Acanthaster planci, commonly known as the crown of thorns, is a sea star that acquires its name from the spikes that surround its limbs. Its fairly flexible spikes are employed for movement and defense against possible threats.
This species is a well-known predator of coral, and in some places, infestations of hundreds of thousands of them have been observed to disrupt coral reefs seriously. The Indo-Pacific area, the Pacific and Indian Oceans, and the west coast of Central America are all home to the crown of thorns starfish.
Appearance
These large starfish, reaching diameters of up to 30 inches, possess a multitude of arms (typically 16-23) that radiate from a broad, rounded central disc. Their most defining characteristic is the abundance of long, venomous spines that cover their entire upper surface. These sharp spines, reaching several inches in length, can easily pierce the skin, adding to the starfish’s intimidating nature.
It exhibits a wide range of colors, including gray, brown, red, purple, and green, often with mottled or patterned markings. Their underside, however, is typically lighter in color, often pale or cream.
The two sets of many tube feet that reach the tips of each arm give it the capacity to grasp objects. They possess specialized digestive glands, also known as pyloric caeca, that extend into each of their arms.
Habitat
In the Indo-Pacific region, the crown of thorns is widely distributed. However, it can be found in tropical and subtropical regions that span from the Red Sea and the coast of East Africa well over the Indian Ocean, throughout the Pacific Ocean, and down to the west coast of Central America. It is probably most prevalent in the region around Australia.
Wherever hard coral colonies or coral reefs are present in the area, chances are that it is there as it provides plenty of food. It uses its great number of limbs, which are located in separate grooves on the oral surface, to climb onto a portion of a living coral colony.
Diet
The Crown of thorns’ hue depends on dietary or geographic location. This starfish feeds on any coral, and the population size, sea circulation, and species diversity impact their dietary inclinations and activity patterns. Branching and table corals, which belong to the same genera as those that are most susceptible to bleaching, are what it normally consumes.
However, it may devour other corals like porites or foliose corals when branching coral growth is inadequate due to an excess of the crown of thorns. Along with eating hard corals, it may also consume soft corals, algae, sponges, and creatures that form encrusting layers.
Reproduction
Depending on the location of each colony, the Crown of thorns spawns periodically in the summertime. Northern hemisphere populations typically spawn between August, whereas southern hemisphere populations typically breed around November and February. The males and females mate by releasing their gametes into the ocean, where they are fertilized.
Crown of thorns emit compounds that cause organisms close to begin reproducing. But not every member of a population spawns at the same moment. It will ascend to a high ledge on a coral column before arching its body to lay its eggs. Then it will vigorously swing its arms and jerk its limbs while it releases gametes from 5 openings from the surface of the body.
Threats
Crown of thorns have long, venomous spikes to defend them against a variety of predators, yet predation still happens, as evidenced by the fact as many adults as 60% within a population could be missing arms. Juveniles exhibit more enigmatic behaviors and reside in cracks and on the underparts of crevices.
Giant triton shells, pufferfish, harlequin shrimp, triggerfish, and lined fireworms are natural predators of Crown of Thorns. They have stiff, plate-like scales and powerful, sharp teeth that enable them to tear off portions of tissue on a Crown of thorns while fixed on a coral.
5 More Facts about the Crown of Thorns
- Crown of thorns is the second largest starfish in the world, reaching a length of 3.2 ft.
- A single Crown of thorn starfish consumes 107 sq ft of corals annually.
- Crown of thorns has eyes on its limbs and a sophisticated visual system.
- The Crown of thorns moves at 1 ft per minute.
- Crown of thorns’ scientific name, Acanthaster, translates from Latin into “thorny star.”
FAQs
Why is the crown of thorns starfish considered a threat to coral reefs?
While crown of thorns starfish naturally prey on coral, outbreaks or overpopulations can devastate reefs by rapidly consuming large coral areas, disrupting the ecosystem.
How do crown of thorns starfish outbreaks occur?
Outbreaks are often linked to factors like nutrient runoff increasing plankton (their larvae’s food), overfishing of natural predators, and warming sea temperatures.
Can crown of thorns’ venom harm humans?
Yes, their venomous spines can cause painful injuries to humans, leading to swelling, nausea, and infection. Handling them without proper care should be avoided.
What adaptations allow crown of thorns to thrive in the ocean?
Their ability to regenerate lost arms, venomous spines for defense, and specialized digestive enzymes to feed on coral give them a significant survival advantage.
Are there efforts to control crown of thorns starfish outbreaks?
Yes, manual removal and injection with bile salts are common management techniques, along with efforts to protect their natural predators like tritons and triggerfish.
Do crown of thorns starfish contribute positively to the ecosystem?
In balanced populations, they help maintain coral diversity by preventing faster-growing corals from dominating reef systems, thus supporting ecosystem health.
