Pulau Hantu Recce Trip

The maiden post on the first field trip on the first day of the year is also the first time for me on Pulau Hantu.

After we arrived, a heavy downpour sent the intrepid explorers scuttling for shelter.

We eventually headed out along the northern coast though the small mangrove patch within the lagoon where it was mostly soft and sandy.

Sponges as well as algae dotted the area and we found quite a few golf ball sponges (Cinachyrella australiensis) along a stretch. These multi-celled animals have small dimples all over giving them a golf ball-like appearance.

The golf ball sponge produce spike-like spicules that act like the skeleton of the sponge.

Sponges are filter feeders that obtaining food by trapping bits of particles in the water. A larger body that is supported by spicules will therefore enable the sponge to trap more food.

The yellow internal skeleton can be seen radiating out from the centre of the sponge. Some of these needle-sharp spicules stick out of the surface and can cause great discomfort if they pierce and break in human skin when handled.

Passing the rock walls, many nerite snails (family Neritidae) were seen on and along the rocky surface facing the sea. These gastropods feed on algae which they scrape off using their rasp-like radula, an action which is similar to licking ice-cream!

Further out, a seasonal Sargassum bloom blanketed most of the reef and we had to thread gingerly to avoid stepping on unseen organisms. These algal blooms supposedly tend to occur between December to February which coincides with heavy rain and temperature changes. Over at the northern shore, algal blooms involving a different group of algae (dinoflagellates) have been blamed for the mass death of fish and other marine organisms a few days before this.

A tiger-tailed sea horse (Hippocampus comes) was found hiding among the coral reef. The sea horse is in fact a rather odd-looking fish. It is a rather weak swimmer but it makes up for it by having a prehensile tail that can grasp seaweed or rocks to prevent itself from being swept away by strong currents.

This grumpy looking red egg crab (Atergatis integerrimus) was sitting in a tide pool but moved away as we approached.

Red egg crabs are reef dwellers and can grow to a width of 10 cm.

Although they look very attractive, the bright colours actually serve to warn predators that it is poisonous.

The toxins they contain are not broken down even after cooking and they should not be eaten.

Lying in a tidal pool among the Sargassum was a Bohol nudibranch (Discodoris boholiensis). This sponge-eating mollusc has the ability to break off non-vital parts of itself when attacked while the main body makes its escape. The lost parts will then regenerate later.

One of the last animals of the day literally warmed the cockles of my heart. A heart cockle (Corculum cardissa) spotted by Peiya.

This mollusc has a shell made up of two parts - one convex side and a slightly flatter side. They have been reported to host photosynthetic algae in its body in a relationship known as symbiosis. The cockle benefits from food produced by its tenant, while the algae is sheltered and protected from predators.

Soon, it was time to go and we had to leave our heart-shaped cockle behind. Cool weather, great company and lots to discover. I could really enjoy this!

Thanks to Ron for the organism ID.

Further reading:

1. Farmer, M. A., Fitt, W. K. and R. K. Trench. 2001. Morphology of the Symbiosis Between Corculum cardissa (Mollusca: Bivalvia) and Symbiodinium corculorum (Dinophyceae). The Biological Bulletin 200: 336-343.