Invertebrate · Molluscs · Clams

Fluted Giant Clam

Tridacna squamosa Lamarck, 1819

syn. Tridacna (Chametrachea) squamosa, Tridacna lamarcki

40 cmCITES IILeast Concern

1639

Tridacna squamosa, commonly known as the fluted giant clam and scaly clam, is a bivalve species belonging to the Cardiidae family. This species is found in the shallow coral reefs of the South Pacific and 🌊 Indian Oceans, along with other large clam species. It can be identified by its distinctive shell with large fluted edges called 'scutes' and a relatively small byssal opening compared to other clams in the Tridacnindae subfamily. The mantle of Tridacna squamosa displays a range of colors, including browns, purples, greens, and yellows arranged in elongated linear or spot-like patterns. It can grow up to 40 centimeters (16 inches) in diameter.

As an adult, Tridacna squamosa remains sessile and its mantle tissues provide a habitat for symbiotic single-celled dinoflagellate algae known as zooxanthellae, which contribute significantly to its nutrition. During the day, the clam spreads its mantle tissue to enable the algae to receive the sunlight necessary for photosynthesis.

This species is naturally found in areas stretching from 🇿🇦 South Africa to the 🌊 Red Sea and the 🇲🇭 Marshall Islands.

Tridacna squamosa can sometimes be kept in aquariums, but it requires moderate care. This clam is considered relatively hardy among the Tridacnidae family. It relies on a moderate level of light since it depends on zooxanthellae for nutrition. These dinoflagellates use the mantle as their habitat. However, Tridacna squamosa is not as reliant on photosynthesis as other tridacnids like Tridacna crocea or Tridacna maxima. It also consumes phytoplankton to supplement its diet.

In both the wild and domestic environments, Tridacna squamosa is a peaceful creature that does not pose a threat to other organisms. However, in an aquarium setting, anemones, triggerfish, and puffers may prey on it, despite its ability to close its shell completely. It is advised to avoid keeping it with anemones, as they may come into close proximity and harm or consume the clam. Before adding clams to an aquarium, they should be examined for Pyramidellidae snails and, if possible, quarantined.

When kept in an aquarium, Tridacna squamosa should be positioned lower in the display. Although some individuals may prefer lying in the substrate, they may occasionally attach their byssal threads to rocks above the substrate.

Like all clams, Tridacna squamosa requires good to excellent water quality, but it can help reduce nitrate levels in a system. These clams are known to consume free nitrates to a certain extent.

Why it's threatened

Biological resource use

Intentional use: (subsistence/small scale) [harvest] · Unintentional effects: (subsistence/small scale) [harvest]

Climate change & severe weather

Habitat shifting & alteration

The extent of fishing of T. squamosa can vary depending on the local coastal communities. For instance, this species (with other large clam species) is opportunistically taken during fishing trips targeting other marine resources such as fish and lobsters (Purcell et al. 2020). On the other hand, in the Republic of Kiribati, all giant clams (including T. squamosa) are heavily exploited for subsistence purposes (Eurich et al. 2023). Large scale harvesting is now limited by protection from CITES.

Climate change could threaten this species. There were some reports of bleaching incidences during past global bleaching events (Junchompoo et al. 2010, Mies et al. 2019). Elevated temperatures were also found to be detrimental to the photosynthetic performance of juveniles (Elfwing et al. 2001) and to impact the development and survival of veligers (Eckman et al. 2019). Furthermore, experiments combining the effects of elevated temperatures and high _p_CO2 levels revealed strong synergistic effects that significantly reduced the survival and growth of juveniles (Watson et al. 2012, Syazili et al. 2020). Notably, ocean acidification alone has sublethal effects on this species, with individuals exhibiting reduced shell growth rates (i.e., lower calcification rates) (Watson 2015, Li et al. 2022).

Other threats mentioned include anthropogenic influences such as coastal development and habitat loss (Neo and Todd 2012). Notably, there have been several studies examining the effects of varying light levels or irradiance on the photosymbiosis process in T. squamosa. Under lower light conditions (i.e., increased sediment output), the photosynthetic performance appeared to be reduced (Blidberg et al. 1999, Tedengren et al. 2000). These studies suggest that the maximum depth distribution of this species could be largely restricted by reduced light availability in areas with higher levels of sediment input.

Threat classification from the IUCN Red List.