The China Clam got its name not because it came from China! They earned their common name because of their beautiful white porcelain-like shells.

It may come as a surprise for you: I have not seen ALL species of giant clams yet, despite having studied them for many years. 🙂

I actually spent most of my research time on just one species – the fluted giant clam, Tridacna squamosa. Over the years, I began to meet the other species while diving recreationally and visiting other marine labs in the region; thus ticking off a few other species such as Tridacna crocea, Tridacna maxima, Tridacna noae, Tridacna derasa, Tridacna gigas, and Hippopus hippopus.

And then, there were the really rare ones that I wonder when and how will I get the chance to meet them… In fact, some of these species are so hard to come by in the wild (either due to limited geographic range or overexploitation) that there are barely any live pictures of them available online for study!

Little did I expect that my recent vacation dive trip to Sabah, Malaysia would help fulfil a small step of my dream to see all species of giant clams! In fact, it was quite silly of me to have ‘forgotten’ that the area where I was going to dive is home to one rare species: Hippopus porcellanus.

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I honestly did not expect myself to find this giant clam – it can be aptly described as an arduous task of finding a needle in the haystack – given its rarity in the wild. The dive group wanted to dive in a healthy coral reef – one that has live corals and shallow so that we don’t exceed our decompression times. As I meandered around the reefs, I was mostly admiring the colourful corals and reef fishes, with the occasional Hawksbill Sea Turtle swimming up to the surface for air.

And then, it caught my eye from a distance. The clam was just right in front of me, sitting majestically among the corals. At first, I thought it was the common Hippopus hippopus – and I would have also been really happy because I’ve yet to encounter a wild one. I swam away twice and went back to admire it twice (*laughs* I couldn’t bear to leave it), before I realise that it isn’t the more common Hippopus! At that moment, I felt as though that I have ‘caught’ sight of a rare Pokémon – another tick on my species check list 😀

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[BEST FIND OF THE TRIP] I was squealing, screaming, and hyper-ventilating underwater when I spotted this Hippopus clam. AND THEN, I did a double-take when I saw the shells closely – IT’S THE RARE HIPPOPUS PORCELLANUS!!!!! (Yes, I confirmed the ID after re-reading my own paper’s description). SO HAPPY THAT I FOUND THIS ON MY OWN!!!!!!! *beaming*

In 1982, a new Hippopus species, H. porcellanus, was described from the Sulu Archipelago, Philippines. Prior to its formal description by Joseph Rosewater, H. porcellanus was commonly referred to as the China Clam in the shell trade. With a restricted geographic range, H. porcellanus has only been recorded from a few locations: Sulu Archipelago and Palawan in the Philippines, Sabah in Malaysia, Sulawesi and Raja Ampat in Indonesia, Palau, and Milne Bay Province (Papua New Guinea).

Description

In the genus Hippopus, there are only two known species: Hippopus hippopus and H. porcellanus. The latter species typically can reach a maximum shell length of 40 cm, with the largest specimen recorded at 41.1 cm. At first glance, the main distinguishing feature of Hippopus species is that their mantle does not extend beyond the shell margins, compared to their Tridacna cousins with extendable mantles.

Unlike the elaborate shells of its closest relative (H. hippopus), the shells of H. porcellanus has a smoother and thinner shell that lacks texture. In the shell trade, this species is often lumped with T. derasa due to its similar shell shape, texture and thickness, but they can be differentiated when looking at the live specimens.

TD shells
Tridacna derasa shells. Credit: Giant Clams in Asia and the Pacific, 1988.
HP shells
Hippopus porcellanus shells. Credit: Giant Clams in Asia and the Pacific, 1988.
HH shells
Hippopus hippopus shells. Credit: Giant Clams in Asia and the Pacific, 1988.

The mantles of H. porcellanus are generally grey or brown, lack hyaline organs (or ‘eye spots’), and the incurrent siphon bears guard tentacles. The latter morphological feature is also useful in telling apart the two Hippopus species (i.e., H. hippopus lacks tentacles on their incurrent siphon). Hippopus porcellanus is usually found free-living on intertidal reef flats, and on the shallow reefs along the edges of lagoons.

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Current Status

Heavy exploitation in the 70s and 80s, from both subsistence and commercial fishing, has decimated populations of H. porcellanus, leading to extirpations. The few surveys conducted to date suggest that H. porcellanus is rare. Some of the healthiest populations are located within southeast Sulawesi (Indonesia) and the Tubbataha Reef Natural Park (Philippines).

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One of the rare species of giant clam: The China Clam, Hippopus porcellanus

Conservation Efforts

On the International Union for Conservation of Nature (IUCN) Red List of Threatened Species, H. porcellanus is listed as ‘Lower Risk/Conservation Dependent’ due to the decline and disappearance of many populations. This status, however, requires updating as previous assessment in 1996 may be outdated.

At the Tubbataha Reefs Natural Park (TRNP), 100 individuals of various sizes (shell length = 8.2–31.3 cm) were found tagged and being monitored. Fortunately for these clams, the TRNP is one of the oldest marine protected area since 1988, and considered one of the best managed marine park internationally.

There are few published data on the reproduction of H. porcellanus, but ~2000 maricultured F1 H. porcellanus individuals were successfully raised to sexual maturity at Palau’s Micronesian Mariculture Demonstration Center facility in the mid-1990s (G.A. Heslinga & T.C. Watson, pers. comm.). In the recent years, the Marine Ecology Research Centre in Malaysia had produced H. porcellanus in limited numbers (E.D. Gomez, pers. obs.), while the Semirara Marine Biology Department in the Philippines produced ~20,000 H. porcellanus juveniles.

What can I do (as an ordinary person)?

References:

  • Dolorosa RG, SF Conales & NA Bundal (2014) Shell dimension-live weight relationships, growth and survival of Hippopus porcellanus in Tubbataha Reefs Natural Park, Philippines. Atoll Bulletin Research, No. 604. Pp. 1–9.
  • Juinio AR, LA Meñez & C Villanoy (1987) Use of giant clam resources in the Philippines. Naga, The ICLARM Quarterly. January 1987. Pp. 7–8.
  • Neo ML, CCC Wabnitz, RD Braley, GA Heslinga, C Fauvelot, S Van Wynsberge, S Andréfouët, C Waters, AS-H Tan, ED Gomez, MJ Costello & PA Todd (2017) Chapter 4. Giant clams (Bivalvia: Cardiidae: Tridacninae): A comprehensive update of species and their distribution, current threats and conservation status. Oceanography and Marine Biology: An Annual Review, Volume 55. Pp. 87–388.
  • Rosewater J (1982) A new species of Hippopus (Bivalvia: Tridacnidae). The Nautilus, 96(1): 3–6.
  • TED Talk on “The fascinating secret lives of giant clams
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