In the scientific world, this subject has been explored and argued for a long time. It has become increasingly obvious as a result of this research that outbreaks are unlikely to be caused by a single source. Instead, it’s more likely that a number of elements work together to create the right conditions for an outbreak to start, including:
- the biological characteristics of crown-of-thorns starfish that allow colonies to grow and reproduce fast in the correct conditions
- reductions in the number of natural predators of crown-of-thorns starfish, which may improve the capacity of crown-of-thorns starfish populations to expand and reach epidemic levels.
- surplus nutrients from run-off or natural upwelling that give additional nourishment for crown-of-thorns starfish larvae to live and reproduce
- Ocean current patterns that disseminate crown-of-thorns starfish larvae in a way that favors outbreak development
- the availability of enough live coral as a food supply to sustain the outbreak’s population.
Why are crown-of-thorns starfish a problem?
Crown-of-thorns starfish outbreaks have wreaked havoc on the Great Barrier Reef’s several reefs since 1962. In the World Heritage Area, a fourth outbreak is now ongoing.
Crown-of-thorns starfish (also known as COTS) are coral-eating marine invertebrates. They’re found on reefs all around the Indo-Pacific, and when the conditions are right, they may spread like a plague, decimating hard coral communities.
After coral bleaching, crown-of-thorns starfish are a major driver of coral loss on the Great Barrier Reef, according to our research.
On the Reef, AIMS manages a large crown-of-thorns starfish monitoring program. Over a 15-year period, this long-term study found that epidemics start in the north and travel south, with ocean currents moving larvae between reefs.
The surveys also reveal that good reefs rebound after outbreaks, but it takes 10 to 20 years. However, reefs that are subjected to additional stresses, such as coral bleaching, cyclones, or poor water quality, take longer to recover, and the coral may not fully recover before the next round of breakouts.
What factors are increasing the frequency of crown-of-thorns starfish outbreaks?
Since the first well-documented outbreaks in the 1960s, the crown-of-thorns starfish (COTS), Acanthaster planci, has been a major problem for managers of Indo-Pacific coral reefs (, also reviewed in ). The devastation caused by high COTS densities (for example) has prompted considerable direct, diver-based control measures. Divers have killed or removed more than 17 million COTS from Indo-Pacific coral reefs since the 1960s, but even with consistent effort, direct control methods have often failed to prevent considerable coral loss, and COTS outbreaks remain a major cause of coral mortality in many locations. Long-term COTS outbreak management that is more effective must be founded on a comprehensive understanding of the underlying causes of outbreaks and how they start. For the first time, we employ qualitative modeling to analyze and assess a wide range of causes and mechanisms in a rigorous and transparent manner, allowing us to prioritize research into the origins of COTS outbreaks.
Several hypotheses have been proposed to explain the occurrence of Acanthaster spp. population outbreaks (reviewed by ), emphasizing either biological traits of COTS, such as rapid growth and phenomenal reproductive capacity, that predispose them to major population fluctuations (e.g., ‘natural causes hypothesis,’ ‘adult aggregation hypothesis,’ ‘prey-threshold hypothesis,’ or anthropogenic changes in environmental conditions that have eroded normal regulatory proc The extent to which anthropogenic disturbances (i.e., coastal development and overfishing) generate or exacerbate outbreaks has a significant impact on determining effective management solutions (e.g., ), although no single hypothesis has unequivocal and universal acceptance. Many biologists and theoretical ecologists agree that a single reason is unlikely to explain the wide range of crown-of-thorns outbreaks (reviewed by ), which range from localized epidemics on small isolated atolls (e.g., Chagos;, Moorea) to chronic, large-scale outbreaks (reviewed by ). (Japan; , Oman; ). This is not to argue that in some cases, a single component (e.g., higher nutrients) or the life history features of Acanthaster alone could not explain the onset and spread of COTS epidemics.
There have been four documented COTS outbreaks on Australia’s Great Barrier Reef (GBR). The first outbreak was discovered in 1962 on Green Island, while many earlier outbreaks may have gone mostly undiscovered. There have been three further rounds of outbreaks since 1962, beginning in 1979, 1993, and 2010. High densities of starfish were originally found on mid-shelf reefs between Cairns and Cooktown during each of these four well-documented outbreaks “initiation box”), and then propagated southwards at rates of 50100 kmy-1 for about 15 years in conformity with prevailing hydrodynamic circumstances. The commencement of main outbreaks north of Cairns has been related to reef-wide outbreaks on the GBR, according to genetic analyses. Moderate degrees of connectivity across reefs on the GBR therefore allow for a more efficient exchange of information “A “traveling wave” of secondary outbreaks spreads distant from the point of origin. It is commonly understood that the massive numbers of larvae produced by dense populations of well-fed starfish (the initial outbreak) will ultimately result in secondary outbreaks on downstream reefs. Understanding the cause(s) of outbreaks, and thus determining the most effective management measures, necessitates a clear focus on the elements that contribute to the initial commencement of different outbreaks (e.g.,), rather than specific patterns of occurrence for secondary waves of outbreaks. These findings will be useful in the numerous parts of the Indo-Pacific region where attempts are being made to investigate and manage recent COTS outbreaks spanning from Oman to Moorea and north to Okinawa.
Though demographic models of vast coral populations predict outbreaks of crown-of-thorns starfish may presently be more frequent and intense than at any time in the past several hundred years, paleontological data linked to the prevalence of past outbreaks is equivocal. This shows that anthropogenic disturbances (such as coastal expansion, poor land-use practices, and overfishing) have had a direct role in increasing the frequency and severity of COTS outbreaks. Alternatively, the growing frequency and diversity of disturbances, as well as their cumulative influence on coral reef ecosystems, may have weakened reef ecosystems’ ability to endure protracted Acanthaster spp. outbreaks. What is known is that the GBR, and reefs in general, will not be able to withstand the levels of disruption generated by COTS outbreaks since the 1980s.
How do you stop crown-of-thorns starfish?
As part of the Marine Park Authority’s Crown-of-thorns Starfish Strategic Management Framework, the Crown-of-thorns Starfish Control Program was formed in 2012 and provides a tactical reaction to outbreaks.
The method employs dedicated vessels with highly trained crews to hand cull starfish using bile salts or household vinegar as a deadly injection. The Crown-of-thorns Starfish Control Program also includes strategic surveillance and monitoring efforts. This ensures that culling efforts are focused on the areas that will provide the most benefit, that progress is tracked, and that pest control outcomes are maintained once they have been reached.
Supporting the environment and Reef communities
The Crown-of-thorns Starfish Control Program provides social and economic benefits to Australians in addition to environmental benefits for the Great Barrier Reef’s health. The program has been delivered in collaboration with the Reef tourism industry through the Association of Marine Park Tourism Operators since its inception (AMPTO). The reef is kept healthy in areas where local tourism firms send their national and international customers to experience the Great Barrier Reef through targeted crown-of-thorns starfish control. More than 100 people, mostly from Queensland, are trained and employed as part of the initiative.
Program growth and funding
At first, the program only had one or two dedicated ships. However, the outbreak that started in the northern management region in 2010 migrated south over time. The Crown-of-thorns Starfish Control Program received more money in 2018. In 2018-19, the program was able to expand from two to six vessels thanks to the additional funding. The expansion of the program allowed for the first time the deployment of crown-of-thorns starfish control vessels in the Marine Park’s far north and far south.
Five crown-of-thorns starfish control vessels have been deployed in the Marine Park’s northern, central, and southern management districts as of 2019-20. Control activities are deliberately tailored within each management region to focus on reefs of high ecological and economic value.
Since 2012, the Australian government has been funding the Crown-of-thorns Starfish Control Program. The Reef Trust Partnership (RTP) between the Great Barrier Reef Foundation (GBRF) and the Department of Agriculture, Water and the Environment provided funding for the Program in 2019-20. (DAWE). The GBRF and the DAWE have fully supported it through the RTP for 2020-22. The GBRF, the Great Barrier Reef Marine Park Authority (the Marine Park Authority), and the Reef and Rainforest Research Centre have formed a strategic collaboration to deliver the Program’s manual in-water control component (RRRC).
What type of pollutant causes outbreaks of crown-of-thorns starfish in the Great Barrier Reef?
The combined consequences of coral bleaching and crown of thorns starfish outbreaks have scientists worried that the Great Barrier Reef will be unable to recover. Dr. Udo Engelhardt*, in a new WWF-Australia research, calls for a crackdown on the “excessive, and often unlawful” use of industrial fertilisers that cause outbreaks.
What is the main predator of the crown-of-thorns starfish?
The gigantic triton snail, humphead Maori wrasse, starry puerfish, and titan trigger fish are all predators of adult crown-of-thorns starfish. Shrimp, crabs, and polychaete worms are all predators of immature starfish.
What happened to the crown-of-thorns?
The thornless remnants are housed in the treasury of Notre-Dame Cathedral in Paris, where they survived a horrific fire that devastated the roof and spire of the church in April 2019.
Why are crown-of-thorns sea star outbreaks problematic in coral reefs?
This coral predator is well-known, and outbreaks of tens of thousands of individuals have been observed to inflict considerable damage to coral reefs in some regions. These outbreaks could be the result of overfishing of the giant triton, the crown-of-thorns starfish’s major predator, or they could be a natural occurrence.
How is the crown-of-thorns starfish threatening the world’s coral reefs?
Coral reefs are a sensitive species that can be harmed by a variety of factors. One of these harmful disruptions is intermittent outbreaks of the Crown-of-Thorns coral killing sea star (Acanthaster planci). These sea star outbreaks pose a threat to our ocean’s health since they feed on and deplete reef-building coral, altering the marine ecosystem’s existing composition.
The reasons and spatiotemporal dynamics of these sea star epidemics were not fully understood until recently. However, a recent study in the south Pacific by Mohsen Kayal et al (2012) was able to explore and detail the full development and process of the outbreak, as well as the repercussions of these epidemics on benthic populations and resident coral eating fish.
Are crown-of-thorns starfish still a problem?
Coral reefs are under jeopardy. Climate change is having an effect, and ravenous crown-of-thorns starfish (COTS) are a persistent problem. They consume coral and wreak havoc on restoration efforts. This puts coral reefs under more strain as they try to recover from periodic bleaching occurrences.