Where are the sand stars?

Was back to Changi this morning with Ron and Yikang. We thought we could do a quick survey of the sand stars (Astropecten sp.) and the button shells (Umbonium vestiarium) for my project. However this morning, we couldn't really find any sand star at the beginning. This is perplexing!

After a thorough hunt by the three of us, only about four or five quite small sized sand stars were found. I'm glad at least there are some. Usually the whole shore is covered with numerous sand stars so we don't know why there was so little of them found. Many questions were raised on my mind.


Nevertheless there were a few other interesting creatures found like this ghost crab.


Several geographical sea hares were also found along the sand and seagrass areas.


Though peacock anemones are not true anemones, their beauty definitely cheers me up.


The find of the day must be this tiny green sea star that I spotted while looking for sand stars. Though not visible in this photo, the central area has knobs forming a ring. It is highly suspected that this is a juvenile knobbly sea star like those found at Changi by the other shore friends before. Glad I could see it for myself.


The underside or the oral view shows the tube feet with suckers.


This part of Changi was still relatively quiet this morning and while the sun was beginning to rise, the trio decided to quickly get a cab to check out another part of Changi where many sand stars were found just two weeks ago.


The entrance to this second stretch is quite rocky and immediately while entering, we found this group of thunder crabs aggregating. Looks like a drama.


I have no idea what have they done or why they are gathering like that? Hehe.


Ron quickly found a stunning orange-red rock star (Asterina coronata). It looks like it is carrying the rock... erh that takes some imagination to picture that.


Putting it into a pool of water made this stunning star relaxed.


We found a total of five rock stars in quick time. Wow! This is another one.


One more, clinging on to the rock.


Peacock anemones are also found at this part of Changi, they are really beautiful.


This is a swimming anemone (Boloceroides mcmurichii) that is quite small in size.


This one is bigger, with longer tentacles as well.


Carpet anemones are no exception. Many were spotted on the two stretches of shore visited today.


This is the ONLY sand star found on the second stretch of Changi shore. The previous batch of five sand stars were not photograph as we were rushing.


The sun rises, the tide returns and off we went for breakfast.

So where are the sand stars?

Were they burrowing deeper? Were they deeper downshore? Were they predated on? Were their prey missing? Did the poachers collect most of them away?

We also hypothesized it might have something to do with the moon. Given the two weeks ago (new moon), plenty of sand stars were found while one month ago (full mooon) only one pathetic sandstar was found on the same place.

However, after a quick check at last year's sand star sighting in Chek Jawa and Changi, the moon does not really affect their activity and spotting by us. Seems weird.

Could it be because of their prey are missing or have moved down to deeper waters? The sand stars mostly eat button shells (Umbonium vestiarium) which we did not find today as well.

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".

Could the absence of button shells in May cause the lowering number of sand stars? Will heavy recruitment of button shells in June/July means the return of sand stars?

There are so many questions unanswered, hopefully we will know why soon.

Reference:
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.