Monday, May 26, 2008

Where are the button shells?

Last Thursday, most sand stars (Astropecten sp.) went missing at Changi shores. Many hypotheses were made and one of which is their food might be not around, thus explaining their absence. On Saturday, Mei lin smsed me that the Creative Kids group found about 10 sand stars and Chay Hoon found many sand stars too yesterday during their Chek Jawa guided walk.

I'm quite convinced that the sand stars are still around, but I believe in lower numbers and it might be due to the absence of button shells (Umbonium vestiarium), the food for the sand stars. I could not find any button shells at Changi last Thursday.

Thus I've decided to check out Chek Jawa with Yikang this morning to look for the button shells since Chek Jawa, as I what know, has the most extensive button shell beds in Singapore.

With the help of Adelle from Nparks, Yikang and I got a ride from the volunteer hub to Chek Jawa. At first entrance of the place, after three months since I last visited, I felt like homecoming. However, the weather did not look too good. Thank God He sustained the clouds and held the rain till we ended the trip and were back to the volunteer hub.

With the aid of GPS points made during our previous surveys, I went back to different exact plots where plentiful of button shells can be found. Berry and Zamri (1983) stated that button shells can be found hidden 0.5cm-1.5cm deep in clean sand, which is true based on my previous experiences. However, I could not find any plots like that at all today! So I dug very much deeper and saw many whitish shells. It was a tiring digging morning to check them out.

Some white shells looks quite indistinguishable of what it belongs to.

But a closer look shows that they are actually button shells.

But they are all dead.

It's not a mass mortality event caused by lowered salinity. It seems to match in line with my hypothesis stated in my God's wonderful creation blog.

According to Berry and Zamri (1983), it was stated that "progression of this cohort (of button shells) indicated that young settling in May-June grew to full size (11-13mm diameter) by January-March the following year and that virtually all died during their second year, presumably having spawned in March-May". This paper also stated "the older cohort were always more abundant upshore than downshore except in May 1982".

Does this explains the absence or death of button shells in May?

There are still some intact shells left but please do not take these shells away though the snail already died. That is because hermit crabs can also make use of the empty shell to reside in it like this one.

I am still relieved to see several sand stars around. We measured twenty over of them today. Wonder if they can survive without button shells for long. They do also feed on detritus.

These sea stars are quite easily spotted when we reached at 8am. But after 9am, it was difficult to find them! They burrow into the sand like the one on the right. This is because these stars have a circadian rhythm which I will study also soon.

That's about all for the button shells and sand stars observations. Meanwhile, other animals were found as well during our working time.

It's always heartening to see new life on the shore. The noble volute is laying eggs on the sand bar. Soon, we shall have many baby ones.

Like Changi, geographical sea hares can be found.

Yikang spotted for his first time an octopus while I was checking on my anemones.

He also chanced upon this brittlestar that is rather large in my opinion.

I'm glad to see the sandfish sea cucumbers still around. I accidentally stepped onto one since they burrowed and I couldn't see them while walking till suddenly a squirt of water flew up. Haha.

The Nparks volunteers found yet another sea cucumber.

This is not a sea cucumber but a peanut worm. My first time seeing it! Wow, Chek Jawa always reveal surprises with every visit. I never get bored with Chek Jawa. This used to be so common in the past that they take them for feeding worms.

I moved down southwards and check out the guided walk. Everyone was enjoying the session.

It's always good to restrict visitors to just the sand bar while hunter seekers bring the animals to a centralized location. Or else, Chek Jawa might be just trampled to death, or loved to death.

Low tide also means feeding time for shore birds!

I overturned rocks near the boardwalk area while approaching back to House no. 1 and found this hoof-shield limpet (Scutus sp.) like the one we found at Changi last week. Cool!

There is a Bailer volute (Melo melo) at the rescue tank of House no. 1. Wow, I've never seen it before and I wonder where it came from.

At the same time, I got my first hand experience to see the fascinating and magnificient mural done during the May Day Outreach.

House no. 1 was also airing the Remember Chek Jawa film as well.

Before leaving, a hornbill was spotted, though this was the only shot I got before it decided to fly away. Hehe.

Wow, what a great day. The rain poured like nobody's business while we were back at the jetty area. We had a good time chatting and refilling ourselves with 100 plus till the rain stopped. The sky cleared up and I took a photo of Pulau Sekudu with a mountain at Johor on the way back. Nice to also get to know some Ubin volunteers today too. Thanks Yikang for coming to help as well.

I have YET cover everything today in this single post. A trip to Chek Jawa after three months means I have to check out also the other groups of marine animals that we used to monitor. The last monitoring session was at January 2008! About four months ago and it has been some time we monitored or checked them already.

If you want to know how the other groups of animals (except button shells and sand stars discussed in this post) fare now, look out for an upcoming post on their progress.

Berry, A.J. and Zamri bin Othman (1983). An annual cycle of recruitment, growth and production in a Malaysian population of the trochacean gastropod Umbonium vestiarium (L.). Estuarine, Coastal and Shelf Science 17: 357–363.


Ivan said...

Maybe the button shells that Ria and I found washed up at East Coast are recently dead ones.

I wonder if the sand stars eat the tiny mussels.

Good to see the baler shell is still there; I wanted to take photos of it when I was guiding yesterday, but it wasn't around. Maybe it was buried.

Kok Sheng said...

That's a good question Ivan. Hope I'll get to test if they do eat the tiny mussels in the near future.