10 February 2009

Cool and quiet at Tanah Merah

A solo trip on an overcast evening at Tanah Merah. A nice change from the frenetic, hot and terribly tiring trips over the last few days.
The shores of Tanah Merah are thick with Cake sand dollars (Arachnoides placenta)! Each of those little spots is a sand dollar! In the distance is the skyline of our business district and you can even see the 'arms' of our container port bristling on the horizon.
The sand dollars look more like biscuits than cakes. They come in various shades of lilac and purple and some are rather pentagonal while others are more circular.I also came across a skeleton (called the test) of a dead Keyhole sand dollar (Echinodiscus truncatus). Unfortunately, I didn't see a living Keyhole sand dollar. These animals are listed as 'Vulnerable' on our Red List.

Keyhole sand dollars have natural slots, hence their common name. The Echinoblog has a fascinating post on the purpose of these slots, as well as why some sand dollars DON'T have slots. ChrisM explains these very well! Go read his posts for all the fascinating details.

The other animal that dominates Tanah Merah are countless Button snails (Umbonium vestiarum)
Large stretches of the sand bar are pock-marked by dots where the tiny snails are buried just beneath the sand surface. Here, they stay safe while they filter feed, more like bivalves than gastropods. Unfortunately these beautiful animals are also listed as 'Vulnerable' on our Red List. Natural sandy shores like Tanah Merah have been reclaimed and there are now very few such suitable habitats for our Button snails.

And where there are Button snails, you can be almost certain to find Moon snails!These predatory snails burrow in the sand for buried prey. And Button snails are a great meal for them. There were lots and lots of these Ball moon snails (Polinices didyma). The snail has a body that can expand many times larger than its shell and uses it to plough in the sand and to envelope its prey.I probed many furrowed trails in the sand, most of which were left by Ball moon snails, before I came across this one Olive snail (Family Olividae). This smooth bullet-shaped snail also hunts buried prey in the sand.

A surprise find in the sand was this Spiral melongena snail (Pugilina cochlidium).Was it also eating Button snails? These snails normally eat barnacles and clams stuck to hard surfaces and rocky areas, so that's where they are usually found.In the sloshing waves on the seaward face of the sand bar was this large sea anemone. It's probably the Plain sea anemone whose name we have yet to learn.And a very large and active peanut worm (Phylum Sipuncula) was thrashing out of the water. I put it back in the water and it immediately burrowed and disappeared into the sand. Peanut worms are unsegmented worms that are very different from the more commonly seen marine worms.I only saw one lonely little Sand star (Astropecten sp.) with uneven arms. Alas, no other stars.

Large amounts of Sea lettuce seaweed (Ulva sp.) was floating near the shore. These were teeming with life. Little hermit crabs, tiny fishes and other small animals.Like this miniature Moon crab!Other larger ones also twirled in and around the ribbons of seaweeds, and were buried in the sand.A splash and some predator had caught its prey?It was a small shrimp tackling a fish very much bigger than itself! The fish was still alive, but only barely. It struggled feebly while the shrimp hung on. Amazing!As the tide came in, I headed back for the high shores. Some of the rocks on the seawall were thickly coated with zoanthids or colonial anemones (Order Zoanthidea). I've not noticed this before.Way on the high water mark were heaps of tiny little shells and bits of animals that probably lived on the shores. It hints at the fascinating marine life that can be seen on our shores if we take the time to look.

Kok Sheng and Mei Lin visited this shore a few days ago and found far more exciting animals including strange snails, slugs and a special star.

Read their posts for all the details!

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