Crown-of-Thorns Starfish Threatens Marine Life in VanuatuCatch of the Week
The crown-of-thorns starfish (COTs), also known as Acanthaster planci, is wreaking havoc on the coral reefs of Vanuatu.
Studies in other countries have shown that as much as 90% of coral reef population can be decimated in a single COTs outbreak which can last from 15 to 20 years, according to the Science Alert of the James Cook University. Vanuatu fisheries officer Jayven Ham adds that COTs is a significant threat to the fisheries and the tourism sectors in the country.
“They are like a thieves the night,” notes Peter Whitelaw, a dive operator in the Northwest Efate area. By day, COTs usually hide under ledges or plate corals, but by night they come out to feed on the coral polyps, unafraid of predators. When they are in plague proportions they cover the reefs and do massive damage not only to the ecosystem but to prime snorkelling and diving sites that tourists specifically visit Vanuatu to see.
If tourism is the main driver of Vanuatu’s gross domestic product, then every effort should be made to protect the coral reefs. Visitor surveys have shown that the coral reefs are one of the major attractions during Vanuatu holidays. Dive operators in Mele Bay, Bokissa, and Northwest Efate have shown that with concentrated effort and mutual support, these large aggregations can be removed once they come into an area, where the availability of boats, scuba tanks and divers makes it feasible to clear COTs from tourism-sensitive areas. The further the outbreak is from a scuba base, the more logistically difficult and expensive it is to completely cull the critters.
Depending on the underwater terrain, COTs groupings devour corals at depths of 20 to 30 meters as they make their way along a coastline. Others stay close inshore if the corals there are succulent. These ones in under 4-meter depths can be removed by village communities with masks, fins, snorkels, hooked wire sticks, gloves, and flour bags. A filled flour bag can either be taken ashore, or the top tied off and the bag left immersed in sheltered waters, so that the COTs will die, having no water flow over their bodies and lacking oxygen after one day. They can then be tipped out of the bag for the fish to eat from the underside. As no poison is used to kill the COTs, the consumed coral can then be seen being recycled through the COTs and become food for some fish. These include the trigger fish, red bass, surgeon fish, and various types of wrasse, from small ones to the Napoleon wrasse.
COTs can realize they are under attack from villagers. If so, they instinctively alert each other via chemical pheromones to move out into deeper waters, out of reach of the snorkellers. Anecdotal information indicates that the COTs can return to shallower corals by night and this is when villagers can remove the greatest number of COTs using underwater flashlights to spot them. However, extreme care must be taken to avoid being spiked by the venomous spines.
The ideal collection strategy is to have snorkellers collecting from shallow reefs at the same time that scuba divers take them out from adjacent depths. This is possible within 15 km of scuba bases, but would only be possible in the outer islands if live-aboard boats with scuba equipment were employed to work with village communities.
After several years, some corals will start to regenerate on totally wiped-out reefs, but they are unlikely to regain their former health for around 15 years. Moreover, some coral and fish species never return to those reefs.
Moses Amos, director of the Vanuatu Department of Fisheries, says efforts to eradicate COTs need to be intensified. Because of the organism’s ability to spawn millions of eggs in a year, clearing of coral reef areas only proves temporary. If no widespread, constant action is taken to curb the COTs population, the coral reefs of Vanuatu stand to lose in a significant way. With the help of the Asian Development Bank, through the Technical Assistance on Strengthening Coastal and Marine Resources Management in the Coral Triangle of the Pacific (CT Pacific Project), cofunded by the Global Environment Facility, the government of Vanuatu is launching a nationwide campaign to ensure that the COTS population is in check and that the damage they cause on coral reefs is minimized.
In September 2013, the Department of Fisheries deployed a team to survey and clean up Tautau Village in Malekula Island in Vanuatu which is both economically and ecologically important. They trained the coastal communities how to safely and effectively control the COTs population in their fishing grounds. From the analysis of this data, a national COTs control campaign using an ecosystems approach will be designed and piloted.
“It is important for people to know how the environment influences the COTs population and how it impacts on the environment,” says Dr. Raoul Cola, regional program manager for the CT Pacific project. “Once people know how natural predators like triton shells and green triggerfish can help keep COTs outbreaks at bay, they will be more conscious of how their activities influence the population of these species as well. For instance, by protecting the COTs’ natural predators, fishers are protecting their own livelihood and food supply.”
“The Department of Fisheries cannot do it alone,” according to director Amos. They will require the help of communities and concerned groups such as the dive tour operators and environmental education groups to effect and maintain COTS population at a healthy level. He welcomes the assistance from the CT Pacific project in addressing the recurring problem of COTs outbreak in Vanuatu. “By addressing this problem, we will help safeguard the health of the coral reef ecosystem and the livelihood and food supply of the coastal communities that depend on this very important resource.”
(With contributions from Lea Tamayo and Raoul Cola)