The Other Side of St. John's Island

Due to the recent rockfall at the intertidal reef that we usually visit at St. John's Island, some of us RMBR Nature Guides decided to check out the shore on the other side of the island to see if it's possible to conduct a guided walk there.

It was mostly a rocky shore, with very few corals, and thus the diversity of marine life was somewhat not as rich as the usual shore that we visit.


Most of the hard corals we saw were really huge though - the one above probably close to a metre wide - indicating that they were probably very old colonies since most corals grow quite slowly.


Among the rocks and few corals, the many Black Sea Cucumbers (Holothuria leucospilota) were probably the most conspicuous.


SY found this Diamond Wrasse (Halichoeres dussumieri) which got itself stranded on some Bryopsis seaweed.


There were quite a number of Land Hermit Crabs (Coenobita cavipes) on the upper shore. These hermit crabs are very much adapted to living on land, and may in fact drown if kept underwater.


Several Branched Anemones (Phymanthus sp.) were spotted as well. Like other sea anemones, they have stinging cells in their tentacles to sting and capture small animals to feed on.


Seeing a Flatworm (Pseudobiceros uniarborensis) swimming always fascinates me, as it is so graceful as it flaps the sides of its mantle!


I found this small Black Long-spined Sea Urchin (Diadema setosum) in a tidal pool. This sea urchin feeds on algae, and its mouth is located underneath.


Since it was a rocky shore, I wasn't surprised to find several Giant Top Shells (Trochus niloticus). These huge shells are collected for food in the region, and also, the shells can be made into pretty glossy buttons when polished.


Another top shell spotted was this Thick Lipped Top Shell (Monodonta labio). Top shells generally feed on algae on the rocks.


Drills (Thais bitubercularis) were found on the rocks too, probably feeding on barnacles. They feed by secreting carbonic acid to soften the shell of the barnacle, and drill a hole through it with their radula.


I'm not entirely sure what snail this is. Could it be a limpet? Guess will have to check with SK again and update later. Update: This is indeed a limpet, Cellana radiata. It is moderately common among breakwater rocks.


Lightning Dove Snails (Pictocolumbella ocellata) were a common sight on most rocky shores of Singapore. These snails feed on algae.


SY found this Spotted-belly Crab (Ozius guttatus) which has very strong pincers, allowing it to crack snails shells to feed on the snail within.

Other than the animals, we found several interesting plants too!


The Beach Gardenia (Guettarda speciosa) was blooming with its pretty and fragrant white flowers.


The Sea Daisy (Wedelia biflora) is a native coastal plant related to the sunflower.


Several Geiger Trees (Cordia sebestena) were planted on the island, and most of them were blooming with bright orange trumpet-shaped flowers.


The fruits of the Geiger Tree turned white as they mature, and is said to be edible.


On one of the Geiger Trees, I found a Mistletoe (Dendrophthoe pentandra) growing on it. Mistletoes are hemi-parasitic plants which can photosynthesize, but at the same time, leech nutrients from the host plants they were growing on. D. pentandra is known to be a butterfly host plant to the Painted Jezebel (Delias hyparete metarete).

While the biodiversity of this shore may not be as high as the one which had the rockfall, it was a good trip nonetheless! :)