14 May 2009

Prickly day on Pasir Ris

The morning began ominously. Dark clouds all around, a drizzle starting up, and a weather front clearly developing from the West.But this is not a big deal to intrepid shore explorers.

Wet weather gear is whipped out and we start checking out the shore.
Alas, lightning soon snuck up on us and we hurried to a nearby shelter. If there's one thing to respect on the shore, it's lightning! Fortunately, the weather soon cleared and we were back on the shore.

Today, lots of Black sea urchins (Temnopleurus sp.) were washed up on one part of the shore. They were in various stages of death and decay.
This was a great opportunity to take photos to show what the sea urchins look like. On the right are the still living sea urchins with their spines. On the left are the skeletons (called the test) of dead sea urchins. Sea urchins like us, have a skin that covers everything including their spines. When they die, the skin rots and the spines fall off.

If we take a closer look at the test, we can learn a few things about sea urchins. The test is a rigid, hollow sphere. It is formed out of large plates which form a pattern that resembles a sliced orange, in multiples of five. To grow larger, each plate is enlarged, and new plates added near the anus (which lies facing upwards, the hole in the test in this photo).
There are little knobs all over the outside of the test. The spines move on these little knobs, articulating somewhat like the ball-and-socket joint of our knees. There are also rows of holes in the test. This is where the tube feet of the living sea urchin emerges.

The mouth of the sea urchin is on the underside.
And if we take a closer look at the mouth, we see five 'teeth'! These are part of a complex jaw structure made of a circle of five plates that meet in the middle to form a beak-like structure. The entire structure can be extended outwards to chomp on their food. It is called the Aristotle’s Lantern after the Greek philosopher Aristotle who first described it. New 'teeth' grow to replace those that are worn down. More about sea urchins.

And if you take a really close look, you will see that nearly every single Black sea urchin has a worm-like animal curled around the mouth!
I find this quite icky! I have no idea what this animal is.
Here's one that looks a half dead, not in its usual curled up position around the mouth. Eew!

Today I also came across one recently dead heart urchin (Order Spatangoida). Some of its spines is still stuck on the test. Heart urchins do resemble sea urchins and these two kinds of animals are indeed grouped together under Subclass Echinoidea.
Heart urchins burrow into the sand and living ones are hardly even seen above ground. Unlike sea urchins which are the same all around, heart urchins have an obvious front end and backside. But like sand dollars (which also belong to the Subclass Echinoidea), heart urchins also have a petal-like structure called a petalloid on the upper surface. The heart urchin's mouth is also on the underside, near the front end. While the anus is on the back end of the body. More about heart urchins.

Pasir Ris has some nice patches of Spoon seagrasses (Halophila ovalis).But these grow on very soft silty sand, so we don't explore them too thoroughly as it's hard to walk without squishing everything.

The seagrasses here are lush with large clean and green leaves!
These seagrasses and the sandy shores around them harbour a wide variety of marine life. I was rather too lazy to photograph intensively today as Kok Sheng and friends were hard at work doing this. They saw lots of interesting snails, a mantis shrimp, sea cucumbers, sea stars, weird worms, octopus, and all kinds of fishes including a tiny Tripodfish.

I'm just going to be lame and leave it to them to blog about their wonderful finds.

Alas, Pasir Ris is one of those highly accessible shores and thus greatly impacted by marine litter that mainly come from recreational users of the park.
Although the cleaners were hard at work this morning on the high tide line, the incoming tide just brings back more of the litter.

This shore also faces other impacts as it is along a major shipping lane that connects to Pasir Gudang in Johor and Sembawang Shipyard on our northern coast.
In addition, the waters off Pasir Ris are dotted with numerous fish farms which of course, result in fish wastes and other effluents.

In May 08, Pasir Ris beach failed the new water quality standards adopted by NEA. The recreational water quality status is reviewed annually. A check on the NEA website today, suggests Pasir Ris continues to fail this water quality standard, although we didn't see the "Don't Swim" sign on the shore today.

More blog posts about this trip

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