In Pursuit of the Little Giants

Latest update September 9, 2019 Started on February 1, 2018

This expedition aims to search for natural recruits of restocked true giant clams and assess the status of wild stocks all over the Philippine waters.

February 1, 2018
Expedition's summary cannot exceed 240 characters


Did you know that the National Geographic Society is currently offering Explorers a variety of funding opportunities in the fields of conservation, education, research, storytelling, and technology? To learn more and apply for a grant click here.
If you're not interested in applying for a grant, click continue below
Supported by:
In The Field

We have Tridacna noae in the Philippines? NO WAY!!

PICTURES: Tridacna noae (left), Tridacna maxima (right)

The Noah’s Giant clam or Tridacna noae is so beautiful that it could be considered as a jewel of the ocean. We believe it has one of the most unique and intricate mantle patterns of all the other giant clam species. Don’t believe us? See for yourself in the picture (left) below! Like most jewels though, the Noah’s giant clam can be quite rare and hard to find. They can only be found in a select few places in the world, and luckily, they can also be found here in the Philippines!

Can you guess where these eye-catching giant clams have been spotted in the country? So far, they have only been seen in Sibulan, Negros and in Palawan. In our surveys however, we also managed to see a few of them in some of the coral reefs of Calaguas, Camarines Norte. We hope that we find more of them in other reef sites in the Philippines as the project progresses!

If you think you’ve seen similar giant clams in your area, you probably saw the Noah’s giant clam more common close relative known as the Tridacna maxima. T. noae and T. maxima look so alike that one might say they could have been twins! Because of this, scientists have also been confusing the two species with each other. In fact, it was only until a few years ago that they were confirmed as separate species because of differences in their DNA.

Don’t worry though, there’s an easier way to identify the Noah’s giant clam. The secret to telling the two twin giant clams apart is by looking at the patterns on their mantles. T. maxima clams have a border of continuous brown dots on the outer edges of their mantle, while T. noae have teardrop-shaped patterns instead. Also, both giant clams also dig into the rocks and corals they are usually found on. Great! Now you too can identify these giant clam species if you ever encounter them.

It’s our mission to paint a clearer picture of our country’s giant clam resources. With every species we encounter, we hope to find out just how many giant clams we still have across the country. If you see the Noah’s giant clam, or any other giant clam for that matter, let us know! Together we can help protect these little giants from disappearing from our beautiful coral reefs.


Borsa, P., Fauvelot, C., Tiavouane, J., Grulois, D., Wabnitz, C., Abdon Naguit, M.R., Andréfouët, S., 2015. Distribution of Noah’s giant clam, Tridacna noae. Mar. Biodivers. 45, 339–344.

Su Y, Hung J-H, Kubo H, Liu L-L (2014) Tridacna noae (Röding, 1798) – a valid giant clam species separated from T. maxima (Röding, 1798) by morphological and genetic data. Raffles Bull Zool 62:124-13

image-1 image-1


You might be wondering why we should be protecting giant clams in the first place. Giant clams actually perform many roles in a coral reef, and they affect the lives of many other marine organisms. Along with corals, they help the reef to thrive. Below are some of the most vital functions they provide:

1) Build and Shape Reefs & Provide Habitats

  • Due to some species growing up to large sizes (1m or more in Tridacna gigas ), their large surface areas and the complexity of their shells add to the overall structure of the reef. These additional spaces are important as they allow more organisms to grow on them.

2) Food & Algae Factories

  • Like most other organisms, giant clams are also prey to some marine animals. The soft tissues of the giant clams serve as food to predators such as pufferfish, triggerfish, crabs, snails, and octopuses. Their gametes also get eaten during times of spawning/release, as well as their feces as they contain nutritional algae.

3) Nurseries for Fish & Eggs

  • Multiple giant clams can help provide shelter and cover for juvenile fish as well as the eggs of various marine animals. For this reason, much smaller fish tend to survive longer from predators which may eventually affect fish catch.

4) Filter & Clean the sea

  • Giant clams help keep seawater clean and control the growth of algae by filtering seawater through their gills.

5) Indicate Reef Health

  • Much like corals, giant clams also undergo “bleaching” when they are stressed or when reef conditions are not optimal. These bleaching events may be due to higher seawater temperatures, increase in sediments, or many other factors.

Bonus: Did you know that giant clams also help the growth of other organisms in the reef? They secrete calcium carbonate, which can help in the growth of shells.

With all of these vital contributions, there's no doubt that we should do what we can to ensure that these giant clams survive for many more generations.

Written by: Eymard John Sy

References: Neo, M. L., Eckman, W., Vicentuan, K., Teo, S. L. M., & Todd, P. A. (2015). The ecological significance of giant clams in coral reef ecosystems. Biological Conservation, 181, 111-123.

Some photos were taken by Dr. Klaus Stiefel

"Filters & Cleans Seawater" photo taken by Eena Nuevas


Did you know that the Philippines host 8 species of giant clams under the family Tridacninae?

Let's start off with the second-largest species, the Tridacna derasa. It is commonly known as the "smooth giant clam" because its shell lacks ornamentation. The largest recorded size is at 51.3 cm and the species have also very attractive colors. The mantle has patterns that look somewhat like party lights due to the neon colors. This is definitely my favorite species!

Due to its ornamental characteristics, the species were also overexploited in the 1980s. Culture of this species was simultaneously done with Tridacna gigas. We hope to see more of this species in our sites. They say it doesn't hurt to have more of that pop of color.

Photos by: Ian Joseph de Guzman and Lala Grace Calle

image-1 image-1


Yes, you've read it right! It's a boring giant clam! But wait until you see this clam, I don't think you'll get bored at all!!

The Tridacna crocea is the smallest species under the Tridacninae family. It's called boring clam because it settles and creates holes insides bommies. The largest recorded size is at 15 cm which is equivalent to a juvenile True giant clam!

Interestingly, we can still find this species in degraded coral reef areas. Look at the color of the mantle. You won't miss this clam underwater even if it's small as a pea!

Photos by: (1) Lala Grace Calle; (2) UPMSI Giant Clam Program

image-1 image-1


In some restocking sites, there have been sightings of baby Tridacna gigas. The photo below is from Camiguin taken by our fellow researcher, Jeremiah Requilme. Our project aims to find recruits in all restocking sites to determine whether the restocked True Giant Clams have been reproducing in the wild.

Currently, the institution along with other collaborators use induced spawning to replenish the population of giant clams. If we find evidence that the once locally extinct clams are finally reproducing without intervention, the clams could be on their way in producing stable local populations that may eventually be economically viable if maintained.

Recently we applied for the S.E.E Initiative grant-funded Trident! It is such a great opportunity for all of the research expeditions all over the world. The initiative could help different groups in their expeditions especially here in the Philippines wherein grants and funding are so limited for scientists. The ROV would be of great help in our research since there is a need for technical help in our giant clam surveys. Our divers and researchers can only survey a maximum of three sites a day and this is only for shallow reefs (4-6 m deep)! The OpenROV Trident would be of great help in our fieldworks since it could check other areas in our sites that we would not be able to survey first-hand.

We hope to see more baby clams and wild ones!

Photo by: Jeremiah Requilme


The program aims to study different sites in Luzon, Visayas, and Mindanao. These sites were part of the restocking projects in the late 1980s up to the 2000s. The areas were carefully established to also look at thermal stress effects on giant clams.

Poster by: UP Marine Science Institute-Giant Clam Program

Expedition Background

A long time ago, giant clams were considered as the ‘Man-Eaters’ of the ocean. They were once thought to be this predator silently waiting on the unsuspecting swimmer to get trapped between those two large valves. But alas! It’s actually the other way around. Giant clams have been exploited since the 1960s because people feast on their tasty meat! In the real world, it is a Man-Eat-Giant-Clams reality. To save the giants, conservation efforts were initiated and still continue to the present. Starting in the 1980s, the Marine Science Institute at the University of the Philippines spearheaded restocking projects that aimed to distribute giant clams all over the Philippines. In 2018, UP MSI embarks on another big project to assess what has happened to those giant clams in their new homes.

DOST-PCAARRD funded the project entitled “Assessing the Status of Giant Clams and Advancing Culture Techniques” which seeks to a) examine the status of giant clam restocking efforts, and b) reveal molecular mechanisms underlying the growth and development of giant clams. All these efforts are aimed to enhance giant clam culture, restocking and conservation efforts. This project aims to reach not only fellow researchers but also communities who will be the actual stewards of the ocean. The power of information has never been this great and it is time to take steps in bridging the gap between science and the community. After all, it is never too late to say, “Keep clam and never give up.” Photo by: Dr. Klaus Stiefel


Contribute to this expedition

Email Address
Number card
Postal Code

Review Your Contribution

You have chosen to contribute to expedition.

Confirm your details:

  • Name:

  • Email:

  • Last 4 digits:

Click below to proceed.

Thank You for Your Contribution!

Fundraising Details:


Tell us how raising these funds will impact your expedition
You're almost there, we just need to know three more things:
Is any part or component of your project funded by the National Geographic Society or a National Geographic Society Grant?
Is anyone on your expedition/project team affiliated, either currently or in the past, with the National Geographic Society?
Did you apply for a grant/funding from the National Geographic Society for this project?
You have a goal to raise by for:
How will raising these funds impact your expedition?
Is any part or component of your project funded by the National Geographic Society or a National Geographic Society Grant?
You’ve responded:
Is anyone on your expedition/project team affiliated, either currently or in the past, with the National Geographic Society?
You’ve responded:
Did you apply for a grant/funding from the National Geographic Society for this project?
You’ve responded:

Thank You

Fundraising is almost live!
Thank you for applying to collect contributions! We will review your request and follow up with next steps via email.
Feel free to email us if you have any questions.