[Blu's Classroom] Marine Protected Animals Get an Upgrade! Can You Identify the 3 Giant Clam Species Commonly Found in Taiwan?

Known as the "roses of the sea," giant clams have become increasingly rare due to overfishing and habitat destruction. In Taiwan, the three species most commonly encountered in the wild are Tridacna maxima, Tridacna noae, and Tridacna squamosa.

Giant clams belong to the phylum Mollusca, class Bivalvia — making them bivalves. They are filter feeders, drawing in seawater through siphons and filtering out food particles. In addition to being significantly larger than most other bivalves, giant clams share another distinctive trait with coral: they host symbiotic algae that give them their vivid colors. These algae enable giant clams to contribute to reef building in coral reef ecosystems, while also helping to filter the water. For these reasons, giant clams are widely regarded as indicator species in many environmental assessment reports.

Let's take a look at the characteristics of Taiwan's three commonly seen giant clam species and how to tell them apart.

Marine Protected Animal — Tridacna maxima

Tridacna maxima

The most frequently seen giant clam on coral reefs, Tridacna maxima uses byssal threads to anchor its shell to rocky substrate, gradually fusing with the reef as it grows. Its wavy mantle harbors symbiotic algae and is often spread open in sunlight to facilitate photosynthesis; it also draws in seawater to filter organic particles. A small-to-medium-sized species, its shell can reach 20–30 cm in length. Due to overharvesting, however, populations have declined in recent years and individuals have shown a trend toward smaller body sizes.

Marine Encyclopedia 2 — Nearshore Coral Reef Edition, p. 434

Tridacna noae

Tridacna noae

A commonly encountered small-to-medium-sized giant clam, Tridacna noae is most readily identified by the teardrop-shaped spots on its mantle. Its ecological habits are similar to those of Tridacna maxima, and it is often found growing alongside stony corals on rocky substrate. The color of the mantle varies according to the composition of its symbiotic algae, ranging from brown and blue-purple to emerald green and reddish-brown. Because it contributes to both algal reef formation and water purification, it is — like other giant clams — an important indicator species of coral reef health.

Marine Encyclopedia 2 — Nearshore Coral Reef Edition, p. 435

Tridacna squamosa

Tridacna squamosa

Tridacna squamosa gets its name from the particularly well-developed scutes on its shell, which bear prominent scale-like, leaf-shaped projections. These projections are often encrusted with corals, sponges, tunicates, and other sessile organisms. This species is less common than Tridacna maxima and Tridacna noae, and tends to inhabit deeper subtidal zones. Its mantle is highly variable in color and typically displays a wavy, patterned texture.

Marine Encyclopedia 2 — Nearshore Coral Reef Edition, p. 436

On 23 May 2022 (Year 111 of the Republic of China calendar), the Ocean Affairs Council announced a proposed revision to Item 5 of the "List of Marine Protected Wildlife," which would designate seven giant clam species — Tridacna rhomboidalis, Tridacna crocea, Tridacna derasa, Tridacna gigas, Tridacna maxima, Tridacna noae, and Tridacna squamosa — as rare and precious marine protected wildlife. The revision has not yet been passed.

Nevertheless, according to a survey conducted by the Ocean Conservation Administration in 2021 (Year 110), Taiwan's giant clam populations have been found to be broadly affected by marine pollution, climate change, harvesting pressure, and human disturbance — resulting in a low proportion of adults, low population density, and an overall decline in numbers.

Should giant clams eventually be listed as "marine protected wildlife," they would, under the provisions of the Wildlife Conservation Act, be fully protected from capture, trade, display, exhibition, possession, import, export, captive breeding, and propagation. Elevating their conservation status and strengthening management would be a meaningful step toward safeguarding these remarkable animals.

Related links:

• Marine Encyclopedia 1 — Northern Taiwan Edition
• Marine Encyclopedia 2 — Nearshore Coral Reef Edition
• Experiencing a Different Kind of Marine Protected Area, Part 1 — Wanggong Austinogebia edulis Breeding Conservation Zone