‘Vulawalu’ is the local name given to the starfish Acanthaster plancii commonly known as Crown-of-Thorns starfish (COTS) referring to the crown of thorns/spikes worn by Jesus during his crucifixion.
The Crown-of-Thorns starfish (COTS) feed on corals for their survival and have a drastic effect on the health of coral reefs all over the world, including the reefs in the Mamanucas. Although this should be a healthy and natural part of the ecosystem, the population explosions of the starfish have caused devastation in many portions of the reefs in the Mamanucas. Since 2006, MES has actively participated in COTS removals in the region. Member resorts are now more aware of the dangers posed by the large numbers of COTS and have designed control methods to bring the numbers to a sustainable level.
Facts about Crown-of-Thorns
CoTs belong to the animal phylum called Echinoderms. The word echinoderm is derived from a Greek word meaning “spiny skin” (spiny = echino, skin = derm). This group includes sea star, sea urchins, sea cucumbers, feather stars and brittle stars.
CoTs share these characteristics with other echinoderms:
- 5 part symmetry (even if they have more than 5 arms).
- No distinctive head or brain.
- Spiny skin with embedded calcareous plates under skin for protection.
- Digestive tract extending nearly to the tips of the arms.
- Thousands of tube feet extending for locomotion and prey.
- Water pressure (hydrodynamics) control for movement of tube feet.
- CoTs number of arms vary from 7 to 26 arms with an average of 15 arms.
- Mouths are located underneath the sea stars.
- CoTs have as many as 9 anuses to process all the coral which they eat.
- There are 5 ‘eyes’ (light sensitive organs) at the tips of the arms that can detect light and dark.
CoTs ‘smell’ their food and feed by extending their stomachs out through their mouths (located under the body) and covering their prey. Digestive acids in the stomach digest the prey in situ, and the starfish absorbs the resulting ‘slurry’. Feeding CoTs release chemicals that attract other CoTs to the area, which may lead to ‘herding’ of CoTs.
CoTs are sexually mature at 2-3 years old (when they are about the size of a dessert plate). They spawn in warmer water temperatures of summer (Dec–Feb) with sperm and egg mixing in the water column leading to fertilisation. When a starfish starts to spawn, the chemicals released trigger off other starfishes in the vicinity. Mass spawning results. Asexually, starfish have amazing regenerating capabilities, if an arm gets cut off, the small piece can grow back into a whole starfish.
CoTs and the Reef
In a balanced environment, CoTs feed on the fast growing corals making room for the slower growing ones. However when the balance is thrown off, CoTs start to eat coral at an unsustainable rate. The cause of these outbreaks is still unknown. They may be natural phenomena occurring throughout history, or they may be caused by human influences. The most effective control method currently is the injecting of sodium bisulfate into the starfish, which kills the organism in a matter of days. However, this method is costly and is not a permanent solution to the problem.
How to control CoTs?
The most effective control method currently is the injecting of sodium bisulphate into the starfish, which kills the organism in a matter of days. However, this method is costly and is not a permanent solution to the problem. Also, rumours that the starfish releases its eggs into the waters after being injected has increased concerns that this control method may have added to more issues. MES currently supports the physical removal and later drying and burning on land of the starfish in the case of any outbreak.