Saturday, December 1, 2012

Surprises among seaweed bloom at Terumbu Semakau

It's the Sargassum seaweed (Sargassum sp.) season where most reefs are ringed by thick blankets of the seaweed. However, this did not stop us from visiting our southern reefs!

Two weeks ago, a group of us visited a submerged reef, Terumbu Semakau which is situated right beside Semakau Landfill and near Pulau Jong (small island in a shape of a bun).

Landing amphibiously is no joke as the zone of thick seaweed sometimes cover scary animals such as Mr S. (stonefish). We carefully made our way into the shore without hurting ourselves or the animals.

Jim managed to spot this well camouflaged and tiny Spotted-tail frogfish (Lophiocharon trisignatus)! 

Frogfishes are interesting because they have a bait-like structure that lures smaller fishes or prey into the area their the mouth and before you know it, the frogfish has gotten its meal.

Where's there to find when almost everything by the reef edge is covered by Sargassum seaweed? I was wrong to think that nothing spectacular could be found. In fact, a huge surprise was right in front of me though it was so well blended into the surrounding.

It's a gianormous cuttlefish!! In fact, this is the Reef cuttlefish (Sepia latimanus) that our local divers frequent see in our deeper waters. Such a privilege to behold and witness this magnificent creature on the intertidal shore for my first time. The eyes are real huge and scary looking though.

How large was it? Judging from this photo with my foot as a scale, it is about 40-50cm long! Wow!!

What else can we find among the bloom of seaweed? Attached on boulders are lots of living animals!

I saw this intriuging clam with zig zag bivalves. Ron suggested that this is likely to be either the Leaf Oyster (Dendostrea sp.) or Giant honeycomb oyster (Hyotissa sp.).

Another interesting find sighted beside a boulder would be this rare Physogyra Coral (Physogyra sp.)! It's only my second time seeing this on our intertidal shores.

What's so special about this coral, other than being rare, is that it has large bubbles that obscure the  skeleton. These are possibly modified tentacles that inflate during the day. The sacs contain symbiotic algae (zooxanthallae) and the expanded surface area probably helps increase photosynthesis activity.

Where the dark crevices are will be the place to find the Cave corals (Tubastrea sp.)! The tentacles are all retracted when the corals are out of water. 

Despite the tons of seaweed that covers most parts of the reef, some hard corals can still be seen along the reef edge.

Terumbu Semakau is home to high densities of hard corals such as the Circular mushroom corals.

Right at the very edge of the reef is a colony of the uncommon Moon coral (Diploastrea heliopora). The corallites are regularly spaced out and give an overall regular tidy pattern.

Just before the sunset, I stumbled upon a Fluted giant clam (Tridacna squamosa)!

Here's a closer look at the not-so-big giant clam. Indeed, Semakau and its surrounding reefs are rich in these charismatic clams.

Many anemones were also sighted on the trip such as this Bulb-tentacled anemone (Entacmea quadricolor).

Ria later showed us her find of the uncommon Fire anemone (Actinodendron sp.).

Like the eastern shore of Semakau which is right across Terumbu Semakau, there are lots and lots of these Magnificent anemones (Heteractis magnifica).

And if you are sharp enough, you can find commensals such as this Five-spot anemone shrimp (Periclimenes brevicarpalis) among the tentacles of the anemone.

Ria shared with us her special find of the day... the Tiger cowrie (Cypraea tigris)! My second time seeing this handsome and huge cowrie.

According to the Singapore Red Data book, although this cowrie was considered one of the commonest cowries of the Indo-Pacific, and present on Singapore reefs in the past, the tiger cowrie is now exceedingly rare.

This is the underside of the cowrie showing both the foot and the pointy projections from the sides of the mantle.

More interesting finds include these Razorfish (Family Centriscidae) which usually swim together and they indeed look at razor blades!

This Orange-white black flatworm which we rarely see on the shore seems to be in season recently as it appeared in most of our southern shore trips.

Just before we left, I found an Alicia sea anemone (Alicia sp.)!

When fully expanded in water, you can see the mouth and the pink stripes on the tentacles. How pretty is this anemone both in looks and in name. But never ever touch this anemone as it stings badly!

More photos of the trip here:

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