Meet the giant clam fam

| Written by Stephanie Cabigao

It is impossible to miss those electric colors—shifting from olive green to brown or dark green to violet; those shining in brilliant shades of blue and green; or the ones freckling in mixed colors of yellow, green, and brown; and especially those looking regal in mottled patterns of yellow-brown, green or gray—when passing through the waters of Silaqui Island in Bolinao, Pangasinan. Their luminescence is matched by their gigantic size, which make them the darling giants of the North.

There are nine extant species of giant clams. Seven of these are found in the Philippines, four of which are home to University of the Philippines Marine Science Institute-Bolinao Marine Laboratory (BML). These giant clams are being cultured both at its onshore hatchery and ocean nursery.

 

A peek through UP Marine Science Institute-Bolinao Marine Laboratory’s ocean nursery at Silaqui Island in Bolinao, Pangasinan

(Video by Rubie Esmolo, UP MSI-BML and Stephanie Cabigao, UP MPRO)

 

Giant clam fam

The bands of olive green to brown or dark-green to violet clams are the Tridacna gigas, more commonly known as the true giant clams, because adults have such immense shells. In the Philippines, they’re called taklobo, a term which applies to most giant clam species, according to administrative aide Julio Curiano Jr. Particularly, these species of T. gigas are locally called bukà, with reference to the clam’s gaping habit, Curiano adds.

Hagdan-hagdan, the Filipino name for Tridacna squamosa, is the type of giant clam in mottled patterns of mixed yellow, green, and brown. Those in brilliant shades of blue and green in linear patterns are called Tridacna derasas. Another member of the BML’s clam fam is the Hippopus hippopus, locally called kukong-kabayo, in mottled patterns of yellow-brown, green, or gray.

The magnificent colors that these species produce are part of a process of symbiosis. Curiano explains that giant clams are symbiotic with zooxanthellae, particularly Symbiodinium microadriaticum. “Zooxanthellae are dinoflagellates that live within the clam’s mantle, where they are able to photosynthesize, reproduce, and grow in large numbers,” Curiano says. He adds that the presence of giant clams makes the ocean conducive for various fish species to reproduce, making it rich and abundant.

 

UP MSI-BML giant clams research assistant Julio Curiano Jr. holds a Tridacna derasa straight out of the ocean nursery. (Photo by Bong Arboleda, UP MPRO)
UP MSI-BML giant clams administrative aide Julio Curiano Jr. holds a Tridacna derasa straight out of the ocean nursery. (Photo by Bong Arboleda, UP MPRO)

 

Giant clams are protandrous, meaning, they begin life as males. Curiano describes how these species are male from zero to seven years old. Thereafter, they are able to release both sperm and egg. He theorizes that since giant clams are sessile creatures—or fixed in one place—they have adapted to become hermaphrodites for their survival. The highest egg production recorded by the Marine Science Institute was 105 million eggs from a 61-cm clam.

However, giant clams are cultured at the BML in a different way from their natural spawning. Curiano says that his team takes 20 giant clams from various cohorts during the spawning phase. “We do away with inbreeding because it has a lesser chance of survival,” he adds.

 

The oldest and the largest

Curiano is a fisheries graduate from Samar. It was only through a job advertisement in a daily newspaper that he learned about giant clams when the BML opened its research aide post. He immediately applied for the post, and soon after, he was seeing these huge clams for the first time in 2006.

He recalls that it was in 1983 when Dr. Edgardo Gomez, in collaboration with Dr. Angel Alcala, surveyed the waters off Bolinao, and eventually discovered the depletion of the giant clams there. That same year, they acquired three juvenile giant clams all the way from the Solomon Islands. Since 1985, the BML has been able to increase the number of giant clams, as well as to distribute them to as far as the United Kingdom and Germany.

Two of the three giant clam pioneers from the Solomon Islands are still alive today, with a massive size of 98.3 centimeters, the largest giant clams recorded in the country. BML also holds the biggest kukong-kabayo (Hippopus hippopus) at 90.3 centimeters, with T. derasa growing as large as 93.6 centimeters; and hagdan-hagdan at 87.6 centimeters. These gentle giants have a lifespan of 50 to 60 years, according to Curiano.

 

Passing through Site 3 of UP MSI-BML ocean nursery where adult and juvenile giant clams are cultured.

(Video by Rubie Esmolo, UP MSI-BML and Stephanie Cabigao, UP MPRO)

 

The parent giant clams are 35 years old today. Currently, the BML watches over a total of 35,687 adult giant clams at its ocean nursery, and about 62,000 juveniles at the hatchery. Curiano explains that they grow these juveniles to about 3 centimeters at the onshore hatchery before they are released into the wild.

 

A giant clam marine reserve

On board the giant clam program are Rubie Esmolo and Vanessa Joy Diamante. Both are research assistants like Julio Curiano. They are also in charge of the BML’s research and extension programs.

“A marine reserve is set to be established soon in collaboration with BML and the local government unit of Bolinao,” Diamante says excitedly. “What the BML and the LGU of Bolinao want is to make this part of Bolinao a protected and ecotourism area. We got word from the LGU that the bill has already been passed calling Bolinao the giant clam capital of the Philippines. So, we are moving forward to our next goal, making the marine reserve happen.”

 

UP MSI-BML giant clams research assistant and extension programs coordinator Vanessa Joy Diamante (Photo by Bong Arboleda, UP MPRO)
UP MSI-BML giant clams research assistant and extension programs coordinator Vanessa Joy Diamante (Photo by Bong Arboleda, UP MPRO)

 

She adds, “The ordinance for establishing the marine reserve is on its way. As we await its public hearing, we are now working with the residents of Silaqui Island on forming a people’s organization that will prepare them as primary point persons of the marine reserve. This will be significant to the lives of the residents of the island as well as to BML, because it will provide us with the financial resources to sustain the training and maintenance of the giant clam nursery.”

Aside from maintaining the giant clam facility, Rubie Esmolo is focused on the upcoming extension activities of the BML. She points out the success of its public information seminar in March with law Prof. Jay Batongbacal on the protection and conservation of Philippine marine biodiversity, particularly at Benham Rise and the West Philippine Sea. Another activity was an open-house exhibit and the launch of the Adopt-a-Clam project in April.

 

UP MSI-BML giant clams research assistant and extension programs coordinator Rubie Esmolo (Photo by Bong Arboleda, UP MPRO)
UP MSI-BML giant clams research assistant and extension programs coordinator Rubie Esmolo (Photo by Bong Arboleda, UP MPRO)

 

The team takes pride with its successful participation in the 4th Asia Pacific Coral Reef Symposium in June, as well as with its several trainings, outreach and environmental programs showcasing the BML’s research initiatives. Esmolo, along with the rest of the team, is looking forward to a bigger and busier year ahead. The BML aims to promote the giant clam program more than ever to heighten the awareness of the public, as well as to strengthen its sustainability so people can enjoy their company for many more generations to come.