Associational refuges among corals mediate impacts of a crown-of-thorns starfish Acanthaster planci outbreak Indirect positive interactions in communities

Interactions among coral populations can moderate the impact of coral predator outbreaks, enhancing community resilience and recovery. This study used predator-exclusion cages and neighbour removals in a field experiment to test how indirect interactions between populations of three coral taxa, Acropora, Pocillopora, and Porites, influenced their survival during an outbreak of the crown-of-thorns starfish, Acanthaster planci, in Moorea, French Polynesia. High densities of corals enhanced survival by generating associational refuges: physical structures that impeded Acanthaster and protected corals, and by simple density-dependent prey dilution that reduced predation rates. Acanthaster showed feeding preferences, resulting in varying intensities of predation on corals, which (1) influenced the type and strength of the associational refuge among corals and (2) resulted in significant loss of the competitive dominants to the benefit of the competitive inferiors. The result was a set of indirect positive interactions (IPIs) that prevented Acanthaster from eradicating Acropora and may have enhanced Porites, a relatively weak competitor among corals. IPIs probably play a key role in many ecosystems, especially in coral reefs in which corals act as engineer species, to reduce impacts of perturbations and enhance community resilience. This study illustrates the importance of IPIs in community regulation with a new conceptual model.     

Predator Crown-of-Thorns Starfish (Acanthaster planci) Outbreak,Mass Mortality of Corals,and Cascading Effects on Reef Fish and Benthic Communities

Outbreaks of the coral-killing seastar Acanthaster planci are intense disturbances that can decimate coral reefs. These events consist of the emergence of large swarms of the predatory seastar that feed on reef-building corals, often leading to widespread devastation of coral populations. While cyclic occurrences of such outbreaks are reported from many tropical reefs throughout the Indo-Pacific, their causes are hotly debated, and the spatio-temporal dynamics of the outbreaks and impacts to reef communities remain unclear. Based on observations of a recent event around the island of Moorea, French Polynesia, we show that Acanthaster outbreaks are methodic, slow-paced, and diffusive biological disturbances. Acanthaster outbreaks on insular reef systems like Moorea''s appear to originate from restricted areas confined to the ocean-exposed base of reefs. Elevated Acanthaster densities then progressively spread to adjacent and shallower locations by migrations of seastars in aggregative waves that eventually affect the entire reef system. The directional migration across reefs appears to be a search for prey as reef portions affected by dense seastar aggregations are rapidly depleted of living corals and subsequently left behind. Coral decline on impacted reefs occurs by the sequential consumption of species in the order of Acanthaster feeding preferences. Acanthaster outbreaks thus result in predictable alteration of the coral community structure. The outbreak we report here is among the most intense and devastating ever reported. Using a hierarchical, multi-scale approach, we also show how sessile benthic communities and resident coral-feeding fish assemblages were subsequently affected by the decline of corals. By elucidating the processes involved in an Acanthaster outbreak, our study contributes to comprehending this widespread disturbance and should thus benefit targeted management actions for coral reef ecosystems.     

Competitors as accomplices: seaweed competitors hide corals from predatory sea stars

Indirect biotic effects arising from multispecies interactions can alter the structure and function of ecological communities—often in surprising ways that can vary in direction and magnitude. On Pacific coral reefs, predation by the crown-of-thorns sea star, Acanthaster planci, is associated with broad-scale losses of coral cover and increases of macroalgal cover. Macroalgal blooms increase coral–macroalgal competition and can generate further coral decline. However, using a combination of manipulative field experiments and observations, we demonstrate that macroalgae, such as Sargassum polycystum, produce associational refuges for corals and dramatically reduce their consumption by Acanthaster. Thus, as Acanthaster densities increase, macroalgae can become coral mutualists, despite being competitors that significantly suppress coral growth. Field feeding experiments revealed that the protective effects of macroalgae were strong enough to cause Acanthaster to consume low-preference corals instead of high-preference corals surrounded by macroalgae. This highlights the context-dependent nature of coral–algal interactions when consumers are common. Macroalgal creation of associational refuges from Acanthaster predation may have important implications for the structure, function and resilience of reef communities subject to an increasing number of biotic disturbances.     

Changes in coral assemblages during an outbreak of Acanthaster planci at Lizard Island, northern Great Barrier Reef (1995–1999)

Population outbreaks of crown-of-thorns starfish (Acanthaster planci L.) represent one of the most significant biological disturbances on tropical coral reefs and have the potential to devastate coral communities, thereby altering the biological and physical structure of reef habitats. This study reports on changes in area cover, species diversity and taxonomic composition of corals during an outbreak of A. planci at Lizard Island, in the northern Great Barrier Reef, Australia. Mean coral cover declined by 28.8% across ten locations studied. However, densities of A. planci, and their effects on local coral assemblages, were very patchy. Declines in coral cover were mostly due to the selective removal of certain coral taxa (mainly Acropora and Pocilloporidae corals); such that the greatest coral loss occurred at locations with highest initial cover of preferred coral prey. Most notably, coral assemblages in back-reef locations were transformed from topographically complex staghorn Acropora-dominated habitats, to relatively depauperate assemblages dominated by alcyonacean soft corals. Although coral loss was greatest among formerly dominant taxa (especially Acropora), effects were sufficiently widespread across different coral taxa, such that overall coral diversity tended to decline. Clearly, moderate outbreaks of A. planci have the potential to greatly alter community structure of coral communities even if they do not devastate live corals. Recovery in this instance is expected to be very rapid given that all coral taxa persisted, and effects were greatest among fast growing corals.     

Defense by symbiotic crustacea of host corals elicited by chemical cues from predator

Summary Observations and experiments carried out on a coral reef off the Pacific coast of Panamá demonstrated that shrimp (Alpheus lottini) and crab (Trapezia spp.) symbionts that protect their host coral (Pocillopora elegans) can detect an approaching sea star predator (Acanthaster planci) by chemical cues. Simulated feeding attacks by Acanthaster in sealed transparent bags elicited only 0.5 defensive responses (snipping at spines and tube feet, jerking the sea star, and snapping) per 3 min; defensive behavior increased significantly to 4 and 5 responses, respectively, for Acanthaster in perforated bags and for Acanthaster in direct contact with coral. Neutralized (boiled) Acanthaster elicited only 3 defensive interactions per 3 min compared with 12 interactions for live Acanthaster. Simulated feeding attacks by Oreaster, a non-corallivorous sea star, elicited only 0.5 defensive responses per 3 min, whereas Oreaster introduced with Acanthaster water increased the level of defensive responses to 7. These results suggest that chemical, and to a lesser extent visual (physical presence and movements of sea star), cues stimulate the defensive behavior of the symbiotic crustaceans. The ability to detect a predator at a distance is probably advantageous because in responding only to an actual threat it minimizes the time the defending symbionts spend in an exposed position on the terminal branches of the host coral and because it alerts the crustaceans to sea stars feeding at night.     

Biochemical investigation of two responses involved in the feeding behaviour of Acanthaster planci (L). I. Assay methods and preliminary results

Material obtained by simple biochemical fractionation of aqueous extracts of coral has been tested for its ability to induce responses normally associated with feeding on live corals in the crown-of-thorns starfish, Acanthaster planci (L.) With the use of a new assay method, it has been shown that both dialysable and non-dialysable components of aqueous coral extract cause cessation of movement, settlement, and eversion of the stomach as if over a whole coral. A second response, apparently of avoidance, seen as a starfish approaches a coral prior to feeding, has also been examined; it is evoked by the dialysable fraction of coral extract.     

Within-colony feeding selectivity by a corallivorous reef fish: foraging to maximize reward?

Foraging theory predicts that individuals should choose a prey that maximizes energy rewards relative to the energy expended to access, capture, and consume the prey. However, the relative roles of differences in the nutritive value of foods and costs associated with differences in prey accessibility are not always clear. Coral‐feeding fishes are known to be highly selective feeders on particular coral genera or species and even different parts of individual coral colonies. The absence of strong correlations between the nutritional value of corals and prey preferences suggests other factors such as polyp accessibility may be important. Here, we investigated within‐colony feeding selectivity by the corallivorous filefish, Oxymonacanthus longirostris, and if prey accessibility determines foraging patterns. After confirming that this fish primarily feeds on coral polyps, we examined whether fish show a preference for different parts of a common branching coral, Acropora nobilis, both in the field and in the laboratory experiments with simulated corals. We then experimentally tested whether nonuniform patterns of feeding on preferred coral species reflect structural differences between polyps. We found that O. longirostris exhibits nonuniform patterns of foraging in the field, selectively feeding midway along branches. On simulated corals, fish replicated this pattern when food accessibility was equal along the branch. However, when food access varied, fish consistently modified their foraging behavior, preferring to feed where food was most accessible. When foraging patterns were compared with coral morphology, fish preferred larger polyps and less skeletal protection. Our results highlight that patterns of interspecific and intraspecific selectivity can reflect coral morphology, with fish preferring corals or parts of coral colonies with structural characteristics that increase prey accessibility.     

Biochemical investigation of two responses involved in the feeding behaviour of Acanthaster planci (L.). III. Food preferences

The arm-withdrawal and settlement responses associated with feeding in Acanthaster planet (L.) are elicited at differing intensities by various species of coral and by extracts of these corals. There is no clear correlation between the strengths of the two responses. The preferences shown by A. planci for certain species of whole coral depend on the previous dietary experience of the starfish, and repeated presentation of an unfamiliar coral may increase its acceptability as food.     

Corallivory in tubelip wrasses: diet,feeding and trophic importance

This paper describes a 2 month study of the patterns of abundance, feeding pressure, diet and feeding selectivity in corallivorous tubelip wrasses (Labridae), rarely studied, yet widespread and abundant group of corallivores on Indo‐Pacific coral reefs. The relative abundance and feeding pressure of corallivorous wrasses and butterflyfishes (Chaetodontidae) in Kimbe Bay, Papua New Guinea, were compared. Overall, tubelip wrasses were more than twice as abundant as corallivorous butterflyfishes and accounted for three times as many feeding bites on corals. The three most abundant tubelip wrasses (yellowtail tubelip Diproctacanthus xanthurus, Allen's tubelip Labropsis alleni and the tubelip wrasse Labrichthys unilineatus) were all obligate corallivores taking > 97% of bites from the surface of live corals. Labropsis alleni and D. xanthurus were highly selective, consuming preferred prey species in proportions significantly higher than expected given their availability. In contrast, L. unilineatus was fairly non‐selective and consumed most corals in direct accordance with their availability. As coral predators, tubelip wrasses are highly comparable to coral‐feeding butterflyfishes in the coral species consumed, range of dietary specialization and their reliance on live coral. Tubelip wrasses, however, may supersede butterflyfishes as the predominant corallivorous family in some Indo‐Pacific locations, and coral‐feeding tubelip wrasses are likely to be severely affected by coral decline.     

Predation on crown-of-thorns starfish larvae by damselfishes

Examining the functional response of predators can provide insight into the role of predation in structuring prey populations and ecological communities. This study explored feeding behaviour and functional responses of planktivorous damselfishes when offered captive reared larvae of crown-of-thorns starfish, Acanthaster sp., with the aim of determining whether these predators could ever play a role in moderating outbreaks of Acanthaster sp. We examined predatory behaviour of 11 species of planktivorous damselfish, testing: (1) the relationship between predator size and predation rate, both within and among fish species; (2) consumption rates on larvae of Acanthaster sp. versus larvae of a common, co-occurring coral reef asteroid Linckia laevigata; (3) maximal feeding rates upon both Acanthaster sp. and L. laevigata; and (4) functional responses of planktivorous fishes to increasing densities of Acanthaster sp. Consumption rates of crown-of-thorns larvae by damselfishes were independent of predator size; however, there was a significant negative relationship between predator size and consumption rate of L. laevigata, when pooling across all predatory species. Some damselfishes, including Acanthochromis polyacanthus and Amblyglyphidodon curacao, consumed larval Acanthaster sp. at a greater rate than for L. laevigata. Most predatory species (all except A. curacao and Pomacentrus amboinensis) exhibited a Type II functional response whereby the increasing feeding rate decelerated with increasing prey density. In addition to revealing that a wide range of planktivorous fishes can prey upon larvae of Acanthaster sp., these data suggest that planktivorous damselfishes may have the capacity to buffer against population fluctuations of Acanthaster sp. Importantly, predators with Type II functional responses often contribute to stability of prey populations, though planktivorous fishes may be swamped by an abnormally high influx of larvae, potentially contributing to the characteristic population fluctuations of Acanthaster sp.     

Consumption of coral propagules represents a significant trophic link between corals and reef fish

Mass spawning of corals provides a large seasonal pulse of high-energy prey that potentially benefits reef fish that are capable of capturing and digesting coral propagules. This study examines the range of fish species that consume coral propagules and also tests whether reef fish experience a significant increase in physiological condition when feeding on coral propagules. Thirty-six species of diurnal reef fish were seen to consume coral propagules released during mass coral spawning. Stomach content analyses of three reef fish species (Pomacentrus moluccensis, Abudefduf whitleyi, and Caesio cunning) revealed that both P. moluccensis and A. whitleyi feed almost exclusively on coral propagules during mass coral spawning. Fish feeding extensively on coral propagules also amassed considerable lipid stores, which could greatly improve the quality and survivorship of their progeny. In contrast, C. cunning consumed only very small quantities of coral propagules, and showed no detectable change in lipid stores during the course of the study. This study provides the first direct evidence that reef fish benefit from mass coral spawning, and reveals a potentially significant trophic link between scleractinian corals and reef fish. Accepted: 9 June 2000     

Near-future ocean acidification enhances the feeding rate and development of the herbivorous juveniles of the crown-of-thorns starfish, <Emphasis Type="Italic">Acanthaster planci</Emphasis>

Population outbreaks of the corallivorous crown-of-thorns starfish, Acanthaster planci, are a major contributor to the decline in coral reef across the Indo-Pacific. The success of A. planci and other reef species in a changing ocean will be influenced by juvenile performance because the naturally high mortality experienced at this sensitive life history stage maybe exacerbated by ocean warming and acidification. We investigated the effects of increased temperature and acidification on growth of newly metamorphosed juvenile A. planci and their feeding rates on crustose coralline algae (CCA) during the initial herbivorous phase of their life history. The juveniles were exposed to three temperature (26, 28, 30 °C) and three pH (NIST scale: 8.1, 7.8, 7.6) levels in a flow-through cross-factorial experiment. There were positive but independent effects of warming and acidification on juvenile growth and feeding. Early juveniles were highly tolerant to moderate increases in temperature (+2 °C above ambient) with the highest growth at 30 °C. Growth and feeding rates of A. planci on CCA were highest at pH 7.6. Thus, ocean warming and acidification may enhance the success of A. planci juveniles. In contrast to its coral prey, at this vulnerable developmental stage, A. planci appears to be highly resilient to future ocean change. Success of juveniles in a future ocean may have carry-over effects into the coral-eating life stage, increasing the threat to coral reef systems.     

Parrotfish predation on massive Porites on the Great Barrier Reef

Parrotfish grazing scars on coral colonies were quantified across four reef zones at Lizard Island, Northern Great Barrier Reef (GBR). The abundance of parrotfish grazing scars was highest on reef flat and crest, with massive Porites spp. colonies having more parrotfish grazing scars than all other coral species combined. Massive Porites was the only coral type positively selected for grazing by parrotfishes in all four reef zones. The density of parrotfish grazing scars on massive Porites spp., and the rate of new scar formation, was highest on the reef crest and flat, reflecting the lower massive Porites cover and higher parrotfish abundance in these habitats. Overall, it appears that parrotfish predation pressure on corals could affect the abundance of preferred coral species, especially massive Porites spp, across the reef gradient. Parrotfish predation on corals may have a more important role on the GBR reefs than previously thought.     

Homing behaviour by destructive crown-of-thorns starfish is triggered by local availability of coral prey

Corallivorous crown-of-thorns starfishes (Acanthaster spp.) can decimate coral assemblages on Indo-Pacific coral reefs during population outbreaks. While initial drivers of population irruptions leading to outbreaks remain largely unknown, subsequent dispersal of outbreaks appears coincident with depletion of coral prey. Here, we used in situ time-lapse photography to characterize movement of the Pacific crown-of-thorns starfish (Acanthaster cf. solaris) in the northern and southern Great Barrier Reef in 2015, during the fourth recorded population outbreak of the starfish, but prior to widespread coral bleaching. Daily tracking of 58 individuals over a total of 1117 h revealed all starfish to move a minimum of 0.52 m, with around half of all tracked starfish showing negligible daily displacement (less than 1 m day⁻¹), ranging up to a maximum of 19 m day⁻¹. Movement was primarily nocturnal and daily displacement varied spatially with variation in local availability of Acropora spp., which is the preferred coral prey. Two distinct behavioural modes emerged: (i) homing movement, whereby tracked paths (as tested against a random-walk-model) involved short displacement distances following distinct ‘outward'' movement to Acropora prey (typically displaying ‘feeding scars'') and ‘homebound'' movement to nearby shelter; versus (ii) roaming movement, whereby individuals showed directional movement beyond initial tracking positions without return. Logistic modelling revealed more than half of all tracked starfish demonstrated homing when local abundance (percentage cover) of preferred Acropora coral prey was greater than 33%. Our results reveal facultative homing by Acanthaster with the prey-dependent behavioural switch to roaming forays providing a mechanism explaining localized aggregations and diffusion of these population irruptions as prey is locally depleted.     

Prey selectivity affects reproductive success of a corallivorous reef fish

Most animals consume a narrower range of food resources than is potentially available in the environment, but the underlying basis for these preferences is often poorly understood. Foraging theory predicts that prey selection should represent a trade-off between prey preferences based on nutritional value and prey availability. That is, species should consume preferred prey when available, but select less preferred prey when preferred prey is rare. We employed both field observation and laboratory experiments to examine the relationship between prey selection and preferences in the obligate coral-feeding filefish, Oxymonacanthus longirostris. To determine the drivers of prey selection, we experimentally established prey preferences in choice arenas and tested the consequences of prey preferences for key fitness-related parameters. Field studies showed that individuals fed almost exclusively on live corals from the genus Acropora. While diet was dominated by the most abundant species, Acropora nobilis, fish appeared to preferentially select rarer acroporids, such as A. millepora and A. hyacinthus. Prey choice experiments confirmed strong preferences for these corals, suggesting that field consumption is constrained by availability. In a longer-term feeding experiment, reproductive pairs fed on non-preferred corals exhibited dramatic reductions to body weight, and in hepatic and gonad condition, compared with those fed preferred corals. The majority of pairs fed preferred corals spawned frequently, while no spawning was observed for any pairs fed a non-preferred species of coral. These experiments suggest that fish distinguish between available corals based on their intrinsic value as prey, that reproductive success is dependent on the presence of particular coral species, and that differential loss of preferred corals could have serious consequences for the population success of these dietary specialists.     

Specialization in habitat use by coral reef damselfishes and their susceptibility to habitat loss

While it is generally assumed that specialist species are more vulnerable to disturbance compared with generalist counterparts, this has rarely been tested in coastal marine ecosystems, which are increasingly subject to a wide range of natural and anthropogenic disturbances. Habitat specialists are expected to be more vulnerable to habitat loss because habitat availability exerts a greater limitation on population size, but it is also possible that specialist species may escape effects of disturbance if they use habitats that are generally resilient to disturbance. This study quantified specificity in use of different coral species by six coral‐dwelling damselfishes (Chromis viridis, C. atripectoralis, Dascyllus aruanus, D. reticulatus, Pomacentrus moluccensis, and P. amboinensis) and related habitat specialization to proportional declines in their abundance following habitat degradation caused by outbreaks of the coral eating starfish, Acanthaster planci. The coral species preferred by most coral‐dwelling damselfishes (e.g., Pocillopora damicornis) were frequently consumed by coral eating crown‐of‐thorns starfish, such that highly specialized damselfishes were disproportionately affected by coral depletion, despite using a narrower range of different coral species. Vulnerability of damselfishes to this disturbance was strongly correlated with both their reliance on corals and their degree of habitat specialization. Ongoing disturbances to coral reef ecosystems are expected, therefore, to lead to fundamental shifts in the community structure of fish communities where generalists are favored over highly specialist species.     

Microhabitat use and prey selection of the coral-feeding snail <Emphasis Type="Italic">Drupella cornus</Emphasis> in the northern Red Sea

Corallivorous gastropods of the genus Drupella are known for population outbreaks throughout the Indo-Pacific region. Despite their potential to destroy wide areas of coral reef, prey preferences have never been analyzed with respect to prey availability, and juvenile ecology and food selectivity remain largely unknown. Here, the influence of water depth, coral abundance, colony shape, prey species, and intraspecific attraction among snails on distribution patterns, prey selection, and microhabitat use of D. cornus was studied in the northern Red Sea. Special emphasis was put on ontogenetic differences. The snails were most abundant in the shallowest reef zone (1 m depth). Adults were associated with several substrates and coral growth forms, whereas juveniles were highly cryptic and restricted to live branching corals. The genus Acropora was significantly preferred over other acroporid and pocilloporid corals. As revealed by resource selection ratios, Acropora acuminata was preferred by juveniles, A. selago by adults. In aquarium experiments, intraspecific attraction was high among both life stages. Overall, significant differences in juvenile and adult microhabitat and prey use suggest that juveniles have more specific habitat requirements, and indicate ecological impacts on coral communities different from that of adults. Prey preferences seem to depend on both coral genus and colony shape. Acropora corals provide the best combination of food and shelter and therefore determine distribution patterns of D. cornus.     

A gonad-stimulating peptide of the crown-of-thorns starfish,Acanthaster planci

The crown-of thorns starfish, Acanthaster planci, has been blamed for coral mortality in a large number of coral reef systems in the Indo-Pacific region. Because population outbreaks of A. planci are closely related to reproduction, it is important to examine the mechanism of reproductive control in this starfish. Previously, a relaxin-like gonad-stimulating peptide (RGP) in starfish Asterina pectinifera has been identified as the gonadotropin responsible for final gamete maturation. On the basis of homology research on RGP cDNAs from several species, this study was carried out to identify gonadotropin in A. planci. The cDNA sequence of RGP was determined using a RACE product of mRNA from the radial nerves of A. planci. The coding DNA sequence consisted of 351 base pairs with an open reading frame encoding a peptide of 116 amino acids (aa), including a signal peptide (29 aa), B-chain (19 aa), C-peptide (44 aa), and A-chain (24 aa). The chemical structure of A. planci RGP was exactly the same as that of A. pectinifera RGP. Furthermore, synthetic RGP could induce gamete spawning and oocyte maturation in the ovarian fragments of A. planci. This strongly suggested that the RGP is a gonadotropin in A. planci.     

Sponge borehole size as a relative measure of bioerosion and paleoproductivity

Bioerosion intensity has been proposed as a measure of paleoproductivity in fossil reefs, but it is difficult to measure directly because fossil corals are often incomplete and because it is difticult to infer the length of time a given coral was exposed to bioeroding organisms. Both nutrient availability and taphonomic factors can affect bioerosion intensity as measured in dead corals. Here, we examine these two effects separately using data from previous studies on bioerosion in modern and fossil corals. Size of individual sponge borings accurately reflects total bioerosion in modern massive and branching corals on the Great Barrier Reef. Total bioerosion in both massive and branching corals decreases outward across the continental shelf, paralleling trends in nutrient availability. Size of individual Cliothosa hancocki borings decreases across the shelf in branching Acropora but not in massive Porites. Fossil sponge borings Entobia convoluta and Uniglobites glomerata in massive corals from Oligocene and Miocene reefs in Puerto Rico are smallest in Oligocene shelf-edge reefs, intermediate in Oligocene patch reefs, and largest in Miocene patch reefs. Both facies-related influence, represented by Oligocene shelf-edge reefs vs. Oligocene patch reefs, and nutrient-related influence, represented by Oligocene vs. Miocene patch reefs, were reflected in the size of sponge boreholes. Size of sponge borings also varies among species of host corals, apparently in relation to skeletal architecture. Borehole size is inversely correlated with skeletal density as measured by the relative proportion of skeleton and pore space in transverse thin section. There is a weak positive correlation between borehole size and corallite diameter. These findings contradict reported positive correlations between total bioerosion and bulk density in modern corals. Borehole size appears accurately to reflect intensity of total internal bioerosion in fossil corals. Facies-controlled taphonomic overprints and influence of skeletal differences between coral species limit the use of sponge borehole size to a rough indicator of paleoproductivity in fossil coral reef environments.     

Recent disturbances augment community shifts in coral assemblages in Moorea, French Polynesia

Coral reefs are often subject to disturbances that can cause enduring changes in community structure and abundance of coral reef organisms. In Moorea, French Polynesia, frequent disturbances between 1979 and 2003 caused marked shifts in taxonomic composition of coral assemblages. This study explores recent changes in live cover and taxonomic structure of coral communities on the north coast of Moorea, French Polynesia, to assess whether coral assemblages are recovering (returning to a previous Acropora-dominated state) or continuing to move towards an alternative community structure. Coral cover declined by 29.7% between July 2003 and March 2009, mostly due to loss of Acropora and Montipora spp. Coral mortality varied among habitats, with highest levels of coral loss on the outer reef slope (7–20 m depth). In contrast, there was limited change in coral cover within the lagoon, and coral cover actually increased on the reef crest. Observed changes in coral cover and composition correspond closely with the known feeding preferences and observed spatial patterns of Acanthaster planci L., though observed coral loss also coincided with at least one episode of coral bleaching, as well as persistent populations of the corallivorous starfish Culcita novaeguineae Muller & Troschel. While climate change poses an important and significant threat to the future structure and dynamics coral reef communities, outbreaks of A. planci remain a significant cause of coral loss in Moorea. More importantly, these recent disturbances have followed long-term shifts in the structure of coral assemblages, and the relative abundance of both Pocillopora and Porites continue to increase due to disproportionate losses of Acropora and Montipora. Moreover, Pocillopora and Porites dominate assemblages of juvenile corals, suggesting that there is limited potential for a return to an Acropora-dominated state, last recorded in 1979.