Parent document

Marine Biology I

Colloquial Meeting of Marine Biology I

Headed by: dr. A. Goldschmid

Author: Pierre Madl

Salzburg, 22nd Nov. 1998 (revised in Dec. 2002)


1. Introduction:

Asteroids (sea stars or pin cushion stars) are mostly detritus feeders, but some are omnivores or even predators. Both species of Culcita (in particular C.coriacea, C.novaeguineae, C.schmideliana) and Acanthaster planci are corallivores. Although the former are feeding on coral polyps, their impact on scleractineans (hard or stony corals) is moderate to neglectable as their dietery uptake only in parts consits of coral polyps. This is not valid for the latter - A.planci is a voracious predator upon sclaractinean corals. A.planci occurs over a wide range, through the tropical waters of the Pacific and Indian oceans, however, it is unknown to waters of the tropical atlantic (Caribean sea).
Although this animal has been around since the very existence of coral reefs, controversy about the nature of the impact of A.planci (also commonly known as Crown of Thorns, for short CoT) on the Great Barrier Reef (GBR) has raged for nearly 50 years. At peak densities, the star fish have killed substantial portions of the reef corals in localized areas of the tropics, but in recent years, its impact on reef ecosystems seem to have a detrimental effect on the already stressed coral communities (coral bleaching due to the rise in sea surface temperature) and reduced the abundance of corals to very low levels. Several hypotheses have been put forward to explain why CoT starfish populations have had large fluctuations in abundance. Two major hypotheses are that crown-of-thorns starfish survivorship has been enhanced by either:

  • increased concentrations of nutrients and hence phytoplankton food for crown-of-thorns starfish larvae or
  • the removal of key predators such as the triton (a predatory mollusc) and red emperor Lutjanus sabae increases survivorship.
Recent evidence supports the first hypothesis, although the effect of reducing predation through fishing pressure cannot be ruled out.
This short article should help to understand the nature of that controversy and help to comprehend the complex interactions involved in the occurrence of this phenomenon.

2. Identification, anatomy, and reproduction of Acanthaster planci:

This sinister looking and rather flattened sea star with a large central disk and 7 to 23 arms (usually 14 to 18) displays on the aboral side elongate spines (ca. 5cm) which make it immediately distinctive (see fig. 1). The body "appears" to be quite stiff, but can bend and twist into all sorts of shapes to fit the contours of the coral substrate it feeds on. The skin is a sensitive membrane, used for extracting dissolved oxygen from the seawater. A meshwork of small magnesium calcite-ossicles, from which project numerous movable and immovable spines, are embedded in the tissue of the body wall. CoTs should be handled carefully, since the long, sharp spines are mildly venomous and can inflict painful, slowly healing wounds - see end of report (8. Toxicity of A.planci).
A series of closely fitted plates, the ambulacral ossicles form a groove and extend in rows along the underside of each arm to converge on the mouth in the center. The anus and one or more madreporites (through which water is drawn in to fill and control the water vascular system) are in the center of the upper disc surface. This system is essential for locomotion of the sea star. A ring canal connected to the madreporite encircles the mouth and gives off 5 radial canals. Each runs along the underside of each arm and ends at the tip in terminal sensory tentacles (fig.5). From the radial canals extend thin-walled cylindrical tentacles, called tube-feet or podia. Each podium is connected to a round muscular sac, the ampulla and constitute a closed unit (fig. 2). When the ampulla contracts, the fluid it contains is forced into the podium, extending it. Small muscles direct the extended podium in one or the other direction (the movements of the body wall and its spines are coordinated by a a skin-receptors themselves connected to a sensory nerve net running just beneath the epidermis; in fact eyespots at the tip of each arm act as light sensors and influence the starfish's movements). The terminal tip of each podium excrete a sticky mucus, which is flared out as a sucker. The batteries of podia in total and their combined efforts move the animal along the substrate (see also figure 8). As this system allows A.planci to move rather slowly over the substrate in search of prey, it becomes more obvious that only sedentary organisms like corals are the main nutritional resource. Depending on the substrate, an adult CoT is able to cover a distance of <1 to 20m an hour. Section 4. (Food Resources and Feeding Patterns) offers a closer look on the feeding patterns of this animal.

Taxonomic rank of A.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


Fig.1 A.planci and epidermal detail (click to zoom in - 112k)


Fig.2 Anatomy of Echinoderms (click to zoom in - 52k)

Reproduction: Like most starfish, A.planci is separate in sexes. It breeds once each year in midsummer, when eggs and sperm are released into the water (fig.3). Group spawning appears to increase the normally rather low chance of fertilization. And during an outbreak and synchronized spawning a fertilization rate of 95% can be reached (when male and female are less than 2m apart, and 25% when 6m apart). As in all asteroids, the number of eggs spawned increases with body size. One large female is capable of producing up to 60E6 eggs per season, so 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.

Larval stages: Eggs and sperms are shed into the seawater; since they can’t survive very long independently, spawning is synchronized by rapid change of temperature or light along with hormones secreted to stimulate others to spawn as well. After fertilization, the zygote divides synchronously into a ciliated blastula, hatches from the egg membrane and forms an infold (blastopore) which later becomes the coelom of the gastrula.
Dipleurula: The left and right hydroenterocoels form outpocketings at the tip of the blastopore (archenteron = embryonic gut cavity) during gastrulation. These pockets of the hydroenteroceoel change to anterior and posterior extensions which fuse with the ectoderm to form the hydropore (lobed pockets).
Auricularia and Bipinnaria: Ciliated lobes separate into arms and elongate; each lobe forms a primary podium and ultimately a radial water canal. The cilia propel the larvae about and produce feeding currents, trapping plankton and directing them to the mouth.
Metamorphosis: After drifting around for 2 to 3 weeks the 0.5mm small larvae starts to morph through the brachiolaria stage (3 small anterior projections), and settles on the sea floor (attached with an external organ to a substrate), to complete its radial symmetry.


Fig.3 Life cycle of A.planci (70k)

Within the first 24 hours, a series of radical changes occur. After several contractions, lateral swellings appear which form the first pair of tube feet. This phase is followed by some more gradual internal changes (formation of cardiac portion, closure of anus (which will reopen after metamorphosis is completed), formation of the nervous system, oral and aboral coelomic extensions separated by mesenteries, and finally the secretion of spicules originating from the mesenchyme - which elaborates into fenestrated plates and terminates by the formation of adult ossicles). This last stage initiates the stars independent existence.
The starfish becomes sexually mature at the end of its second year. Being a rapid grazer of coral polyps, it takes only 3 to 4 years for the CoT to reach a reasonable size of 30cm; this rapid boost in growth and development, thus facilitates its escape through the mortality risks of juvenile coral-reef asteroids.

3. Distribution of A.planci:

The large scale distributions if asteroids are affected by water-current pattern:
Primary outbreaks (CoT populations that are comprised of 100 of thousands individuals) may be influenced by the cohesive transport of larvae and substantial nourishment of the larval stage by an excess supply of nutrients. In fact, the timing of any outbreak appears to be correlated with eutrophication (organic mater and microorganisms such as bacteria - which triggers phytoplankton blooms), water temperature, and salinity. Such sources may be found along the shoreline of the Great Barrier Reef. Cairns and Green Island (heavily beaten tourist locations since the early 1960’s) could contribute due to elevated P- and N-containing DOM into the Coral Sea. Other sources are found in agricultural run-off from north-Queensland's sugar-cane industry (mediated by the Burdekin River, 150km south of Townsville -see fig.4). Heavy industry like those found in Gladstone (pollution, dredging activities, etc.) or simply by excessive fishing and shell collection (removal of predators such as C.tritonis - see predation).
In any case, this influx can be triggered by heavy rain, excessive land clearing, intensive agriculture, the destruction of rainforests or mangroves and other combining factors. Alternatively, outbreaks may be caused by over-fishing and collection of the fish and mollusks that normally feed on A.planci as well as the release of large quantities of persistent pesticides like DDT, Dieldrin, Endrin, etc., which kill the starfish’ natural predators. Controversy is still prevailing as industry interests, conservation movements, and scientific investigation not necessarily work hand in hand. In any case, once an outbreak take off at a particular site, secondary outbreaks usually propagate southwards at an annual rate of 75km per years (mainly due to larval transport mediated by the South-Equatorial and east-Australian water currents) and can last from 2 to 4 years.


Fig.4 The GBR, Cairns Section, and Green Island (180k)

4. A.planci’s Food Resources and Feeding Patterns:

A.planci has a large potential for food input per unit biomass, which facilitates rapid growth; a young species can transform from the juvenile to the adult feeding biology within a 1 month transition period. It will reach a total diameter of about 25cm after just 2 years.
A.planci feeds mainly hermatypic (reef building) scleractinian corals and shows a marked preference for acroporids (Acropora spp. and Montipora spp.), the largest genus of scleractinian corals (fig.4).

Taxonomic rank of stony corals:
PHYLUM Cnidaria (Gk. knide, nettle)
CLASS Anthozoa (Gk. anthos, flower + zoon, animal)
SUBCLASS Hexacorallia (Gk. hexa, six) 6-parted symmetry
ORDER Scleractinia (Gk, skleros, hard) Stony corals with a heavy external calcareous skeleton arranged in a hexamerous cycle.
FAMILY: almost any family is affected by A.planci predation: the most common species are found among the: Acroporidae (see fig. 5), Agariciidae, Faviidae, Poritidae, etc.

Fig.5 Two A.planci residing on a coral block crowned by an Acropora coral (90k)

A brief look at the Anatomy of Scleractinian Corals:
The polyps of scleractinian corals are similar to those of sea anemones but are usually smaller (fig.6). Although, there are some solitary species, most are connected together in colonies by means of a lateral fold of the body wall. A calcium-carbonate skeleton is secreted by the epidermis of the undersurface of the connecting sheet and the lower part of the polyp. The living colony thus usually has the form of a thin sheet resting on top or wrapped around a huge skeleton that is actually external to the coral tissue. The lower part of the polyp is situated within a skeletal cup, the bottom of which contains radiating septa that project up in folds in the base of the polyp. It is actually this very thin organic tissue the star fish feed on. For an in-depth look on coral anatomy visit the PNG web-page.


Fig.6 Coral Anatomy (150k)

Feeding patterns of A.planci: COTs are generalized predator of hermatypic (reef building) corals, with a preference for branching and tabular corals like Acropora spp. (as outlined above). 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. Whilst eating they secrete a chemical which attracts other starfish to the area, until large aggregations of starfish are grouped together. A.planci is therefore able to kill medium sized coral colonies entirely, but only partially larger ones; although in large numbers, they can kill over 90% if the living corals cover extensive areas. And this is probably the atypical pattern of outbreaks over the past 40 years; the crowd of grazing starfish can even kill massive Porites colonies that are several hundred years old. In the long run, the absence of these slow growing corals completely alter species composition of the reef community. It has to be mentioned though, that nematocysts of branching corals seem to have no effect on crown-of-thorns; those of massive corals have been shown to produce an adverse reaction. This possibly explains why these types of corals are least preferred as a source of food by crown-of-thorn starfish.
In special cases, defensive capabilities of a preyed coral and even nips from the claws of resident crabs (Trapezia sp. in branching coral species) or harlequin shrimps may deter a single CoT (see also predation).
Although A.planci is a specialist in the sense that it has a definite preference for acropoids, it is a generalist in that it accepts a variety of foods depending upon availability and circumstances. At the end of a mass CoT outbreaks, when the preferred corals become scarce, A.planci can feed on other organisms like Hydrozoa (Milleporina or fire corals), other Anthozoa (like Otocorallia Alcyonacea, Helioporacea, Gorgonacea, Ellisellidae which includes sea whips), Actinaria (sea anemones), and even on sponges, mollusks, and algae. Among echinoderms kept in captivity, even cannibalism has been documented when deprived of any alternative food supply. This has never been observed in the wild, as most starfish in mass outbreaks seem to die due to diseases, before ever reaching this stage. Indeed, it seems that diseases are one method of how mass outbreaks regulate themselves.

Fig.7 CoTs feeding (200k)

Fig.8 Close-up of a CoT (100k)

How can this species create such damage?

The aboral side of A.planci is not made of a thick and rigid test that characterizes other asteroids; it is rather elastic and pliable which allows it to crawl out and wrap itself around the pointed tips of branching corals. It is maybe this plasticity of the body which gives juvenile A.planci its early ability to attack coral polyps and to undertake adult feeding bahavior early in life.

Under normal conditions, it is not uncommon to spot a few starfish and to see where it has fed on a coral over night. CoTs are extraoral grazers; they feeds by turning their stomach outward (an area equivalent to that of its oral disk - see also fig.9), press it against the coral and digest it. Once the stomach is pushed out through the mouth it secretes digestive enzymes on to the polyps which break down the coral's living tissue into a sort of "polyp soup". After several hours, specialized cilia convey this solution to the caeca where it is absorbs through the stomach wall (this process is called extracellular digestion). In fact this oral part of a CoT starfish (dotted with shorter and blunter spines - fig.8), is known to some predating fish; they flip them over on their backs before starting to chew on the soft parts of the echinoderm (see predation).
When, the next morning, the stomach is withdrawn and the starfish moves under the coral for daytime shelter, a round white, dead patch of coral is left. The extruded stomach of a 2-year old A.planci would cover an area of about 160cm2. Even though they feed mostly during the night time hours, during a 9h feeding session (followed by an 12-70h fasting period) an adult starfish is able to consume about 5 to 6m2 of living coral per year. It is known, though that these echinoderms may survive without feeding for several months, by utilizing deposited energy reserves stored in its body.


Fig.9 Stomach folds of CoT (123k)


5. Effects on Coral-Reef Communities:

Spines in sediments from fossil reefs (dating back some 3500 years) proof that they have been an important part of reef life ever since. Like hurricanes, starfish outbreaks play a role in maintaining high species diversity on the reef; but recent mass outbreaks as seen on the Great Barrier Reef seem to be more devastating than in the past.
A.planci is the only coral-reef asteroid known to cause major second-order and third-order 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.
  • 3rd order effects: increased carrying capacity of herbivorous fish feeding on algae as well as a decrease in abundance of corallivores.



Fig.10 Population fluctuations (50k)

Figure 10 depicts the periodical fluctuations of coral regeneration and outbreaks of A.planci. Outbreaks itself, last for about 4-5 years (may differ from reef to reef) and end suddenly once food becomes scare or the starfish die of diseases. The time frame between outbreaks used to be 15 years, enough to allow fast growing coral species to recover to pre-outbreak levels. CoTs found today along the GBR, still belong to the massive occurrence observed in 1979.
A similar outbreak (peaking in 1981 and 82), in the waters of Iriomote Island (southern Japan). It had killed virtually all the corals on a large study reef. This sudden loss of live coral precipitated major changes in the physical and biological character of the coral reef. About 2 years following the A.planci outbreak, most of the erect coral (Acropora) canopy had collapsed as a result of bioerosion and water movement. Compared with the live reef, the dead reef exhibited low structural complexity. By 1986 all of the corals were broken apart and the reef formation had been converted into a flat plain of unstructured coral rubble. The degeneration of the reef was correlated with marked changes in the fish community. As the topographic complexity of the reef decreased, the numbers of associated fish species and their abundances also declined. Fish that fed exclusively on live coral tissues disappeared completely from the dead reefs. The declines in fish with other diets, for example, planktivores, herbivores, and omnivores, were believed to be due in large measure to the loss of habitat and to the overall declines in prey on the degraded reef.

The recent events of Crown of Thorns Starfish outbreak since 1996
Scientists researching the Great Barrier Reef say another outbreak of the Crown of Thorns Starfish has begun. In regular intervals scientists are taking boat trips out to Arlington Reef off Cairns and Kelso Reef off Townsville?. It seems that unlike in previous outbreaks they are not considering A.planci as such an ecological disaster these days and are not focusing on eliminating them. The Great Barrier Reef Marine Park Authority (GBRMPA) is also conducting a CoT Watch program which involves community monitoring the star fish. It could well be that these rather passive stands towards this phenomenon, could interfere with CoT-induced damages as the 1998 mass bleaching event of corals around the world undoubtly deprived them of their main nutritional basis.

6. Selected Predators feeding on A.planci:

As long as the new generation of CoTs are still in the planktonic phase, any filter feeding organism is capable to (passively) prey on eggs and larvae (refer to Life Cycle). These are mainly Porifera (sponges), Bivalvia (shells like giant clams, pearl shells), and Tunicata (sea squirts). Unfortunately, in many tropical countries, filter feeders like Tridacna have been extensively collected and wasted for the curio trade.
Once they metamorphose to the benthic form, the number of predators narrows to those who can actively approach, attack, and devour juvenile CoTs. Such predators capable of feeding on juveniles and small adult A.planci, are found among Annelida (worms), Crustacea (crabs and shrimps), Gastropoda (Trochus, Conus, Cassis), among others. The spectrum of echinovorous animals becomes even less when adult CoTs are on the menu; species capable of doing so are the Triton shell and several carnivorous fish.

  • Annelida
Taxonomic rank:
PHYLUM Annelida (L. annel, ringed) ringed animal
CLASS Polychaeta (Gk. polys, many + chaite, hair) many haired animal
ORDER Amphinomida (Gk. amphi, around + ?) fireworms
FAMILY Amphinomidae (Gk. amphi, around + ?)

This small predator and scavenger is commonly known as bristle or fire worms. Its flattened dorso-ventrally body with dense and protective bundles of setae, give this species a characteristic appearance. It approaches the juvenile CoTs laterally by nibbling its way from the tip of an arm towards the disk.


Fig.11 Pherecardia striata (70k)

  • Crustacea
Taxonomic rank:
PHYLUM Arthropoda (Gk. arthr-, joint + pod, foot)
SUBPHYLUM Crustacea (L. crusta, crust) hard surfaced animal
CLASS Malacostraca (Gk. malac-, soft + ostracon, shell) soft shelled animal
ORDER Decapoda (Gk. deca, ten) ten-footed animal
INFRAORDER Caridea (Gk. cary-, hearty?)
FAMILY Gnathophyllidae (Gk.gnath, jaw + phyll-, leaf)

The pink, white and blue coloring of the harlequin shrimp (Hymenocera picta) makes it very noticeable as it moves around slowly in male-female pairs. With its vivid colors, it has a deterring effect on attacking fish. The shrimp attacks the less protected tissues of a juvenile sea star by turning the animal over. As it also feeds on other starfish (Fromia, Nardoa, Linckia, etc.) it is not known to what an extent these shrimps affects CoT population (fig.13).
The Phyllognathia ceratophthalma is a less noticeable echinoderm predator as it is not as common than the above.


Fig.12 Gnathophyllidae (80k)

Fig.13 H.picta in an attempt to turn over Leiaster (80k)

Taxonomic rank:
PHYLUM Arthropoda (Gk. arthr-, joint + pod, foot)
SUBPHYLUM Crustacea (L. crusta, crust) hard surfaced animals
CLASS Malacostraca (Gk. malac-, soft + ostracon, shell) soft shelled animal
ORDER Decapoda (Gk. deca, ten) ten-footed animal
SUBORDER Pleocyemata (Gk. ?)
INFRAORDER Brachyura (Gk. brachy, short + ura, tail) short-tailed animal
FAMILY Trapeziidae (Gk. ?)

Trapezia are usually associated with corals or other invertebrates. Both species shown here help prevent corallivores from eating the live coral tissue (fig.14) They do not feed on the starfish themselves, but rather fiercly attack the slowly approaching invader by pinching the highly sensitive podia which prompts the starfish to turn back (fig.15).

Fig.14 Trapeziidae (180k)

Fig.15 Crab fighting off a CoT attack (85k)

  • Mollusca
Taxonomic rank:
PHYLUM Mollusca (L. mollos, soft) soft bodied animals
CLASS Gastropoda (Gk. gaster, belly + pod, foot) as snail, limpets, and slugs
SUBCLASS Prosobranchia (Gk. prosos, forward + branchios, gills) slow creepers
ORDER Mesogastropoda (Gk. meso, middle + gaster, stomach) middle footed
SUPERFAMILY Cymatiacea (Gk. cymatos, ?)
FAMILY Ranellidae (Gk. ?)

This giant triton Charonia tritonis (fig.16) has been and among many other tropical nations still is heavily collected for the ornamental shell trade, leading some people to suggest that its increasing rarity is leading to CoT outbreaks, there is as yet no conclusive evidence for this.
As well as being naturally rare, experiments have shown that tritons tend to prefer other asteroids such as Linckia laevigata, Culcita novaeguineae and Naroda species, rather than CoTs. But if it does get hold of one, the muscular foot of the giant triton restrains its prey (fig.17). The starfish is held, slit open with a radula - a cutting organ rather like a band saw - and the proboscis inserted to suck on the soft tissue of the echinoderm (mostly the gonads, caeca, etc.). C.tritonis can eat up to three A.planci per month. Small starfish are normally ingested whole by the triton, but larger ones are able to fight off an attack by simply leaving behind that part of the body that is tackled - usually the arm, which is regenerated later on. After the meal has been concluded the Triton regurgitates spines and other skeletal material.


Fig.15 Charonia tritonis (43k)

Fig.17 C.tritonis feeding on A.planci (170k)

Fig.18 C.tritonis after the feast (80k)

  • Pisces
Taxonomic rank:
PHYLUM Chordata backboned animals
SUBPHYLUM Vertebrata (Gk. vertebros, spine)
CLASS Actinopterygii (Gk. actinos, ray + ptergy, fin) Bony fish
ORDER Perciformes (Gk. ?)
FAMILY Lethrinidae - Emperors
SUBFAMILY Lethrininae -

This species usually occurs in schools in sand or coral rubble areas. It approaches echinoderms by picking them up at one arm and turning them over to feed on the oral part of the starfish. Molluscs and crustaceans are also included in its dietary habits Unfortunately it is a favorite among anglers as it is a good food fish.


Fig.19 Lethrinus nebulosus (60k)

Taxonomic rank:
PHYLUM Chordata backboned animals
SUBPHYLUM Vertebrata (Gk. vertebros, spine)
CLASS Actinoptergyii (Gk. actinos, ray + ptergy, fin) Bony fish
ORDER Perciformes (Gk. ?)
FAMILY Lutjanidae - Snappers
SUBFAMILY Lutjaninae -

Species feed on fishes, crabs, stomatopods, other benthic crustaceans, cephalopods, and occasionally on echinoderms. It is often encountered in the vicinity of lagoons, and over adjacent sand flats. Can occur in schools or as solitary individuals. Again it is appreciated as a food fish and commercially important but in certain regions of the Indian Ocean, large individuals are known to cause ciguatera poisoning.


Fig.20 Lutjanus sebae (70k)

Taxonomic rank:
PHYLUM Chordata backboned animals
SUBPHYLUM Vertebrata (Gk. vertebros, spine)
CLASS Actinoptergyii (Gk. actinos, ray + ptergy, fin) Bony fish
ORDER Perciformes (Gk. ?)
SUBORDER Labroidei (L. labbra, lip) lipfish
FAMILY Labridae - Wrasses
SUBFAMILY Cheilininae -

Most labrids are benthic feeders; they prey mainly on invertebrates with hard parts such as shelled mollusks, sea urchins, sea stars, and crustaceans. Besides that, this species is one of the few predators of other toxic animals such as sea hares, and boxfishes. They crush the animals with their pharyngeal teeth. The wrasses are diurnal; they are among the first fishes to retire to an inactive state on the bottom with the approach of darkness and among the last to resume activity the following morning. It has been a popular species for spear fishermen in the past, and was taken in large quantities by commercial fisherman on the Great Barrier Reef. Nowadays, larger species (can reach up to 2m in length) are frequently fed by divers (dive tourism, even though it is quite wary and solitary) which trains it away from its natural food-sources.


Fig.21 Cheilinus undulatus (65k)

Taxonomic rank:
PHYLUM Chordata backboned animals
SUBPHYLUM Vertebrata (Gk. vertebros, spine)
CLASS Actinoptergyii (Gk. actinos, ray + ptergy, fin) Bony fish
ORDER Tetraodontiformes (Gk. tetra, four + dental, tooth )
FAMILY Balistidae - Triggerfish

The orange-green striped Triggerfish Balistapus undulatus reaches 30cm in length and the Titan Triggerfish Balistoides viridescens that can be up to 75cm long are known to feed on CoT. Pseudobalistes flavimarginatus with likewise sharp teeth has been observed to attack (and take bites out of) crown-of-thorns with apparent immunity. But they also feed on a variety of other benthic organisms such as algae (often coralline red algae), fishes, mollusks, tunicates, brittle stars, urchins, polychaetes, sponges, and hydrozoans. Females of B.viridescens guarding their nest are reported to have attacked divers.

Fig.22 Balistapus undulatus (80k)

Fig.23 Balistoides viridescens (60k)

Taxonomic rank:
PHYLUM Chordata backboned animals
SUBPHYLUM Vertebrata (Gk. vertebros, spine)
CLASS Actinopterygii (Gk. actonis, ray + ptegy, fin) Bony fish
ORDER Tetraodontiformes (Gk. tetra, four + dental, tooth )
FAMILY Tetraodontidae (Gk. tetra, four + dental, tooth) - Pufferfish

A.planci is also preyed upon by a variety of pufferfish, which are sometimes taken for food (although poisonous if prepared not adequately - Arothron hispidus contains TTX, a toxic tetrodotoxin. Puffers feed on calcareous or coralline algae, detritus, mollusks, tunicates, sponges, corals, zoanthid anemones, crabs, tube worms, sea urchins, brittle stars, hermit crabs, hydroids, and of course echinoderms. With its powerful teeth, used for chewing corals, it make easy work on starfish spines and all the rest. The trigger fish preys on adult starfish by seizing it by an arm and turn it over before biting into the soft parts. Where a puffer has eaten a starfish there is often a neat ring of discarded spines.


Fig.24 Arothron stellatus (75k)

Fig.25 Arothron hispidus (70k)

7. Controlling A.planci outbreaks:
Labor-intensive though it is, there have even been projects that involved injecting the offending starfish with a variety of poisons, such as formaldehyde (40% HCHO-gas in water, or formalin; i.e. 1 part of formaldehyde and 19 parts H2O yields a 5% formalin solution), copper sulfate (CuSO4), sodium hypochlorite (NaClO), ammonia (NH3), ammonium hydroxide (NH4OH), compressed air, and acetic acid (CH3COOH). Currently, the most environmental tolerable control method of this kind is diluted sodium-bisulfate (NaHSO4·H2O). Whatever solution is used, it is important to inject it into several areas of the starfish in order to make sure that it does not reject a damaged arm and regenerate it. Although this method is effective, it is too expensive and time-consuming to be widely used. The most cost-effective method known at present is to enlist the help of amateur divers and remove the starfish by hand. An even cheaper option is to keep munching CoTs out of an area is obtained by installing a wide-meshed fence.
At the peak of the last A.planci outbreak, up to 15000 individuals have been caught in one single day. But poisoning or removal by hand are likely localized measures, tending to be used only in popular tourist areas and providing cosmetic, short-term solutions, which prevent further reef damage only until the next outbreak.
The implementation of biological controls (such as diseases or predators) may be successful but it should be borne in mind that not all biological control programs undertaken by man have been successful. Many of them have caused far greater problems in the environment than the original problems they were meant to overcome.
With or without such action, most of the stars disappear, and if the time between outbreaks is long enough, sea-surface temperatures do not exceed the thermal tolerance threshold, then new corals will settle, will thrive and replace those lost.
8. Boom & Bust Cycle of A.planci:
CoT occurs throughout the Indo–Pacific and shows a classical boom–bust population dynamics with low background densities and intermittent outbreaks (see fig.10). Three waves of population outbreaks have affected Australia's GBR since the 1960s. The waves of outbreaks appear to start at the northern section of the GBR and progress southward through the central GBR, causing devastating effects on the coral fauna and the associated reef-ecosystem (see fig.4). Extensive surveys by the GBR Marine Park authorities have shown that protection from fishing affects the frequency of outbreaks - that is, the relative frequency of outbreaks on reefs that were open to fishing was 3.75 times higher than that on no-take reefs in the mid-shelf region of the GBR, where most outbreaks occur, and seven times greater on open reefs if all reefs were included. However, the explosive appearance of CoT-outbreaks is coupled to a likewise rapid and massive die-off. The reasons behind are probably not so much related to the scarcity of food resources but rather linked to a probable viral infestation with lethal effects on the dense CoT-population. Echinoderms are deuterostomes and thus are rather primitive compared to vertebrates (they lack notochords and do not possess an adaptive immune system). Recent evidence suggests that these sea stars are subject to massive viral infection and show a similar seasonal die-off characteristics as observed in the sea slug Elysia chlorotica. During mass mortality, these slugs produce large quantities of nuclear and cytoplasmic retroviral particles, apparently from endogenous retrovirus (ERV). The biological significance of this virus induction has not been well evaluated, but it is likely to be involved in the phased mass mortality of these slugs. Similar mass mortalities are observed in maricultural practices, like that in 1994, when the French oyster aquaculture industry crashed, as well as in 1999, when a similar crash was seen in Japan. Other major crashes in commercial shellfish populations have also been experienced, such as in the shrimp aquaculture in China.

Fig.26 Manual control methods (200k)

9. Toxicity of A.planci:
The disc and arms are covered with a soft skin and 100s of stout-hinged spines 2-3 cm long, each with a 3-sided blade at the tip. The spines are covered by a thin skin containing two types of glands which are thought to produce a venom and mucus.
The tissues of an A.planci contain toxic saponins (a group of natural steroids), and are not only very nasty to humans but also poisonous 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 (oedema), 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). Multiple stinging can cause excruciating pain (which may last several hours), fainting, nausea and vomiting. The swelling may persist for a number of days. Where the victim has suffered multiple wounds, the whole limb may stiffen and swell. In such cases, the patient may experience a numbness around the wounds and the swollen area may become extremely itchy. Repeated envenomation over days or weeks can lead to much more severe responses to successive stinging in some individuals.
  • If infection develops in the punctured wounds, lymph glands in the arm pit or groin may become tender or swollen.
  • 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.
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 effected area in 50°C hot water. Thoroughly clean and disinfect the wound to prevent 2ndary infection (e.g. Tetanus).


References: Are increased nutrient inputs responsible for more outbreaks of crown-of-thorns starfish? An appraisal of the evidence by J.Brodie, K.Fabricius, G.De’ath, & K.Okaji 2005 - Marine Pollution Bulletin 51, 266-278. Chordate Zoology by P.S. & J.K.Dhami; R.Chan & Co Publ.; 1991 - India
Coral Reef Animals of the Indo-Pacific by T.M.Gosliner, D.W.Behrens, G.C.Williams; Sea Challengers 1996 - USA
Echinoderm Studier 1-4 by M.Jangoux, J.M.Lawrence; A.A.Balkema Publ. 1989 – NL
Fishes of the GBR and Coral Sea by Randall J.E., Allen G.R., Steene R.C.; University of Hawaii Press; Honolulu 1990 - USA
Great Barrier Reef; Mead & Becket; Reader's Digest Services Pty Ltd.; Sydney 1984 - AUS
Greenpeace Book of Coral Reefs, by S.Wells, N.Hanna; Sterling Publ. 1992 - USA
Guidelines for Managing Risks in Recreational Water issued by the Australian Government - NHMRC. 2008 - AUS
Impacts of Climate Change on Australian Marine Life: Part C; edited by Alistair J. Hobday, Thomas A. Okey, Elvira S. Poloczanska, Thomas J. Kunz, Anthony J. Richardson; CSIRO Marine and Atmospheric Research 2006 - AUS
Living Invertebrates by R.&M.Buchsbaum, V.&J.Pearse; Boxwell Publ. 1986 - USA
No-take reserves protect coral reefs from predatory starfish by H.Sweatman in Current Biology , Vol.18/14: 598-599
Sea Stingers and other venomous and poisonous Marine Invertebrates of WA by L.Marsh WA-Museum 1986 - AUS
Starfish Wars - Coral Death and Crown of Thorn by R.Raymond, McMillan Co. 1986 - AUS
Pesci e Coralli del Mar Rosso di A.Mojetta, A.Ghisotti, Mondadori, Milano 1996 - ITA
Red Sea Invertebrates by P.Vine; Immel Publ. 1986 - UK
The Blue Planet by Fothergill A., Allen D., Allen P.; ABC/BBC 2002 - UK/AUS
Viruses and the Evolution of Life by L.P.P.Villarreal; ASM Press 2005 - USA
Zoology Intl ed. By R.L.Dorit, W.F.Walker, R.D.Barnes; Saunders Publ. 1991 - USA
Sites of Interest on the WWW:

Crown of Thorn links:
Life cycle:
Long Term CoT Monitoring:
History of outbreaks:
1996 outbreak:
Charonia home page:
Reef stress by Acanthaster:
Causes of reef damage:
Fish Species database:
GBR-Acanthaster planci:
Coral reef-picture gallery:
Acanthaster image:
Crown of thorn on Sulawesi:
Crown of thorns in Malaysia:
Triton shell:
Nudibranch site: