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The resilience of Moorea Island's coral reefs has been extensively discussed. In this debate, and despite their greater exposure to anthropogenic disturbances, shallow reef flats have often been overlooked compared to oceanic forereefs. This study assesses changes in the reef flat habitats over 67 years (1955–2022) in Tiahura in the northwest of Moorea, using a combination of modern satellite imagery, vintage aerial photographs and a habitat mapping survey conducted in 2023. Remotely sensed data provided time series of coral habitat surface area changes could be in some cases corroborated by historical literature reports and in situ observations from 1972 to the present, although historical data were scarce, heterogeneous, and informed at a different level of descriptions (e.g., coral cover) than the habitat scale. Contrary to expectations, the period from 1955 to 1977, perceived as pristine, exhibited a significantly lower extent of coral habitat compared to the subsequent period marked by coastal development and anthropogenic disturbances. To discuss resilience of coral habitats across the 67-year period, we relied on habitat surface changes. To understand the changes and evaluate the coral habitat resilience of the Tiahura reef flats, it was crucial to differentiate the barrier from the fringing reefs due to their distinct exposure to physical disturbances during the 1970s. The fringing reef, unlike the barrier reef, experienced substantial human-induced structural and hydrodynamical modifications. Concluding or not on coral habitat resilience depends on the period considered: 1955–2022 or 1977–2022. Beyond the Tiahura case study, we highlight the importance of defining the temporal reference for any resilience analysis, by taking into account the stability of hydrodynamic conditions that affect sedimentation and lagoon water levels. [ABSTRACT FROM AUTHOR]

Crown-of-thorns seastar (CoTS, Acanthaster cf. solaris) outbreaks remain a significant cause of coral loss on the Great Barrier Reef (GBR) and across the West-Pacific Ocean. Previous outbreaks on the GBR have only been discovered once fully established, which constrains opportunities for effective control. Early detection of outbreaks would provide an important opportunity for early intervention and increase understanding of outbreak cause(s). Here, we assess the utility of environmental DNA (eDNA) monitoring to detect the initiation of a population outbreak at Lizard Island over five years (2019–2023), compared with density estimates obtained using Scooter-Assisted Large Area Diver-based (SALAD) surveys. At each of the five eDNA sampling sites, 30 replicate samples were collected annually and analysed with CoTS-specific primer sets and digital droplet PCR. Both methods detected distinct increases in CoTS densities from 2020/21 onwards, indicating the start of a new population outbreak. A large part of the observed variation in eDNA (expressed as the percentage of positive samples) was explained by changes in recorded CoTS density, confirming that eDNA data provide a quantitative estimate for adult CoTS abundance. SALAD surveys and eDNA are new and complementary monitoring methods that facilitate early detection of CoTS outbreaks, which will enable more effective management intervention. [ABSTRACT FROM AUTHOR]

Outbreaks of crown-of-thorns starfish (COTS) pose a major threat to coral reefs in the Ashizuri-Uwakai National Park, Japan, which is partially affected by the Kuroshio Current. The purpose of this study was to identify the upstream areas of the Kuroshio significantly contributing to the supply of larvae to this area, where the larvae are most likely to reach within the Ashizuri-Uwakai area (inter-connectivity), and to clarify the connectivity within the park (intra-connectivity). Using a hydrodynamic model based on a 12-year dataset with a high spatial resolution (ca. 2 km), this study evaluated the transport and dispersion processes into and within the region, although the proportion of particles reaching the Ashizuri-Uwakai area the major sources were Tanegashima and Yakushima islands and the east coast of Kyushu. Grid cells with a high supply from these source areas were identified within Ashizuri-Uwakai and quantitatively shown to have high sink strength in the southwestern and cape areas. We were also able to show where particles released within Ashizuri-Uwakai tend to accumulate. Since locations with high sink strength generally coincided with diving sites and areas where conservation activities have been conducted, strengthening conservation activities in these locations can be considered to be effective in controlling outbreaks of COTS. [ABSTRACT FROM AUTHOR]

Population irruptions of crown-of-thorns seastar (CoTS, Acanthaster spp.) represent a perennial threat to Indo-Pacific coral reefs. Age determination of CoTS is challenging, thereby hindering understanding and management of this nuisance species. Telomeres, which are protective DNA structure found at the ends of eukaryotic chromosomes that shorten at each cell division, have been used to estimate age in wild animals. To investigate the use of telomeres in CoTS, we optimized a quantitative PCR protocol to measure relative telomere length (rTL) in CoTS for the first time. Comparing rTL among four age groups (4, 7, 16, > 24 months post-settlement), we found that adult CoTS generally exhibit shorter rTL than juveniles, which is the first evidence of age-related telomere attrition in CoTS. However, there was large within-age class variation, and no significant relationships were found between adult CoTS rTL and potential age-indicating external features. Furthermore, we found accelerated telomere attrition under sub-optimal diet, where individuals that were fed crustose coralline algae for 16 months exhibited shorter rTL than their counterparts fed on coral. A positive correlation was found between rTL of tube feet and pyloric caeca, suggesting synchronization of telomere dynamics across somatic tissues in CoTS. Overall, our results suggest that rTL could be used to classify CoTS into broad age groups, though individual variation constrains the ability to resolve specific cohorts. The present study contributes to the understanding of telomere dynamics in marine invertebrates, while laying the groundwork for future research into rTL as biomarker for age and potentially stress for CoTS. [ABSTRACT FROM AUTHOR]

Abstract Background Many echinoderms form seasonal aggregations prior to spawning. In some fecund species, a spawning event can lead to population outbreaks with detrimental ecosystem impacts. For instance, outbreaks of crown-of-thorns starfish (COTS), a corallivore, can destroy coral reefs. Here, we examine the gene expression in gravid male and female COTS prior to spawning in the wild, to identify genome-encoded factors that may regulate aggregation and spawning. This study is informed by a previously identified exoproteome that attracts conspecifics. To capture the natural gene expression profiles, we isolated RNAs from gravid female and male COTS immediately after they were removed from the Great Barrier Reef. Results Sexually dimorphic gene expression is present in all seven somatic tissues and organs that we surveyed and in the gonads. Approximately 40% of the exoproteome transcripts are differentially expressed between sexes. Males uniquely upregulate an additional 68 secreted factors in their testes. A suite of neuropeptides in sensory organs, coelomocytes and gonads is differentially expressed between sexes, including the relaxin-like gonad-stimulating peptide and gonadotropin-releasing hormones. Female sensory tentacles—chemosensory organs at the distal tips of the starfish arms—uniquely upregulate diverse receptors and signalling molecules, including chemosensory G-protein-coupled receptors and several neuropeptides, including kisspeptin, SALMFamide and orexin. Conclusions Analysis of 103 tissue/organ transcriptomes from 13 wild COTS has revealed genes that are consistently differentially expressed between gravid females and males and that all tissues surveyed are sexually dimorphic at the molecular level. This finding is consistent with female and male COTS using sex-specific pheromones to regulate reproductive aggregations and synchronised spawning events. These pheromones appear to be received primarily by the sensory tentacles, which express a range of receptors and signalling molecules in a sex-specific manner. Furthermore, coelomocytes and gonads differentially express signalling and regulatory factors that control gametogenesis and spawning in other echinoderms.

Context: Crown-of-thorns starfish (Acanthaster spp., hereafter COTS), the most destructive predator of corals, selectively consume specific corals. However, their feeding selectivity varies among reef regions and differs from their feeding preferences in laboratory experiments. Aims: In this study, the impacts of selective feeding of Acanthaster sp. on the coral community in the South China Sea were explored. Methods: COTS predation on 701 coral colonies and 24 coral genera during 2018−2019 was evaluated. Key results: Montipora had a greater scar cover (57%) than did Pocillopora (27%) because of COTS predation. Additionally, the relative abundance of encrusting Montipora (heat-tolerant corals) decreased from 40 to 14%, whereas that of branching Pocillopora (less heat-tolerant corals) increased from 40 to 60%. Moreover, the rare genera Millepora and Astreopora had the greatest scar cover (from 78 to ~100%) and feeding electivity values (from 0.66 to ~0.98), and were thus positively selected by COTS for predation. Further regional comparisons showed four types of feeding selection worldwide. Conclusions: Less heat-tolerant coral became predominant in the coral community owing to selective feeding of COTS. COTS could consume rare, less-preferred corals by changing feeding selections. Implications: These findings suggest that COTS not only directly consume coral individuals but also indirectly change the coral community composition, which is potentially related to the vulnerability of the coral community to global warming. Field surveys found that the selective feeding of crown-of-thorns starfish on coral reefs of the South China Sea differed from that in other coral reef regions worldwide. The dominant genera, Montipora and Pocillopora , have differing damages because of the selective feeding, leading to an altered coral community that is likely to be vulnerable to ocean warming. This case study suggests that crown-of-thorns starfish not only directly consume coral individuals but also may indirectly affect the vulnerability of the coral community to climate warming. [ABSTRACT FROM AUTHOR]

The short spined crown-of-thorns starfish Acanthaster brevispinus inhabits deeper water soft bottom habitats, in contrast to the more infamous Indo-Pacific Acanthaster species complex of which population outbreaks have been responsible for widespread coral mortality throughout the Indo-West Pacific region. Acanthaster brevispinus has not previously been regarded as a threat to corals or coral reefs. Here, we report A. brevispinus occurring on mesophotic off-reef or inter-reef habitats in 20–70-m depths dominated by solitary corals off both the western and eastern coasts of Australia. On Ningaloo Reef, A. brevispinus were found on mushroom coral (Cycloseris distorta) beds using an underwater towed camera and further exploration using a remotely operated vehicle (ROV) confirmed predation by A. brevispinus on C. distorta. On the southern Great Barrier Reef, A. brevispinus in large numbers were found in habitat dominated by the dendrophylliid Heteropsammia cf. cochlea. Predation on H. cf. cochlea was also directly observed. This is the first confirmed report of predation on hard corals by A. brevispinus, and while there are yet to be any records of population outbreaks of this species, such outbreaks could have a significant effect on mesophotic solitary coral assemblages. [ABSTRACT FROM AUTHOR]

Background: Many echinoderms form seasonal aggregations prior to spawning. In some fecund species, a spawning event can lead to population outbreaks with detrimental ecosystem impacts. For instance, outbreaks of crown-of-thorns starfish (COTS), a corallivore, can destroy coral reefs. Here, we examine the gene expression in gravid male and female COTS prior to spawning in the wild, to identify genome-encoded factors that may regulate aggregation and spawning. This study is informed by a previously identified exoproteome that attracts conspecifics. To capture the natural gene expression profiles, we isolated RNAs from gravid female and male COTS immediately after they were removed from the Great Barrier Reef. Results: Sexually dimorphic gene expression is present in all seven somatic tissues and organs that we surveyed and in the gonads. Approximately 40% of the exoproteome transcripts are differentially expressed between sexes. Males uniquely upregulate an additional 68 secreted factors in their testes. A suite of neuropeptides in sensory organs, coelomocytes and gonads is differentially expressed between sexes, including the relaxin-like gonad-stimulating peptide and gonadotropin-releasing hormones. Female sensory tentacles—chemosensory organs at the distal tips of the starfish arms—uniquely upregulate diverse receptors and signalling molecules, including chemosensory G-protein-coupled receptors and several neuropeptides, including kisspeptin, SALMFamide and orexin. Conclusions: Analysis of 103 tissue/organ transcriptomes from 13 wild COTS has revealed genes that are consistently differentially expressed between gravid females and males and that all tissues surveyed are sexually dimorphic at the molecular level. This finding is consistent with female and male COTS using sex-specific pheromones to regulate reproductive aggregations and synchronised spawning events. These pheromones appear to be received primarily by the sensory tentacles, which express a range of receptors and signalling molecules in a sex-specific manner. Furthermore, coelomocytes and gonads differentially express signalling and regulatory factors that control gametogenesis and spawning in other echinoderms. [ABSTRACT FROM AUTHOR]

Despite the notoriety of the corallivorous crown of thorns starfish (COTS, Acanthaster sp.), with population outbreaks that decimate reefs throughout the Indo‐Pacific, the physiology of the juvenile stage remains poorly understood. We determined the feeding rate and metabolic rate of juvenile COTS during their initial algae‐eating stage. The metabolic rate of juveniles after their ontogenetic diet transition from a diet of coralline algae to coral was also investigated. We found that the weight‐specific metabolic rate of both the herbivorous (mean = 0.052 mg O2 g−1 h−1) and corallivorous (mean = 0.034 mg O2 g−1 h−1) juveniles increased exponentially with juvenile size. Juveniles consumed ~4 mm2 of algae (Amphiroa sp.) in 1 day, and consumption rate also increased with juvenile size. Juveniles may impact the distribution of coralline algae for other herbivores on coral reefs and the settlement habitat for many invertebrate larvae. Increased metabolism of both herbivorous and corallivorous juveniles with size is indicative of their increasing ecological impact as they grow, highlighting the importance of understanding the juvenile physiology of influential species such as COTS. [ABSTRACT FROM AUTHOR]

The coral reef habitats have been facing insightful threats from natural and anthropogenic sources across the world; while natural threats are creating major ecological pressure with the maximum percentage of devastation to the entire ecosystems. The Acanthaster planci (L) or Crown-of-Thorns Sea star (CoTS) is known as potential natural predator of corals and can disrupt the entire reef ecosystem with their outbreaks within the much-stipulated time. CoTS are reported from all the reef areas of Andaman and Nicobar Islands with a mean density of 0.71/hectare within the range of 1.08±0.33 to 0.40±0.18 per hectare between North & Middle Andaman and Nicobar respectively. The distributional pattern of CoTS signifies that the reef crest represents maximum occurrence in comparison with reef slop and reef top; while an inversely proportional relationship can be seen between the occurrence of individuals and depth gradients. Maximum association of the CoTS is recorded with acroporidae corals while corallivorous impacts of CoTS are also recorded with poritidae corals which are not much reported across the world. No observation on the population outbreaks of CoTS was made during the decadal study period from Andaman and Nicobar Islands while the density is intrinsically noted within the limit of the natural population level of CoTS. The presence of natural predators like CoTS in Andaman and Nicobar Islands used to take a leading role in the balancing of reef ecology which denotes the healthy reef ecosystem of this archipelago. [ABSTRACT FROM AUTHOR]

Crown-of-thorns seastars (COTS, Acanthaster spp.) are a major contributor to coral mortality across the Indo-Pacific and can cause extensive reef degradation. The diet preferences of COTS can influence coral community structure by predation on fast-growing genera such as Acropora and avoidance of rare coral genera. In non-outbreaking populations, this preference can increase species diversity. The feeding biology of Acanthaster cf. solaris was compared at two sites (Shark Alley and Second Lagoon) on One Tree Island reef, located in the southern Great Barrier Reef, to determine whether the availability of Acropora influences differences in COTS movement, feeding preference and feeding rates within the same reef system. Acanthaster cf. solaris were tracked daily for five days across both sites, with measurements of movement, feeding scars and coral composition recorded over this time. While Shark Alley and Second Lagoon have similar live coral cover (40 and 44 % respectively), Shark Alley has significantly lower Acropora availability than Second Lagoon (2 vs 32 %). The feeding rate of COTS was significantly different between Shark Alley and Second Lagoon (259.8 and 733.8 cm2 of coral per day, respectively), but did not differ between seastar size (25–40 cm and >40 cm). Acanthaster cf. solaris showed preference for Pocillopora , Seriatopora , Acropora and Isopora and an avoidance of Porites at both sites. The results suggest that for coral reef sites where Acropora is not dominant, COTS outbreaks may be less likely to initiate, with comparatively low feeding rates found in comparison to coral reefs where Acropora is dominant. • Feeding behaviour of crown-of-thorns seastars (COTS) were compared across two sites. • Feeding rates were higher in sites with high Acropora availability. • Movement rates and feeding preferences did not differ between sites. • Feeding preferences are similar between stable and outbreaking populations. • Reefs where Acropora is rare are less able to support COTS outbreaks. [ABSTRACT FROM AUTHOR]

Abstract 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

Pieh MRP encountered non-anthropogenic phenomena, precisely massive coral bleaching in 2016, 2017, and massive predators from Acanthaster planci outbreaks in 2018. This study aimed to understand the pattern of coral reef diversity in the core zone and utilization in the MRP area and compare it to non-MRPS locations that accept the same non-anthropogenic pressure conditions. Coral fish sampling using a UVC is categorized into three zones: the core zone, the utilization zone, and outside the MRP area. 8 Families of coral reef fishes were counted based on categories of level function in ecologies and economy. Taxonomic distinctiveness estimates were calculated mathematically for each sample, including species richness and taxonomic diversity were compared among zonation area. Pearson's Coefficient Correlation Matrix was used to measure the correlation relationship between zonation areas. There are 91 species of fish and 3002 individuals found. The richest family in the MRP Core Zone and MRP Utility Zone was Acanthuridae with 20 species and non-MRP has a lower species richness and abundance of fish communities. The dominant species in Pieh MRP was Ctenochaetus striatus with average abundant per site (21.3 ± 7.62, n = 3). Acanthuridae represents 55.98% of the total biomass in MRP-Core Zone, 63.13% in MRP-Utility Zone, and 41.55% in Non-MRP Area. This study showed the number of species and populations from corallivores fishes have decreased but has been an increase in herbivorous and carnivore diversity. The diversity indices (H') and ENS also shows no differ significantly between zonation. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In the face of increasing cumulative effects from human and natural disturbances, sustaining coral reefs will require a deeper understanding of the drivers of coral resilience in space and time. Here we develop a high‐resolution, spatially explicit model of coral dynamics on Australia's Great Barrier Reef (GBR). Our model accounts for biological, ecological and environmental processes, as well as spatial variation in water quality and the cumulative effects of coral diseases, bleaching, outbreaks of crown‐of‐thorns starfish (Acanthaster cf. solaris), and tropical cyclones. Our projections reconstruct coral cover trajectories between 1996 and 2017 over a total reef area of 14,780 km2, predicting a mean annual coral loss of −0.67%/year mostly due to the impact of cyclones, followed by starfish outbreaks and coral bleaching. Coral growth rate was the highest for outer shelf coral communities characterized by digitate and tabulate Acropora spp. and exposed to low seasonal variations in salinity and sea surface temperature, and the lowest for inner‐shelf communities exposed to reduced water quality. We show that coral resilience (defined as the net effect of resistance and recovery following disturbance) was negatively related to the frequency of river plume conditions, and to reef accessibility to a lesser extent. Surprisingly, reef resilience was substantially lower within no‐take marine protected areas, however this difference was mostly driven by the effect of water quality. Our model provides a new validated, spatially explicit platform for identifying the reefs that face the greatest risk of biodiversity loss, and those that have the highest chances to persist under increasing disturbance regimes. [ABSTRACT FROM AUTHOR]

Outbreaks of predatory crown-of-thorns seastars (COTS) can devastate coral reef ecosystems, yet some corals possess mutualistic guardian crabs that defend against COTS attacks. However, guarded corals do not always survive COTS outbreaks, with the ecological mechanisms sealing the fate of these corals during COTS infestations remaining unknown. In August 2008 in Moorea (17.539° S, 149.830° W), French Polynesia, an unusually dense multi-species aggregation of predators was observed feeding upon guarded corals following widespread coral decline due to COTS predation. Concurrent assaults from these amplified, mixed-species predator guilds likely overwhelm mutualistic crab defense, ultimately leading to the fall of guarded corals. Our observations indicate that guarded corals can sustain devastating COTS attacks for an extended duration, but eventually concede to intensifying assaults from diverse predators that aggregate in high numbers as alternative prey decays. The fall of guarded corals is therefore suggested to be ultimately driven by an indirect trophic cascade that leads to amplified attacks from diverse starving predators following prey decline, rather than COTS assaults alone.

Outbreaks of predatory crown-of-thorns seastars (COTS) can devastate coral reef ecosystems, yet some corals possess mutualistic guardian crabs that defend against COTS attacks. However, guarded corals do not always survive COTS outbreaks, with the ecological mechanisms sealing the fate of these corals during COTS infestations remaining unknown. In August 2008 in Moorea (17.539° S, 149.830° W), French Polynesia, an unusually dense multi-species aggregation of predators was observed feeding upon guarded corals following widespread coral decline due to COTS predation. Concurrent assaults from these amplified, mixed-species predator guilds likely overwhelm mutualistic crab defense, ultimately leading to the fall of guarded corals. Our observations indicate that guarded corals can sustain devastating COTS attacks for an extended duration, but eventually concede to intensifying assaults from diverse predators that aggregate in high numbers as alternative prey decays. The fall of guarded corals is therefore suggested to be ultimately driven by an indirect trophic cascade that leads to amplified attacks from diverse starving predators following prey decline, rather than COTS assaults alone.

Background: Chemosensation is a critical signalling process for all organisms and is achieved through the interaction between chemosensory receptors and their ligands. The Crown-of-thorns starfish, Acanthaster planci species complex (COTS), is a predator of coral polyps and Acanthaster cf. solaris is currently considered to be one of the main drivers of coral loss on the Great Barrier Reef in Queensland, Australia. Results: This study reveals the presence of putative variant Ionotropic Receptors (IRs) which are differentially expressed in the olfactory organs of COTS. Several other types of G protein-coupled receptors such as adrenergic, metabotropic glutamate, cholecystokinin, trace-amine associated, GRL101 and GPCR52 receptors have also been identified. Several receptors display male-biased expression within the sensory tentacles, indicating possible reproductive significance. Conclusions: Many of the receptors identified in this study may have a role in reproduction and are therefore key targets for further investigation. Based on their differential expression within the olfactory organs and presence in multiple tissues, it is possible that several of these receptor types have expanded within the Echinoderm lineage. Many are likely to be species-specific with novel ligand-binding affinity and a diverse range of functions. This study is the first to describe the presence of variant Ionotropic Glutamate Receptors in any Echinoderm, and is only the second study to investigate chemosensory receptors in any starfish or marine pest. These results represent a significant step forward in understanding the chemosensory abilities of COTS. [ABSTRACT FROM AUTHOR]

Abstract Numerous hypotheses have been put forward to account for population outbreaks of crown-of-thorns starfishes (CoTS, Acanthaster spp.), which place specific importance on either pre- or post-settlement mechanisms. The purpose of this review is to specifically assess the contributions of pre- versus post-settlement processes in the population dynamics of CoTS. Given the immense reproductive potential of CoTS (>100 million eggs per female), persistent high densities would appear inevitable unless there were significant constraints on larval development, settlement success, and/or early post-settlement growth and survival. In terms of population constraints, pre- and post-settlement processes are both important and have additive effects to suppress densities of juvenile and adult CoTS within reef ecosystems. It is difficult, however, to assess the relative contributions of pre- versus post-settlement processes to population outbreaks, especially given limited data on settlement rates, as well as early post-settlement growth and mortality. Prioritising this research is important to resolve potential effects of anthropogenic activities (e.g., fishing) and habitat degradation on changing population dynamics of CoTS, and will also improve management effectiveness. [ABSTRACT FROM AUTHOR]

Outbreaks of coral-eating crown-of-thorns sea stars (CoTS; Acanthaster species complex) cause substantial coral loss; hence, there is considerable interest in developing prevention and control strategies. We characterized the microbiome of captive CoTS and assessed whether dysbiosis was evident in sea stars during a disease event. Most tissue types had a distinct microbiome. The exception was female gonads, in which the microbiomes were highly variable among individuals. Male gonads were dominated (>97% of reads) by a single Mollicutes-related operational taxonomic unit (OTU). Detailed phylogenetic and microscopy analysis demonstrated the presence of a novel Spiroplasma-related bacterium in the spermatogenic layer. Body wall samples had high relative abundance (43 to 64% of reads) of spirochetes, likely corresponding to subcuticular symbionts reported from many echinoderms. Tube feet were characterized by Hyphomonadaceae (24 to 55% of reads). Pyloric cecal microbiomes had high alpha diversity, comprising many taxa commonly found in gastrointestinal systems. The order Oceanospirillales (genera Endozoicomonas and Kistimonas) was detected in all tissues. A microbiome shift occurred in diseased individuals although differences between tissue types were retained. The relative abundance of spirochetes was significantly reduced in diseased individuals. Kistimonas was present in all diseased individuals and significantly associated with diseased tube feet, but its role in disease causation is unknown. While Arcobacter was significantly associated with diseased tissues and Vibrionaceae increased in diversity, no single OTU was detected in all diseased individuals, suggesting opportunistic proliferation of these taxa in this case. This study shows that CoTS have tissuecharacteristic bacterial communities and identifies taxa that could play a role in reproduction and host health. IMPORTANCE Coral-eating crown-of-thorns sea stars (CoTS; Acanthaster species complex) are native to the Indo-Pacific, but during periodic population outbreaks they can reach extreme densities (>1,000 starfish per hectare) and function as a pest species. On the Great Barrier Reef, Australia, CoTS have long been considered one of the major contributors to coral loss. There has been significant investment in a targeted control program using lethal injection, and there is interest in developing additional and complementary technologies that can increase culling efficiencies. The biology of CoTS has been studied extensively, but little is known about their associated microbiome. This cultivation-independent analysis of the CoTS microbiome provides a baseline for future analyses targeting the functional role of symbionts, the identification of pathogens, or the development of reproduction manipulators. [ABSTRACT FROM AUTHOR]

Venomics research is being revolutionized by the increased use of sensitive -omics techniques to identify venom toxins and their transcripts in both well studied and neglected venomous taxa. The study of neglected venomous taxa is necessary both for understanding the full diversity of venom systems that have evolved in the animal kingdom, and to robustly answer fundamental questions about the biology and evolution of venoms without the distorting effect that can result from the current bias introduced by some heavily studied taxa. In this review we draw the outlines of a roadmap into the diversity of poorly studied and understood venomous and putatively venomous invertebrates, which together represent tens of thousands of unique venoms. The main groups we discuss are crustaceans, flies, centipedes, non-spider and non-scorpion arachnids, annelids, molluscs, platyhelminths, nemerteans, and echinoderms. We review what is known about the morphology of the venom systems in these groups, the composition of their venoms, and the bioactivities of the venoms to provide researchers with an entry into a large and scattered literature. We conclude with a short discussion of some important methodological aspects that have come to light with the recent use of new -omics techniques in the study of venoms.

Research on the coral-eating crown-of-thorns starfish (CoTS) has waxed and waned over the last few decades, mostly in response to population outbreaks at specific locations. This review considers advances in our understanding of the biology and ecology of CoTS based on the resurgence of research interest, which culminated in this current special issue on the Biology, Ecology and Management of Crown-of-Thorns Starfish. More specifically, this review considers progress in addressing 41 specific research questions posed in a seminal review by P. Moran 30 years ago, as well as exploring new directions for CoTS research. Despite the plethora of research on CoTS (>1200 research articles), there are persistent knowledge gaps that constrain effective management of outbreaks. Although directly addressing some of these questions will be extremely difficult, there have been considerable advances in understanding the biology of CoTS, if not the proximate and ultimate cause(s) of outbreaks. Moving forward, researchers need to embrace new technologies and opportunities to advance our understanding of CoTS biology and behavior, focusing on key questions that will improve effectiveness of management in reducing the frequency and likelihood of outbreaks, if not preventing them altogether. [ABSTRACT FROM AUTHOR]

Coral reefs are under threat from a variety of sources including the corallivorous seastar, Acanthaster cf. solaris. (Crown of Thorns Seastar; CoTS). Outbreak prediction is a strategic component of managing the impact of this boom and bust species. Details on the fate and dispersal of planktonic life stages are limited, with CoTS larval stages indistinct morphologically from many other asteroid larvae. Given the similarity of many larvae, quantification of marine larvae stages is a major challenge for marine ecologists. We describe a quantitative polymerase chain reaction (qPCR) assay that enables the enumeration of CoTS larvae in field collected plankton samples. Specific primers for the mitochondrial cytochrome oxidase subunit 1 gene (mtCOI) were developed and validated for specificity and sensitivity. Larval culture experiments with CoTS allowed us to determine the mtCOI copy number per larval stage which aided in relating copy numbers in the plankton to actual larval densities. We found the mtCOI copy number varied 3.6-fold across all CoTS planktonic life stages from unfertilised oocyte to competent brachiolaria and this variation was taken into account when determining CoTS larval densities in field samples on the Great Barrier Reef (GBR). CoTS larvae were detected at many locations in the CoTS 'initiation box' on the GBR between Cairns and Lizard Island in December 2014 with the highest mean CoTS larval density at 36.9 (23.7-84.3) CoTS larvae m between Rudder and Tongue Reef (16.233°S, 145.643°E). Field negative samples taken outside spawning season along with DNA extraction recovery experiments confirmed our sampling, extraction and assay methods were robust. This method will greatly help further studies on understanding CoTS larval ecology and outbreaks, with methods developed also important tools for other ecologically and commercially important marine species. [ABSTRACT FROM AUTHOR]

Coral-eating crown-of-thorns starfish ( Acanthaster sp.) often exhibit dramatic population outbreaks, suggesting that their local abundance may be relatively unchecked by predators. This may be due to high concentrations of anti-predator chemicals (saponins and plancitoxins), but the effectiveness of chemical deterrents in protecting Acanthaster sp., especially spawned eggs, from predation remains controversial. We show that planktivorous damselfishes will readily consume food pellets with low proportions (≤80%) of eggs of crown-of-thorns starfish. However, all fishes exhibited increasing rejection of food pellets with higher proportions of starfish eggs, suggesting that chemicals in eggs of crown-of-thorns starfish do deter potential predators. Interestingly, palatability thresholds varied greatly among the nine species of planktivorous fish tested. Most notably, Amblyglyphidodon curacao consumed food pellets comprising 100% starfish eggs 1.5 times more than any other fish species, and appeared largely insensitive to increases in the concentration of starfish eggs. After standardising for size, smaller fish species consumed a disproportionate amount of pellets comprising high proportions of starfish eggs, indicating that abundant small-bodied fishes could be particularly important in regulating larval abundance and settlement success of crown-of-thorns starfish. Collectively, this study shows that reef fishes vary in their tolerance to anti-predator chemicals in crown-of-thorns starfish and may represent important predators on early life-history stages. [ABSTRACT FROM AUTHOR]

Understanding the influence of environmental factors on the development and dispersal of crown-of-thorns seastars is critical to predicting when and where outbreaks of these coral-eating seastars will occur. Outbreaks of crown-of-thorns seastars are hypothesized to be driven by terrestrial runoff events that increase nutrients and the phytoplankton food for the larvae. In addition to increasing larval food supply, terrestrial runoff may also reduce salinity in the waters where seastars develop. We investigated the effects of reduced salinity on the fertilization and early development of seastars. We also tested the interactive effects of reduced salinity and reduced pH on the hatching of crown-of-thorns seastars. Overall, we found that reduced salinity has strong negative effects on fertilization and early development, as shown in other echinoderm species. We also found that reduced salinity delays hatching, but that reduced pH, in isolation or in combination with lower salinity, had no detectable effects on this developmental milestone. Models that assess the positive effects of terrestrial runoff on the development of crown-of-thorns seastars should also consider the strong negative effects of lower salinity on early development including lower levels of fertilization, increased frequency of abnormal development, and delayed time to hatching. [ABSTRACT FROM AUTHOR]

The dispersal potential of crown-of-thorns starfish (CoTS) larvae is important in understanding both the initiation and spread of population outbreaks, and is fundamentally dependent upon how long larvae can persist while still retaining the capacity to settle. This study quantified variation in larval survivorship and settlement rates for CoTS maintained at three different densities of a single-celled flagellate phytoplankton, Proteomonas sulcata (1 × 103, 1 × 104, and 1 × 105 cells/mL). Based on the larval starvation hypothesis, we expected that low to moderate levels of phytoplankton prey would significantly constrain both survival and settlement. CoTS larvae were successfully maintained for up to 50 days post-fertilization, but larval survival differed significantly between treatments. Survival was greatest at intermediate food levels (1 × 104 cells/mL), and lowest at high (1 × 105 cells/mL) food levels. Rates of settlement were also highest at intermediate food levels and peaked at 22 days post-fertilization. Peak settlement was delayed at low food levels, probably reflective of delayed development, but there was no evidence of accelerated development at high chlorophyll concentrations. CoTS larvae were recorded to settle 17-43 days post-fertilization, but under optimum conditions with intermediate algal cell densities, peak settlement occurred at 22 days post-fertilization. Natural fluctuations in nutrient concentrations and food availability may affect the number of CoTS that effectively settle, but seem unlikely to influence dispersal dynamics. [ABSTRACT FROM AUTHOR]

The unanticipated impacts of consumers in fragmented habitats are frequently a challenge for ecosystem management. On Indo-Pacific coral reefs, crown-of-thorns sea stars (Acanthaster spp.) are coral predators whose outbreaks cause precipitous coral decline. Across large spatial scales, Acanthaster densities are lower in large no-take Marine Protected Areas (MPAs) and reefs subject to limited human exploitation. However, using a combination of observational and manipulative experiments, we found that Acanthaster densities within a network of small, no-take MPAs on reef flats in Fiji were ~2–3.4 times greater inside MPAs than in adjacent fished areas and ~2–2.5 times greater than the upper threshold density indicative of an outbreak. This appeared to result from selective Acanthaster migration to the coral-rich MPAs from fished areas that are coral-poor and dominated by macroalgae. Small MPAs can dramatically increase the cover of foundation species like corals, but may selectively attract coral predators like Acanthaster due to greater food densities within MPAs or because the MPAs are too small to support Acanthaster enemies. As coral cover increases, their chemical and visual cues may concentrate Acanthaster to outbreak densities that cause coral demise, compromising the value of small MPAs. An understanding of predator dynamics as a function of habitat type, size, and fragmentation needs to be incorporated into MPA design and management. [ABSTRACT FROM AUTHOR]