The disappearance of Tridacna maxima could be due to Singapore’s reef bed not being a suitable home for them, said Dr Neo.
“This species needs a good surface to bore itself into the rubble rock, but there are a lot of loose rubble rocks in our reef bed due to years of development,” she said. “It is unsurprising that this species cannot thrive in Singapore’s unconsolidated seabed.”
Their absence could also be due to misidentification of the species, as well as the poor water quality that is not conducive for the species’ survival, she added.
Giant clams in peril
Dr Neo’s finding about the small giant clam’s disappearance in Singapore comes amid the global review of the conservation status of all 12 species of giant clams – the first since 1996 – that assesses how big of an extinction threat these iconic animals face at the global level.
The latest update by the IUCN, which maintains a “Red List” that tracks the conservation status of species worldwide, found that many of these marine creatures may be more threatened with extinction than previously believed.
Established in 1964, the IUCN Red List – which currently has more than 166,000 species on it – is one of the world’s most comprehensive information sources on the global extinction risk status of animal, fungus and plant species.
The species have been assessed and are categorised as either extinct, extinct in the wild, critically endangered, endangered, vulnerable, near threatened, least concern or data deficient.
At the global level, the IUCN found that half of the 12 giant clam species are now threatened with extinction, referring to those in the categories of being vulnerable, endangered or critically endangered.
The largest of them all, Tridacna gigas, is now listed as critically endangered, two notches up from its previous listing of being vulnerable.
Two other giant clam species – Tridacna derasa and Tridacna mbalavuana – are now listed as being endangered, when previously they were considered vulnerable.
For Hippopus hippopus and Hippopus porcellanus, they are now considered vulnerable, when previously they were considered to be at lower risk of extinction.
Rounding up the six is Tridacna squamosina. This species was rediscovered only after the 1996 assessment, and is now considered endangered.
The other half of the 12 species are classified as least concern or data deficient.