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Population irruptions of the western Pacific crown-of-thorns sea star (Acanthaster sp.) are a perennial threat to coral reefs and may be initiated by fluctuations in reproductive or settlem...

Climate change and population irruptions of crown-of-thorns sea stars (Acanthaster sp.) are two of the most pervasive threats to coral reefs. Yet there has been little consideration regardi...

Crown-of-thorns sea stars (Acanthaster sp.) are among the most studied coral reef organisms, owing to their propensity to undergo major population irruptions, which contribute to significant coral loss and reef degradation throughout the Indo-Pacific. However, there are still important knowledge gaps pertaining to the biology, ecology, and management of Acanthaster sp. Renewed efforts to advance understanding and management of Pacific crown-of-thorns sea stars (Acanthaster sp.) on Australia’s Great Barrier Reef require explicit consideration of relevant and tractable knowledge gaps. Drawing on established horizon scanning methodologies, this study identified contemporary knowledge gaps by asking active and/or established crown-of-thorns sea star researchers to pose critical research questions that they believe should be addressed to improve the understanding and management of crown-of-thorns sea stars on the Great Barrier Reef. A total of 38 participants proposed 246 independent research questions, organized into 7 themes: feeding ecology, demography, distribution and abundance, predation, settlement, management, and environmental change. Questions were further assigned to 48 specific topics nested within the 7 themes. During this process, redundant questions were removed, which reduced the total number of distinct research questions to 172. Research questions posed were mostly related to themes of demography (46 questions) and management (48 questions). The dominant topics, meanwhile, were the incidence of population irruptions (16 questions), feeding ecology of larval sea stars (15 questions), effects of elevated water temperature on crown-of-thorns sea stars (13 questions), and predation on juveniles (12 questions). While the breadth of questions suggests that there is considerable research needed to improve understanding and management of crown-of-thorns sea stars on the Great Barrier Reef, the predominance of certain themes and topics suggests a major focus for new research while also providing a roadmap to guide future research efforts.

Pacific crown-of-thorns starfish (Acanthaster cf. solaris) are known to be widely distributed, and previous studies (showing limited genetic structure) suggest that there are high levels of connectivity at regional scales. It is possible, however, that methods used in previous studies (e.g., microsatellites) did not effectively resolve genetic differentiation and structure for crown-of-thorns starfish. This study examined patterns of genetic structure for populations of the A. cf. solaris in the Ryukyu Archipelago and at Miyazaki, Japan, using restriction-site-associated DNA sequencing (RADseq) analysis, to identify genome-wide single nucleotide polymorphism (SNP) loci to examine genetic diversity and gene flow of CoTS populations. We obtained 186 biallelic SNPs completely shared among 33 individuals by utilizing the published genome sequence of CoTS. Population genomic analysis with biallelic SNPs confirmed that there is limited genetic differentiation and seemingly strong connectivity and gene flow among CoTS populations in the Ryukyu Archipelago and at Miyazaki, Japan. Our findings likely reflect the rapid range expansion of CoTS through southern Japan or panmixia facilitated by the northward flowing Kuroshio Current.

In the last decades, managers and local communities have been turning to active restoration as a mechanism to recover damaged reefs affected at an unprecedented rate because of climate change, anthropogenic activities, and natural events, such as outbreaks of the crown-of-thorns starfish (COTS) Acanthaster spp. A coral restoration experiment was conducted in the southern Gulf of California (24°N, 110°W) starting in December 2017. By early 2018, unusually high numbers of Acanthaster cf. solaris appeared at the restoration plots causing significant coral mortality. Fragment survivorship was significantly influenced by site with corals at Roca Swan showing a longer survival probability time [297.43 (SE 16.38) d] compared to El Corralito [133.81 (SE 7.73) d]. From April 2018 to June 2019, average abundance of A. cf. solaris had surpassed 800 ind ha–1 at three sites, and their feeding resulted in high fragment mortality ranging from 39% at Roca Swan to 88% at El Corralito—a strong contrast to other restored reefs along the eastern Pacific where starfish were absent and annual fragment mortality was A. cf. solaris outbreak in 2017–2018, severely hindering success of coral restoration programs.

Resumen Introducción: Una de las amenazas actuales para los arrecifes de coral es la pérdida de cobertura de coral vivo. La depredación masiva asociada con los brotes poblaciones de la estrella corona de espinas, amenaza la permanencia de los arrecifes. Desde 2017, ha habido evidencia de un incremento en la densidad de el asteroideo y de un incremento en la mortalidad coralina en el sur del golfo de California. Objetivo: Describir el primer evento de depredación sobre corales por Acanthaster planci en la isla Espíritu Santo, golfo de California, México. Métodos: visitamos el arrecife El Corralito nueve veces entre 2017 y 2019, realizando censos visuales en transectos errantes y de banda (25 x 3m) para determinar la densidad de la estrella, su comportamiento y daño. Monitoreamos la depredación sobre las colonias de Pavona gigantea durante siete meses. Resultados: La densidad promedio de individuos en El Corralito en 2018-19 fue 607.40 ind/ha. La depredación del asteoroideo fue evidente en más del 60% de los individuos diagnosticados (N=827), con las afectaciones más grandes en las colonias de P. gigantea (80%). El 63% de los 129 de los individuos del asteroideo observados estaban alimentándose principalmente sobre Porites panamensis (68% de los casos). Las lesiones agudas indican que el evento de depredación está activo. En 81 días, se perdieron 25m 2 de una de las colonias monitoreadas. Conclusiones: Existe un evento de brote poblacional activo con consecuencias negativas significativas sobre el arrecife El Corralito, el cual puede ocasionar pérdida de cobertura de coral en pocos meses. El monitoreo y el manejo son necesarios para establecer las razones que llevaron a brote poblacional y para controlarlo. Abstract Introduction: One of the current threats to coral reefs is the loss of live coral cover. Massive predation associated with population outbreaks of the crown of thorns seastar, threatens the permanence of the reefs. Since 2017, there has been evidence of an increase in the density of the asteroid and an increase in coral mortality in the southern gulf of California. Objective: To describe the first event of massive predation on corals by Acanthaster planci in Espiritu Santo Island, gulf of California, Mexico. Methods: We visited El Corralito reef nine times between 2017 and 2019, using errant and band transect (25 x 3 m) visual censuses to determine Star density, behavior and damage. Over seven months, we monitored predation on colonies of Pavona gigantea. Results: The mean density of individuals in El Corralito in 2018-2019 was 607.40 ind/ha. Asteroid predation was evident in more than 60 % of diagnosed individuals (N = 827), with the greatest affectations in the P. gigantea colonies (80 %). 63 % of the 129 observed asteroid individuals were feeding mainly on Porites panamensis (68 % of cases). Acute injuries indicate that the predation event is active. In 81 days, 25 m2 of one of the monitored colonies were lost. Conclusions : There is an active outbreak event with significant negative consequences on the El Corralito reef, which could determine the loss of coral cover in a few months. Monitoring and management are required to establish the reasons that led to the outbreak and to control it.

Environmental DNA (eDNA) represents an emerging opportunity for species monitoring in the marine environment. One aspect that poses challenges is the ability to detect target DNA without the complexity of specialized laboratory equipment. Lateral flow is an analytical technique that has been adopted in point‐of‐care diagnostics for human, veterinary, and agricultural health. Here, we aim to use lateral flow assay as a detection method for eDNA monitoring using a commercially available nucleic acid lateral flow device (PCRD™) in combination with previously developed species‐specific mtDNA primers. Episodic population explosions of coral‐eating crown‐of‐thorns sea star (CoTS) contribute significantly to the coral reef crisis on tropical Pacific coral reefs. Laboratory testing revealed our lateral flow assay developed for CoTS was as sensitive as digital droplet PCR and able to detect

This study was aimed to determine the abudance crown of thorn starfish (Acanthaster planci L.) in the Gulf of Tomini, Central Sulawesi. The study was conducted in February─April 2019 preliminary method used a purposive sampling (determining the sampling point for transect sampling) and the belt transect method which is 20 x 2 m. Sampling of A. planci was carried out at 4 stations. Data collected were the number of individuals, measurement of environmental parameters including Temperature, pH, Salinity, DO and Substrate observations on habitat. Based on the results of the study, 48 individuals at all stations and the abundance of A. planci in the Gulf of Tomini, Central Sulawesi were in the natural/normal category with a value of 0.01 ind/m2─0.25 ind/m2.

Aquatic stressors are known to cause biological impairment that can result in biodiversity loss in several Marine Pro-tected Areas (MPA), including in Menjangan Island, West Bali National Park. The objectives of this study wereto cor-relate the changes in water quality parameters with the biological effect of Crown-of-Thorns starfish (CoTS) population dynamics and to assess the most applicable parameters for continuous environmental monitoring. Field observations and surveys were conducted three times in 2017, during the wet season, dry season and season transition, in order to assess the effect of seasonal variability. Redundancy Analysis (RDA) was performed to determine the relationship be-tween water quality parameters (temperature, dissolved oxygen, pH, salinity, turbidity, total suspended solids, dissolved inorganic nitrogen and phosphate, and chlorophyll-a) and phytoplankton as the indicator of CoTS larvae food supply. The results demonstrate that salinity, turbidity, and dissolved inorganic nitrogen (DIN) are responsible for the 47.7% of phytoplanktonvariation, which supports the hypothesis of nutrient enrichment as the trigger of CoTS population in-crease. CoTS outbreak is predicted to occur during the wet season, in areas with high salinity, moderate turbidity, and high DIN, so the outbreak may be related to a high rainfall rate that deliver a high nutrient loading on this region and thus management actions can be initiated during this specific period.

The crown-of-thorns starfish (COTS), Acanthaster cf. solaris, is one of the main contributors to declines in coral cover on the Great Barrier Reef (GBR) and remains one of the major acute disturbances on coral reefs throughout much of the Indo-Pacific. Extensive control programs on the GBR involve manual culling of COTS in the field, and research is needed to inform these management efforts. Data from the Great Barrier Reef Marine Park Authority’s (GBRMPA) COTS control program provide near-real-time CPUE (Catch-Per-Unit-Effort, COTS culled per minute) data ideal for operational decision-making but these must be converted to density estimates before they can be related to ecological status of reefs or incorporated into ecological models. We developed conversions between common COTS field survey methods (i.e. manta tow, SCUBA transect searches) and COTS control program CPUE data using estimates of sightability and detectability. We used a population model and COTS size-structure data from COTS control program culling efforts to estimate that, on average, only 19% of 1-yr-old COTS (1–15 cm) are available to be culled. Finally, we developed a CPUE-COTS density relationship to estimate the threshold levels of COTS that prevent net growth of hard corals. Culling programs should therefore aim to achieve CPUEs below these ecological thresholds in order to effectively promote coral growth and recovery. These ecologically sustainable thresholds of COTS density varied depending on hard coral cover. For example, for 35% fast-growing coral cover, COTS culling needs to continue until CPUE decreases to below 0.05 COTS/min (1 COTS per 20 min) in order to prevent coral decline, whereas if coral cover is higher (80%), then a higher target threshold CPUE of ca. 0.08 COTS/min (ca. 3 COTS per 40 min) may be ecologically sustainable. These estimates underpin the current pest management rules being implemented by the GBRMPA in its COTS control program.

Crown-of-thorns starfish, Acanthaster planci (COTS), are common in coral reefs of Indo-Pacific Ocean. Since they are highly fecund predators of corals, periodic outbreaks of COTS cause substantial loss of healthy coral reefs. Using complete mitochondrial DNA sequences, we here examined how COTS outbreaks in the Ryukyu Archipelago, Japan are reflected by the profile of their population genetics. Population genetics of the blue starfish, Linckia laevigata, which lives in the Ryukyu Archipelago, but not break out and the northern Pacific sea star, Asterias amurensis, which lives in colder seawater around the main Islands of Japan, were also examined as controls. Our results showed that As. amurensis has at least two local populations that diverged approximately 4.7 million years ago (MYA), and no genetic exchanges have occurred between the populations since then. Linckia laevigata shows two major populations in the Ryukyu Archipelago that likely diverged ∼6.8 MYA. The two populations, each comprised of individuals collected from coast of the Okinawa Island and those from the Ishigaki Island, suggest the presence of two cryptic species in the Ryukyu Archipelago. On the other hand, population genetics of COTS showed a profile quite different from those of Asterias and Linckia. At least five lineages of COTS have arisen since their divergence ∼0.7 MYA, and each of the lineages is present at the Okinawa Island, Miyako Island, and Ishigaki Island. These results suggest that COTS have experienced repeated genetic bottlenecks that may be associated with or caused by repeated outbreaks.

Crown-of-thorns starfish Acanthaster planci (COTS) outbreaks are a major cause of coral cover loss on the Great Barrier Reef (GBR), with manual culling having only localised success. The endangered giant triton snail Charonia tritonis is a natural predator of COTS, although aquarium and field observations indicate the intensity of direct predation may be inadequate to significantly mediate outbreaks. However, their mere presence can elicit a chemically induced sensory behavioural response which may suppress COTS populations when in non-outbreak status. While there is increasing knowledge of the sensory biology of both species, little is known regarding giant triton snail numbers on the GBR or about how they move and occupy space, making it difficult to determine their true zone of influence and thus their capacity to disrupt COTS behaviour. We used passive acoustic telemetry to establish short-term activity space and movement patterns of giant triton snails on the GBR. Individuals were tracked for up to 41 d, were observed to travel 234.24 m d-1, with a mean total cumulative distance travelled at night (1923.19 m) nearly double that observed during the day (1014.84 m). These distances encompass those reported for COTS (10.3 m d-1) and align with COTS nocturnal behaviour. Space utilisation distributions (UDs) revealed a mean (±SD) home range of 1179.40 ± 659.40 m2 (95% UD) and a core area of 195.68 ± 141.31 m2 (50% UD). Revealing the short-term movement patterns of this natural COTS predator within a reef environment advances knowledge of its spatial ecology and will provide information for its future conservation and for COTS management efforts.

Population irruptions of crown-of-thorns starfish (Acanthaster spp.) contribute greatly to the degradation of coral reefs throughout the Indo-Pacific. Effective management of these population irruptions is limited, in part, by incomplete knowledge of their early life history. Importantly, there are very limited data on the distribution and abundance of newly settled crown-of-thorns starfish (0 + starfish, in their first year since settlement). Extensive sampling was conducted around the circumference of three distinct mid-shelf reefs (at 1–18 m depths) in the central Great Barrier Reef (GBR), during active population irruptions, in May–June 2017, to quantify the occurrence and densities of settlement-stage starfish (2–65 mm diameter) and relate patterns of abundance to distinct habitat features at the scale of individual reefs. Overall, 140 settlement-stage starfish were detected across 1242 quadrats (1 m2). Settlement-stage starfish were recorded from 31 out of 42 sites (73.8%) at mean densities of 0–0.77 starfish m−2. Both estimated densities and the likelihood of occurrence of settlement-stage starfish within quadrats increased overall with the proportion of coral rubble (and dead intact corals), were greatest at intermediate depths (8–14 m), but decreased with the proportion of live hard coral. At the scale of individual reefs, settlement-stage starfish occurred most frequently in south-western and northern fore reef habitats. Our results suggest that settlement and/or early post-settlement survival of crown-of-thorns starfish is greatest in relatively shallow waters of obliquely exposed fore reef habitats where there is high cover of coral rubble. The specific occurrence of these habitat types (within spur and groove systems and rubble slips) provides an opportunity to concentrate searches and increase effective sampling of settlement-stage starfish, though these habitats are relatively widespread and unlikely to constrain the population replenishment or population irruptions of crown-of-thorns starfish on the GBR.

The estimation of larval dispersal on an ecological timescale is significant for conservation of marine species. In 2018, a semi-population outbreak of crown-of-thorns sea star, Acanthaster cf. solaris, was observed on a relatively isolated oceanic island, Ogasawara. The aim of this study was to assess whether this population outbreak was caused by large-scale larval recruitment (termed secondary outbreak) from the Kuroshio region. We estimated larval dispersal of the coral predator A. cf. solaris between the Kuroshio and Ogasawara regions using both population genomic analysis and simulation of oceanographic dispersal. Population genomic analysis revealed overall genetically homogenized patterns among Ogasawara and other Japanese populations, suggesting that the origin of the populations in the two regions is the same. In contrast, a simulation of 26-year oceanographic dispersal indicated that larvae are mostly self-seeded in Ogasawara populations and have difficulty reaching Ogasawara from the Kuroshio region within one generation. However, a connectivity matrix produced by the larval dispersal simulation assuming a Markov chain indicated gradual larval dispersal migration from the Kuroshio region to Ogasawara in a stepping-stone manner over multiple years. These results suggest that the 2018 outbreak was likely the result of self-seeding, including possible inbreeding (as evidenced by clonemate analysis), as large-scale larval dispersal from the Kurishio population to the Ogasawara population within one generation is unlikely. Instead, the population in Ogasawara is basically sustained by self-seedings, and the outbreak in 2018 was also most likely caused by successful self-seedings including possible inbreeding, as evidenced by clonemate analysis. This study also highlighted the importance of using both genomic and oceanographic methods to estimate larval dispersal, which provides significant insight into larval dispersal that occurs on ecological and evolutionary timescales.

Many predators reported to feed on crown-of-thorns starfish (CoTS, Acanthaster spp.) are generalist and opportunistic feeders. However, research into predation on CoTS tends to examine these predator–prey interactions in isolation, and it remains unknown whether many potential predators will prey on CoTS when other, potentially more palatable, food sources are available. Assessing predatory responses to changes in prey availability is critical for gauging the capacity of predators to regulate prey populations. Here, we explored prey preferences and tested for prey switching across nine species of planktivorous damselfish offered varying densities of Pacific CoTS (Acanthaster cf. solaris) larvae versus larvae of a common and co-occurring starfish, Linckia laevigata. Results show that planktivorous damselfishes will consume crown-of-thorns starfish larvae, even in the presence of alternative prey. Feeding responses varied among the nine planktivorous predators with five damselfishes (Acanthochromis polyacanthus, Amblyglyphidodon curacao, Dascyllus reticulatus, Pomacentrus amboinensis and Pomacentrus moluccensis) exhibiting increased consumption of Acanthaster larvae with increasing density, despite the presence of alternative prey. Moreover, Abudefduf sexfasciatus and P. amboinensis exhibited preference for larvae of A. cf. solaris over larvae of L. laevigata. Despite these predation patterns, prey switching between starfish larvae was not observed. These results add to a growing body of evidence which suggests that predators of the early life stages of A. cf. solaris could be important in regulating settlement and recruitment patterns of this starfish, especially at low, non-outbreak, densities.

The characterization of gene expression in gametes has advanced our understanding of the molecular basis for ecological variation in reproductive success and the evolution of reproductive isolation. These advances are especially significant for ecologically important keystone predators such as the coral-eating crown-of-thorns sea stars (COTS, Acanthaster) which are the most influential predator species in Indo-Pacific coral reef ecosystems and the focus of intensive management efforts. We used RNA-seq and transcriptome assemblies to characterize the expression of genes in mature COTS gonads. We described the sequence and domain organization of eight genes with sex-specific expression and well known functions in fertilization in other echinoderms. We found unexpected expression of genes in one ovary transcriptome that are characteristic of males and sperm, including genes that encode the sperm-specific guanylate cyclase receptor for an egg pheromone, and the sperm acrosomal protein bindin. In a reassembly of previously published RNA-seq data from COTS testes, we found a complementary pattern: strong expression of four genes that are otherwise well known to encode egg-specific fertilization proteins, including the egg receptor for bindin (EBR1) and the acrosome reaction-inducing substance in the egg coat (ARIS1, ARIS2, ARIS3). We also found histological evidence of both eggs and sperm developing in the same gonad in several COTS individuals from a parallel study. These results suggest the occurrence of hermaphrodites, and the potential for reproductive assurance via self-fertilization. Our findings have implications for management of COTS populations, especially in consideration of the large size and massive fecundity of these sea stars.

The extreme reproductive potential of the crown-of-thorns starfish (CoTS) Acanthaster sp. is a key trait used to explain their population outbreaks. Despite their highly defended morphology, sublethal predation is prevalent, as documented here for 2 outbreak populations in the Great Barrier Reef: Davies Reef and Lynch's Reef (arm damage 73.0 and 58.3%, respectively). It is not known how this trauma affects reproductive potential as a quantitative change in gonad production. We investigated the variability in gonad weight in the arms of uninjured CoTS. For CoTS with injured arms, we assessed the impact of arm injury and regeneration on gonad development at the level of the whole individual and among arms. The gonad index (GI) was lower in CoTS with 3 or more injured arms on Davies Reef, but not Lynch's Reef. At the level of individual arms, arm damage (25-100% of individual arm lost at Davies Reef and 10-100% at Lynch's Reef) resulted in a lower gonad weight compared to intact arms. Arms regenerating following total arm loss had a lower gonad weight than intact arms, even for arms that were 50-74% (Davies Reef) and 75-99% regenerated (Lynch's Reef). For uninjured CoTS, we show strong support for GI estimates based on extrapolation from one arm, and that inclusion of more than 4 arms resulted in marginal reduction in error. It is clear that sublethal injury can have a significant effect on gonad production in CoTS, with implications for population control given the reproductive potential of this species.

The Acanthaster planci species-complex [Crown-of-Thorns Seastar (COTS)] are highly fecund echinoderms that exhibit population outbreaks on coral reef ecosystems worldwide, including the Australian Great Barrier Reef. A better understanding of the COTS molecular biology is critical towards efforts in controlling outbreaks and assisting reef recovery. In seastars, the heterodimeric relaxin-like gonad stimulating peptide (RGP) is responsible for triggering a neuroendocrine cascade that regulates resumption of oocyte meiosis prior to spawning. Our comparative RNA-seq analysis indicates a general increase in RGP gene expression in the female radial nerve cord during the reproductive season. Also, the sensory tentacles demonstrate a significantly higher expression level than radial nerve cord. A recombinant COTS RGP, generated in a yeast expression system, is highly effective in inducing oocyte germinal vesicle breakdown (GVBD), followed by ovulation from ovarian fragments. The findings of this study provide a foundation for more in-depth molecular analysis of the reproductive neuroendocrine physiology of the COTS and the RGP.

Outbreaks of crown-of-thorns starfish (Acanthaster spp.) represent a major threat to coral reef ecosystems throughout the Indo-Pacific, and there is significant interest in whether no-take marine reserves could moderate the frequency or severity of outbreaks. Herein, we investigate whether the incidence and severity of sublethal injuries among juvenile Pacific crown-of-thorns starfish (Acanthaster cf. solaris, max diameter = 45 mm) differs between areas that are open versus closed to fishing, between microhabitats (i.e. dead coral substratum versus live coral) and with body size. The majority (180 out of 200) of juvenile starfish had conspicuous injuries, presumably caused by predation. The incidence of injuries in juvenile starfish was negatively related to body size, but links between body size and severity of injuries were only evident in individuals collected from dead coral microhabitats. Small (3 mm radius) starfish from dead coral microhabitats had injuries to 68.06% of arms, compared to 12.00% of arms in larger (12 mm radius) starfish from the same microhabitat. Juvenile starfish associated with dead coral habitats had a higher incidence (95 vs. 87% respectively) and severity (i.e. the percentage of injured arms; 21 vs. 6%) of injuries, compared to those associated with live corals. Interestingly, there was no difference in the incidence or severity of injuries between areas that are open versus closed to fishing. Our results show that small juvenile A. cf. solaris are extremely vulnerable to sublethal, if not lethal, predation, and predation risk declines as they grow and change their microhabitat. Predation during and immediately following settlement is, therefore, likely to have a major influence on population dynamics and ontogenetic changes in microhabitat use for A. cf. solaris.

New asterosaponin, acanthaglycoside G (1), along with three previously known steroidal oligoglycosides (2‒4), were isolated from the ethanolic extract of the starfish Acanthaster planci, collected off the coast of Vietnam. The structure of 1 was mainly elucidated by extensive NMR and ESIMS techniques as sodium 6-O-{β-D-fucopyranosyl-(1→2)-β-D-quinovopyranosyl-(1→4)-[β-D-quinovopyranosyl-(1→2)]-β-D-quinovopyranosyl-(1→3)-β-D-quinovopyranosyl}-6α-hydroxy-5α-pregn-9(11)-en-20-one-3β-yl sulfate. Compounds 3 and 4 showed slight cytotoxic activities against cancer RPMI-7951, HT-29, and MDA-MB-231 cell lines, but effectively inhibited in non-toxic concentrations colony formation of HT-29 and MDA-MB-231 cells and cell migration of MDA-MB-231 cells. Compounds 1 and 2 were inactive or less active, respectively.

The crown-of-thorns starfish (COTS) is a coral predator that is widely distributed in Indo-Pacific Oceans. A previous phylogenetic study using partial mitochondrial sequences suggested that COTS had diverged into four distinct species, but a nuclear genome-based analysis to confirm this was not conducted. To address this, COTS species nuclear genome sequences were analysed here, sequencing Northern Indian Ocean (NIO) and Red Sea (RS) species genomes for the first time, followed by a comparative analysis with the Pacific Ocean (PO) species. Phylogenetic analysis and ADMIXTURE analysis revealed clear divergences between the three COTS species. Furthermore, within the PO species, the phylogenetic position of the Hawaiian sample was further away from the other Pacific-derived samples than expected based on the mitochondrial data, suggesting that it may be a PO subspecies. The pairwise sequentially Markovian coalescent model showed that the trajectories of the population size diverged by region during the Mid-Pleistocene transition when the sea-level was dramatically decreased, strongly suggesting that the three COTS species experienced allopatric speciation. Analysis of the orthologues indicated that there were remarkable genes with species-specific positive selection in the genomes of the PO and RS species, which suggested that there may be local adaptations in the COTS species.

Crown-of-thorns starfish (Acanthaster spp.) is reported to have exceptional reproductive capacity, but this has been largely inferred based on the overall weight of gonads (and mostly for females), and there are limited estimates of the concentration of gametes within gametogenic tissues. This study quantified gamete concentrations for both male and female Pacific crown-of-thorns starfish (Acanthaster cf. solaris), collected on Australia’s Great Barrier Reef in 2014–2019. Gamete concentrations varied greatly among female starfish (12,338–133,810 oocytes g−1), such that the estimated reproductive capacity ranged from 400-mm diameter approached 53 billion sperm. This study reaffirms that crown-of-thorns starfish have exceptional reproductive capacity, which is strongly size-dependent, but also varies greatly among individuals. Importantly, individual variation in reproductive output may be important in understanding for population irruptions of Acanthaster spp., and their concomitant effects on reef ecosystems.

Population outbreaks of the corallivorous crown-of-thorns seastar (CoTS; Acanthaster spp.) are significant threats to the Indo-Pacific reefs. Although recent research demonstrated that environmental DNA (eDNA) techniques could improve CoTS monitoring, the interpretation of surveillance results has been limited by uncertainties about eDNA dynamics. Here, we conducted aquarium experiments to identify biotic and abiotic factors affecting the shedding and degradation rates of CoTS eDNA. In the first experiment, we investigated the effect of two temperatures (24 and 28 °C) and three feeding treatments (no coral, coral accessible and coral inaccessible) on eDNA shedding rate of laboratory-raised 8-month-old juvenile CoTS. In the second experiment, we quantified CoTS eDNA degradation rate under three temperatures (24, 26 and 28 °C). We found that eDNA shedding rate was affected by feeding treatment (p

Gastropod molluscs are among the most abundant species that inhabit coral reef ecosystems. Many are specialist predators, along with the giant triton snail Charonia tritonis (Linnaeus, 1758) whose diet consists of Acanthaster planci (crown-of-thorns starfish), a corallivore known to consume enormous quantities of reef-building coral. C. tritonis are considered vulnerable due to overexploitation, and a decline in their populations is believed to have contributed to recurring A. planci population outbreaks. Aquaculture is considered one approach that could help restore natural populations of C. tritonis and mitigate coral loss; however, numerous questions remain unanswered regarding their life cycle, including the molecular factors that regulate their reproduction and development. In this study, we have established a reference C. tritonis transcriptome derived from developmental stages (embryo and veliger) and adult tissues. This was used to identify genes associated with cell signalling, such as neuropeptides and G protein-coupled receptors (GPCRs), involved in endocrine and olfactory signalling. A comparison of developmental stages showed that several neuropeptide precursors are exclusively expressed in post-hatch veligers and functional analysis found that FFamide stimulated a significant (20.3%) increase in larval heart rate. GPCRs unique to veligers, and a diversity of rhodopsin-like GPCRs located within adult cephalic tentacles, all represent candidate olfactory receptors. In addition, the cytochrome P450 superfamily, which participates in the biosynthesis and degradation of steroid hormones and lipids, was also found to be expanded with at least 91 genes annotated, mostly in gill tissue. These findings further progress our understanding of C. tritonis with possible application in developing aquaculture methods.

The crown-of-thorns seastar (COTS; Acanthaster spp.) inhabits coral reefs across the Pacific Ocean. Based on studies in the Western Pacific, when densities exceed ∼15 specimens per ha, coral reef degradation due to COTS predation may occur. There is little information about the role of COTS on coral reefs in the tropical eastern Pacific, although previous studies suggested it was not a concern to coral reef conservation in Mexico. In this study, we estimated the abundance and impact of COTS on coral reefs at Espiritu Santo Archipelago National Park (Gulf of California) over a period of 12 years (2005–2016). The mean density (pooled among sites and over time) of COTS was 70 ± 5.1 ind. ha–1 (mean ± SE), with a maximum value of 143.6 ± 30.3 ind. ha–1, recorded in 2006. Densities changed significantly over time and spatially. The highest values were observed at sites located on the west side of the islands. Density was not correlated with seawater temperature or live coral cover. The absence of evidence of major live coral cover declines associated with predation by COTS, even though high densities were observed through the years in the region, lead us to conclude that this seastar does not appear to threaten coral reefs at Espiritu Santo. However, continued monitoring of COTS is required to help understand density fluctuations and to identify threshold densities needed to cause major coral damage in the region.

Coral reef is an ecosystem which provides suitable habitats for sgroups of biota that has important ecological and economic values which can be used as bio-indicators to assess the health of the environment. Research on megabenthic fauna in Kendari waters and its surroundings, Southeast Sulawesi was carried out at nine permanent stations in 2015 to 2018. The data was collected using the Benthos Belt Transect method that modified from the Belt Transect method on 8 types or groups of megabenthos in these waters. The purpose of this study was to determine the density fluctuation of megabenthic fauna over the years. The mean density of individuals found at each station during the study did not differ significantly. The Kruskal-Wallis test on density of megabenthic fauna during this period of times did not show a significant difference (H = 28.511 > df 7 = 14.067). Drupella spp. was the group species of megabenthic fauna with the highest density each year (1,079-1,738 ind/ha), while lobster was the group species of megabenthic fauna with the lowest density each year (0 - 39.7 ind/ha). The crown of thorns starfish Acanthaster planci had the highest fluctuation where density increased from 28.3 to 71.4 ind/ha.

Molecular clock calibration is central in population genetics as it provides an accurate inference of demographic history, whereby helping with the identification of driving factors of population changes in an ecosystem. This is particularly important for coral reef species that are seriously threatened globally and in need of conservation. Biogeographic events and fossils are the main source of calibration, but these are known to overestimate timing and parameters at population level, which leads to a disconnection between environmental changes and inferred reconstructions. Here, we propose the Last Glacial Maximum (LGM) calibration that is based on the assumptions that reef species went through a bottleneck during the LGM, which was followed by an early yet marginal increase in population size. We validated the LGM calibration using simulations and genetic inferences based on Extended Bayesian Skyline Plots. Applying it to mitochondrial sequence data of crown-of-thorns starfishAcanthaster spp., we obtained mutation rates that were higher than phylogenetically based calibrations and varied among populations. The timing of the greatest increase in population size differed slightly among populations, but all started between 10 and 20 kya. Using a curve-fitting method, we showed thatAcanthasterpopulations were more influenced by sea-level changes in the Indian Ocean and by reef development in the Pacific Ocean. Our results illustrate that the LGM calibration is robust and can probably provide accurate demographic inferences in many reef species. Application of this calibration has the potential to help identify population drivers that are central for the conservation and management of these threatened ecosystems.

The corallivorous Crown-of-Thorns Starfish (CoTS, Acanthaster spp.) has been linked with the widespread loss of scleractinian coral cover on Indo-Pacific reefs during periodic population outbreaks. Here, we re-examine CoTS consumption by coral reef fish species by using new DNA technologies to detect Pacific Crown-of-Thorns Starfish (Acanthaster cf. solaris) in fish faecal and gut content samples. CoTS DNA was detected in samples from 18 different coral reef fish species collected on reefs at various stages of CoTS outbreaks in the Great Barrier Reef Marine Park, nine of which had not been previously reported to feed on CoTS. A comprehensive set of negative and positive control samples confirmed that our collection, processing and analysis procedures were robust, although food web transfer of CoTS DNA cannot be ruled out for some fish species. Our results, combined with the (i) presence of CoTS spines in some samples, (ii) reported predation on CoTS gametes, larvae and settled individuals, and (iii) known diet information for fish species examined, strongly indicate that direct fish predation on CoTS may well be more common than is currently appreciated. We provide recommendations for specific management approaches to enhance predation on CoTS by coral reef fishes, and to support the mitigation of CoTS outbreaks and reverse declines in hard coral cover.

BackgroundPopulation outbreaks of the crown-of-thorns starfish (Acanthaster plancisensu lato; COTS), a primary predator of reef-building corals in the Indo-Pacific Ocean, are a major threat to coral reefs. While biological and ecological knowledge of COTS has been accumulating since the 1960s, little is known about its associated bacteria. The aim of this study was to provide fundamental information on the dominant COTS-associated bacteria through a multifaceted molecular approach.MethodsA total of 205 COTS individuals from 17 locations throughout the Indo-Pacific Ocean were examined for the presence of COTS-associated bacteria. We conducted 16S rRNA metabarcoding of COTS to determine the bacterial profiles of different parts of the body and generated a full-length 16S rRNA gene sequence from a single dominant bacterium, which we designated COTS27. We performed phylogenetic analysis to determine the taxonomy, screening of COTS27 across the Indo-Pacific, FISH to visualize it within the COTS tissues, and reconstruction of the bacterial genome from the hologenome sequence data.ResultsWe discovered that a single bacterium exists at high densities in the subcuticular space in COTS forming a biofilm-like structure between the cuticle and the epidermis. COTS27 belongs to a clade that presumably represents a distinct order (so-called marine spirochetes) in the phylumSpirochaetesand is universally present in COTS throughout the Indo-Pacific Ocean. The reconstructed genome of COTS27 includes some genetic traits that are probably linked to adaptation to marine environments and evolution as an extracellular endosymbiont in subcuticular spaces.ConclusionsCOTS27 can be found in three allopatric COTS species, ranging from the northern Red Sea to the Pacific, implying that the symbiotic relationship arose before the speciation events (approximately 2 million years ago). The universal association of COTS27 with COTS and nearly mono-specific association at least with the Indo-Pacific COTS provides a useful model system for studying symbiont-host interactions in marine invertebrates and may have applications for coral reef conservation.

This study of the crown-of-thorns starfish Acanthaster planci in New Caledonia enables us to compare its biological parameters with those from different areas in the Indopacific. Acanthaster has been observed in about fifty locations on the Grande Terre and Loyalty Islands. The density of populations was usually below 0.5 per 100 m2. However a few locations with higher densities were found which should be monitored. A monthly sampling of the population was conducted for fifteen months at Maitre Islet, the station with the highest density (3.3 per 100 m2). Morphometric relationships and the reproductive cycle were defined. Breeding occurred during the warm season, from November to February. The allometric growth of the gonads showed that the 40 cm diameter specimens may have up to sixty times more oocytes than 25 cm diameter ones and can produce up to sixty million oocytes per spawning season.

Population outbreaks of Crown-of-Thorns Starfish (COTS; Acanthaster spp.) are a major contributor to loss of hard coral throughout the Indo-Pacific. On Australia’s Great Barrier Reef (GBR), management interventions have evolved over four COTS outbreaks to include: (1) manual COTS control, (2) Marine Protected Area (MPA) zoning, and, (3) water quality improvement. Here we evaluate the contribution of these three approaches to managing population outbreaks of COTS to minimize coral loss. Strategic manual control at sites reduced COTS numbers, including larger, more fecund and damaging individuals. Sustained reduction in COTS densities and improvements in hard coral cover at a site were achieved through repeated control visits. MPAs influenced initial COTS densities but only marginally influenced final hard coral cover following COTS control. Water quality improvement programs have achieved only marginal reductions in river nutrient loads delivered to the GBR and the study region. This, a subsequent COTS outbreak, and declining coral cover across the region suggest their contributions are negligible. These findings support manual control as the most direct, and only effective, means of reducing COTS densities and improving hard coral cover currently available at a site. We provide recommendations for improving control program effectiveness with application to supporting reef resilience across the Indo-Pacific.

Gonad index and maturity stages of gonad were compared between aggregated and dispersed subpopulations of Acanthaster planci in Okinawa Island in 1988 and 1989. Duration of spawning activities were different between the two subpopulations: the aggregated animals spawned in a period similar to that reported by previous workers, but the dispersed animals began to spawn 2 to 3 weeks later than the aggregated ones. These data suggested that a conspecific stimulus enhanced synchronous spawning activities in the aggregated subpopulations and that spawning activities might have occurred sporadically in the dispersed animals.

El Niño Southern Oscillation (ENSO) events modulate oceanographic processes that control temperature and productivity in tropical waters, yet potential interactions with low frequency climate variability, such as the Pacific Decadal Oscillation (PDO), are poorly understood. We show that ENSO and PDO together predicted (i) maximum sea-surface temperatures (SST), which were associated with coral bleaching and declines in coral cover, and (ii) maximum chlorophyll-a concentrations, which were associated with high densities of coral-predatory Acanthaster starfish, across the tropical north Pacific Ocean since 1980. Asynchrony between the positive PDO and negative ENSO (i.e., La Niña) was associated with peaks in annual SST. By contrast, synchrony between the positive PDO and positive ENSO (i.e., El Niño) was associated with peaks in chlorophyll-a. Both conditions led to ecological disturbances and significant loss of coral cover, however, spatial models revealed where impacts to reefs were expected under varying climate scenarios. The 2015/17 ENSO event was coupled with a positive PDO and resulted in high SST and Acanthaster abundances in eastern Micronesia, while positive coral growth occurred in western Micronesia. Our novel approach for forecasting coral growth into the future may be applicable to other oceanic regions with differing oceanographic modulators.

The corallivorous Crown-of-Thorns Starfish (CoTS, Acanthaster spp.) has been linked with the widespread loss of scleractinian coral cover on Indo-Pacific reefs during periodic population outbreaks. Here, we re-examine CoTS consumption by coral reef fish species by using new DNA technologies to detect Pacific Crown-of-Thorns Starfish (Acanthaster cf. solaris) in fish faecal and gut content samples. CoTS DNA was detected in samples from 18 different coral reef fish species collected on reefs at various stages of CoTS outbreaks in the Great Barrier Reef Marine Park, nine of which had not been previously reported to feed on CoTS. A comprehensive set of negative and positive control samples confirmed that our collection, processing and analysis procedures were robust, although food web transfer of CoTS DNA cannot be ruled out for some fish species. Our results, combined with the (i) presence of CoTS spines in some samples, (ii) reported predation on CoTS gametes, larvae and settled individuals, and (iii) known diet information for fish species examined, strongly indicate that direct fish predation on CoTS may well be more common than is currently appreciated. We provide recommendations for specific management approaches to enhance predation on CoTS by coral reef fishes, and to support the mitigation of CoTS outbreaks and reverse declines in hard coral cover.

Outbreaks of the crown-of-thorns starfish Acanthaster planci have received increasing attention due to their negative impacts on coral reefs. However, outbreaks of A. planci in Chinese seas are still poorly understood. Coral reefs in the Xisha Islands (Paracel Islands), South China Sea, have been monitored during 2005 and 2019, including hard coral coverage, larval recruitment rates, density of coral reef fish and the populations of A. planci . This study aims to analyse the regular pattern regarding outbreaks of A. planci in the main islands of Xisha Islands, the causes of outbreaks of the crown-of-thorns starfish Acanthaster planci , and the solutions for controlling the outbreaks of the crown-of-thorns starfish Acanthaster planci . Monitoring coral reef ecosystems on the main islands of Xisha Islands from 2005 to 2019 showed that the cycle of Acanthaster planci outbreaks in Xisha Islands is about 15 years. These 15 years can be divided into two phases, in which the period of A. planci outbreak is about 5 years, and the recovery period of coral reefs is about 10 years. When A. planci outbreak from 2006 to 2010, the coral reef cover rate decreased from more than 60% to less than 5%. During the recovery period from 2011 to 2019, the coverage of coral reefs gradually increased to around 15%, at the same time the coral recruitment and coral reef fish increased. Further analysis showed that the occurrence of A. planci in Xisha Islands is mainly related to typhoon weather, reduction of coral reef fish, global warming and human activities. The passage of the typhoon brought a large number of nutrients, which led to the increase of plankton, leading to the survival rate of larvae of A. planci . Global warming and a decline in coral reef fish could lead to a greater percentage of the eggs of A. planci hatching and surviving. Based on 15-years monitoring data, it is highly possible that Xisha Islands are entering the next outbreak cycle of A. planci , and therefore measures should be taken to prevent the coral reef ecosystem from being destroyed again. Outbreaks of the crown-of-thorns starfish A. planci should be controlled in several ways. Direct control methods including physical removal of individual starfish and cutting individuals into multiple pieces were most often used methods to kill starfish. The most effective methods to control A. planci require injecting individual starfish with lethal chemicals, including sodium bisulfate, powdered citric acid, vinegar and thiosulfate-citrate-bile-sucrose agar (TCBS). Releasing the predator of A. planci of their different life cycle was also an effective way to control A. planci . The Giant Triton Shells ( Charonia tritonis ), the Napoleon Maori Wrasse ( Cheilinus undulatus ), Starry Puffer ( Arathron stellatus ) and Titan Trigger Fish ( Ballistoides viridescens ) were the main predator of the crown-of-thorns starfish A. planci . Moreover, regular monitoring of the starfish A. planci should be conducted in the Xisha Islands for early warning of outbreaks.

Outbreaks of the Pacific Crown-of-thorns Starfish Acanthaster cf. solaris are a major contributor to the sustained loss of coral, and the long-term degradation of Australia's Great Barrier...

Coral cover has declined markedly in the recent past in many regions of the world, including the Great Barrier Reef (GBR), Australia. The major causes of this decline are generally considered to be mortality associated with large-scale severe disturbances (i.e. catastrophic mortality), such as Acanthaster planci outbreaks, cyclones and bleaching. However, background rates of mortality (i.e. not associated with catastrophic disturbance), are rarely quantified, but without these it is difficult to assess the relative importance of these 2 types of mortality (catastrophic and background). We quantified spatial and temporal variation in catastrophic and background whole-colony mortality of the common reef coral Acropora millepora over 24 mo at 2 sites in 3 regions separated by 700 km along the GBR. The study period included 2 cyclones and a flood. Overall mortality rates were exceptionally high. Of 180 colonies tagged in April 2009, only 36 (20%) were alive in April 2011, and 68% of this mortality occurred in intervals following the 3 large disturbances. Background mortality rates were also high in the Palm Islands, where they approached 40% yr-1 compared to

We thank John Lucas, Peter Moran and the late Masashi Yamaguchi for their help with and encouragement of this work. We also thank Russ Babcock and 3 anonymous reviewers for critical review of the manuscript and Carina Cartwright for her assistance in the field and in the pain staking microscope work involved in this study. Funding for the original study was provided by the Crown of Thorns Starfish Research Committee of the Great Barrier Reef Marine Park Authority, Townsville, Australia.

Declines in coral cover across the Indo-Pacific are associated with multiple stressors of global ocean change, and this is exacerbated by population outbreaks of the coral-eating crown of thorns starfish (COTS), Acanthaster spp. We investigated the growth and feeding responses of the corallivorous juvenile stage of COTS and their coral food, Acropora spp., to near-future ocean warming and acidification. Juvenile COTS and Acropora spp. were exposed to three temperatures (26, 28, 30 °C) and three pH levels (NIST scale: 8.0, 7.8, 7.6) in a flow-through cross-factorial experiment. Increased temperature and acidification had independent positive effects on growth and feeding of juvenile COTS. They grew faster and were larger under these conditions, but weighed less at low pH. Accelerated growth of juvenile COTS under ocean acidification conditions was decoupled from skeletogenesis with increased size largely due to development of soft tissue. Juveniles reared at 30 °C also had the greatest number of spines. To assess the recovery of Acropora spp. following sublethal COTS predation in warm and acidified conditions, corals that had been preyed on by the juveniles for 1 week were removed and held in experimental conditions to monitor their growth and survival. The stress from warming and predation had an interactive effect in reduction in coral growth. Mortality of corals was highest following predation and in the 30 °C treatments. There was no direct effect of acidification on growth or survival of Acropora spp. following predation. It appears that COTS juveniles may benefit from near-future warming and acidification. Thus, changing climate may increase the threat of this predatory starfish to coral reefs.

During the period of June 1975 to August 1975, observations on living habit and some ecological aspects of Acanthaster planci were made at Pulau Tikus, Seribu Islands. The observations, limited to 8 metres deep, were made at the outer reef located south of Pulau Tikus, covering an area of about 4000 square metres. The density of living stony corals and the damaged caused by the feeding activities of A. planci were also studied. The results show that the average numbers of A. planci per month is 20 individuals per 4000 m2. The sizes of the starfish vary between 26-41 cm in diameter and the number of arms between 10 - 18. The moving distance of the starfish is 0.3 - 8 metres in 24 hours. The stony corals affected are Acropora squamosa (BROOK), A. spathulata (BROOK), A. Latistella (BROOK), A. quelchi (BROOK), Fungia sp.. Montipora ramosa BERNARD, Porites sp., DipIoria sp., and Goniatrea sp.

Large-scale population outbreaks of the crown-of-thorns starfish (COTS, Acanthaster spp.) have occurred in every nation with substantial coral reefs in the Indo-Pacific during the past few decades. While a multitude of control efforts have been trialed to combat the outbreaks, an efficient solution has remained elusive. Recent developments have however introduced single-shot injection methods using bovine derivatives (bile salts) and household products (vinegar) that have proven effective at culling COTS. In this study we use a Multiple-Before-After-Control-Impact (MBACI) experimental design to conduct an assessment of the environmental impact of using household vinegar as a chemical for culling COTS. During our six-week assessment we found no changes in coral cover or coral disease. Furthermore, while video recordings documented a number of fish species consuming decaying COTS, we found no evidence of changes in fish abundance or the presence of fish disease, despite densities of injected COTS far exceeding those recorded during natural outbreaks. The efficiency of scavenging fish ensured that few traces of decaying COTS were visible 72 h post-injection. The lack of any observed environmental impact supports our conclusion that vinegar is a low-risk chemical for use in COTS control. Because vinegar is highly accessible, low in cost, and effective at killing COTS without harm to non-target organisms, it has the potential to become a powerful new tool to defend the reef against COTS outbreaks.

The complete mitochondrial genome of the widespread and common Indo-Pacific sea star Archaster typicus has been sequenced in this study. The mitogenome is 16,230 base pairs (bp) in length, with 13 protein coding genes (PCGs), 22 tRNAs and 2 rRNAs. Gene order of its PCGs and rRNAs matches those of nine other asteroid taxa included for comparison in this study, and it has a similar nucleotide composition of 33.08% A, 26.38% T, 25.53% C and 15.01% G nucleotides. Phylogenetic analyses place A. typicus as the sister group to Acanthaster spp., consistent with previous inferences.

The coral reef ecosystem in Indonesian as part of Coral Triangle Region has been significantly decreasing in the last decades. This damage has been known widely due to coastal development, pollution, and uncontrolled fishing and harvesting. Among other many living species in the environment, the existence of coral reefs is directly related to the existence of Drupella sp. and Acanthaster planci as the coral predators, while the existence of the predators also related to the Napoleon wrasse and Giant triton/ Trumpet shell as the top predator. This study discusses the interaction among the coral reefs, the predators and the top predators, which is represented in a dynamical model of predator-prey-top predator. In the absence of top predators, the system is reduced as a two-predator-prey model with only one surviving predator, Acanthaster planci, which has more effective predation behavior. The role of Napoleon wrasse as a top predator of both Acanthaster planci and Drupella sp. is significantly important to protect the coral reef from the excessive predation from Acanthaster planci and Drupella sp. A stable co-existence is shown between coral reef, Acanthaster planci and Napoleon wrasse. With the appearance of Giant tritons which predate only Acanthaster planci, a co-existence between five species may occur with abundant species of Giant triton.

We investigated how density and aggregation influence crown-of-Thorns starfish Acanthaster planci reproductive success, using an empirically-Tuned, individual-based simulation model that incorporates spatial and temporal biological stochasticity associated with spawning, and a kinetics model of fertilisation that explicitly incorporates the probability of polyspermy. Greater aggregation of individuals relieved Allee fertilisation dynamics, particularly at low densities, leading to higher rates of successful monospermic fertilisation and allowing populations to produce many more zygotes. This is likely more important to smaller, rather than larger, populations, due to limited and more variable reproductive success. In higher density populations a fertilisation optimum was observed at moderate levels of aggregation, above which monospermic fertilisation plateaued or even declined. This was likely due to 2 factors: The spatial dynamics of gamete plume dispersal and polyspermic fertilisation. Comparison of in situ natural spawning aggregation with model results indicates a cost-benefit equilibrium may exist between aggregation and reproductive success, and that relief from mechanisms limiting aggregation (for example, decreased relative predator abundance) may permit increased aggregation resulting in greater fertilisation and zygote production. We propose an Allee threshold of 3 starfish ha-1 (for starfish of a mean diameter 345 mm), below which reproductive capacity is greatly reduced regardless of aggregation level. These preliminary findings posit aggregation as a key factor in outbreak formation that may feasibly be incorporated into preventative management strategies to detect and define incipient outbreak conditions and to mitigate subsequent risk.

Asteroidea, starfish, constitutes a major part of the macrobenthos in most marine environments. Being members of the echinoderms, they have a nervous system with no well-defined central nervous system. Accordingly, starfish are assumed to pick up rather limited information from the surroundings, and it is also often assumed that most of their behaviors are guided by olfaction. Here, the sensory biology of starfish is reviewed in order to evaluate these assumptions. There is a vast amount of behavioral data dealing with mechanoreception, chemoreception, and combinations of the two (chemosensory-mediated rheotaxis), but the receptors have not yet been identified and almost nothing is known about the physiology behind these senses. What can be concluded from the available data is that starfish possess a sense of touch, some are able to sense gravity and many display positive rheotaxis, moving up currents. A number of starfish species use olfaction during foraging and prey localization. Interestingly, eyes are also present in most starfish, and recent studies have documented that in Linckia laevigata and Acanthaster planci vision plays a major role in seeking out their feeding grounds. The physiology and structure of the eyes filter out small moving objects while optimizing the contrast between the large stationary objects (e.g., coral boulders in the habitat) and the surrounding water. These new results demonstrate the importance of controlling the visual environment when conducting experiments on starfish behavior.

Outbreaks of Crown-of-Thorns Starfish (COTS; Acanthaster planci ) are a major cause of destruction of coral communities on the Australian Great Barrier Reef. While factors relating to population explosions and the social interactions of COTS have been well studied, little is known about the neural mechanisms underlying COTS physiology and behaviour. One of the major classes of chemical messengers that regulate physiological and behavioural processes in animals is the neuropeptides. Here, we have analysed COTS genome and transcriptome sequence data to identify neuropeptide precursor proteins in this species. A total of 48 neuropeptide precursors were identified, including homologs of neuropeptides that are evolutionarily conserved throughout the Bilateria, and others that are novel. Proteomic mass spectrometry was employed to confirm the presence of neuropeptides in extracts of radial nerve cords. These transcriptomic and proteomic resources provide a foundation for functional studies that will enable a better understanding of COTS physiology and behaviour, and may facilitate development of novel population biocontrol methods. Significance The Crown-of-Thorns Starfish (COTS) is one of the primary factors leading to coral loss on the Great Barrier Reef, Australia. Our combined gene and proteomic findings of this study reveal the COTS neuropeptidome, including both echinoderm-like neuropeptides and novel putative neuropeptides. This represents the most comprehensive neuropeptidome for an echinoderm, contributing to the evolving knowledge of the COTS molecular neurobiology that may assist towards the development of biocontrol methods.