Who would have thought trudging through mud could be so much fun?

Barely half an hour after arriving on Sentosa's western shore, the place reveals itself to be a smorgasbord of crabs, snails, starfish and other creatures.

I am here for the Tanjong Rimau tour, which takes the public to the intertidal area near Siloso headland.

It reopens next month after a hiatus and shows visitors a different side to an island better known for its hotels, amusement rides and World War II structures.

"Sentosa is actually quite wild - a lot of people don't realise the kind of marine biodiversity we have in our waters," says my guide Tammy Lim, 35, an assistant manager in environmental management at the Sentosa Development Corporation, which has been running the tours since 2018.

After meeting at Siloso Point at the crack of dawn, we start walking to the coastal forest - home to trees such as sea hibiscus and sea almond.

Inside, we hear the dry, screechy call of a kingfisher and the ringing of cicadas, who also make their presence felt through "cicada rain", a euphemism for cicada excrement.

But the intertidal zone - the section of beach between the high and low tide marks - is what we are really here for. The tours happen when the tides are lowest - that is, around the full and new moon.

Sentosa's Tanjong Rimau tour, officially known as the Siloso Headland Intertidal Programme, covers a 550m stretch of coastline facing the mainland. It forms more than a third of the length of the coastline which wraps around the Tanjong Rimau headland.

The tour does not go as far west as it used to, as the cliff face was eroded by heavy rain earlier this year and could pose a safety hazard.

Ms Lim, who has a degree in zoology from the University of Tasmania, leads me through the intertidal zone. We wend our way around the sargassum seaweed, tape seagrass and conglomerate rock, and get up close with the creatures.

One of these is the blue-lined flatworm, whose elegant, paper-thin form belies its role as a voracious predator. The flatworm secretes digestive enzymes, which act externally on prey such as clams. It then sucks the meal up, Ms Lim says.

Later, we get up close with a feisty mantis shrimp in one of the intertidal pools.

"Spearers" and "smashers" can be found on these shores. The one we encounter happens to be a "spearer", she says. "It's got sharp spikes to grip fish and slash them."

But the "smashers" are not to be messed with either. "One punch can break human bone or the glass of a fish tank."

Another happy find is a male fiddler crab, whose cumbersome, reddish-orange pincer slows it down and makes it easier for predators to spot it. The oversized appendage is not useful for feeding, but the crab waves it around to attract a mate.

"It's the 'handicap principle'. Despite this handicap, they are still able to get enough food and avoid predators. It means they have really good genes, therefore the females find them attractive," Ms Lim says.

It is important to be cautious while exploring these shores, as venomous creatures such as stonefish can be found here.

Ms Lim also shows us the empty shell of a cone snail, which injects venom into worms, small fish and other prey. Its venom can also cause paralysis, even death, in humans.

As we explore, we notice other things. A lone heron scouring the shore, the coiled cast of an acorn worm and traces left by a ghost crab in the sand. A piece of decaying wood plays host to sea cockroaches, purple climber crabs and onch slugs.

Reflections at Keppel Bay, gleaming across the water, reminds me how close we are to the hubbub of the mainland - over 500m away, in fact.

The narrow strip of sea between us was a busy channel for trade ships in the colonial era. Mariners passing through the Dragon's Teeth Gate - a pair of jagged, protruding rocks flanking the channel - were guided by beacons at Tanjong Rimau and at Labrador Park on the mainland opposite.

Today, we spot no ships, but encounter sea traffic of a different kind: a family of otters heading westwards.

More fun facts: Starfish can regrow their lost limbs. Barnacles, meanwhile, have penises that go to great lengths to fertilise nearby mates - extending several times the length of their bodies.

Ms Lim hopes the tours will spark interest in Singapore's biodiversity and encourage people to do more to protect it.

Tanjong Rimau, after all, is home to several species that are endangered in Singapore - such as the coastal horseshoe crab, chiton (a type of marine mollusc) and mosaic reef crab, one of the most poisonous crabs on Singapore's shores.

"There's so much that is still not known about Sentosa's wildlife," she says. "There's still so much to be discovered."

Tours for July and Aug 12 will be suspended in line with the latest Covid-19 restrictions.