Crown-of-thorns Starfish Outbreaks Research Articles

Genomic Single Nucleotide Polymorphism (SNP) markers and mitochondrial haplotypes illuminate the origins of Crown-of-Thorns Starfish (Acanthaster solaris) outbreaks in the South China Sea.

Outbreaks of the coral predator Crown-of-Thorns Starfish (CoTS) pose a severe threat to coral reefs in the Indo-Pacific Ocean. In 2018, the South China Sea (SCS) experienced significant CoTS outbreaks, leading to extensive coral mortality across the Xisha, Zhongsha, Dongsha, and Nansha Islands, severely impacting the coral reef ecosystem. To explore the origins of these outbreaks, we conducted a comprehensive genomic analysis using data from genomic single nucleotide polymorphism sites (SNPs) and mitochondrial haplotypes. Our analysis reveals that CoTS populations in the SCS, which exhibit moderate genetic diversity and may have undergone positive selection or population expansion. There was limited genetic differentiation among CoTS populations from XS, ZS, and NS groups. Especially between the XS and ZS groups, there was almost no genetic differentiation. The populations from XS, ZS, and NS groups have strong genetic connections with populations in Vietnam and the Philippines. There was high gene flow from Vietnam to the Xisha Islands and from the Philippines to the Nansha Islands, suggesting that the CoTS populations in these regions primarily originate from these neighboring countries. The comprehensive analyses of SNP and mitochondrial genomes have provided valuable insights into the population genetics of CoTS. This research has generated significant genomic resources and facilitated important studies on the genetics of the CoTS species. By identifying potential source populations and understanding the genetic basis of their spread, managers can develop more effective conservation strategies to protect vulnerable coral reef ecosystems in the SCS.

THREE-DECADE changes of reef cover in Pulau Layang-Layang, Malaysia using multitemporal Landsat images

Over the years, coral reefs in the South China Sea have degraded and faced severe threats from rapid development, coral bleaching, and Crown-of-Thorns Starfish (COTS) outbreak. There is limited knowledge relating to the effects of anthropogenic disturbances and natural events on the coral reefs of Pulau Layang-Layang. This study aims to assess reef cover changes by utilizing Landsat satellite images spanning from 1989 to 2022. Using the object-based image analysis method, this study classified the reef cover into three categories: coral, rock and rubble, and sand. The supervised classification had an overall accuracy of 86.41–87.38 % and Tau's coefficients of 0.80–0.81. The results showed island development and construction of artificial bird sanctuary have led to an increase in coral cover. Furthermore, it was illustrated that the impact of COTS outbreaks in 2010 and 2020 differed significantly, with the latter showing no signs of recovery. Our study underscores the importance of timely intervention to mitigate the spread of COTS. This study provides insights into the resilience and vulnerability of these ecosystems in the face of various stressors.

Stochastic dynamics of coral reef system with stage-structure for crown-of-thorns starfish

The outbreak of crown-of-thorns starfish (CoTS) is one of the most critical biological disturbances in coral reef systems and contributes greatly to the degradation of coral. Although many studies have focused on coral-CoTS interactions, there is no effective method for suppressing CoTS outbreaks in the long term, in part because of incomplete knowledge of their life cycle. In this paper, a stochastic system is formulated to characterize the interactions among coral, immature CoTS, and mature CoTS, where environmental noise is introduced into the growth of coral. The existence and uniqueness of a global positive solution with any given initial value are investigated, sufficient conditions are established for the extinction of CoTS, and the existence and uniqueness of a stable stationary distribution are explored by applying the Markov semigroup theory. In particular, by solving the Fokker–Planck equation, the approximate expression of the probability density function of the distribution around its quasi positive equilibrium is expounded under certain parametric restrictions. By employing Milstein’s higher-order method, numerical simulations are presented to validate the theoretical results. This study reveals that coral are more vulnerable and are more likely to go extinct in the presence of strong noise, while weak noise is more conducive to the existence of a stable stationary distribution, which implies the long-term persistence of coral and CoTS.

The effect of catchment load reductions on water quality in the crown-of-thorn starfish outbreak initiation zone

Crown-of-Thorns Starfish (CoTS) population outbreaks contribute to coral cover decline on Indo-Pacific reefs. On the Great Barrier Reef (GBR), enhanced catchment nutrient loads are hypothesised to increase phytoplankton food for CoTS larvae in the outbreak initiation zone. This study examines whether catchment load reductions will improve water quality in this zone during the larval period. We defined the i) initiation zone's spatial extent; ii) larval stage's temporal extent; and iii) water quality thresholds related to larval food, from published information. We applied these to model simulations, developed to quantify the effect of catchment load reductions on GBR water quality (Baird et al., 2021), and found a consistently weak response of chlorophyll-a, total organic nitrogen and large zooplankton concentrations in the initiation zone. Model results indicate marine and atmospheric forcing are more likely to control the planktonic biomass in this zone, even during major flooding events purported to precede CoTS outbreaks.

Reconstructing past disturbance in coral communities using U-Th dating of dead coral skeletons

Abstract In the absence of detailed broad-scale studies, both spatially and temporally, the overall status (disturbed, recovering, or in decline) of many of the reefs that make up the Great Barrier Reef remains uncertain. Moreover, of the numerous and varied threats, their relative role in impacting individual reefs is generally unclear. Here, we adopt a novel approach to reliably reconstruct historical disturbance events at Rib and Davies Reefs, two mid-shelf reefs, using uranium-thorium (U-Th) dating of dead corals. Corrected 230Th ages obtained from dead Acropora spp. bracket time periods of lowest coral cover observed during independent ecological surveys in the late 1980s and 2000s at 1988.2 ± 1.3 and 2003.9 ± 6.2 CE, shortly after the arrival of crown-of-thorns starfish (CoTS) at Rib Reef in 1983–1985 and 2000–2002, respectively. At Davies Reef, 230Th ages dated to 1999.2 ± 1.2 CE when coral cover was halved as a result of Cyclone Tessi and an “unknown” disturbance in 2000–2001. Prior to modern surveys, there is remarkable overlap in 230Th ages between reefs, with repeated peaks in the age distribution having a return period of ~10–15 years, akin to the periodicity of modern CoTS outbreaks. Our findings suggest that U-Th dating of dead corals can provide a robust foundation for understanding disturbance history and show promise in contributing to the effective monitoring of coral communities by providing a reliable benchmark with which to assess recovery.

Preparing for and managing crown-of-thorns starfish outbreaks on reefs under threat from interacting anthropogenic stressors

Crown-of-thorns starfish (CoTS) outbreaks rank among the greatest threats to coral throughout the Indo-Pacific. In the future, reefs already stressed by CoTS will be further burdened by overfishing and nutrient loading. How much these two factors will exacerbate CoTS outbreak severity is still uncertain. Furthermore, the CoTS management literature has focused on the Great Barrier Reef, whereas outbreak damage is rising across the Indo-Pacific. Here, we use a metacommunity model to simulate CoTS outbreaks in areas with high and growing levels of fishing pressure and offshore nutrient input. We model outbreaks on reefs adjacent to two cities within the range of CoTS that have less prior literature coverage: Cebu City, Philippines, and Jeddah, Saudi Arabia. We observe that the combination of population increases and urbanization of previously rural areas can drive complex patterns of multi-stressor interaction. We find that CoTS removal on intermediate spatial scales significantly improves regional-scale coral health, and provide guidelines under which each of four CoTS management strategies is optimal for conservation. We find that coral decline due to overfishing can be sharper on reefs with CoTS, and that nutrification can induce a shift from discrete outbreak waves to continuous CoTS presence. Our work shows the importance of long-term planning for reef management, and highlights how reef stressors can interact in potentially unforeseen ways.

A Review of the Giant Triton (Charonia tritonis), from Exploitation to Coral Reef Protector?

Charonia tritonis (Charoniidae), one of the largest marine gastropods and an echinoderm specialist, preys on Crown-of-Thorns starfish (CoTS), a recurring pest that continues to be a leading cause of coral mortality on Indo-Pacific reefs. Widespread historical exploitation has impacted their numbers, with standing populations considered rare throughout their habitat. Their life-stage attributes, i.e., teleplanic larvae, planktotrophic phase spanning years permitting transoceanic dispersal, and recruitment to coral reefs through oceanic influx with intense larval mortality, have likely hindered their recovery. Decline in numbers is hypothesised to account partially for periodic CoTS outbreaks, yet predator-prey dynamics between these two species that might influence this are poorly understood. The C. tritonis excretory secretome elicits a proximity deterrence effect on CoTS, the nature of which is under investigation as a possible tool in CoTS biocontrol scenarios. However, specificity and zone of impact in situ are unknown, and whether the mere presence of C. tritonis and/or predation pressure has any regulatory influence over CoTS populations remains to be established. The fundamental taxonomy and distinctive characteristics, biology and ecology of C. tritonis is summarized, and knowledge gaps relevant to understanding their role within coral reefs identified. Information is provided regarding exploitation of C. tritonis across its habitat, and prospects for conservation interventions, including captive rearing and stock enhancement to repopulate local regions, are discussed. Its predator-prey ecology is also examined and potential to mitigate CoTS considered. Recommendations to direct future research into this predator and for its inclusion in a CoTS integrated pest management strategy to improve coral reef health are offered.

Crown-of-Thorns starfish (COTS) outbreak in Sogod Bay, Southern Leyte, Philippines

Sogod Bay is known for its high diversity and abundance of hard coral. However, this resource is under threat due to the coral predator, crown-of-thorns starfish (COTS) Acanthaster spp. The findings of 2021 COTS outbreaks in reefs belonging to territorial waters of Liloan, Libagon, San Francisco, Malitbog, and Padre Burgos, Southern Leyte, are reported here. The lowest COTS count was recorded for Padre Burgos while highest in Malitbog with 13 and 20 COTS 100 m-2, respectively, exceeding the outbreak threshold of 0.25 COTS 100 m-2. COTS collected from Malitbog, although highest in number, weighed lightest (251 ± 128g) while heaviest in San Francisco (621 ± 250g). The majority of COTS collected were in the juvenile stage with sizes ranging from 6-15 cm, corresponding to COTS age of 1-2 years. Regarding COTS sexes, the proportion of female COTS was higher relative to male COTS in Padre Burgos and Malitbog while lower in Libagon, Liloan, and San Francisco. A trend in the low total count of COTS regenerating arm was observed, indicative of the absence of COTS predator. Overall, the findings of this study imply that the COTS outbreak in Sogod Bay is a recurring phenomenon. Thus management efforts should be directed into areas with the over-the-outbreak threshold of COTS. The large quantities of COTS observed in Sogod Bay, Southern Leyte would further necessitate an improved management strategy, to reduce the detrimental impact of COTS outbreaks in the reef ecosystem. Periodic monitoring of COTS along Sogod Bay is recommended to reveal the extent of damage and potential clean-up efforts. Conduct of trainings to include Information, Education, and Communication (IEC) campaign to municipalities categorized under active outbreak status is also recommended. Finally, studies are warranted to look into COTS population replenishment, and outbreak drivers.

Suppressing the next crown-of-thorns outbreak on the Great Barrier Reef

Crown-of-thorns starfish (COTS) outbreaks are a globally significant driver of coral mortality in the Indo-Pacific and work synergistically with other disturbances. We argue that our improved understanding of COTS ecology and ability to monitor their populations, combined with new efficiencies in COTS control technologies, provides a sound basis for attempting to suppress COTS outbreaks on the GBR before they reach full outbreak status. This conclusion is based on research on the GBR which we have synthesised to develop a new, pragmatic approach to managing primary outbreaks. We also outline key actions that must be undertaken in order for suppression to be successful, providing clear direction for future management action. The next COTS outbreak on the GBR is predicted to begin between 2025 and 2027, consequently efforts to detect and suppress pre-initiation populations must start no later than the summer of 2022–2023.

Crown-of-Thorns Starfish Larvae Can Feed on Organic Matter Released from Corals

Previous studies have suggested that Crown-of-Thorns starfish (COTS) larvae may be able to survive in the absence of abundant phytoplankton resources suggesting that they may be able to utilize alternative food sources. Here, we tested the hypothesis that COTS larvae are able to feed on coral-derived organic matter using labeled stable isotope tracers (13C and 15N). Our results show that coral-derived organic matter (coral mucus and associated microorganisms) can be assimilated by COTS larvae and may be an important alternative or additional food resource for COTS larvae through periods of low phytoplankton biomass. This additional food resource could potentially facilitate COTS outbreaks by reducing resource limitation.

Effectiveness of the removal of coral-eating predator Acanthaster planci in Pulau Tioman Marine Park, Malaysia

Population outbreaks of the coral-eating predator crown of thorns starfish (COTS), Acanthaster planci are responsible for large-scale disturbance of coral reefs throughout the Indo-Pacific. In response, attempts are often made to control COTS outbreaks in protected areas. For instance, volunteers remove thousands of sea stars every year in Malaysia. This study reports the status of the COTS population in the Pulau Tioman Marine Park and examines the effectiveness of the seasonal sea star removal programme. After the 2009 removal season, we monitored COTS densities and coral assemblages before and after a 6-month no-removal season at sites with and without COTS removal efforts. We recorded high COTS densities up to 330 ind. ha−1 at a few sites independent of removal effort. In fact, removal only temporarily reduced large individuals from local populations. Moreover, after the no-removal season, sites with COTS removal had increased live coral cover, but sites without COTS removal had a drastic decrease in live coral cover, with Acropora spp. being most affected. Therefore, this study suggests that the current seasonal removals could promote coral health, despite the high density of COTS.

Spatiotemporal modelling of crown‐of‐thorns starfish outbreaks on the Great Barrier Reef to inform control strategies

Summary Cyclical outbreaks of pests can impact the functioning of entire ecosystems. An eminent example is outbreaks of crown‐of‐thorns starfish (COTS; Acanthaster planci) that cause substantial coral mortality on the Great Barrier Reef (GBR). We analyse COTS abundance and outbreaks with a Bayesian spatiotemporal model applied to a long‐term survey of the GBR (1985–2014). We assess the relative increase in COTS abundance beyond that explained by a reef's location and explanatory covariates, and thereby incorporate local reef characteristics into the identification of outbreaks, while allowing for both randomness and predictable patterns in the development of outbreaks. The model results confirm that waves of COTS outbreaks originate near Lizard Island (14·67⁰S) and progress in a northwesterly or southeasterly direction, with the southward wave progressing about 60 km year−1. The model reveals several previously unidentified hotspots with high average COTS abundance. The abundance of COTS may also have decreased on reefs protected from fishing after an expansion of protected areas within the GBR Marine Park in 2004, which suggests that closing reefs to fishing may help control COTS. Synthesis and applications. In this study, we use 30 years of data from the Great Barrier Reef to show that the timing and geographic location of crown‐of‐thorns starfish (COTS) outbreaks can be modelled by incorporating covariates, spatial and spatiotemporal dependence within a single coherent framework. The model can be used to identify areas of high average COTS abundance, to assess the impact of fishery management actions such as no‐take areas and to identify areas where waves of outbreaks may originate. The identification of outbreaks from noisy long‐term spatially extensive data may help managers choose appropriate control strategies. This modelling approach is applicable to other ecosystems where outbreaks of damaging pests occur.

Localized outbreaks of Acanthaster planci at an isolated and unpopulated reef atoll in the Chagos Archipelago

Outbreaks of the crown-of-thorns starfish (COTS), Acanthaster planci, have occurred at many locations throughout the Indo-Pacific and are a major contributor to widespread coral loss and reef degradation. The causes of outbreaks remain controversial, but are commonly attributed to anthropogenically elevated nutrients and/or over-fishing. If so, it seems unlikely that outbreaks would occur in reef systems that are largely isolated from anthropogenic disturbances. However, high densities of COTS were recently observed on reefs in the Chagos Archipelago, a remote group of atolls and banks within the central Indian Ocean, which experience very limited anthropogenic influence. Aggregations of COTS were first noticed at Eagle Island in 2012, which, although unquantified, appeared to be at outbreak levels, and very high densities (1624 km−2) were subsequently recorded at Danger Island in 2013. While these islands are uninhabited by humans, it is possible that nutrient inputs result from upwelling zones around the Archipelago, or high densities of breeding seabirds. Among islands within the Great Chagos Bank, densities of the red-footed booby Sula sula ranged from 8 to 7888 individuals km−2, with associated guano input ranging from 96 to 25,381 kg island−1 year−1. However, Danger and Eagle Islands where high COTS densities were recorded, had both high and low levels of guano production, respectively, which suggests that outbreaks may not be directly linked to guano nutrient enrichment. Other factors which might be responsible for intermittent COTS outbreaks should be considered in isolated reef systems such as the Chagos Archipelago.

Ecologically based targets for bioavailable (reactive) nitrogen discharge from the drainage basins of the Wet Tropics region, Great Barrier Reef

A modelling framework is developed for the Wet Tropics region of the Great Barrier Reef that links a quantitative river discharge parameter (viz. dissolved inorganic nitrogen concentration, DIN) with an eutrophication indicator within the marine environment (viz. chlorophyll-a concentration, chl-a). The model predicts catchment-specific levels of reduction (%) in end-of-river DIN concentrations (as a proxy for total potentially reactive nitrogen, PRN) needed to ensure compliance with chl-a ‘trigger’ guidelines for the ecologically distinct, but PRN-related issues of crown-of-thorns starfish (COTS) outbreaks, reef biodiversity loss, and thermal bleaching sensitivity. The results indicate that even for river basins dominated by agricultural land uses, quite modest reductions in end-of-river PRN concentrations (∼20–40%) may assist in mitigating the risk of primary COTS outbreaks from the mid-shelf reefs of the Wet Tropics. However, more significant reductions (∼60–80%) are required to halt and reverse declines in reef biodiversity, and loss of thermal bleaching resistance.

Origins and Implications of a Primary Crown-of-Thorns Starfish Outbreak in the Southern Great Barrier Reef

The crown-of-thorns starfish (COTS) is a major predator of hard corals. Repeated COTS outbreaks in the Cairns and Central sections of the Great Barrier Reef (GBR) have been responsible for greater declines in coral cover than any other type of disturbance, including cyclones, disease, and coral bleaching. Knowledge of the precise timing and location of primary outbreaks could reveal the initial drivers of outbreaks and so could indicate possible management measures. In the central GBR, COTS outbreaks appear to follow major flooding events, but despite many years of observations, no primary outbreak has ever been unequivocally identified in the central and northern GBR. Here we locate a primary outbreak of COTS on the southern GBR which is not correlated with flooding. Instead it appears to have been the result of a combination of life history traits of COTS and prevailing oceanographic conditions. The hydrodynamic setting implies that the outbreak could disperse larvae to other reefs in the region.

Model to manage and reduce crown-of-thorns starfish outbreaks

The crown-of-thorns starfish (COTS) Acanthaster planci is one of the largest causes of coral cover loss on Australia's Great Barrier Reef. Numerous trophic-mediated and anthro- pogenic-related hypotheses, singly or in combination, have been proposed to explain COTS out- breaks, but the evidence remains inconclusive. There is, however, an urgent need for effective control and mitigation strategies. We develop a model of intermediate complexity for ecosystem assessments to describe the trophic interactions between juvenile and adult COTS and 2 groups of coral (fast- and slow-growing corals). By fitting to available data, the impact of prey-switching behaviour by COTS and its effects on the system are quantified. Simulations are used to evaluate the effects of (1) predation by large fish on adult COTS, (2) predation by benthic invertebrates on juvenile COTS, and (3) manual removal of adult COTS. The results highlight the effectiveness of invertebrate predation at reducing juvenile COTS numbers and suggest that manual removal is unlikely to be an effective control method except on a small scale. Our model focuses on the importance of trophic interactions in COTS control and provides an initial platform for future work which foresees the estimation of the effects of key predators, no-take areas, anthropogenic nutrient enhancement, and reef connectivity in mediating the spatio-temporal heterogeneity of COTS outbreaks.

The role of protein extracts in the induction of disease in Acanthaster planci

Thiosulfate–citrate–bile–sucrose agar (TCBS) has been shown to induce pathogenesis in the crown-of-thorns starfish (COTS), Acanthaster planci, providing potentially novel options to control COTS outbreaks, but the mechanistic basis for this effect is unknown. This study explores reactions of COTS to individual ingredients of TCBS, testing for allergic reactions versus pathogenesis. Four out of nine TCBS chemical ingredients tested induced allergic reactions and death in injected COTS. Peptone 10gl−1 and oxgall 8gl−1 induced 100% mortality, while yeast extract and agar induced death in 40% and 20% of COTS, respectively, 48h after injection. Peptone was evaluated at three different concentrations (10g, 5g, and 1gl−1). Peptone 10gl−1 induced 100% mortality, peptone 5gl−1 killed 60% of injected COTS, and peptone 1gl−1 induced death in only 20% of challenged COTS, indicating that toxicity of peptone is concentration-dependent. Sodium citrate induced moderate mucus production in all COTS challenged, but disease did not progress and COTS completely recovered after 52h. The remaining ingredients in TCBS did not produce any kind of clinical signs of disease. Peptone, oxgall, and yeast are potentially useful in controlling outbreaks because these protein extracts can be safer to use compared to previously used noxious chemicals. In addition, lowered concentrations are required to kill COTS, therefore increasing efficiency by saving time, money, and effort in COTS control programs.