04 May 2011

Checking up on an oil-slicked East Coast shore

A beautiful swimming crab with bold rings on its legs! How nice to see the crab on a stretch of East Coast Park that was affected by the oil spill nearly a year ago.
This is probably Charybdis annulata that I seldom see.

Here's a photo of the crude oil I saw landing on this stretch of East Coast shore on 26 May. I last visited this shore in July 2010 when the shore was clean, but was a little quiet. But Ivan visited on 22 Apr (facebook) and saw a shore that seemed a little more lively. So early this morning, I headed out to have a look.
There were a few pretty Sally-lightfoot crabs (Grapsus albolineatus) scuttling about near the seawall. On the rocks, some smaller Purple climbing crabs (Metopograpsus sp.). In the water, I saw a few small Flower crabs (Portunus pelagicus).
I was surprised to see a rather large oyster (Family Ostreidae) on the rocky shore. Usually, these are vandalised before they reach this size. I also saw one small Spotted top shell snail (Trochus maculatus).
I saw several small Gold-spotted mudskippers (Periophthalmus chrysospilos) near the seawall. They are less shy at night and easier to sneak up to for a photo.
One sign of health of a shore is to see what lives under a stone. And it seems pretty lively here, with colourful sponges, ascidians and other encrusting marine life on the underside. Beneath the stones, I saw one sea anemone. There was even one mother snail patiently laying her eggs under the stone.
Here's a closer look at the mama snail (probably a triton snail, Family Ranellidae) and the little clusters of eggs that she was patiently laying. I carefully turned the rock back the way I found it.
The tide wasn't very low this morning, so not much of the sand bar was exposed. Although this is a reclaimed shore, in the past, the sandy shore was teeming with Cake sand dollars (Arachnoides placenta) and Button snails (Umbonium vestiarum). All kinds of other special creatures are also sighted here.

I saw many Cake sand dollars, though it was too dark and the tide wasn't really low enough to see the full extent of their presence on the shore. There were many tiny and small ones and a few large ones.
Living sand dollars are purplish, white ones are
the skeletons of dead sand dollars.
I also saw many Button snails. These used to be super abundant before the oil spill. This morning, they were not as abundant as before, but I saw many signs of them on the sand where they lie buried leaving tiny indentations. I dug up a few to take a photo of them.
Usually, they will burrow immediately back into the sand with vigorous lashings of their leaf-like foot. Today, only a few did so and very slowly. Perhaps, like the Common sea stars that Janette studied for the oil spill impact, the animals on the oil slicked shores are not as healthy as usual?
I dug a little deeper beneath where the Button snails were buried. The sand beneath is dark and it smells faintly of crude.
I saw a large Lined moon snail (Natica lineata) ploughing through the sand just beneath the waves.
There were several of the more common Oval moon snails (Polinices mammila). And some fragments of sand collars, which are the egg mass of moon snails.
I saw many Spotted moon crabs (Ashtoret lunaris) scuttling about just beneath the waves. This one is pestering a huddle of Tidal hermit crabs (Diogenes sp.) that have gathered in a group. Perhaps to 'exchange' shells? Or to feed on something tasty?
This group of large Striped hermit crabs (Clibanarius infraspinatus) were clearly gathered around to feast on a jellyfish that was already half buried in the sand. Only the thick purplish tentacles were sticking out.
I saw a few burrowing Acorn worms (Class Enteropneusta) producing very long coils of 'processed sand'. And one Smooth sea cucumber buried in the sand.
The tide was too high for me to explore much, so I didn't come across the intriguing patch of seagrasses that Ivan saw here. Let's hope this shore will recover fully soon!

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