Hippopus porcellanus was first described from the Sulu Archipelago, Philippines, in 1982 (Rosewater 1982). This species may sometimes be mistaken for Tridacna derasa due to the similar shell shape and texture.

Hippopus porcellanus has a restricted geographic distribution being found in only six regions across the Philippines, Indonesia, Palau, Papua New Guinea, and East Malaysia. Despite extensive surveys, this species appears to be generally rare and occurs in low abundance. There is strong evidence of population decline; reports from the Philippines found intense exploitation of this species for the ornamental shell trade between 1978 and 1985 (i.e., approximately 152,895 pairs of shells were exported). This past exploitation level contrasts with present rarity and provides an appropriate proxy to assess population decline. It is inferred that H. porcellanus has had a population reduction of at least 30% over three generation lengths (= ~45 years, since ca 1979). Given that it is associated with coral reefs, there is evidence of declining quality of habitats in this period. This inference may also be corroborated by the observed recovery period of >20 years that it took for the numbers of H. porcellanus to increase (but this was not further explained) after protection was afforded to the Tubbataha Reef Natural Park (TRNP).

This species continues to face fishing pressures where individuals are collected for the ornamental trade. Consumption of the species has not been directly mentioned, but this species is implied to be used for food in local communities. On the other hand, ex situ conservation has been primarily challenging as adult broodstocks are difficult to obtain owing to the species’ rarity. As a result, mariculture research on this species has been limited to a handful of studies. The success rates of mariculture are low, with no restocking reported. Therefore, the population decline is projected to continue in the future as the causes of reduction may not have ceased. Further work on the potential for mariculture to protect or enhance wild populations is important for future conservation. CITES provides important ongoing protection for this species.

On the basis of the inferred population decline based on past catch data (30% over three generation lengths) this species is assessed as Vulnerable (VU A2bd). It should be noted the species also has a small area of occupancy (AOO is 192 km²), and it is inferred to have a small global population (fewer than 6,000 mature individuals), which further puts the species at risk. Further information about ongoing harvest within the current AOO that indicates any acceleration of decline may prompt an urgent reassessment.

Hippopus porcellanus is known only from the Sulu Archipelago and Palawan (Philippines), Sabah (Malaysia), Sulawesi and Raja Ampat (Indonesia), Palau, and Milne Bay Province (Papua New Guinea) (Neo et al. 2017). 

Hippopus porcellanus appears to be generally rare throughout its known range (Alcala 1986, Villanoy et al. 1988, Juinio et al. 1989, Calumpong and Cadiz 1993, Kinch 2002, Rehm et al. 2022).

Most survey efforts have been in the Philippines. Earlier reports observed very few individuals (n < 5) during surveys across the Philippines (Alcala 1986, Juinio et al. 1989, Calumpong and Cadiz 1993). In 1993, only empty shells of this species were encountered by Estacion et al. (1993) in the Tubbataha Reef Natural Park (TRNP). In the same year, Calumpong and Cadiz (1993) found a few individuals, suggesting that the species is rarely present or was overexploited in the reefs of Tubbataha. This contrasts with earlier reports of exploitation of this species in large numbers for the ornamental shell trade between 1978 and 1985 (Rosewater 1982, Villanoy et al. 1988), indicating that the populations were previously much higher at the start of a time span three generation ago for this species (ca 1979). Comparison of capture rates from the 1980s and later studies indicates an overall decline of around 30%, which is probably indicative of broader trends across its range.

In general, the information on population numbers of H. porcellanus in Indonesia is limited. Despite the extensive surveys of giant clams (Tridacninae) in Indonesia, this species appears to be restricted to Sulawesi (Arbi 2010) and Raja Ampat (Wakum et al. 2017). According to a comparison table by Wakum et al. (2017), the abundances of this species at three sites (names in brackets) were broadly categorised from abundant (Perairan Amdui) to sparse (Kepulauan Roon and Teluk Doreri). Arbi (2010) reported 18 individuals of this species from surveys across northern Sulawesi (seven sites), while Wakum et al. (2017) reported 14 individuals from surveys across Raja Ampat (three sites).

In Papua New Guinea (PNG), the occurrence of H. porcellanus was first reported by Kinch (2002). Specifically, the report stated that this species was the rarest among the giant clam species (i.e., 0.3 ind./ha, in Chesher 1980). However, the latter source requires verification as the citation provided pre-dated this species’ description in 1982 (Rosewater 1982). There appears to be no other records of this species in the recent years, hence, its presence in PNG requires verification.

In Palau, the presence of this species was initially confirmed by Schneider and Foighil (1999). However, a previous survey by Hardy and Hardy (1969) did not report the species. The most recent survey by Rehm et al. (2022) also did not encounter any H. porcellanus, suggesting the rarity of the species in Palau’s reefs. According to the Palau Mariculture Demonstration Center (PMDC), they had approximately 15 individuals of this species for spawning with a small, cultured batch of juveniles (M.L. Neo pers. obs. 2023).

This species occurs over a small, patchy but well documented range, and currently is rare in areas where it is found. In other giant clam species, the lowest observed population densities are 0.2–0.3 individuals per hectare (Neo et al. 2017); within the area of occupancy (AOO) of H. porcellanus, this would indicate a total living population of 3,840–5,760 individuals.

The generation length for this species is not known, but information for the closely related species Hippopus hippopus can be used as a proxy, which gives an estimated generation length of 15 years.

Hippopus porcellanus is usually found free-living on intertidal reef flats (Pasaribu 1988) and shallow reefs along the edges of lagoons (Dolorosa et al. 2014). Due to its rarity, the ecology of this species is poorly studied or understood.

All species of giant clam are known to be simultaneous hermaphrodites. For H. porcellanus, there have been only a few published data on its reproduction (Alcazar et al. 1987, Calumpong et al. 1993).

This species has been successfully cultured in a handful of facilities (e.g., Marine Ecology Research Centre in Malaysia, Semirara Marine Hatchery Laboratory in the Philippines, Palau Mariculture Demonstration Center in Palau) but in limited numbers (E.D. Gomez pers. obs. 2017, M.L. Neo pers. obs. 2023). In a separate observation for H. porcellanus, the PT. Dinar Darum Lestari aquaculture facility, Bali (formerly the CV. Dinar facility) had numerous broodstock specimens in 2005 (J.W. Fatherree pers. comm. 2024). As a follow-up in 2023, the facility lost all their H. porcellanus stock to severe bleaching events where individuals appeared more vulnerable to bleaching compared to other giant clam species (J.W. Fatherree pers. comm. 2024).

Heavy exploitation (i.e., overfishing) from both subsistence and commercial fishing has decimated populations of H. porcellanus, leading to extirpations (Calumpong and Cadiz 1993, Dolorosa et al. 2014). The shells of this species are highly valuable in the international shell trade (Villanoy et al. 1988). According to Villanoy et al. (1988), approximately 20% of sampled shells (n = 69) were identified as H. porcellanus. Between 1978–1985, approximately 37% of total exports were of this species (equivalent to about 152,895 pairs). The most commonly exported shell size of this species was 6–18 cm (equivalent to 92.8% of total exports).

Climate change could threaten this species. In a separate observation, the PT. Dinar Darum Lestari aquaculture facility, Bali (formerly the CV. Dinar facility) had numerous broodstock specimens in 2005 (J.W. Fatherree pers. comms. 2024). As a follow-up in 2023, the facility lost all their H. porcellanus stock to severe bleaching events where individuals appeared more vulnerable to bleaching compared to other giant clam species (J.W. Fatherree pers. comms. 2024).

The range of this species is impacted by intense human population expansion and urban development (NOAA 2024), and is likely to face significant threats from habitat loss in future. The recent rise of the shell handicraft trade in China may affect this species especially in the northern part of its range; shell products of H. porcellanus were observed in shops at Tanmen Village, Hainan Island (M.L. Neo, pers. obs. 2018, NOAA 2024).

Although this species has not been specifically mentioned for harvesting as food, the areas where this species occurs were known to fish for giant clams for their edible meat.

This species is most well-known for its shells in the wildlife trade. Before its formal description in 1982, this species, which is also known as the China clam, was already common in the shell trade (Rosewater 1982). According to Villanoy et al. (1988), approximately 20% of sampled shells (n = 69) were identified as H. porcellanus. In 1978–1985, approximately 37% of total exports were of this species (equivalent to about 152,895 pairs). The most commonly exported shell size for this species was 6–18 cm (92.8% of total exports).

Although there have been mariculture programmes, this species appears to not be traded yet under the name H. porcellanus (Vogel and Hoeksema 2024).

All giant clams (subfamily Tridacninae) are listed in Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) on the basis of so-called 'look-alike species', i.e., species whose specimens in trade look like those of species listed for conservation reasons (Wells 1997). Thus, CITES regulates the international trade in any of their parts (shells, tissues, alive or dead). This species suffered extreme declines prior to CITES listing in 1985.

In situ protection of stocks: H. porcellanus is legally protected under the respective wildlife and fisheries laws in the Philippines and Malaysia.

In the Philippines, reports suggest that the numbers of this species have recovered after more than 20 years of protection in the Tubbataha Natural Reef Park (TRNP), a designated marine protected area and sanctuary. In 1993, only empty shells of this species were encountered by Estacion et al. (1993) in TRNP. In the same year, Calumpong and Cadiz (1993) found a few individuals of this species, suggesting that it is rarely present or was overexploited in the reefs of Tubbataha. Notably, a follow-up study in 2009 reported population recovery of this species in TRNP following more than 20 years of protection (Dolorosa et al. 2014). Nearly 100 individuals of various sizes (shell length = 8.2–31.3 cm) were found tagged and monitored at the TRNP (Dolorosa et al. 2014).

Wildlife trade: According to the CITES Trade Database (Vogel and Hoeksema 2024), this species is not officially traded, but there have been past reports of trade in the Philippines (Juinio et al. 1987). Species identification between the two Hippopus species could explain the lack of records for H. porcellanus, as the shells of both species appear morphologically similar at first glance.

Stock enhancement through mariculture: Broadly, researchers have remarked that the rare occurrence of H. porcellanus has made it difficult to study its reproductive biology in captivity and in the wild (Juinio et al. 1989). Only a few data have been published on the reproduction of this species (Alcazar et al. 1987, Calumpong et al. 1993), but ~2,000 maricultured F1 individuals were successfully raised to sexual maturity at Palau’s Micronesian Mariculture Demonstration Center (MMDC) facility in the mid-1990s (G.A. Heslinga and T.C. Watson pers. comm. 2017). Currently, only a handful of facilities (e.g., Marine Ecology Research Centre in Malaysia, Semirara Marine Hatchery Laboratory in the Philippines, and Palau Mariculture Demonstration Center in Palau) are producing cultured H. porcellanus but in limited numbers (E.D. Gomez pers. obs. 2017, M.L. Neo pers. obs. 2023). In a separate observation, the PT. Dinar Darum Lestari aquaculture facility, Bali (formerly the CV. Dinar facility) had numerous broodstock specimens in 2005 (J.W. Fatherree pers. comms. 2024). As a follow-up in 2023, the facility lost all their H. porcellanus stock to severe bleaching events where individuals appeared more vulnerable to bleaching compared to other giant clam species (J.W. Fatherree pers. comms. 2024).

A key challenge in scaling up this species’ mariculture is the difficulty in obtaining suitable parent broodstock (PMDC pers. comm. 2023). As these animals are rare in the wild, the number of individuals used for previous spawning attempts has limited the production of juveniles. Moreover, the cultured juveniles have generally poor survival and growth rates (PMDC pers. comm. 2023). The poor success of H. porcellanus mariculture puts this species at greater risk of extinction.

This species has been assessed as a proposed endangered species in a status review for the US Endangered Species Act (NOAA, 2024).