Re-seeding programmes on over 50 reefs are securing the survival of the giant clam for at least another generation, according to World Wildlife Fund-Philippines.

giant clam
©Kurt Domingo
The true giant clam (Tridacna gigas), 40 of which were transplanted last month to a new home in Batangas province, Philippines.

The clams, the world's largest bivalve mollusks and the star of lurid but mostly imaginary literary and cinematic depictions of trapped divers, can live for over a century. They have been known to exceed 1.4 metres in length and weigh in at over 260 kilograms.

Once common throughout Philippine reefs, excessive hunting for the food, pet and curio trade all but depleted the wild giant clam population by the mid-1980s, prompting the IUCN to classify them as vulnerable.

An attempt to restore natural clam populations is now being spearheaded by Dr. Suzanne Mingoa-Licuanan of the University of the Philippines Marine Science Institute in partnership with World Wildlife Fund-Philippines.

"Several species of laboratory-raised giant clams have been re-seeded in over 50 reefs nationwide, significantly bolstering wild stocks and ensuring their survival for at least another generation," said WWF Project Manager Paolo Pagaduan.

By way of example, a fresh batch of 40 true giant clams (Tridacna gigas) wrapped in watertight plastic bags made the journey last month from rearing laboratories in the west of the country down the coast to their new homes in Batangas province on Santelmo Reef, a prized snorkeling site being restored with the help of WWF and a nearby ecotourism development.

With an average length of 36 centimetres and weighing almost 10 kilograms, each of the 40 clams was painstakingly but successfully laid to rest - alive of course - in pre-designated nooks and crannies. Some 102 clams were planted in the same area last November and another 35 are being grown for transplanting in coming months.

"When we planted the first batch last November, all clam mantles were pale ochre. Now, each clam shows off electric hues of blue and violet - an indicator that the area is conducive to clam growth," said Pagaduan.

"It is hoped that baby clam recruits will eventually appear to seed outlying areas in Batangas."

Giant clams are an integral part of the reef, serving as nurseries for a host of fish and invertebrate species including damsels, gobies and tiny commensal crustaceans such as shrimp.

Sedentary organisms like sponges, tunicates, corals and algae find giant clam shells perfect substrates for attachment. Giant clams also act as filter feeders, sifting planktonic debris from the water for food thereby improving overall water quality.

Adapted from materials provided by World Wildlife Fund.