teamseagrass: Sentosa's last resort

Aug 23, 2009

Sentosa's last resort

The shore below Tanjong Rimau is Sentosa’s last resort for the corals and seagrasses that used to grow all around Singapore’s largest southern island. To get data on the extent and health of the shore’s seagrasses shore over the seasons, TeamSeagrass monitors this narrow stretch of sand and rubble that straddles the island’s natural cliffs and a sloping seawall.

Thanks to a last minute round-up of gullible souls, we had enough volunteers on 21 Aug Friday to brave the soul-sapping journey across the causeway and within sight of a monstrous money-sucking pit. The team was joined by the water quality monitoring team from Singapore Polytechnic.

There are three parallel sites. As the reef flat is not wide enough for the standard 50m transect line, the volunteers use a semi-random sampling procedure, throwing the quadrant within the site boundaries and charting their observations wherever it falls.

The team managed to elude ferocious peafowl and suspicious hotel guards to plunge down the treacherous heights of the seawall. It was still dark when the monitoring began, so torches were needed.

On the exposed flat, the seagrasses grew mainly close to the seawall, while the outer fringe consisted of rubble, seaweed and corals.

Soft corals are quite common, even close to the seawall.

There are also scattered colonies of hard corals, mainly faviids or Porites.

The two species of seagrass known to occur here are the massive Enhalus acoroides and the puny Halophila ovalis.

Various seaweed, which are to seagrass like what flatworms are to nudibranchs, also cover the flat. Sargassum appears to be in mild bloom, while luxurious growths of Caulerpa cover parts of the sand.

Many little creatures, such as this banded hermit crab, lurk among the seaweed, using these ‘plants’ as food or shelter.

After the monitoring, there was a little time to hop around the shore and rock pools further down.

Before it got too bright, octopuses could be seen dawdling on the rubble. From a pale bleachy colour, they quickly activate their chromatophores to match the substrate when they sense an alien presence.

Red egg crabs, though locally threatened, are not uncommon here. A floral egg crab was also spotted. Both these crustaceans are known to harbour toxins, making them excellent choices for a last meal. Many hairy crabs lurk on the outcrops, but their camouflage helps to hide these animals unless they make a sudden movement.

Another disguised creature is the brown sweetlips. This inch-long juvenile was hovering in a pool pretending to be a piece of debris.

Frilly tentacled anemones are also quite common in rocky crevices. They are quite variable in colour, but the ones here tend to be the standard issue green variety.

Apart from the ubiquitous transparent long-armed shrimps, some little tide pools also contained these 2 cm-long striped shrimps. Arthur Anker, an expert in decapods, particularly snapping shrimps, has identified this to be Athanas dimorphus. Unlike most other snapping shrimps, which live in a burrow, these shrimps didn’t seem to retreat anywhere but simply darted about when disturbed.

Up on the rocks below the cliff, the crew found lots of barnacles, sea slaters, nerites, limpets and other splash zone dwellers. Lightning dove snails were particular abundant, gathering in small groups on algae-covered stones.

While the team was exploring, a mysterious man came down and prowled around the shallow water with a little plastic bag. We are unable to confirm if he survived the incoming tide.

By about eight, the work area was fully immersed. Some of the team had to be dragged kicking and screaming back to base, but most complied after threats to stuff a hairy crab down their throat. As the photo shows, they were happy to raise their arms in relief at surviving another morning on a shore exposed to the dangers of desperate resorts.

Those who survived the morning’s trip are: Serene, Kah Ming, Joo Yong and Chia Rui, Abby and Chung Fong.

Other posts about this trip