Masahra Ogura at Tokai University, Japan, has measured crown-of-thorns starfish algae (observed), percent migrating at speeds of up to 546 meters per day. © 2003 Sigma Xi, The Scientific Research Society. Reproduction 48 American Scientist, Volume 91 with permission only. Contact [email protected]. bances are of two types: acute and 1,000 chronic. Acute, natural disturbances include river plumes, tropical cyclones and warm-water events resulting in 800 bleaching. These events kill coral, thereby providing free space that is rapidly colonized by filamentous and 600 then fleshy algae. Chronic disturbances come in the form of increased nutrient concentration and the influence of in- 400 creased turbidity—at least 90 percent of the nutrients from land runoff arrive attached to mud particles. Corals can slowly recover from tissue remnants or 200 mean herbivorous fish per hectare through recruitment of larvae from healthier reefs. The recovery rate de- pends on nutrient concentration and 0 the number of herbivorous fish avail- 0 5 10 15 20 25 30 35 40 able to consume algae. mean visibility (meters) It is not necessary to calculate her- Figure 7. In Australia’s Great Barrier Reef, a relation exists between visibility and the abun- bivorous fish dynamics because people dance of herbivorous fish. These data were averaged for 10 years of surveys at 48 reefs scat- do not target herbivorous fish in the tered along a 400-kilometer stretch of the coast. In the model, visibility is used as a proxy for Great Barrier Reef; their abundance is herbivorous fish prevalence. predicted by water visibility. It is thus sufficient for the model to set the pre- The model predicts reef health as pa- curtailed. At least as important, the vailing visibility conditions from field rameterized by algal cover in a 400- model enables one to quantify the ef- observations. The mean visibility has kilometer-long stretch of the Great Bar- fects of various scenarios for control of apparently halved since 1927—that is, rier Reef (Figure 9). Without human land-use activities—anywhere from turbidity has doubled—in the Low influences, coastal runoff degrades the “do nothing” to “strict control.” It of- Isles area near Port Douglas. reef in a zone whose width and degree fers decision makers and the public a Corals spawn each year at night in of impact vary with latitude, with max- science-based tool to decide what activ- the early summer, on a date set by the imum damage in the Cairns region. Im- ities should be allowed, and how they moon phase. In the model, the spawn pacts within the zone vary considerably should be controlled, on land and at material is carried by water currents owing to the passage of tropical cy- sea, in order to produce a desired state for about 10 days, a conservative esti- clones; as a result, reefs outside the of health for coral reefs. The model mated time of survival for coral larvae coastal zone are occasionally covered could presumably also be used to test capable of recruitment, by which time with algae. The model further predicts the impact on reef health of various lev- most of the coral larvae have left their that, with human activities on land, the els of fishing for herbivorous fish; this natal reef. The currents are affected by zone of damage has already grown does not apply to Australia’s Great Bar- tides, forcing by the Coral Sea and much larger than the natural state and rier Reef at present, but the question is wind, resulting in connectivity among will increase in size and intensity in the relevant to most reefs elsewhere in the reefs (Figure 8). Recruitment rates were future, unless human influences are world, including Micronesia and the calculated for every spawning year since 1969, when reliable wind data be- 4,500 came available. Outside of spawning periods, coral populations on individ- 4,000 ual reefs are isolated from each other. 3,500 Natural disturbances were deter- mined from historical records of river 3,000 floods and of the trajectory and inten- 2,500 sity of tropical cyclones, for which data 2,000 also are available since 1969. The coral die-off from tropical cyclones was cal- 1,500 number of particles culated from the trajectory and intensi- 1,000 ty of the storms, using an empirical function derived from surveys of coral 500 cover immediately before and after the 50 hours0 100 hours passage of a storm. From models of Figure 8. As visualized from the oceanographic model for Bowden Reef in the Great Barrier river plumes, we extracted two key pa- Reef, mass spawning of corals creates a plume (left) of coral larvae over the reef. This plume rameters: the minimum salinity and slowly mixes and is diluted by ambient oceanic waters while at the same time being carried the duration of the river plume at each away by the oceanic currents (right). Larvae from one reef can settle on other reefs. This process reef. These parameters in turn were enables degraded reefs to recruit coral larvae from healthier reefs. The distribution of source used to calculate the die-off of coral. and sink reefs varies yearly with the wind after annual coral spawning. © 2003 Sigma Xi, The Scientific Research Society. Reproduction with permission only. Contact [email protected]. 2003 January–February 49 without with human influence human influence

100

algal cover (percent) algal cover 20

Figure 9. Model of coral health in this 400-kilometer-long stretch of the Great Barrier Reef was run with and without human influences. The parameter for reef degradation is algal cover. These results suggest that a wide swath is degraded by human activities on land, particularly in near- shore and mid-shelf reefs. The immediate cause of coral death at some sites may be natural, acute disturbances such as hurricanes and river floods. Anthropogenic effects, via land runoff, on water quality appear responsible for the failure of reefs to recover after disturbance. This results in a long-term decline in reef health.

fungid submassive massive 70 foliose encrusting tropical branching (other) 60 cyclone tabulate Acropora Justin other Acropora digitate Acropora 50 branching Acropora

40 Acanthaster planci 30

hard coral cover (percent) cover hard coral 20

0 1994 1995 1996 1997 1998 1999 2000 2001 2002 year

Figure 10. Annual surveys of hard corals at Rib Reef on the Great Barrier Reef show the effects of disturbances such as tropical storms and out- breaks of the coral-eating, crown-of-thorns starfish, Acanthaster planci. Such disturbances have different effects on corals with different growth forms. The horizontal plates of fast-growing table Acropora spp. rapidly overgrow other corals but are easily broken during tropical cyclones and are a preferred food for crown-of-thorns starfish. Massive corals grow slowly, their round shape helps limit storm damage, and their perforate skeleton allows coral tissue to be sequestered during episodes of stress from reduced salinity, sedimentation and eutrophication associated with agricultural runoff and sewer outfalls. After such disturbances, the dead corals are colonized by filamentous or fleshy algae. Algae also replace corals by direct overgrowth. In the photograph (right), the brown seaweed Lobophora variegata is growing up around the branches of Porites cylin- drica, smothering the coral tissue (shown by the dead, white skeleton where the researchers removed the algae covering the coral tissue). © 2003 Sigma Xi, The Scientific Research Society. Reproduction 50 American Scientist, Volume 91 with permission only. Contact [email protected]. U.S. Mariana Islands, where these fish jective should be prevention, not pheric Administration, IBM-Australia, are relentlessly pursued. demonstration, of extensive degrada- Katie Marshall, Simon Spagnol, Richard tion. Effective monitoring programs Brinkman, Brian King, Katharina Fabri- Limitations to Action must go beyond documentation of cius, Angus Thompson, Greg Coleman and Like all ecosystem models, our model coral reef demise and be used as tools William M. Hamner. has limitations. These include un- to guide responses that prevent out- known or poorly understood ecosys- right mortality. Bibliography tem processes, the lack of sufficient Examples from Guam and Hawaii Ayukai, T., and E. Wolanski. 1997. Importance data on predisturbance water quality show that once a reef has been killed, it of biologically mediated removal of fine or habitat status, the lack of data from cannot be restored, even by importing sediments from the Fly River plume, Papua New Guinea. Estuarine, Coastal and Shelf Sci- undisturbed sites and inadequacies in outside corals, unless the underlying ence 44:629–639. the measurement of water-quality para- cause—for example, soil erosion in the Birkeland, C. E. 1997. Life and Death of Coral meters. Additional ecological processes adjoining catchment—is first ad- Reefs. New York: Chapman and Hall. could be added to the model, but this dressed. The most logical approach to Done, T. J. 1992. Phase shifts in coral reef com- does not make it more useful because coral reef restoration is to alleviate munities and their ecological significance. these new processes require additional those conditions that caused the de- Hydrobiologia 247:121–132. parameters for which data are unavail- cline and allow natural recovery to oc- Fabricius, K., and E. Wolanski. 2000. Rapid smothering of coral reef organisms by mud- able. Prediction of the response of a cur. More specifically, restore the wa- dy marine snow. Estuarine, Coastal and Shelf reef to human influences is thus inher- ter and substratum quality that allows Science 50:115–120. ently uncertain. corals and other reef organisms to suc- McCook, L. J. 1999. Macroalgae, nutrients and Unfortunately, uncertainty in ecosys- cessfully reproduce and recruit. This phase shifts on coral reefs: Scientific issues tem models cannot readily be quanti- means controlling poor land-use prac- and management consequences for the fied; too often, this is used as an excuse tices that spill mud, nutrients and pes- Great Barrier Reef. Coral Reef 18:357–367. for inactivity, citing that “more re- ticides into coral reef waters; manag- Richmond, R. H. 1993. Coral reefs: Present problems and future concerns resulting search is needed before a sound deci- ing fisheries through quotas and from anthropogenic disturbance. American sion can be made.” Rather, the major fishing-gear restrictions; reducing Zoologist 33:524–53 impediment at this point appears to be tourism impacts; and establishing ma- Wolanski, E. 2001. Oceanographic Processes of Coral political will. Scientists could do much rine protected areas. Science has a cru- Reefs. Physical and Biological Links in the Great more to exert influence—for example, cial role to play in demonstrating the Barrier Reef. Boca Raton, Fla.: CRC Press. by translating existing scientific data connections between land and reef into the social and economic costs of ecosystems and the profound effects inaction and making this information those connections can have. available to stakeholders and the broad- Links to Internet resources for “Mud, er community. Otherwise, “proof” of Acknowledgments Marine Snow and Coral Reefs” are impacts will have to wait for serious The authors thank the Australian Institute available on the American Scientist Web site: degradation—and in comparison to of Marine Science, the University of Guam http://www.americanscientist.org/ current data, rather than to the undoc- Marine Laboratory, the STAR program of articles/03articles/wolanski.html umented predisturbance state. Clearly the U.S. Environmental Protection this outcome must be avoided. The ob- Agency, National Oceanic and Atmos-