Control and Management of Crown-of-Thorns Starfish (COTS)

1. Control and Management of Crown-of-Thorns Starfish (COTS)

2. Introduction • The Crown-of-Thorns starfish is one of only a few animals that feed on living coral tissue (corallivores) and grows to over a foot across with 10-20 arms • The starfish is named for the dense covering of long, sharp spines on its upper surface. Scientists believe that this starfish has lived on the reef for tens of thousands of years.

3. The crown of thorns starfish is found throughout the Indian and Pacific Oceans and belongs to the family of Echinoderms. Taxonomic rank of Acanthaster planci: PHYLUM Echinodermata, (Gk.: echino, spike + derma, skin) spiny-skinned animals) CLASS Asteroidea, (Gk.: aster, star) sea stars or starfish) ORDER Valvatida, (Gk.: valvata, flap) valve – like) FAMILY Acanthasteridae (Gk. acantha, thorn + aster, star) thorned starfish)

4. At low densities, the Crown-of-Thorns starfish is a ‘normal’ part of the reef’s ecology. However, when the starfish population reaches the level where coral is being consumed faster than it can grow, this situation is known as an ‘outbreak’ • Research suggests that when the numbers of crown-of-thorns starfish is around 30 per hectare of coral reefs, an ‘outbreak’ can dramatically reduce coral cover, resulting in a major disturbance to the whole system.

5. Spawning of A. planci Reproduction • Like most starfish, A. planci is separate in sexes (dioecious) • Reproduction of the starfish is called spawning. Once each year in midsummer, eggs and sperm are released into the water and are fertilized. • Group spawning increases the normally rather low chance of fertilization (fertilization rate of 95% can be reached when male and female are less than 2m apart, and 25% when 6m apart).

6. A mature female A. planci Eggs after fertilization • Recent studies have shown that a large female starfish (about 40 cm in diameter) is capable of producing up to 60 million (60E6) eggs per season. Hence, when A. planci do occur in high numbers, their reproductive potential is enormous. Their populations can quickly increase by as much as six orders of a magnitude over several breeding seasons.

7. LIFE CYCLE OF Acanthaster planci Planktonic stage After 2-3 weeks After 2 days (feed on algae) 6 months (start to feed on corals End of 2nd year (sexually mature)

8. Gastrula Bipinnaria Young Sea Star Brachiolaria

9. Juveniles of A. planci feeding on Acropora sp.

10. Feeding Patterns • A. planci is knownfor its voracious appetite for hard living corals, especially the branching and table corals like Acropora spp. and Montipora spp. • During an outbreak, they often eat together in groups feeding from the deeper areas of the reef all the way up to the reef crest. While eating, they secrete a chemical which attracts other starfish to the area,

11. Oral side of the starfish showing everted stomach folds digesting an Acropora • When preferred corals become scarce, A.planci will feed on the massive colonies of Porites corals, fire corals, feather stars, sea whips, sea anemones, and even on sponges, mollusks, and algae. • COTS feed by turning their stomach outward and secrete digestive enzymes which break down the coral's living tissue into "polyp soup". Specialized cilia convey this solution to the caeca where extracellular digestiontakes place.

12. After feeding, it moves on leaving a patch of white coral skeleton • It usually feeds twice a day for several hours • Small and juvenile COTS feeds at night, to avoid predators which are active during the day. • Depending on its size the COTS can eat from 2 to 6 sq. meters of coral a year

13. Schematic diagram of a common sea star

14. Humphead Napoleon wrasse Giant triton shell Puffer fish Crown of Thorns Starfish Predators

15. Polychaete worm Harlequin shrimp Trigger fish

16. Effects on Coral Reef Communities • 1st order effects: predation results in reduction of abundance and surface cover of living corals, species composition, species diversity, and colony size distribution. • 2nd order effects: increase in surface cover by algae, and occasionally by other encrusting animals such as soft corals; consequently leading to a decrease in topographic complexity of the reef community.

17. 3rd order effects: increased carrying capacity of herbivorous fish feeding on algae, as well as, a decrease in abundance of corallivores.

18. Control Programs • Hand collection

19. Currently, the most effective control method is injection with copper sulphate. Previous methods have involved injection with formalin, ammonia, ammonium hydroxide or acetic acid . • CRC reported the success of injecting a new 'dry acid' compound, sodium bisulphate, into crown of thorns outbreaks.

20. Applying quicklime directly on them. • The use of underwater fences has recently proven to be successful as a means of excluding adult starfish. Unfortunately, • high costs of erecting and maintaining these structures •  probably only useful for protecting small areas of reef

21. Theories for COTS Outbreak While there have been many theories on the causes of outbreaks of the Crown-of-Thorns starfish, there are three theories that are supported by scientists. These theories are: Fluctuations in COTS populations are a natural event Increased survival of COTS larvae as linked to human activities Removalofnaturalpredators of the COTS has allowed populations to expand

22. Natural event theory • Crown-of-Thorns starfish have a number of unique adaptations that lend themselves to large fluctuations in numbers Some of these are: • High fertilization rates and can produce large numbers of eggs – an average female COTS produces 12-24 million eggs • A larval dispersal phase in which to “migrate” via prevailing water currents • Rapid growth reaching reproductive maturity within two years • Relatively long-lived (probably more than 8 years) allowing successive breeding seasons

23. Fluctuations in temperature, salinity or availability of planktonic food There has been some suggestion that outbreaks of the COTS are linked to the timing of the El Niño-Southern Oscillation (ENSO) system which can cause dramatic shifts in local climate around the Pacific Ocean. Low salinity also increases the survival of the larvae. • Effects Of Heavy Rains Dr. Birkeland of UOG (1982, 1989)suggested thatheavy rains cause water with low salinity, high sediment and high nutrient loads to be washed into the waters, therefore, increasing the amount of plankton necessary for survival of the COTS larvae He contends that outbreaks of COTS can frequently be predicted 3 years following heavy rains exceeding intensities of 30cm in 24 hours.

24. Increased larval survival as linked to human activities • Sediment runoff and declining water quality due to human activities have increased phytoplankton bloom optimizing the survival of the COTS larvae

25. predator removal • Fishing and shell collecting have led to decreased numbers of predators of the crown-of-thorns starfish, thereby allowing starfish populations to increase beyond natural levels. • However, none of these predators appear to feed exclusively on the starfish and predation rates of many of these species on crown-of-thorns starfish are unknown.

26. Management The Great Barrier Reef Marine Park Authority’s (GBRMPA) approach to the management of COTS on the Great Barrier Reef is to address the human activities that potentially cause or exacerbate outbreaks, rather than attempting widespread eradication of populations of the species. This is preferable for a number of reasons: • The human activities constitute significant threats in their own right, and need to be addressed irrespective of their potential roles in COTS outbreaks • Wide scale eradication is difficult to justify in the absence of definitive information on the dynamics of COTS outbreaks • Attempts to eradicate outbreak populations at reef-wide scales have been costly and labor intensive to sustain

27. COTS control at key sites • GBRMPA grants permits for localized, small scale crown-of-thorns starfish control programs at key tourism or research sites. • Research and monitoring It is especially important to monitor the dynamics of COTS populations and their effects on coral reefs. This will provide more information on outbreak patterns and the environmental factors associated with outbreaks. • Sample of the COTS Survey Formused by the GBRMPA in their monitoring activities

28. Addressing the possible causes of outbreaks While there is no consensus as to the cause of crown-of-thorns starfish outbreaks, the most effective strategy to address the issue is to directly address those activities suspected of contributing to outbreaks – over fishing of predators, and nutrient runoff into the Great Barrier Reef. • Reduce over fishing • Address declining water quality - This includes measures to address land use practices and runoff of sediment, nutrients and pollution from coastal areas into coral reef areas • Protect marine biodiversity and ecosystem function - MPAs, CZMP, etc.

29. Summary • Crown-of-thorns starfish outbreaks cause significant disturbance to coral reefs over a wide geographic area • It is possible that the observed frequency of crown-of-thorns starfish outbreaks could have a long term detrimental effects on the abundance and community dynamics of coral reefs • At present, the Great Barrier Reef is experiencing its third major series of outbreaks, which is following a similar pattern to that recorded during the previous two series of outbreaks • Despite considerable scientific research, the cause of crown-of-thorns starfish outbreaks and the role of human activities as a causal factor are still uncertain

30. The two most plausible linkages between outbreaks and human activities involve the removal of predators and declining water quality. Recent research has provided additional evidence that increased nutrient runoff from coastal areas is linked to outbreak events. • The widespread eradication of crown-of-thorns starfish outbreaks is not supported, nor does it appear to be technically feasible. However the GBRMPA grants permits for localized starfish control activities at key tourism and research sites. • The GBRMPA is involved in research and monitoring programs to assess the extent and intensity of outbreaks, and provides advice on crown-of-thorns starfish control measures

31. Toxicity of A. planci The tissues of an A. planci contain toxic saponins, and are not only poisonous to humans but also to insects and soil organisms by suppressing plant growth. The starfish therefore cannot be used either for food or fertilizer. • Symptoms in case of injury: • A puncture wound from a spine is intensely painful, causing swelling (edema), redness with a dark blue center (erythema), heat and numbness of the surrounding areas. • Stinging by 10 or more spines may result in vomiting which can recur every few hours for several days (if the victim suffered multiple wounds, apart from getting very itchy, the whole limb may stiffen, and swell). • If infection develops in the punctured wounds, lymph glands in the arm pit or groin may become tender or swollen.

32. Often spine tips break off in the wound resulting in complications for weeks or even months. A spine tip in the finger can result in swelling and stiffness caused by the growth of granulation tissue typical of a foreign body reaction. In severe cases bone-destroying (osteolytic) processes may cause narrowing of a joint by destruction of cartilage, which requires surgery. Treatment: Any embedded pieces of spine should be removed – any spine in a joint represents a surgical emergency. Most marine poisons are destroyed by moderate heat. If possible submerge the affected area in 50°C hot water. Thoroughly clean and disinfect the wound to prevent secondary infection (e.g. Tetanus).