Tridacna maxima is widely distributed across the Indo-Pacific region. Reef surveys generally confirm that this species is abundant throughout its geographic range and there are strong signs of natural recruitment replenishing local stocks. In some regions, the distribution of this species is patchy, but the numbers appear to be moderately stable. There is no strong evidence to suggest a decline in global population (i.e., no incidences of local extinctions), but the species continues to face localised threats including overharvesting in specific communities for local consumption or the aquarium trade. In some regions where this species occurs in very shallow and accessible areas, populations can become highly vulnerable to fishing pressures. Additionally, it is vulnerable to the impacts of ocean warming, which affects its symbiotic relationship with photosynthetic algae and its overall habitat stability. Ongoing monitoring is important to provide early warning of potential future declines.

The broad geographic distribution of this species may provide a resilience buffer against localised adverse events (e.g., climate variability), making it less vulnerable to extinction on a global scale. However, this broad presence brings other challenges such as accurate species identification (i.e., discovery of cryptic species). For instance, what was once considered this species includes species like T. noae and T. elongatissima, which have only recently been recognised as distinct. This confusion can complicate conservation strategies and population assessments. CITES provides ongoing protection for this species.

While the mariculture knowledge of T. maxima is well-established and successful in raising cultured individuals, there have been fewer efforts in translocating or restocking the cultured clams for conservation, or these efforts are not well understood or underreported (i.e., it is unclear whether efforts have led to an increase in stock numbers). In addition, breeding programmes typically use a limited number of genetic populations. This narrow genetic basis could reduce the species’ resilience to environmental changes and diseases in the future. Therefore, the population may decline in the future as the causes of reduction may not have ceased. The recent availability of the T. maxima genome also opens up new avenues for studying its population genetics, emphasising the importance of conserving genetically diverse populations.

On the basis of the moderately stable population size with adequate measures to implement conservation strategies when needed, this species is listed as Least Concern.

Tridacna maxima is the most cosmopolitan giant clam species in the Indo-Pacific. It is found from the Red Sea to the Pitcairn Islands and from southern Japan to South Africa (Neo et al. 2017).

Throughout its geographic distribution, this species is still reasonably abundant in many areas (Neo et al. 2018, Rehm et al. 2021, Dolorosa et al. 2024). In many areas, it is the most abundant and common giant clam species (Apte et al. 2010, Rossbach et al. 2021, Lee et al. 2022). Although it is abundant, an increasing number of studies are reporting declines in populations compared to past numbers (e.g., Neo and Todd 2013, Van Wynsberge and Andréfouët 2017, Van Wynsberge et al. 2018). As reviewed by Neo et al. (2017), the lowest density reported was 0.3 individuals per hectare at Pari Island, Indonesia (Eliata et al. 2003), while the highest density reported was 544,000 individuals per hectare at Tatakoto Atoll, Eastern Tuamotu Archipelago, French Polynesia (Gilbert et al. 2006). So far, there have been no reports of local extinctions anywhere (Neo et al. 2017), suggesting that the global population (and subpopulations) have been stable over the decades.

Like other giant clam species such as Tridacna crocea and Tridacna squamosa, this species exhibits high genetic connectivity within regional waters but limited genetic exchange across larger geographic areas. According to Kochzius and Nuryanto (2008), populations can be categorised into four distinct groups: (1) Red Sea, (2) Indian Ocean and Java Sea, (3) Indonesian throughflow and seas east of Sulawesi, and (4) Western Pacific. In another recent study by Fauvelot et al. (2020), the COI+16S phylogeny revealed that this species comprised five sub-clades: one from the Red Sea, two from the Western Indian Ocean and two from the Western Pacific Ocean. As a species that reproduces by spawning, this species relies on surface ocean currents to disperse its pelagic larvae. However, this dependency on specific current patterns also implies that the risk of local extinction could be elevated, particularly if these currents shift or if barriers to larval dispersal arise.

The mariculture knowledge of this species is well-established and successful in raising cultured individuals (Alcazar and Solis 1986, Militz and Southgate 2021, Su et al .2021), and there have been some attempts to translocate cultured clams of this species for enhancement programmes (e.g., restocking purposes in Cook Islands, French Polynesia, Federated States of Micronesia, Samoa, Republic of Kiribati, Marshall Islands, Solomon Islands, Fiji, Vanuatu, Tonga, Palau, and Taiwan) (Neo et al. 2017). However, the outcomes of translocating these cultured clams for conservation are not well understood or underreported (i.e., it is unclear whether efforts have led to an increase in stock numbers).

This species typically dwells in shallow areas of reefs and lagoons, rarely beyond a depth of 10 m; although there have been several records of this species occurring at depths of >20 m. For instance, a live individual was observed at 21.2 m at the Dongsha atoll (Neo et al. 2018) and three Muséum national d'histoire naturelle in Paris (MNHN) recovered individuals from depths of 26 m, 28-32 m and 39 m, respectively (J.J. ter Poorten pers. comms. 2024). It is one of the four boring (sometimes referred to as burrowing) Tridacna species (along with T. crocea, T. noae and T. elongatissima). Juveniles of this species are usually fully embedded in the reef substratum, but older individuals eventually outgrow the bored concavity and become partially embedded only. In areas characterised by high densities, such as the enclosed lagoons of French Polynesia, some individuals can be found on sand (Van Wynsberge et al. 2016). A persistent characteristic among the boring tridacnines is the tendency to byssally attach to the inside of the borehole. This species sometimes grows up to 35 cm, with the largest individual collected (from Fanning Island, Republic of Kiribati) measuring 41.7 cm (Stasek 1965).
br/All species of giant clams are known to be simultaneous hermaphrodites. There is limited information regarding the reproductive periodicity of this species. In Malaysia (Tan and Yasin 2000), the spawning season for this species on Rengis Island was from April to July, which coincided with the dry season. In French Polynesia (Van Wynsberge et al. 2017), the spawning season for this species in two lagoons (Tubuai and Tatakoto) was around June and July, which appeared to coincide with high oceanic water inflow and a decrease in lagoon water temperature. According to Mingoa-Licuanan and Gomez (2007), this species exhibits male maturity at 13 cm and female maturity at 14 cm, but no age was provided.

Through mariculture (Jameson 1976, Alcazar and Solis 1986, Estacion et al. 1986), there is a good understanding of T. maxima’s reproduction potential. There is good mariculture interest in this species as it is popular in the aquarium trade (Mies et al. 2017, Militz and Southgate, 2021, Vogel and Hoeksema 2024). This species is also often used as a model organism in ecological studies focused on investigating the growth and survival of juvenile clams (Grice and Bell 1999, Mohammed et al. 2019), as well as their behaviour (Dumas et al. 2014, Dehaudt et al. 2019).

There is some evidence to demonstrate the presence of T. maxima can produce beneficial outcomes for coral reef ecosystems. For instance, the net primary productivity of a T. squamosa (28.16 g O₂ m^-2 d^-1) is greater than that of many other coral reef primary producers including macroalgae, crustose coralline algae, and hard corals (Neo et al. 2015). With respect to biomass production, the Tatakoto atoll population of T. maxima in the French Polynesia has a high-standing crop (1,041 kg dry weight ha^-1) and high productivity, being capable of producing 238 kg dry weight ha^-1 yr^-1 of biomass (Neo et al. 2015). With respect to calcium carbonate production, the natural T. maxima atoll populations in French Polynesia are also capable of producing 23–37 tonnes ha^-1 yr^-1 and are so dense that they create small islands called mapiko (Gilbert et al. 2006). Similar to T. crocea, another unique ecological role is bioerosion as T. maxima is capable of eroding rubble that can result in a localised scale of reef attrition (Neo et al. 2015). Furthermore, the T. maxima are known hosts of the cyclopoid copepod species (Anthessius alatus and Anthessius amicalis), pea crabs (Ostracotheres tridacnae and Xanthasia murigera), and pontoniinid shrimps (Anchistus demani, Anchistus miersi, and Conchodytes tridacnae) (Neo et al. 2015).

The extent of fishing of T. maxima can vary depending on the local coastal communities. For instance, T. maxima (and other large clam species) is opportunistically taken during fishing trips targeting other marine resources such as fish and lobsters (Purcell et al. 2020). In the Republic of Kiribati, all giant clams (including T. maxima) are heavily exploited for subsistence purposes (Eurich et al. 2023). On the other hand, it is relatively untargeted by fishers in areas where larger species occur, and high densities of the species are still observed on some isolated and enclosed reefs of the Central Pacific (Van Wynsberge et al. 2016). As this species is highly popular in the aquarium trade, numerous South Pacific nations (such as Fiji, Solomon Islands, Vanuatu, and the Federated States of Micronesia) were extracting their wild T. maxima for live exports in the early 1990s and 2000s, which appears to have impacted populations (Neo et al. 2017).

Climate change could threaten this species. Massive mortalities due to climate variability (i.e., high water temperatures) have been reported from the isolated populations of this species in the atolls of French Polynesia (Andréfouët et al. 2013, Van Wynsberge and Andréfouët 2017) and Lakshadweep Reefs (Apte et al. 2019). In addition, thermal stress alone can cause the degradation and death of Symbiodiniaceae cells (Dubousquet et al. 2016) and reduce fertilisation success in this species (Armstrong et al. 2020). Experimental studies combining the effects of elevated temperatures and pCO₂ levels found that elevated temperatures exert a stronger impact on this species’ physiology than acidification (Armstrong et al. 2020, Brahmi et al. 2021). These collectively suggest that variability in thermal conditions could be detrimental to this species in the future.

This species typically is exploited at the domestic level for local consumption. In French Polynesia (Tubuai and Austral islands), where T. maxima (known as ‘pahua’) is widely found, it is the primary target for fishing as food (Larrue 2006). In Sabah-Malaysia, giant clams (including T. squamosa and T. maxima) are regularly consumed as traditional food cuisines (Abd-Ebrah and Peters 2021, 2022). Elsewhere, T. maxima (lumped together with other giant clams) continues to be harvested for subsistence purposes to varying extents (i.e., opportunistic to intensive harvesting) across its range (Purcell et al. 2020, Eurich et al. 2023).

In the 1990s, T. maxima shells were used in various forms in the ornamental shell trade. In the Philippines, these shells had the lowest market demand and were sold cheaply (Juinio et al. 1987). In Palau, the then Micronesian Mariculture Demonstration Center (MMDC, now known as PMDC) sold T. maxima shells as earrings, pins and shell crafts (Heslinga 1996).

Cultivated T. maxima is primarily marketed in the live aquarium trade (Mies et al. 2017, Vogel and Hoeksema 2024), but a limited use for restocking (Neo et al. 2017). While most of the individuals sold for the aquarium trade appear to be cultured, the export of species from Viet Nam is mainly of wild stock origin (Mies et al. 2017). The vast majority of giant clams exported to Western countries are for international trade, which is almost entirely the aquarium industry (Mies et al. 2017). In a unique case study, the small-scale mariculture of highly valued T. maxima in some atolls of French Polynesia offered valuable alternative livelihoods to local communities (Andréfouët et al. 2018). Since 2012, this species has been the focus of commercial mariculture activities, making French Polynesia one of the main exporters of giant clams for the aquarium trade.

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).

In situ protection of stocks: T. maxima has legal protection under the respective wildlife and fisheries laws in the following countries: Australia, China, Taiwan, Japan (Okinawa), India, Indonesia, Malaysia, Myanmar, Philippines, Singapore, Thailand, Viet Nam, South-east African countries (including Somalia, Comoros, Kenya, Madagascar, Mauritius, Mayotte, Mozambique, Seychelles, South Africa, and Tanzania), New Caledonia, Solomon Islands, and Pitcairn Islands. In contrast, the South Pacific nations (such as Papua New Guinea, Federated States of Micronesia, Palau, Marshall Islands, Samoa, Tokelau, Tonga, and Vanuatu) protect their wild stocks by introducing restrictions on harvesting wild giant clams (such as using size, weight or bag limits, gear restrictions or permits) or introducing restrictions on individual uses, including recreational, tourism, and aquaculture. The levels of enforcement of laws, however, are unclear and underreported.

Stock enhancement through mariculture: As this species is thought to be common and widespread throughout its geographic range, there have been limited efforts to restock and enhance its stocks. However, there is evidence of intensive collection of wild clams for exporting in the aquarium trade (Neo et al. 2017, Vogel and Hoeksema 2024). While the species has been bred mainly for the aquarium trade (Wabnitz et al. 2003), wherever aquaculture and mariculture efforts exist (or were active) (e.g., Cook Islands, French Polynesia, Federated States of Micronesia, Samoa, Republic of Kiribati, Marshall Islands, Solomon Islands, Fiji, Vanuatu, Tonga, Palau, and Taiwan), they have also contributed to restocking efforts (Neo et al. 2017). Should the species require enhancement programmes elsewhere, the mariculture techniques are well-established.

Wildlife trade: Since the 1980s, the giant clam species with the most colourful mantles, T. crocea and this species, have been the most popular in the aquarium trade (Mies et al. 2017, Vogel and Hoeksema 2024). In general, T. maxima is the most imported species in the wildlife trade (Vogel and Hoeksema 2024). The trade numbers of T. maxima are made up of both wild-sourced clams from primarily Viet Nam and French Polynesia and cultured clams from Australia, the Marshall Islands, and Micronesia (Vogel and Hoeksema 2024). Based on the CITES Trade Database, Micronesia, Australia, Marshall Islands, Tonga, and Vanuatu were some of the major exporting countries for cultured T. maxima between 2011 and 2019 (Vogel and Hoeksema 2024). Notably, the trade numbers for T. maxima were higher in recent years (2011–2019) compared to 2001–2010, suggesting demand for the species. Between 2001 and 2019, the import-export of live T. maxima was far greater than that of shells (Vogel and Hoeksema 2024). In general, it appears that several cultivation programmes are focused on growing giant clams for the global marine aquarium trade (Mies et al. 2017, Militz and Southgate 2021).

This species has been assessed as a proposed threatened species in a status review for the US Endangered Species Act, also on the basis of being a look-alike species to other protected species (NOAA, 2024).