First and foremost, thank you to my collaborators, Professor LIM Po Teen, Dr LEAW Chui Pin, and Professor Aileen TAN, as well as the Malaysia Marine Park for supporting our field research to survey the giant clam populations in the Perhentian Islands, Terengganu! Also, thanks to L’Oréal Singapore For Women in Science National Fellowship for supporting my research! 🙂

Field sampling for giant clam tissues to examine the population genetic structure in Perhentian Islands. Credits: Lim Zhen Fei.

Field site: Perhentian Islands

Perhentian Islands is a popular diving destination located on the east coast of Peninsular Malaysia. The cluster is made up of two major islands: Pulau Perhentian Kechil and Pulau Perhentian Besar, and smaller islands such as Pulau Rawa, Pulau Seringgih, and Pulau Rhu.

Bachok Marine Research Station (BMRS), IOES

BMRS is located along the coast of Bachok, which is approximately 45 minutes drive away from the nearest airport in Kota Bahru. The current head of the station, Professor LIM Po Teen’s research group is studying the microalgae diversity and ecology, especially those that cause the harmful algae blooms (HABs). The station is strategically located in the outskirts of the South China Sea, making it an important site for gathering information on the marine environment. My first visit to BMRS was in April 2016 to discuss on possible collaboration for working on the giant clam populations, and almost a year later, we successfully secured some funds to do the work!

Field surveys and sampling for giant clams

We were interested in answering two main questions: 1) What is the current population status of giant clams in Perhentian Islands? and 2) What is the population genetic structure for giant clams in this region with respect to the entire South China Sea?

Field survey and sampling of giant clams

During our surveys, we collected both species and ecological data to supplement towards analysing their population status and distribution. We would photograph each clam encountered in our belt transect, and measure them individually.

Collecting morphological data on each giant clam encountered during the surveys.

For a selected group of giant clams, we would retrieve a small mantle tissue sample for genetic analyses. This process of mantle biopsy can be tough, especially when we ‘miss’ the tissue and the clam has retreated completely! A lot of patience and waiting is necessary to also avoid stressing out each clam.

Step by step on how to perform a mantle biopsy.

Some interesting observations from this work…

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It is always lovely to see giant clams on the reefs, especially to document their ecological roles on coral reefs. One of such roles is how they are shelters and refuges for various reef animals. On this trip, I found sea cucumbers wedged next to the clam’s bottom, an entire anemone hosting little clownfish attached to the shell valve, and a resting flatworm on the upper shell edge. The most ‘shocking’ find for me is seeing wild pyramidellid snails – an ectoparasite species known to giant clams!

Pyramidellid snails (also known as pyrams in short) are generalist type predatory snails that feeds on their hosts. These snails are a nuisance in maricultured clams, occurring in very high densities and parasitising on the baby clams. In some case studies, they can cause widespread mortalities in culture setting. During this set of surveys, I have observed this twice, and for one observation, egg masses were also seen next to the parent snails (see photo slide). Although wild pyram populations are most likely controlled by natural predators such as wrasses, this is my first time spotting them in the wild!

Giant clam numbers in Perhentian Islands are astounding for me. At one dive site, there would be giant clams all around me! Happiness! 🙂 At the same time, we also observed a moderate number of dead giant clam shells on the reefs. We cannot be certain what are the causes of mortalities as post-mortem requires the tissues to be present.


The good news is, there appears to be a steady recruitment of young giant clams on these reefs. What joy for me too, as baby giant clams can be quite hard to find in the wild! I’m especially excited because we found a wide size range of baby fluted giant clams (also known as Tridacna squamosa; see my previous post on species identification) on these reefs, which I have not observed in many other places. I also found my smallest baby fluted giant clam at the size no bigger than a jelly bean! I can’t wait to see the other outcomes of this research work. 🙂

Spot the baby Tridacna squamosa in this photo.

Research opportunities

For those who are interested to carry out research around Perhentian Islands, please contact Professor LIM Po Teen through this website.

Finally, not forgetting to thank the students, Li Keat and Zhen Fei for their hard work in performing the surveys and sampling. Looking forward to writing up the paper with them! 😀

Survey buddies. Clockwise from left: Dr LIM Po Teen (in orange), LEE Li Keat and LIM Zhen Fei.