Around 200 tonnes of illegally harvested giant clam shells worth nearly $25 million (£18 million) have been seized in the Philippines, according to a BBC report.

The seizure is one of the largest ever hauls of the endangered giant clam species. They are increasingly vulnerable to poaching, both for their meat and shells, which are used as a replacement for ivory in jewellery and decorations.

Four suspects have been arrested on an island in the ecologically protected province of Palawan.

Giant clams can grow larger than one metre across, and weigh up to 250kg. They are seen as vital to the local marine ecosystem. The Philippines is home to most of the world's giant tropical clam species. Jovic Fabello, spokesman for the Palawan Council for Sustainable

Development, said that the seized shells included Tridacna gigas, the world's largest clam. Tridacna gigas contain marine algae which are a food source for many of the fish species eaten by humans.

"Taking the giant clams from their natural habitat is a form of inter-generational crime," he told the AFP news agency. "It will permanently affect the marine ecosystem and future generations will be deprived of the benefits accruing from it," he added.