21 June 2009

A closer look at Hantu

Today was an odd tide: 0.4m for three hours. Hmm. So we visited, just a small team, to see what would happen.One thing about going at a not-so-low tide, and at night, is that all the hard corals are still submerged, and have their tentacles expanded.

Hard corals are colonial animals, each colony made up of many polyps. The polyps look like sea anemones, with a body column ringed by tentacles. As you can see from the photos, the polyps can tuck their tentacles into their body column.

A hard coral that's half in and half out of water allows us to have a look at both the hard skeleton that the polyps produce (called a corallite), as well as the polyps! This colony has large, deep hexagonal corallites that resemble a honeycomb.
Here's a colony with corallites that form a ladder-like pattern. The polyps are rather rectangular.
And one with corallites that form columns of hexagonal corallites.
Hard corals are identified by, among others, the shape of their corallites. So it's difficult to to be sure of the identity of a living hard coral with the polyps expanded. The above corals are probably all Favid corals (Family Faviidae).

Some hard corals have really tiny polyps, like this branching Montipora hard coral (Montipora sp.)
All hard coral polyps have tentacles that are smooth and unbranched. Such animals belong to Order Sclerectinia, the hard corals.

Soft corals are also colonial animals with many little polyps living together. This is a leathery soft coral (Family Alcyoniidae) with tiny polyps living in a shared leathery tissue which is rather pimply.
As you can see, the tiny polyps have branched tentacles. These belong to Order Alcyonacea, the soft corals.

How nice to come across some Blue corals (Heliopora coerulea) today with their tentacles expanded! Also a colony of tiny polyps, this creature is rather confusing. Although the colony has a hard skeleton, it is not grouped with hard corals. As you can see, the polyp has branched tentacles!
Also the colony is often brown and doesn't appear blue at all. It is the internal skeleton that is blue, due to the iron salts that are incorporated into the skeleton. On the outside, it is usually brown because the thin layer of brownish living tissue. This animal belongs to its own Order Helioporacea and is considered a living fossil!

Besides reefs, Pulau Hantu also has some Tape seagrass (Enhalus acoroides) growing in the large lagoon. Today, while waiting for the tide to go down, I took a closer look at these seagrasses.

There is an amazing micro-habitat on the long blades of seagrasses! Lacy hydroids and green lumps of colonial ascidians grow on the blades. All kinds of other encrusting lifeforms create miniature meadows. It's a meadow within a meadow!
Tiny snails graze on the scummy stuff that coats the leaf blades.
And when these snails die, tiny hermit crabs take over their shells. There were lots of these snails and hermits in their shells on the seagrass blades.
Seagrass blades are also a great place to lay eggs.
And pretending to be an innocous lump was this tiny little bobtail squid!
Back to those green ascidians that look like gum drops. Earlier on, Marcus shared photos of slugs that look like these ascidians! I paid close attention to them today but failed to find any slugs.
But I did notice that some of the colonies that remained underwater seemed bright blue.

There were lots of Common sea stars (Archaster typicus) in all the lagoons of Hantu. I took a really close look at one. A sea star's body surface is not smooth. It has all kinds of bumps, lumps and ridges. These may help to provide a space between sediments and body for freshly oxygenated water to flow across. Or it may prevent encrusting animals from settling on the star.
The white structure is the madraporite, through which the sea star sucks in water to power its body.

My special find of the day was this very shy peacock anemone with a small mouth.
It has a very long slender body column, an outer ring of very long tentacles that is lightly banded. And an inner ring of very short tentacles.
As I took flash photos of the animal, it slowly retracted into the sand. It seems quite sensitive to light.

I also saw a lot of fishes today!

And James came across many many dead cone snail shells. We must investigate the reefs more thoroughly when we return at a lower tide.

Today I trudged through all three lagoons on Pulau Hantu. Well, four if you include the water body between Hantu Besar and Hantu Kechil.
In between, I came across a little gecko. It didn't rush away quickly as most geckos would. But eventually, it did amble off.
It has little spikes on its tail, and looks like a darker version of the many geckos we saw at Pulau Semakau. I'm not really good at terrestrial and vertebrates, so I'll just stop here. It was cute though.

Soon enough it was sunrise, with the barely born cresent new moon and the bright morning star that is Venus still in the sky. James has a great shot of the sky on his blog.
Pulau Hantu lies just across a narrow channel from the petrochemical installations on Pulau Bukom.
Despite this, Pulau Hantu still harbours marvellous marine life. Besides intertidal life, the Hantu Bloggers also conduct regular dives at Hantu to see our living reefs. More about Pulau Hantu, how to get there and what to see and do.

On the way home, I noticed some dredging going on near Pulau Hantu. I don't recall seeing any Port Marine Notices about this. Hmmm.
The sun rises over the city skyline as a massive container ship heads out to sea.
We often forget that Singapore is very much a maritime city.

Other blog posts about this trip

1 comment:

  1. That's an amazing macro of the madreporite! Looks like going over all 3 lagoons is very worth it, I shall do so next time.

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