BANGKOK (AFP) - Hermit crab numbers in southern Thailand have boomed as foreign tourists have stayed away - so much so that the national park authority appealed on Friday (Nov 6) for the public to donate extra shells for them to live in.

The population of the crustaceans, which protect themselves by wearing and living inside the discarded shells of other animals, has exploded on some islands in the Mu Koh Lanta National Park. Marine biologists believe the lack of tourists could be a factor.

The kingdom's economy is highly dependent on foreign visitors but it is expecting a tiny fraction of the nearly 40 million international arrivals it recorded last year, after the coronavirus pandemic brought global air travel to a near-standstill.

"The reason (we need shells) is because of surging numbers of hermit crabs, I think tens of thousands," Mu Koh Lanta National Park director Veerasak Srisatjung told Agence France-Presse.

Some crabs, having outgrown their previous homes, have moved into pieces of rubbish such as cans, glass bottles or caps, and Mr Veerasak said authorities had detected a shell shortage about a week ago.

The national park authority urged people to post or courier donations of cone-shaped shells to its office in Krabi province.

So far, about 200kg of shells have been pledged, and volunteers can help distribute the shells at a special Thai Father's Day event on Dec 5.

Marine biologist Thamasak Yeemin from Ramkhamhaeng University agreed that the population boom could be linked to the tourism shutdown.

"If there's a low number of tourists and fewer activities in the coastal areas that might be a possible factor explaining the high survival rates," he told AFP, adding that weather, sea currents, plankton supply and predators were other influences.