25 May 2009

Sea Fan Garden at Changi

A bloom of sea fans flourish in the murky waters off Changi!
Only the very tippy tips of these branching colonies of animals can be seen, even at the lowest tides.

They come in various colours.
And are found with other animals of the shore such as the flower-like Peacock anemones.
Sea fan generally need a hard surface to grow on, so they are usually found near rocky areas.
Where they sprout all over the place!
Although I did see one sprouting in the seagrass area!
Nearer the shore, there were smaller colonies that were out of water at low tide.
The one on the left is quite gnarly and the one on the right kind of looks like a candelabra. I still don't know the identity of these sea fans that we commonly see on our shores.

But I've recently learnt that this kind with the flattened 'stems' and polyps only on the sides of the 'stems' might be Echinogorgia.
In my experience, Changi has the largest number and variety of sea fans of all our shores, except for Beting Bronok.

So what are sea fans? They are colonial animals. Each branching colony is made up of tiny polyps that look like sea anemones: with a body column topped by tiny tentacles.
Also called Gorgonians because they belong to the Order Gorgonacea, the polyps are supported by a central rod made of a tough but flexible protein called gorgonin that is similar to the material produced in the horns of animals. Many species incorporate calcium into the gorgonin. Some reinforce this further with an arrangement of sclerites (tiny bits of calcium). The living polyps share a thin skin over this support.

The colony usually branches only on one plane, which is angled to maximise the flow of water so the polyps can filter out edible bits.

Here's another photo of polyps expanded in a submerged portion of a sea fan.
As you can see, sedimentation does bung up the colony. While our sea fans seem to be able to put up with murky water, sediment in the water is like haze in the air. It makes it unpleasant for animals and they have to expend energy to clean themselves.

A wide variety of tiny animals are often found in sea fans.
Like the tiny spindle cowrie (Family Ovulidae) in the right side of the photo. These snails actually eat the sea fan, and are usually perfectly camouflaged to match the sea fan in colour and texture. The above snail is probably Segal's spindle cowrie (Cymbovula segaliana).

I couldn't get close to the sea fans in deeper waters, but managed to catch a shot of a nearly invisible shrimp on this sea fan! All you can see of the creature are its eyes!
The rocky area also provides hard surfaces for tough corals to grow.
The two most commonly seen hard corals on Changi are this green one with neat hexagonal corallites (probably from Family Faviidae), and the tough Zebra hard coral (Oulastrea crispata).
Hard corals are also colonial animals. Each patch is made up of tiny polyps that create a hard skeleton or corallite from calcium carbonate.

Alas, it was sad to find one large sea fan on the high shore.
It was clearly uprooted by a fishing line that was entangled in its branches. This must have happened recently as the polyps on the sea fan were still alive.

Because this is what a dead sea fan looks like.
Stripped of the living polyps, only the hard 'stem' remains behind.

I also saw lots of other interesting marinelife in the seagrass area nearby. Hopefully, this is a sign of recovery from recent 'beach improvement'.

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