12 April 2009

Living reefs of Pulau Hantu

What a fabulous way to spend Easter holidays, sunrise on the reefs of Pulau Hantu at low tide!
Pulau Hantu has among the best reefs that are easily accessible to the public. And it's been months since we last visited. How are they doing?

Very well, it appears!The visibility was fantastic, and the hard corals were amazing. In the crowd of corals above are boulder-shaped Porites hard corals, Favid corals, and a lovely Lettuce coral (Pavona sp.), with seagrasses too!

Hard corals form the base of a reef, providing hiding places and food for all kinds of animals.A special coral is the Ridged plate coral (Pachyseris sp.), here next to some Anemone hard corals (Goniopora sp.) which have long flower-like tentacles and are often mistaken for anemones.
Another hard coral often mistaken for a sea anemone is this Torch anchor coral (Euphyllia glabrescens) which so far, I've only seen on Pulau Hantu and Pulau Semakau.
There were also several Ridged plate corals (Merulina sp.) in different colours. I don't see this coral too often.And it's always a delight to encounter the Galaxy corals (Galaxea sp.) with their star-like polyps. Hard corals are a colony of tiny animals called polyps living together. Each polyp creates a hard skeleton, and the joined up skeletons of countless polyps creates the fabulous shapes of hard corals.I came across this strange hard coral. I don't know what it is.

Pulau Hantu is one of the best places to see mushroom corals. These are so fabulous that I've done a separate post about them.

Besides hard corals, Pulau Hantu also has lots of soft corals. These come in fantastical shapes and colours. Some resemble discarded surgical gloves.Others look like strange stubby sculptures in rainbow colours.

Like hard corals, soft corals are also colonial animals. Each humungous soft coral is made up of countless tiny little polyps. But instead of a hard skeleton, these share a common tissue that feels leathery. Thus they are sometimes also called Leathery soft corals.
When the polyps are expanded, the leathery soft coral colony appears fuzzy and furry. But the polyps can retract completely into the shared tissue, leaving a smooth surface.
Here's a closer look at the tiny polyps of a leathery coral. The polyps of soft corals have branched tentacles.
Here's a closer look at another kind of leathery coral with different shape and arrangement of polyps.

A confusing kind of coral is the Blue coral (Heliopora coerulea). It has a hard skeleton, but its polyps have branched tentacles so it is classified together with soft corals.
This odd situation is because these corals are considered living fossils! Blue corals are living relicts of fossil species known from more than 100 million years ago. Most other corals have an evolutionary age of only several hundred thousand years. Their internal skeletons are blue, hence their common name. The blue colour is due to the iron salts that are incorporated into their skeletons. On the outside, they are usually brown because the thin layer of living tissue that covers the outer surface of the skeleton is brownish.

Elsewhere on the reef, there are lots of colonial anemones or Zoanthids (Order Zoanthidea).
Soanthids don't produce a hard skeleton. Instead, their skin is leathery and composed partly of chitin, the same substance that insect exoskeletons are made of!

Other relatives of hard corals include sea anemones. And Pulau Hantu has many of them.The most interesting of which are the Giant carpet anemones (Stichodacytla gigantea) which are often home to False clown anemonefishes (Amphiprion ocellaris). Today, I only managed to photograph this tiny little fish with one and a half stripes. These was another anemone with larger fishes, but they refused to come out of hiding.

The others also saw a Magnificent sea anemone (Heteractis magnifica), a Bubble tip sea anemone (Entacmea quadricolor) and there were lots of Frilly sea anemones (Phymanthus sp.) of all kinds, as well as Wriggly star anemones. But the most stunning find was Sam's encounter with a huge Haekel's anemone (Actinostephanus haekeli).

Other Cnidarians seen included lots of jellyfishes!

For Echinoderms, today lots of Red feather stars (Class Crinoidea) were sighted. There were also plenty of Common sea stars (Archaster typicus) in the sandy silty lagoon.
Including this 'mating' pair of a small male locked onto a much larger female. She seems to be trying hard to get away from him! Hmm, previously, when I saw small Common sea stars, I assumed they were juveniles. Now, I wonder if they are just smaller males. There's so much more to learn about our shores.

I had a bit of luck with fishes, as they are really hard to photograph.A tiny electric-blue fish stopped for a few seconds to let me attempt to photograph it. This fish may be the juvenile of the Threespot damselfish (Pomacentrus tripunctatus) which is rather dull-coloured as an adult.

And then, there was this splendidly coloured fish that tried to pretend to be sargassum seaweed and stayed very very still.I think it's some kind of wrasse, possibly the Weedy wrasse (Pteragogus sp.)?
After a while, it zipped away to a better hiding place, at the same time changing its colours! Ivan also saw the Carpet eelblenny (Congrogadus subducens) and a moray eel (Family Muraenidae).

The most amazing vertebrate sighting must be by Alicia and Andy. They each separately saw the Yellow-lipped sea krait (Laticauda colubrina)! Wow!

There were lots of sightings of nudibranchs as well. The Glossodoris atromarginata were everywhere, as well as Jorunna funebris and Discodoris boholiensis. Phylids seen included Phyllidiella pustolosa and Sam saw a Phyllidiella varicosa! Ivan spotted a Chromodoris lineata and a green Ceratosoma was also seen.

But the most special snail was Alicia's find of a living Sundial snail (Architectonica sp.)! I shall leave it to the others to blog about these and their other special finds.

I spent quite a bit of time also exploring the mangroves of Pulau Hantu! Here's an entire post about them!
It's amazing that such a spectacular shore with marvellous marine life still exists just opposite the major industrial installations of Pulau Bukom. We hope it can remain this way for all Singaporeans to appreciate and enjoy.

The Hantu Bloggers regularly conduct dives at the reefs of Pulau Hantu, and they just had a fantastic Anniversary dive there!

So come and see Singapore's very own reefs for yourself!

More information about Pulau Hantu on the wildsingapore website.

Thanks to Andy, Alicia and Sam and Kenerf for providing such a fantastic breakfast after the trip, and everyone for the many fabulous finds!

Other blog posts about this trip

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