Natural regeneration on Singapore's artificial shores and structures is happening now - unintentionally, with zero replanting.
A coral reef has settled naturally on the seawalls at Tanah Merah Ferry Terminal, mangroves have taken root on the artificial seawalls at Pulau Hantu - the trees are from diverse species and are tall and healthy. Seagrass meadows thrive inside the Tanah Merah artificial lagoon. And I was astonished to see a lot of corals, as well as seagrasses and other marine life at East Coast Park, on artificial reclaimed land.
I first noticed mangrove trees on Pulau Hantu's artificial seawalls in April 2009. They were already well established and had probably been growing there for some time.
The different mangrove trees seen included common ones like api-api bulu, perepat, nyireh bunga, bakau putih, tumu and bakau kurap. There are also those listed as vulnerable on our Red List, such as tengah putih and bakau pasir.
The structure of the wall may have had a part to play in this. While the top part of the wall is sealed and smooth (the gaps between the rocks filled up with cement), the lower part is made up of unsealed rocks.
Wild about Singapore's nature
Nature activist and environmentalist Ria Tan is passionate about Singapore's marine life, to say the least.
The 54-year-old runs popular wildlife website WildSingapore, a one-stop platform for those who want to learn about Singapore's natural heritage and how to do more for nature conservation.
For the last 15 years, Ms Tan has been monitoring about 40 Singapore shores regularly, making about 100 surveys a year with a small team of hardcore volunteers.
Her blog, Wild Shores of Singapore, can be found on the website, which includes an online guide to Singapore's common marine life.
Ms Tan also provides free use of more than 40,000 photos of Singapore's reefs, seagrass meadows, mangroves and more.
The retired civil servant trains nature guides and helped set up guided walks at Chek Jawa, Pulau Semakau and the Sisters' Islands Marine Park.
She started TeamSeaGrass, which has about 200 volunteers regularly monitoring the seagrass on Singapore's shores.
Ms Tan also volunteers with the Mega Marine Survey of Singapore, an initiative that takes stock of Singapore's marine biodiversity, in a collaboration with the National Parks Board.
As part of the Friends of Ubin Network, she organised Ubin Day the past two years.
An associate of the Lee Kong Chian Natural History Museum, Ms Tan also volunteers as a guide with the nature group Naked Hermit Crabs.
She has co-authored the Chek Jawa Guidebook, the Wild Singapore coffee-table book and Southern Shores guidesheet.
She is currently working on new marine nature guidebooks for Singapore.
Perhaps if we build our seawalls with mangrove colonisation in mind we can have lovely green seawalls in Singapore!
Besides the big trees on the seawall itself, there are also lots of little mangrove trees settling in the lagoon. Hopefully, they will get the chance to grow up.
With a mangrove forest, the island would be one of the few places in Singapore where a nice range of shore ecosystems exist in a continuum, as nature meant it - mangroves, seagrass meadows and coral reefs.
I have even seen mangrove trees settling on artificial seawalls on our northern coast, including at Kranji near the Kranji Dam.
And at Tanah Merah, there are two large patches of critically endangered smooth ribbon seagrasses, which were previously found only at Pulau Ubin's Chek Jawa and Cyrene Reef near Jurong Island. The structure of the lagoon - a shallow sheltered sandy spot protected by seawalls with natural vegetation on the shore - may have helped to allow the seagrasses to settle naturally.
They are dotted with many living haddon's carpet anemones and home to a variety of small creatures such as hermit crabs, snails and fishes, and sea cucumbers too. Three other species of seagrasses have settled on this artificial shore: spoon seagrass, tape seagrass and the critically endangered sickle seagrass.
Among the amazing creatures I encountered here were a spotted eagle ray.
Lush seagrasses are also thriving at East Coast Park. The spoon seagrass and needle seagrass is home to many sea stars, colourful sea cucumbers and rarely seen fig snails.
We have even seen lush growths of needle seagrass in the lagoon used for wakeboarding.
Although we have yet to see signs of dugong feeding-trails on the seagrasses growing on these artificial shores, we have regularly seen dugong feeding-trails on seagrass meadows elsewhere in Singapore.
A reef has settled naturally on the artificial seawalls at Tanah Merah Ferry Terminal. A wide variety of corals and marine life can be found there.
Amazingly, these corals survived the massive oil spill of May 2010 and global coral-bleaching in the same year that hit this stretch of shore.
Among the hard corals are large colonies of delicate branching and plate-forming corals, as well as less common species such as lettuce coral, Horn coral and even rarer species such as cabbage coral .
The structure of the wall may have helped to allow the corals to settle here naturally. There is a wide platform of open rocks which seems to be at the perfect level for them to grow.
Artificial shores such as East Coast Park are locations of some of the most spectacular marine sightings. For instance, a huge mother hawksbill sea turtle came ashore there to lay eggs in 2013, and baby sea turtles were seen hatching at East Coast Park in 2006.
Otters have also been spotted at East Coast Park, as well as Tanah Merah's artificial shores.
Why should we care about mangroves growing on our seawalls, or seagrass and corals surviving on our artificial shores?
Mangroves and other natural ecosystems such as seagrasses and coral reefs can help maintain good water quality.
They can be living barriers that may help mitigate the impact of rising seas and climate change, such as flooding, saltwater intrusion into freshwater supplies and the impact of more severe weather.
Natural and wild ecosystems that are self-generating and self-sustaining are relatively inexpensive to maintain and provide a wider spectrum of experiences compared with manicured gardens.
They can be beautiful and provide recreational enjoyment.
Easy access will allow schools bountiful opportunities for nature-related learning.
If massive reclamation plans are to go ahead at East Coast Park and other spots, this could be done to allow and encourage natural regeneration.
We could build structures which allow reefs to settle on the outside of seawalls, and encourage mangroves and seagrasses to grow on the inside of seawalls and shallow lagoons.
By naturalising canals leading to the sea, we would enjoy a continuum of freshwater wetlands to mangroves.
Imagine what's possible - kilometres of reefs and natural marine ecosystems at our doorstep - Singapore's "Great Barrier Reef" on the mainland, for all in the city to enjoy.