The Singapore freshwater crab, which is threatened by extinction, is now slowly growing in numbers in the wild following efforts to recover them. - ST/ANN
SINGAPORE: An endangered freshwater crab found only in Singapore is bearing the fruits of conservation - literally.
The Singapore freshwater crab (Johora singaporensis) was first bred by researchers from the National Parks Board (NParks) in a laboratory and some were introduced into a stream in Bukit Batok in 2018.
Now, these released crabs have successfully established a population of their own, NParks told The Straits Times on Feb 11.
“This means they are surviving, even breeding the next generation of crabs in the wild,” said Karenne Tun, group director for NParks’ National Biodiversity Centre. Reproduction is an indicator that a species is doing well as it suggests that the animals have adapted to their environment and are producing viable offspring.
NParks was responding to queries from ST about Singapore’s efforts to conserve freshwater species, following a recent global study published on Jan 8 in the scientific journal Nature that highlighted the plight of these organisms.
The study, the first-of-its-kind to assess how threatened freshwater animals are with extinction, had found that close to one-quarter of the 23,496 known species of freshwater fauna are threatened with extinction.
The study, which involved a global team of researchers, also assessed that about 65 per cent of the world’s remaining wetland habitats are under moderate-to-high levels of threat.
Freshwater habitats include lakes, rivers, ponds, streams and wetlands. Freshwater organisms include fish, crustaceans like crabs and shrimps, hemiptera - a category of insects including water bugs and aphids – and odonates, which are predatory flying insects like dragonflies and damselflies.
Pollution, dams and water extraction, habitat loss and agriculture were some of the key threats facing such species, the study found. Climate change impacts, such as rising temperatures and severe weather events, can also affect these species, the study noted.
The situation in Singapore reflects the global trend, with 111 of the Republic’s 277 freshwater species listed as threatened with extinction in the third edition of the Singapore Red Data Book - the database of the local conservation status of Singapore’s flora and fauna.
This means that over a third of Singapore’s freshwater fauna population are at risk of extinction. They include freshwater fishes, decapod crustaceans, dragonflies and damselflies.
Another 27 freshwater species are presumed to be nationally extinct – which means they have not been seen in Singapore over the last 50 years. They include odonates such as the rare basker (Urothemis abbotti), lesser splayed clubtail (Burmagomphus plagiatus) and splayed clubtail (Burmagomphus divaricatus).
The main drivers of loss of freshwater species are habitat loss and degradation, said Associate Professor Darren Yeo, head of the Lee Kong Chian Natural History Museum at NUS.
“In some cases, the species were forest specialists. Since much of Singapore’s original forest cover is gone, there simply aren’t enough habitats available to support them,” said Yeo, who was not involved in the study.
Other threats Singapore’s freshwater fauna species face include poaching for aquarium trading or climate change-induced changes to the water regime such as flooding and extreme drought, said NParks.
The global study also identified the proportion of crustaceans, freshwater fishes and odonates facing extinction, with crustaceans being of greatest concern. Some 30 per cent of crustaceans and 26 per cent of freshwater fishes today face a high risk of extinction. Odonates trail closely behind, with 16 per cent facing extinction.
“Decapod crustaceans, especially freshwater crabs, are more susceptible to threats often because they do not disperse well and are very localised in their distributions,” said Yeo, who specialises in freshwater biodiversity and ecology. Not dispersing well means an animal is limited in its ability to spread over a wider area.
Damming of river mouths for reservoirs would also affect certain decapod crustaceans that need to migrate between freshwater rivers and the coastal marine waters, he said.
Dr Tan Heok Hui, a fish scientist at the Lee Kong Chian Natural History Museum at NUS, who was part of the study, said the assessment of freshwater fishes was not yet complete, but preliminary findings already showed 26 per cent were threatened with extinction.
“If the day comes that all freshwater fishes are assessed, this figure could possibly rise in light of further forest degradation, water pollution, global warming and sea-level rise,” he said.
The study had found that fishes face the widest variety of threats, which include being frequently affected by invasive species and disease, agriculture and overfishing.
Freshwaters support over 10 per cent of all known species, but only cover less than 1 per cent of the Earth, the study noted, with global data and assessments for freshwater fishes and invertebrates remaining scant.
It is particularly important to conserve freshwater species as they represent a large proportion of global diversity concentrated in an important habitat that occupies a small area globally, said Yeo. “This makes the freshwater species disproportionately diverse and threatened,” he said.
These species are not only vital to overall biodiversity but also contribute to freshwater ecosystems such as performing vital ecological roles like nutrient cycling - how nutrients move through an ecosystem - to help ensure the ecosystem is healthy.
As part of its conservation efforts, NParks carries out surveys of key freshwater habitats regularly to monitor these ecosystems, such as the freshwater streams in Bukit Timah Nature Reserve.
However, further studies are needed to address the knowledge gaps, such as how changes in land use and climate change affect these freshwater habitats, said Tun from NParks.
To narrow the gap, long-term data from comprehensive surveys can help researchers understand these ecosystems better and develop strategies to restore them, she added.
In 2015, NParks launched the Species Recovery Programme to help conserve native flora and fauna species by increasing their populations and strengthening their chance of survival in the wild.
Among more than 40 animal species under the programme, six are freshwater fauna species, said Tun. Besides the Singapore freshwater crab, other freshwater species NParks has successfully bred and released into the wild are the muff river prawn and the swamp forest crab.
Citing an example of how the critically endangered Keli bladefin catfish (Encheloclarias kelioides) was found in Singapore for the first time in the Central Catchment Nature Reserve in August 2022, Tan said long-term protection for habitats like the nature reserves are important for conservation.
Yeo said the conservation of freshwater species like the iconic Singapore freshwater crab also instils a sense of pride in being able to have stewardship in local native fauna.
“The awareness and protection of these natural freshwater habitats, which might otherwise be out of sight and out of mind, also benefit other less prominent but equally important species – both freshwater and terrestrial – living in the same area,” he said. - The Straits Times/ANN
