NSS Kids’ Fun with Intertidal Marine Life at Sentosa (Singapore)

Text and Photos by Gloria Seow, Education Committee Chairperson

Weekend intertidal walks are few and far between in any given year, as such walks in places like Sentosa island and Changi beach (southern and eastern part of Singapore respectively) are possible only if the tide falls to 0.2 metres and below. Another inconvenience involves the tendency of ultra-low tides to be in the pre-dawn hours and on weekdays. So we counted ourselves lucky to be out jaunting around Tanjong Rimau, a rare natural shore located just beyond Rasa Sentosa Resort, on the clear Sunday morning of 24 July 2016 just after the sun had peeked above the horizon.

 Located just beyond Rasa Sentosa Resort, the exposed rocky shoreline of Tanjong Rimau yielded bountiful sightings.

Uncle Marcus Ng was our erudite lead guide, assisted by Auntie Juria Toramae and Uncle Ivan Kwan who moved ahead as scouts. First up, we found an ethereal Blue-lined Flatworm (Pseudoceros concinnus) in the shallows, a regular encounter on many of our intertidal habitats. Continuing the blue theme, we saw a Pimply Phyllid Nudibranch (Phyllidiella pustulosa), a sea slug around 4 cm long with a hard body sporting clustered bumps called tubercles. Some tubercles even come in colours such as pink, red, grey or green. Kids and their parents were intrigued by the profusion of soft and hard corals, anemones, sponges, seagrass and seaweed that characterise this stretch of wild rocky shoreline.

Next, Auntie Gloria came across an exposed Snapping Shrimp  (family Alpheidae). Unfortunately, this nervous critter was so stressed by our presence that it dropped its pincer as it ducked under a rock. Thankfully, lost pincers can regenerate with time. Like many crustaceans, the Snapping Shrimp can willingly shed its claws when threatened or attacked, as it is better to lose a pincer than its life. Of its two pincers, the enlarged one can produce a one-of-a-kind sound, so loud that it can stun tiny fish prey and even crack the shells of small clams. Snapping Shrimps are responsible for the regular pops that one hears around intertidal areas.

The Pimply Phyllid Nudibranch is a lovely 4-cm long sea slug with clustered tubercles.

We had a really adorable baby Reef Octopus (family Octopodidae) swimming around our booties and wellies. Uncle Marcus gently lifted it out of the water to the delight of many. In general, octopus can survive for between 30 to 60 minutes on land, as oxygen diffusion can still take place through moist skin. It is known to crawl around to get from intertidal pool to pool, or to feed on shellfish or snails found above the waterline. 

An adorable baby Reef Octopus was observed swimming around our booties and wellies.

One of the kids reported seeing a ‘snake’. Upon investigation, it turned out to be a shudder-inducing metre long Giant Reef Worm (Eunice aphroditois). Uncle Marcus said that this was a fierce predator best left alone as it can deliver a nasty bite. Equally crabby creatures populate the intertidal environment. In quick succession, we found a Spotted-belly Forceps Crab (Ozius guttatus) that had both pincers raised in attack-defence mode, as well as the highly poisonous Red Egg Crab (Atergatis integerrimus) that took on a crouched defensive stance. 

Our seekers Auntie Juria and Uncle Ivan brought back several interesting finds including a huge Spider Conch Shell (the classic looking shell that people can hold to their ears to ‘hear’ the sea), as well as a Giant Top Shell Snail (Tectus niloticus), an enormous snail with a pyramidal shell. Other marvellous encounters included the Black Long Sea Cucumber (Holothuria leucospilota), Blue Jorunna Sponge (Neopetrosia spp) and Leather Coral (Sarcophyton spp). 

The rare Masked Burrowing Crab we found is likely the first sighting for Sentosa.

Fortunately or unfortunately, we had our most significant sighting when the group had already dispersed. Auntie Gloria noticed a strange ‘unicorn’ crab barely 3 cm across on a sandy substrate between the rocks. Uncle Marcus promptly identified it as the rare Masked Burrowing Crab (Gomeza bicornis). He pronounced that this was likely the first sighting for Sentosa. The perceived ‘unicorn’ is actually a pair of long antennae joined together with interlocking hairs. The united antennae are speculated to form a breathing tube, used when the crab buries itself in the sand with only the tip of its antennae visible. We were jubilant at this find, a cool lifer for Auntie Gloria, Uncle Tim and Auntie Lena.