Tuesday, May 27, 2008

Chek Jawa after four months

Following yesterday's post focusing on mainly button shells, sand stars and other marine animals, this post is a continuation on the other groups of animals that we have been monitoring. It has been four months since effort was taken to check the health of Chek Jawa properly.

As I entered the entrance of the sand bar, the first thing that caught my attention was the increase in the density and number of tubeworms. I remember the sand bar was quite barren last year.

Immediately, I went to check the anemone number 25 just beside the floating pontoon. Glad its still there but it doesn't look as green as it used to be. Instead it looks pale.

This photo was the last documentation we had of the exact anemone (number 25). This was taken by Ria Tan during January 2008. It shows a darker green coloration on the oral disk.

Many other anemones were also pale-looking as well. What caused this? Could it be the higher temperature in the weather this period? Could it be similar to the coral bleaching in Sentosa since carpet anemones also harbour zooxanthallae?

An interesting sight where a large volute shell is stuck to the mouth of the small carpet anemone. Could it be feeding a volute snail? I turned a bit to check, there was a striped hermit crab inside. Not sure if the hermit crab will survive hiding in the shell in the end.

Nevertheless, some anemones seem to be doing well. Yikang showed me this anemone which looks healthy in terms of colour and its size is humungeous.

Two-15cm rulers cannot even cover its diameter. It is about 35-40cm in diameter. Wow!

Now over to the peacock anemones. They seem to be doing okay.

The area where we used to survey peacock anemones still thrives with several of them. Can you see them from this photo.

The first photo of this collage is not a peacock anemone but I added it in since it is part of the previous photo.

How about sand dollars? They are doing very well mostly at the northern sand bar. Can you see the circular outlines?

A closer look reveals several sand dollar outlines and their movement.

They come in various sizes and cover a dense area of the sand bar.

How the sand dollars look like after removing the top sand.

This sand dollar is quite large as you can see with the hand of Yikang as a scale.

Ron who was guiding all along with Ubin volunteers told me that common sea stars were not spotted since the last time I did during January 2008. I believe their population has badly been depleted since the mass death. These common sea stars remaining are likely to be survival of the mass mortality event. Dr Lane suggested that they could have burrowed deep down to avoid the freshwater influx.

Good thing is that I have the GPS location of the isolated patch where common sea stars were last sighted. We took quite some time to search but to no avail. Finally I saw a star shaped thing with most part already burrowed. It is the common sea star and there's two, they were pseudo-copulating.

This is one of them.

And another one of the common sea star. Glad they are still around.

According to Run et al. (1988), the spawning season of these sea stars is in late June and July. So let's hope they will be back in larger numbers soon.

Last but definitely not the least, I went to check out the mussel beds. The mussel beds are fascinating because they were not around before the mass death. The conditions after the mass death created a niche for them to colonize since they are known to be invasive.

What intrigues me is that the huge patches of mussel beds moved westwards towards the high shore area. Can you see the patches nearer to the solitary sonneratia tree?

And more patches can be found nearer to the boardwalk and the rocks.

Though I didn't have the manpower to walk the boundaries with a GPS set, the estimated blue dotted part of the map shows the transition of these mussel beds westward. The maroon red parts are where the mussel beds were during January 2008.

Why did they move towards the higher shore direction. Well, we know that they like lower salinity. Could it be because the salinity seaward has higher and they prefer to be nearer to the high shore where there is a release of freshwater from the coastal forest or mangroves especially after a rain? This is a hypothesis.

Another discovery will be that these mussels have grown! They are about 2cm in length while those that I found in August last year were about 1cm in length.

I wonder if the sand stars eat these mussels to survive since button shells are now not around till later.

There's so much to learn from Chek Jawa given that it is really dynamic. Constant checking is important for us to understand the shore better and learn new things out from it. Let's hope the next check will reveal Chek Jawa to be recovering even better.

Run, J. Q., C. P. Chen, K. H. Chang, and F. S. Chia. (1988). Mating behavior and reproductive cycle of Archaster typicus(Echinodermata: Asteroidea). Marine Biology 99: 247-253.

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.

Friday, May 16, 2008

Talk at NUS Faculty of Science Open House

Dear all, I will be sharing with prospective students during NUS Science Open House on Sat 24/5/08 regarding my experience in doing a research project on Chek Jawa. Feel free to come and listen. :-)

Date: 24 May 2008

Location: LT27

Talk Title: Life and death at Chek Jawa. A UROPs research experience in Life Sciences

Talk duration: 15 min (between 2:00-3:30pm)

Speaker name: Mr. LOH Kok Sheng

Speaker profile:

Mr. Loh graduated from Serangoon Junior College and joined NUS in 2005, majoring in life Sciences with specialization in Biology. In July 2007, he received the MOE Teaching Award. Mr. Loh has great interests in ecological work and did an UROPS project under the supervision of N. Sivasothi, Peter Todd and Dan Rittschof. His project aimed to study the mass mortality and recruitment of macrofauna at Chek Jawa in Pulau Ubin. Since the project has application value in understanding and conserving the Singapore macrofauna at Chek Jawa, Mr. Loh’s achievement has been featured in Embracing passion, NUS Advertorial and The Straits Time (March 25 2008). In this talk, Mr. Loh will share with the audience his experience in project work (UROPS) in Life Sciences and highlight those qualities that he has developed through this project as a junior scientist.

More about the Open House: http://www.science.nus.edu.sg/openhouse/index.htm