16 November 2008

Changi with baby Knobbly sea star

Changi on a Sunday evening at low tide is popular with ordinary people. Families with small children, friends in groups.
Some groups are exploring thoroughly and have brought lots of gear to do so.In the plastic bag was a seahorse, which she said she was going to release after showing it to her friends. The basket held mostly molluscs.Elsewhere on the shore, holes were dug here and there.And groups of animals were seen on the shores, perhaps viewed and then left behind.
Alas, there was a more than usual trash build up on the shores.In deeper waters were several groups of people using cast nets. This large group appears to be very interested in the process.

Our rich shores certainly attracts a wide variety of people. As the sun set, most of the people left.There was a bloom of Mexican seaweed (Caulerpa mexicana), here seen growing among the taller Fern seagrasses (Halophila spinulosa).Here's a closer look at the more slender seaweed, against the larger seagrasses. More about how to tell apart seagrasses and seaweeds.

Among the 'vegetation' were all kinds of small animals.There were several of these Sea pencils among the seaweeds as well as in sandy areas. They were quite small. The Sea pencil is a sea pen (Order Pennatulacea).Just like this Flowery sea pen (Family Veretillidae). Each is a colony of tiny polyps. There were a few Haddon's carpet anemones (Stichodactyla haddoni) (photo on the left) with tiny anemone shrimps on them. A small anemone I saw on a shell might be the Tiny carpet anemone (Stichodactyla tapetum) and not a small Haddon's carpet anemone. I didn't encounter any of the other commonly seen anemones. There were also not many peacock anemones (Order Ceriantharia).

As for crustaceans, there were glimpses of Moon crabs (Family Matutidae) and lots of tiny crabs of all kinds. Small snapping shrimps (Family Alpheidae) peeked out of burrows before disappearing.The most commonly seen crustacean on this shore are the hermit crabs: the Tidal hermit crabs (Diogenes sp.) and Striped hermit crabs (Clibanarius sp.). Those on Changi often have one or more sea anemones on their shells.Larger shrimps (Family Penaeidae) remained buried in the sand and only came out well after dark.Also buried in the sand was a small patch of Button shell snails (Umbonium vestiarum). The snails seem a little larger than when we saw them at our last visit. These delightful snails come in an astonishing variety of shell patterns and colours.Other burrowing snails include the predatory moon snails (Family Naticidae). While the white Ball moon snail (Polinices didyma) is commonly seen, the Pink moon snail is less often encountered. The one I saw was hardly bigger than a seagrass leaf! It refused to come out to show its pretty foot.Fortunately, Chay Hoon found another one, which was bigger. We had a look at it in the plastic tray where it could not burrow into the sand, so that we can see its prettily patterned foot. We then released the snail.We also saw the rather rarely encountered Lined moon snail (Natica lineata). Like other moon snails, the front part of the body is shaped like a shovel, and it has a large broad foot. With these, the moon snail bulldozes beneath the sand for buried prey.As our moon snail starts to burrow, it disturbs a buried hermit crab that gives it a nip with its pincers.The snail very quickly makes a U-turn, whereupon it disturbs yet more buried hermit crabs. The fast moving snail soon glides into less hostile territory.

Other molluscs encountered included plenty of Window pane shells (Placuna sp.), several Noble volutes (Cymbiola nobilis), some juvenile Gong-gong (Strombus canarium). We didn't see the Bailer volute (Melo melo) this time.

Our Northern shores have a rich variety of echinoderms.
There were plenty of small and large Thorny sea cucumbers (Colochirus quadrangularis) (photo on right) and one small Warty sea cucumber (Cercodemas anceps) (photo on left). There were also many Ball sea cucumbers (Phyllophorus sp.) and I saw one Smooth sea cucumber. Ivan and Marcus also saw some Garlic bread sea cucumbers (Holothuria scabra). There were also lots and lots of very large White sea urchins (Salmacis sp.), with many skeletons of dead urchins too.A little later as the tide went further down and it got dark, the Sand stars (Astropecten sp.) came out. There were also some Cake sand dollars (Arachnoides placenta) in a pool.

But the Star Find of the Day was made by none other than Chay Hoon. She found a baby Knobbly sea star (Protoreaster nodosus)!It was really cute and small! (Fortunately, Chay Hoon had a rule for scale).Here's a closer look at the upperside.And a closer look at the underside.It has pretty pink tube feet, and tiny little bivalved pedicellaria.WOW! It's great to know that there are Knobbly sea stars even on our Changi shores. We hope the fantastic marine life on this shore continues to thrive and that the visitors to these shores will be gentle with them.

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