VietNamNet Bridge - Phu Quoc residents and tourists on September 19 were surprised to see thousands of holothurians on the coast of Phu Quoc island, from Dinh Cau to Cua Lap.

Collecting sea cucumbers on the coast.

As holothurians are expensive, locals flocked to the coast to collect them. Some families caught hundreds of kilos.

The beach in front of Eden Phu Quoc Hotel in Duong To Commune, Phu Quoc Island had thousands of holothurians.

Many tourists also joined locals to catch holothurians and sold them on the spot for VND70,000 ($3.2) per kilo.

Hotels had to assign their staff to collect dead holothurians on the beach to prevent pollution.

Nguyen Van Thuong, a veteran swimmer, said: "In the past Phu Quoc sea had a lot of holothurians, but because of overexploitation, we now have to go very far to catch them. The Phu Quoc sea usually has big waves this season but this is the first time I have seen holothurians wash ashore like this."

Most people in Phu Quoc said that it was an unusual phenomenon.

Nguyen Van Long, a man in Duong To Commune, said on September 18-19 his family collected about 100 kilos of holothurians.

Long estimated that about two tons of holothurians had washed ashore this time.

Locals said this was the first time the phenomenon had happened on Phu Quoc.

Dr. Vu Ngoc Long, Director of the Southern Institute of Ecology, said perhaps the coral ground in this area had been damaged.

According to Long, tourism activities, and the exploitation of groupers and sea cucumbers in Phu Quoc have severely damaged coral bottoms, and that is why the phenomenon had occurred.

Long said as fishing boats used large rakes to sweep the surface of the seabed, especially the ancient coral reefs, or used chemicals and explosives in fishing, the habitat of sea cucumbers had been affected.

"When they lose their habitat, the sea cucumber resistance to large waves declines. The major change in the tides and large waves below the surface will sweep things in the seabed up, including sea cucumbers, and push all ashore," Long said.

Dr. Do Van Tu, form the Institute of Ecology and Biological Resources, also said that perhaps the habitat of sea cucumbers in the area had been destroyed or contaminated from the use of chemicals or explosives to catch fish by fishermen.

"In normal environmental conditions, sea cucumbers rarely are washed away from their habitat. Only when sea cucumbers are weak or the habitat is destroyed does that phenomenon occur," Tu said.

Dr. Dang Huy Huynh, Vice President of the Vietnam Association for Conservation of Nature and Environment, said environmental pollution might be the cause.

Huynh said that with the bustling operation of tourism, aquaculture and fishing in Phu Quoc, the local government should be mindful of the waste problem.

 Drying sea cucumbers in the sun.

Dr. Vu Ngoc Long said this was the reproductive season of sea cucumbers. This season usually lasts for about two months, and it is also the time when the number of sea cucumbers greatly increases.

However, catching of sea cucumber should be avoided at this time as the species is a link in the material shipping process in the seabed.

If sea cucumbers are overexploited, the balance will be broken and the self-protection of coral ecosystems under the sea will be harmed.

Long also warned that dead sea cucumbers will change very quickly. Their bodies can contain toxic algae and fungi, so people should not eat dead holothurians.

What is a sea cucumber?

Sea cucumbers are marine animals with a leathery skin and an elongated body containing a single, branched gonad. Sea cucumbers are found on the sea floor worldwide. They serve as a useful role in the marine ecosystem as they help recycle nutrients, and break down detritus and other organic matter after which bacteria can continue the degradation process.

Sea cucumbers can be found in great numbers on the deep seafloor, where they often make up the majority of the animal biomass. At depths deeper than 8.9 km, sea cucumbers comprise 90% of the total mass of the macro-fauna.

Mai Nguyen