Giant clams, the largest living mollusks, are iconic inhabitants of coral reefs and critical players in reef ecosystems. Known for their impressive size and vibrant colors, these bivalves are vital for nutrient cycling, reef-building processes, and habitat provision. Yet, despite their ecological importance, giant clams are facing mounting threats, and there is ongoing debate about whether placing them on the endangered species list would aid or hinder their conservation.

Threats facing giant clams

Giant clams are increasingly vulnerable due to a combination of natural and human-induced threats. Overexploitation for their meat, shells, and aquarium trade, compounded by habitat destruction from coastal development and pollution, has caused significant population declines in many regions. Climate change exacerbates these challenges, with rising ocean temperatures and acidification impairing their ability to form shells and maintain symbiotic algae crucial for their growth and survival.

Marine heatwaves and acidifying waters are particularly problematic for giant clams. Like corals, they can experience bleaching, expelling their algae under stress, which compromises their energy supply. Additionally, sediment-heavy runoff and declining water quality further limit suitable habitats.

Despite existing protections under Appendix II of the Convention on International Trade in Endangered Species (CITES), which regulates international trade, these pressures persist, raising questions about whether additional measures are needed.

Weighing the benefits of endangered species listing

Adding giant clams to the endangered species list could provide several benefits:
Stronger legal protections: Inclusion would make it illegal to harm, trade, or harvest giant clams in jurisdictions where the listing applies, reinforcing current protections and enabling stricter enforcement.
Increased conservation funding: An endangered status often attracts funding for conservation programs, such as habitat restoration, captive breeding, and the establishment of marine protected areas (MPAs).
Enhanced public awareness: Official recognition of their endangered status can highlight the plight of giant clams, rallying public support and encouraging sustainable practices in fishing, aquaculture, and tourism.
Habitat safeguarding: Protecting giant clams indirectly benefits entire reef ecosystems. As keystone species, their conservation supports the biodiversity and stability of coral reefs.

The risks and limitations of listing

While the benefits are compelling, listing giant clams as endangered could have unintended consequences:
Economic impacts on local communities: In Southeast Asia and the Pacific Islands, many communities rely on giant clams for food and income. Harvest restrictions could threaten livelihoods, especially in areas where clams are a traditional protein source. Alternative resources may not always be accessible or sustainable.
Enforcement challenges: Protecting marine species in vast, remote areas is inherently difficult. Without effective enforcement, illegal poaching and trade may persist, undermining the listing’s intent.
Shift to black markets: Restricting legal trade could increase demand on the black market, driving up prices and incentivizing illegal activity. This risk is especially pronounced for species like Tridacna gigas, prized for its meat and decorative shells.
Barriers to research: Scientists studying giant clams may face additional regulatory hurdles, such as obtaining permits for specimen collection. These restrictions could hinder research critical for developing effective conservation strategies and breeding programs.

Alternatives and complementary approaches

Rather than solely relying on endangered species listing, innovative and adaptive strategies may be more effective in conserving giant clams while balancing ecological and socio-economic needs:
Targeted aquaculture programs: Breeding clams in controlled environments can bolster wild populations. Programs that acclimate young clams to warmer, more acidic waters may help enhance their resilience to climate change.
Symbiotic algae selection: Providing clams with algae strains tolerant to higher temperatures and light levels could improve their survival in changing conditions.
Habitat protection and expansion: Identifying and safeguarding potential new habitats, particularly in deeper waters less affected by heatwaves, could provide refuges for clams under stress.
Citizen science and education: Engaging local communities and the public through citizen science programs can increase awareness and foster support for conservation efforts. Highlighting giant clams as flagship species for coral reef protection may also generate broader environmental benefits.

Balancing conservation and community needs

Striking a balance between conservation and human reliance on giant clams is essential. Local communities must be included in conservation planning to ensure their needs and traditional practices are respected. Co-management approaches that involve stakeholders in decision-making can promote sustainable use while protecting giant clams.

The IMARCS Foundation is pioneering novel research with giant clams and exploring their positive impacts on coral reefs. This research prioritizes resilience-building measures that look to mitigate current threats and prepare these ecosystems for a changing climate, as well as act as important buffers for carbon sequestration and ecosystem restoration.


References

Watson, S.-A., & Neo, M. L. (2021, December 13). Our iconic giant clams face new threats from warmer waters and acidic oceans – let’s buy them time. The Conversation. https://theconversation.com/our-iconic-giant-clams-face-new-threats-from-warmer-waters-and-acidic-oceans-lets-buy-them-time-172607

Lucas, J. S. (1994). The biology, exploitation, and mariculture of giant clams (Tridacnidae). Reviews in Fisheries Science, 2(3), 181–223. https://doi.org/10.1080/10641269409388557

Watson, S.-A. (2015). Giant clams and rising CO2: Light may ameliorate effects of ocean acidification on a solar-powered animal. PLoS ONE, 10(6), e0128405. https://doi.org/10.1371/journal.pone.0128405

Poutiers, J. M. (1998). Bivalves: Tridacnidae. In K. E. Carpenter & V. H. Niem (Eds.), FAO Species Identification Guide for Fishery Purposes (pp. 123–145). FAO.