THE strip of mangroves and mudflats at the edge of the Sungei Mandai Besar river may not be as well-known here as the ones at Sungei Buloh or Pasir Ris Park. But it is home to the largest horseshoe-crab concentration in the world, and two-thirds of Singapore's mangrove species.
Migratory birds also use it as a feeding ground to supplement the food they find from the shores of Sungei Buloh. As birdwatcher Alan Owyong noted: "Without Mandai, there's no Sungei Buloh."
These were among the findings presented by researchers, students and amateur naturalists at a recent conference, the first to focus on the Mandai mangrove, leading to calls to protect the area.
This habitat contains a full ecosystem in a sliver of land, said National University of Singapore (NUS) biology lecturer N. Sivasothi, one of the conference organisers.
At 15.4ha, it may be larger than mangrove strips in Pasir Ris or Labrador, but much smaller than the 100ha of Sungei Buloh, said Mr Sivasothi, who has been studying the site since 1987 and teaching students there.
The mangroves consist of a strip of coast beyond what used to be the Keretapi Tanah Melayu railway, which was cleared in 2011 after a landmark deal with Malaysia.
The studies presented at the conference in August and held at NUS ranged from how wildlife there live to the way mangroves act as sponges for chemical pollution.
Nature Society outreach officer Kerry Pereira described how mangrove horseshoe crabs breed year-round at the mudflat near Kranji, while a National Parks Board staff member listed the snails, crabs and other creatures found only in Mandai during the five-year, ongoing Comprehensive Marine Biodiversity Survey of marine life here.
Mr Owyong pointed out that whimbrels, plovers and other shorebirds move between Sungei Buloh's mudflats and Mandai's, near Kranji.
The site, however, lacks legal protection. The Government has zoned it as a reserve site, which means it could be subject to future development. But there are those who believe that the area needs formal management to conserve it.
Mandai faces several threats, said NUS geographer Dan Friess, including pollution from upstream and offshore and erosion by currents and ship wakes.
And the damming of Kranji reservoir nearby means less sediment is being deposited at the site.
There are gaps in tree cover there, and spots where mangrove trees have toppled as their roots lack support.
So is it worth protecting?
"In Singapore, we have very few places that are left over from wild forests," Mr Sivasothi said. "In Mandai, we have something unique - this remnant of nature which is a fragment to be enhanced."