Establishment of the photosymbiosis in the early ontogeny of three giant clams

Distribution and morphology of zooxanthellae were investigated histologically and ultrastructurally in veligers and juveniles of three giant clam species, Tridacna crocea, T. derassa, and T. squamosa. No zooxanthellal cells were associated with gametes. In veliger larvae, zooxanthellae were ingested and digested in the stomach. Within several days after metamorphosis from veliger to a juvenile clam, the zooxanthellal tube, in which zooxanthellae were packed, elongated from the stomach toward the mantle. Zooxanthellae in the tube appeared in a line, and we designated the appearance of the lined zooxanthellae in the mantle of juvenile clams as the first sign of the establishment of symbiosis. The zooxanthellal tubular system developed as the clams grew, particularly in the mantle margin, and then hypertrophied siphonal tissue formed. In zooxanthellal tubes, zooxanthellae usually had intact ultrastructures suggesting that they were photosynthetically active, while the stomach always contained degraded zooxanthellae that were probably discharged from the zooxanthellal tube. Giant clams probably digest zooxanthellae directly, and ingest the secreted photosynthates from zooxanthellae. There may be a selection mechanism to discharge unhealthy zooxanthellae from the mantle into the stomach. In addition to zooxanthellae, digested diatoms and other unidentified digested materials in the stomach suggest that filter-feeding also contributes to giant clam nutrition.     

Clamming up: environmental forces diminish the perceptive ability of bivalve prey

The lethal and nonlethal impacts of predators in marine systems are often mediated via reciprocal detection of waterborne chemical signals between consumers and prey. Local flow environments can enhance or impair the chemoreception ability of consumers, but the effect of hydrodynamics on detection of predation risk by prey has not been investigated. Using clams as our model organism, we investigated two specific questions: (1) Can clams decrease their mortality by responding to predators? (2) Do fluid forces affect the ability of clams to detect approaching predators? Previous research has documented a decrease in clam feeding (pumping) in response to a neighboring predator. We determined the benefits of this behavior to survivorship by placing clams in the field with knobbed whelk or blue crab predators caged nearby and compared mortality between these clams and clams near a cage-only control. Significantly more clams survived in areas containing a caged predator, suggesting that predator-induced alterations in feeding reduce clam mortality in the field. We ascertained the effect of fluid forces on clam perception of predators in a laboratory flume by comparing the feeding (pumping) behavior of clams in response to crabs and whelks in flows of 3 and 11 cm/s. Clams pumped significantly less in the presence of predators, but their reaction to blue crabs diminished in the higher velocity flow, while their response to whelks remained constant in both flows. Thus, clam reactive distance to blue crabs was affected by fluid forces, but hydrodynamic effects on clam perceptive distance was predator specific. After predators were removed, clams exposed to whelks took significantly longer to resume feeding than those exposed to blue crabs. Our results suggest that prey perception of predators can be altered by physical forces. Prey detection of predators is the underlying mechanism for trait-mediated indirect interactions (TMIIs), and recent research has documented the importance of TMIIs to community structure. Since physical forces can influence prey perception, the prevalence of TMIIs in communities may, in part, be related to the sensory ability of prey, physical forces in the environment that impact sensory performance, and the type of predator detected.     

Estuarine Vegetated Habitats as Corridors for Predator Movements

Abstract: The spatial proximity of one habitat to another can strongly influence population and community dynamics. We investigated whether the proximity of intertidal oyster reefs to vegetated estuarine habitats, salt marshes, and seagrass beds, affects the abundance and community structure of benthic macroinvertebrates on reefs and predator-prey interactions between mobile predators and bivalves living on reefs. Benthic macroinvertebrate abundance was highest on reefs spatially separated from salt marshes. Macroinvertebrate species richness was highest on reefs separated from both salt marshes and seagrass beds. Comparisons of predation on juvenile bivalves transplanted to reefs for 7–12 days indicated that survivorship of clams was greatest on reefs spatially separated from both salt marshes and seagrass beds, whereas reef proximity to vegetated habitats did not affect the survivorship of oysters. The foraging behavior of blue crabs may explain patterns of macroinvertebrate abundance and clam survivorship among reefs with different proximity to vegetated habitats. In experiments conducted in 30-m² field enclosures, blue crabs had higher predation rates on hard clams transplanted onto artificial reefs adjacent to salt marshes or seagrass beds than on reefs separated from both habitats by unvegetated sand bottom. Thus, vegetated habitats appeared to act as corridors by facilitating the access of blue crabs to oyster reefs and enhancing the intensity of blue crab predation. Such an understanding of the effects of landscape characteristics of estuarine habitats on their value as habitats for estuarine organisms can be used to predict the consequences of habitat fragmentation on ecosystem function and to improve strategies for habitat and species conservation and restoration.     

Predators selectively graze reproductive structures in a clonal marine organism

Although the fitness consequences of herbivory on terrestrial plants have been extensively studied, considerably less is known about how partial predation impacts the fitness of clonal marine organisms. The trophic role of Caribbean parrotfish on coral reefs is complex: while these fish are important herbivores, as corallivores (consumers of live coral tissue), they selectively graze specific species and colonies of reef-building corals. Though the benefits of parrotfish herbivory for reef resilience and conservation are well documented, the negative consequences of parrotfish grazing for coral reproductive fitness have not been previously determined. We examined recently grazed colonies of Montastraea annularis corals to determine whether grazing was positively associated with coral reproductive effort. We measured gonad number, egg number and size, and proportional reproductive allocation for grazed and intact coral colonies 2–5 days prior to their annual spawning time. We found that parrotfish selectively grazed coral polyps with high total reproductive effort (number of gonads), providing the first evidence that parrotfish selectively target specific tissue areas within a single coral colony. The removal of polyps with high reproductive effort has direct adverse affects on coral fitness, with additional indirect implications for colony growth and survival. We conclude that chronic grazing by parrotfishes has negative fitness consequences for reef-building corals, and by extension, reef ecosystems.     

A geological perspective on the degradation and conservation of western Atlantic coral reefs

Continuing coral‐reef degradation in the western Atlantic is resulting in loss of ecological and geologic functions of reefs. With the goal of assisting resource managers and stewards of reefs in setting and measuring progress toward realistic goals for coral‐reef conservation and restoration, we examined reef degradation in this region from a geological perspective. The importance of ecosystem services provided by coral reefs—as breakwaters that dissipate wave energy and protect shorelines and as providers of habitat for innumerable species—cannot be overstated. However, the few coral species responsible for reef building in the western Atlantic during the last approximately 1.5 million years are not thriving in the 21st century. These species are highly sensitive to abrupt temperature extremes, prone to disease infection, and have low sexual reproductive potential. Their vulnerability and the low functional redundancy of branching corals have led to the low resilience of western Atlantic reef ecosystems. The decrease in live coral cover over the last 50 years highlights the need for study of relict (senescent) reefs, which, from the perspective of coastline protection and habitat structure, may be just as important to conserve as the living coral veneer. Research is needed to characterize the geological processes of bioerosion, reef cementation, and sediment transport as they relate to modern‐day changes in reef elevation. For example, although parrotfish remove nuisance macroalgae, possibly promoting coral recruitment, they will not save Atlantic reefs from geological degradation. In fact, these fish are quickly nibbling away significant quantities of Holocene reef framework. The question of how different biota covering dead reefs affect framework resistance to biological and physical erosion needs to be addressed. Monitoring and managing reefs with respect to physical resilience, in addition to ecological resilience, could optimize the expenditure of resources in conserving Atlantic reefs and the services they provide.     

Multiple spawning events and sexual reproduction in the octocoral Sarcophyton elegans (Cnidaria: Alcyonacea) on Lizard Island, Great Barrier Reef

Sarcophyton elegans is a common symbiotic (zooxanthellate) octocoral species in the shallow waters of the Great Barrier Reef (GBR). Study of a population at Lizard Island (14°40′S, 145°28′E) on the GBR from October 1991 to January 1994 revealed that, as is typical of tropical alcyonarian corals, S. elegans is a gonochoric broadcast spawner with a 1:1 sex ratio. Sexual reproduction was closely correlated with colony size, with first reproduction at 13-cm basal stalk circumference for females and 12 cm for males. Oogenesis took 19–24 months, with a new cycle commencing every year, and spermatogenesis took 10–12 months. The majority of gametes were released during the annual austral mass coral spawning event after the full moon in November, but gametes were also released after the full moon in each month between August and February. All autozooid polyps participated in reproduction, but those at the outer edge of a colony released their gametes first. During subsequent months, the polyps closer to the center of the colony released their gametes. This is a novel strategy of gamete release, reported here for the first time, which accommodates the demands of feeding and reproduction in a different way than other corals where individual polyps have separate feeding or reproductive roles. Colonies upstream in the prevailing current spawned up to 1 month earlier than those downstream and ceased 1 month earlier. The mechanism controlling this spatial differentiation in spawning time, repeatedly observed over three seasons, is unknown. Sarcophyton elegans appears to have a dual strategy of providing protection for its gametes by releasing most of them concurrently with the single, annual mass spawning of a large number of cnidarians, while also hedging its bets by individual colonies spawning a fraction of their gametes over an extended period of 6 months.     

Coral identity underpins architectural complexity on Caribbean reefs

The architectural complexity of ecosystems can greatly influence their capacity to support biodiversity and deliver ecosystem services. Understanding the components underlying this complexity can aid the development of effective strategies for ecosystem conservation. Caribbean coral reefs support and protect millions of livelihoods, but recent anthropogenic change is shifting communities toward reefs dominated by stress-resistant coral species, which are often less architecturally complex. With the regionwide decline in reef fish abundance, it is becoming increasingly important to understand changes in coral reef community structure and function. We quantify the influence of coral composition, diversity, and morpho-functional traits on the architectural complexity of reefs across 91 sites at Cozumel, Mexico. Although reef architectural complexity increases with coral cover and species richness, it is highest on sites that are low in taxonomic evenness and dominated by morpho-functionally important, reef-building coral genera, particularly Montastraea. Sites with similar coral community composition also tend to occur on reefs with very similar architectural complexity, suggesting that reef structure tends to be determined by the same key species across sites. Our findings provide support for prioritizing and protecting particular reef types, especially those dominated by key reef-building corals, in order to enhance reef complexity.     

Biannual spawning, rapid larval development and evidence of self-seeding for scleractinian corals at an isolated system of reefs

Some of the most important demographic parameters underlying the resilience of coral communities are determined by their patterns of reproduction. In this study, a variety of methods were used to investigate the patterns of spawning, larval development and dispersal for scleractinian corals at an isolated reef system off northwestern Australia. Two distinct periods of gamete maturation and multi-specific spawning occurred each year, during Spring and Autumn, in contrast to the single season of mass spawning described on most other reefs around Australia. The subsequent rates of embryogenesis and larval development were among the fastest described for corals, with pre-competency periods of approximately 3 days. Within 3 days of spawning, slicks of spawn and current drifters had dispersed up to 5 km, and up to 10 km after 6 days, while the times taken for drifters to travel between adjacent (>240 km) reef systems were similar to or greater than the upper competency periods of most coral larvae. Thus, under these conditions, the entire reef system, and to some extent the reefs within the system, may largely be self-seeded; rates of immigration from other systems are probably insufficient to rapidly increase the recovery of communities within years of a major disturbance. These results have implications for the management of isolated reef systems, highlighting the need to minimize local stressors and maximize community resilience to the increasing scale of disturbance and habitat fragmentation.     

Spatiotemporal variability in recruitment around Iriomote Island, Ryukyu Archipelago, Japan: implications for dispersal of spawning corals

Spatiotemporal recruitment patterns of scleractinian corals were investigated around Iriomote Island, Ryukyu Archipelago, Japan, in relation to adult coral cover in 2005 and 2006. Although almost all corals were broadcasting spawners, the relationship between recruitment and adult coral cover differed among coral families (Acroporidae, Poritidae, and Pocilloporidae), likely due to differences in embryonic development time. For spawning pocilloporid corals, whose larvae develop relatively more rapidly, recruitment was higher at sites where adult coral cover was higher. In contrast, recruitment was not related to adult coral cover in acroporid and poritid corals, whose embryonic development times were relatively slow. Moreover, recruitment of acroporid corals varied between years, and recruitment was greater at leeward compared to windward reefs for a few days after spawning. These results suggest that embryonic development time and wind-driven surface currents affect larval dispersal and subsequent recruitment patterns at a local scale. Based on embryonic development time, some spawning corals are more likely to have higher rates of self-seeding than others. Our results predict that among spawning corals, local populations of acroporid and poritid corals, whose larvae potentially disperse over long distances and recruit in neighboring reefs, are more resilient to local disturbances than those of pocilloporid corals, whose recruitment relies upon local stock.     

Siphon nipping facilitates lethal predation in the clam Mesodesma mactroides (Reeve, 1854) (Mollusca: Bivalva)

In soft sediment marine communities, fishes frequently bite off extended siphons of buried clams; the consequential shortening of the siphon is known to reduce burial depth of the clams, secondarily increasing their vulnerability to lethal excavating predators. In this study, siphon nipping on the yellow clam, Mesodesma mactroides, was simulated by removing the top 6.6–30% of siphons. This caused a burrow reduction in 25–75%, respectively, compared to control individuals with intact siphons, in field and laboratory trials. To examine subsequent consequences of reduced burial depth, we exposed nipped and intact clams to potential predators in the laboratory simulating the observed natural clam abundance. Artificially nipped clams were consumed twice as much as control clams. The present results suggest that sympatric croppers contribute to the stock recovery failure by facilitation of lethal predation and that re-seeding to increase the local abundance of M. mactroides should be an essential aspect of conservation efforts in South America.     

Ecological versatility and the decline of coral feeding fishes following climate driven coral mortality

Coral reefs are under threat due to climate-mediated coral mortality, which affects some reef coral genera more severely than others. The impact this has on coral reef fish is receiving increasing attention, with one focal area assessing impacts on fish that feed directly on live coral. It appears that the more specialised a species of corallivore, the more susceptible it is to coral declines. However data are sparse for the Indian Ocean, and little is known about why some corals are preferentially fed upon over others. Here I assess feeding specialisation in three species of coral feeding butterflyfish in the Chagos Archipelago, central Indian Ocean, assess the food quality of the coral genera they target and document patterns of decline in the Seychelles following a severe coral mortality event. Cheatodon trifascialis was the most specialised coral feeder, preferentially selecting for Acropora corals, however, when Acropora was scarce, individuals showed considerable feeding plasticity, particularly for the dominant Pocillopora corals. C. trifasciatus also preferentially fed on Acropora corals, but fed on a much more diverse suite of corals and also displayed some selectivity for Porites. C. auriga is a facultative corallivore and consumed ∼55% live coral, which lies within the wide range of coral dependence reported for this species. C:N ratio analysis indicated Lobophyllia and Acropora have the highest food quality, with Pocillopora having the lowest, which conforms with diet selection of corallivores and helps explain preferential feeding. Obligate specialist feeders displayed the greatest declines through coral mortality in the Seychelles with obligate generalists also declining substantially, but facultative feeders showing little change. Clearly a greater understanding of the species most vulnerable to disturbance, their habitat requirements and the functional roles they play will greatly assist biodiversity conservation in a changing climate.     

Size-dependent photosynthetic performance in the giant clam <Emphasis Type="Italic">Tridacna maxima</Emphasis>, a mixotrophic marine bivalve

Giant clams form a symbiosis with photosynthetic algae of the genus Symbiodinium that reside in clam mantle tissue. The allometry of symbiont photosynthetic performance was investigated as a mechanism for the increasing percentage of giant clam carbon respiratory requirements provided by symbionts as clam size increases. Chlorophyll fluorescence measurements of symbionts of the giant clam Tridacna maxima were measured during experiments conducted in September of 2009 using specimens 0.5–200 g tissue wet weight (3–25 cm long), collected from waters around southern Taiwan (N 21°36′, E 120°47′) from July to August of 2009. Light-dependent decreases in effective quantum yield (∆F/F _m′) calculated as the noontime maximum excitation pressure over PSII (Q _m), relative electron transport rates (rETR), and dark-adapted maximum quantum yield (F _v/F _m) all varied as a quadratic function of clam size. Both Q _m and rETR increased as clam size increased up to ~10–50 g then decreased as clam size increased. F _v/F _m decreased as clam size increased up to ~5–50 g then increased as clam size increased. Chlorophyll fluorescence measurements of rETR were positively correlated with gross primary production measured during chamber incubations. Overall, symbionts of mid-sized clams ~5–50 g exhibited the highest light-dependent decreases in effective photosynthetic efficiencies, the highest relative electron transport rates, and the lowest maximum photosynthetic efficiencies, and symbiont photosynthetic performance is allometric with respect to host clam size.     

How well do sunken vessels approximate fish assemblages on coral reefs? Conservation implications of vessel-reef deployments

The amount of artificial habitat (termed ??artificial reef??, AR) in marine systems is rapidly increasing, yet the effect of most types of AR on reef communities remains unknown. We examined the role of well-established vessel-reefs in structuring coral reef fish assemblages by comparing assemblages on 7 World War II wrecks (>65?years old) to those on interspersed coral patch reefs of comparable size in a tropical lagoon. Fish abundance, species richness, diversity and feeding guild structure on wrecks were similar to natural reefs; however, species composition differed between the two reef types (R?=?0.189?C0.341, average dissimilarity: 67.3?C68.8?%). Despite being more species-rich and diverse, fish assemblages on larger wrecks were less similar to assemblages on their adjacent natural reefs than smaller wrecks. Wrecks may also have affected fish abundance on adjacent natural reefs, with reefs adjacent to larger wrecks supporting higher abundances than reefs adjacent to smaller wrecks. Our results indicate that increases in vessel-reef habitat may not greatly affect reef fish assemblage parameters, but may affect the relative abundances of particular species.     

Ecology of Echinometra mathaei (Echinoidea: Echinodermata) at Diani Beach,Kenya

Studies were carried out on the inner and outer coral reefs at Diani Beach on the Kenya coast to assess the distribution, density and behaviour of Echinometra mathaei (de Blainville). Transects 1 m wide were run on the two reefs in April, June and September, 1970. Test measurements on representative samples from the animal populations on both reefs were also taken. Direct observations on specimens of E. mathaci in selected rock pools on the outer reef were made to determine their movement, gregariousness, homing and feeding behaviour. Population density was higher on the inner reef furthest from the sea at low tide than on the outer reef. On the submerged inner coral reef at low tide, E. mathaei occurred mainly exposed on the seaweeds, but, on the exposed outer reef, its main niches were crevices in rock pools and under coral ledges. Sizefrequency distributions revealed that smaller individuals occurred on the inner reef and larger ones on the outer reef. The growth rate of E. mathaei was estimated from the positions of modal values, calculated from size-frequency distributions. No gregarious or homing behaviour was observed and, once settled in a suitable crevice, E. mathaei showed little movement.     

Paralytic shellfish toxins sequestered by bivalves as a defense against siphon-nipping fish

Saxidomus giganteus (butter clams), are known to sequester diet-derived paralytic shellfish toxins (PST), highly potent neurotoxins, in their siphons. Captive staghorn sculpins (Leptocotus armatus), a marine fish species known to crop bivalve siphons, developed a significant aversion to siphons from toxic but not non-toxicS. giganteus following a single conditioning feeding of toxic siphon tissues. Control fish showed no aversive response to siphons from non-toxicS. giganteus during 11 feeding sessions over 56 d. Aversive and non-aversive behavior varied with the toxicity of the siphons, but not with the geographic origin of the clams. Both experimental and control fish ate freely and showed no aversion to siphons from toxic littleneck clams (Protothaca staminea). Littleneck clams, unlikeS. giganteus, retain PST in their visceral mass but not in their siphons. Both toxic and non-toxicS. giganteus extended their siphons significantly more often and higher above the sediment surface during dark hours, but toxicS. giganteus extended their siphons higher than non-toxic individuals. These results support the hypothesis that siphon-nipping by fish may have selected for the retention of PST in butter clam siphons as a chemical defense.     

Forest conservation delivers highly variable coral reef conservation outcomes

Coral reefs are threatened by human activities on both the land (e.g., deforestation) and the sea (e.g., overfishing). Most conservation planning for coral reefs focuses on removing threats in the sea, neglecting management actions on the land. A more integrated approach to coral reef conservation, inclusive of land-sea connections, requires an understanding of how and where terrestrial conservation actions influence reefs. We address this by developing a land-sea planning approach to inform fine-scale spatial management decisions and test it in Fiji. Our aim is to determine where the protection of forest can deliver the greatest return on investment for coral reef ecosystems. To assess the benefits of conservation to coral reefs, we estimate their relative condition as influenced by watershed-based pollution and fishing. We calculate the cost-effectiveness of protecting forest and find that investments deliver rapidly diminishing returns for improvements to relative reef condition. For example, protecting 2% of forest in one area is almost 500 times more beneficial than protecting 2% in another area, making prioritization essential. For the scenarios evaluated, relative coral reef condition could be improved by 8-58% if all remnant forest in Fiji were protected rather than deforested. Finally, we determine the priority of each coral reef for implementing a marine protected area when all remnant forest is protected for conservation. The general results will support decisions made by the Fiji Protected Area Committee as they establish a national protected area network that aims to protect 20% of the land and 30% of the inshore waters by 2020. Although challenges remain, we can inform conservation decisions around the globe by tackling the complex issues relevant to integrated land-sea planning.     

Seasonality of coral reproduction in the Dampier Archipelago,northern Western Australia

Coral spawning in Western Australia (WA) occurs predominantly in the austral autumn in contrast to the Great Barrier Reef (GBR) on Australia’s east coast where most spawning occurs in spring. Recent work, however, suggests a second spawning period in northern WA with at least 16 Acropora spp spawning in spring or early summer. This discovery has initiated a re-examination of reproductive seasonality in northern WA, particularly on inshore reefs adjacent to large development projects, such as the site of this study in Mermaid Sound, in the Dampier Archipelago. Three locally abundant taxa, Porites spp, Pavona decussata and Turbinaria mesenterina were sampled monthly from September 2006 to May 2007 to determine sexuality, the mode of reproduction and the time of gamete maturity. All three taxa were gonochoric broadcast spawners. Porites spp. colonies were mature in November and December, P. decussata in March and April. In contrast, most colonies of T. mesenterina contained mature gametes for up to 5 months beginning in November, suggesting either individuals are releasing gametes on multiple occasions, or they retain mature gametes for more than 1 month. Field surveys to determine the reproductive status of the remaining coral assemblage were conducted prior to the full moon in October 2006 and March 2007. Only four species contained mature gametes in October 2006. In contrast, 55 species contained mature gametes in March 2007. We conclude that the major spawning season of corals on shallow-inshore reefs in the Dampier Archipelago is autumn, although taxa that spawn in spring and summer include Porites spp., Acropora spp. and possibly T. mesenterina that are numerically dominant at many of these sites. Consequently, management initiatives to limit the exposure of coral spawn to stressors associated with coastal development may be required in up to five months per year.     

Reproduction and recruitment of scleractinian corals in a high-latitude coral community, Amakusa, southwestern Japan

Reproduction and recruitment in high-latitude coral populations in Japan have been little studied. A comprehensive study of the reproduction and early life history was conducted on nine common scleractinian coral species in Amakusa, southwestern Japan (32°N) from 2001 to 2003 including; (1) fecundity (the proportion of colonies with mature eggs), (2) timing and synchrony of spawning, (3) initial larval settlement pattern, (4) recruitment, (5) post-settlement mortality. The fecundity was high (76.7–100%) in six of seven species examined in 2002 and 2003. Annual spawning of the seven species occurred from mid July to August in 2001–2003, when seawater temperature was at the annual maximum. Spawning was highly synchronised among conspecific colonies and species in 2002 and 2003, with five species spawning five to nine nights after the full moon and another two spawning around the new moon. Temporal patterns of larval settlement of three spawning species during the first 10 days after spawning were similar to those of other spawning species from low latitudes. The number of scleractinian recruits on settlement plates, deployed from July to October (the major recruitment period at the study site), was low (2 recruits/m²) for the three consecutive years. Post-settlement mortality of 1–1.5 month old spat of five species ranged between 88 and 100% over 3–10 months in the field, similar to the values reported for both high and low latitude species (>94–99%). Among the key stages examined, the low recruitment rate may be the most important step in limiting successful reproduction and recruitment of these high-latitude scleractinian populations. The low recruitment rate may be attributable to (1) the reduced influx of larval supply from other coral populations, which are smaller and more isolated at high-latitudes and (2) the longer precompetent larval phase of broadcast-spawning corals which results in an increased chance of larvae being dispersed away from parent populations.     

Using Coral Disease Prevalence to Assess the Effects of Concentrating Tourism Activities on Offshore Reefs in a Tropical Marine Park

Abstract: Concentrating tourism activities can be an effective way to closely manage high‐use parks and minimize the extent of the effects of visitors on plants and animals, although considerable investment in permanent tourism facilities may be required. On coral reefs, a variety of human‐related disturbances have been associated with elevated levels of coral disease, but the effects of reef‐based tourist facilities (e.g., permanent offshore visitor platforms) on coral health have not been assessed. In partnership with reef managers and the tourism industry, we tested the effectiveness of concentrating tourism activities as a strategy for managing tourism on coral reefs. We compared prevalence of brown band disease, white syndromes, black band disease, skeletal eroding band, and growth anomalies among reefs with and without permanent tourism platforms within the Great Barrier Reef Marine Park. Coral diseases were 15 times more prevalent at reefs with offshore tourism platforms than at nearby reefs without platforms. The maximum prevalence and maximum number of cases of each disease type were recorded at reefs with permanently moored tourism platforms. Diseases affected 10 coral genera from 7 families at reefs with platforms and 4 coral genera from 3 families at reefs without platforms. The greatest number of disease cases occurred within the spatially dominant acroporid corals, which exhibited 18‐fold greater disease prevalence at reefs with platforms than at reefs without platforms. Neither the percent cover of acroporids nor overall coral cover differed significantly between reefs with and without platforms, which suggests that neither factor was responsible for the elevated levels of disease. Identifying how tourism activities and platforms facilitate coral disease in marine parks will help ensure ongoing conservation of coral assemblages and tourism.