22 July 2013

Cowrie surprise at Sekudu

It looks just like an ascidian, but this is a cowrie! I've never seen one like this before.
Pulau Sekudu lies just off Chek Jawa and never fails to surprise with its rich diversity of life. Sadly, we noticed some changes in the habitat on our trip today.

Here's what the snail looks like with the bright red body mantle retracted.
Later on, I came across another kind of cowrie that I've not seen before.
Here's what they look like with their body mantle covering the shell. Thanks to Hoong Wei Wong who suggested that these look like Cypraea saulae and Cypraea gracilis!
Other cowries seen include many Miliaris cowrie (Cypraea miliaris) and fewer Onyx cowries (Cypraea onyx) than in the past.

Pulau Sekudu has many interesting nudibranchs. But some are hard to spot. Can you spot the Sponge nudibranch (Ategema spongiosa) in this photo? It's quite large and looks just like a boring sponge or dead coral rubble in texture and shape, complete with holes and bumps all over the body.
Other nudibranchs may look like blobs, especially when stranded out of water: Jorunna funebrisDendrodoris fumata, Thordisa villosa and Ategema intecta.
We also came across more of the Fine-lined flatworms that seem to only be common in Chek Jawa and Pulau Sekudu. They were huge!
I saw 8 large Knobbly sea stars (Protoreaster nodusus). But no young ones.
There were a few large Biscuit star (Goniodiscaster scaber) and one Eight-armed sand star (Luidia maculata), as well as as many Plain sand stars (Astropecten sp.). But I didn't see any other kinds of sea stars.
The two huge Long spined black sea urchins (Diadema sp.) were still there! I saw one large pink Thorny sea urchin (Prionocidaris sp.) and a few Black sea urchins (Temnopleurus sp.). There were lots and lots of White sea urchins (Salmacis sp.). And I saw two Blue feather stars. Kok Sheng and Ivan saw special sand dollars: the Pink sand dollar (Peronella lesueuri) and  but I only found the common Cake sand dollar (Arachnoides placenta).
I saw many small but well formed sea fans. But mostly two kinds: Candelabra sea fans and Gnarled sea fans.I looked and didn't find any ovulid snails or other commensals like brittle stars and clams. I also saw one short sea whip. I didn't see any Skinny sea fans.
I saw three small colonies of Pink flowery soft corals (Dendronephthya sp.). But couldn't find any of the snails that often live and feed on them.
There were some ball flowery soft corals (Family Nephtheidae) and they had commensals. Tiny porcelain crabs and white snapping shrimps. But I didn't come across any False coweries in them.
There were several kinds of sponges growing on the coral rubble, but not a wide variety and they didn't encrust the rubble densely.
We also saw several small colonies of smooth boulder-shaped Pore corals (Porites sp.). But I didn't come across the other kinds of hard corals that I saw during our trip last year.
It looks like this Mud crab (Scylla sp.) has just moulted! See how much larger the crab is compared to its 'old skin'! Mud crabs are those that we eat in Singapore's famous chilli crabs.
This is the only octopus I saw on the trip, a tiny little one.
There are lots and lots of Haddon's carpet anemones (Stichodactyla haddoni) on Pulau Sekudu! There were also many Swimming anemones (Boloceroides mcmurrichi), the rubbly area was carpeted with Posy anemones. There were also some flowery sea pens (Family Veretillidae), lots of Common sea pens (Pteroides sp.) and some Common peacock anemones (Order Ceriantharia). Also abundant on the shore were Broad zoanthids (Palythoa mutuki) that looked much larger than the usual kind that I see elsewhere.
There are all kinds of fishes on this shore even at low tide. Small ones like. While big ones splash around us in deeper water. I didn't see any fish traps or drift nets laid on Pulau Sekudu today.
There were also a few clumps of nice long Tape seagrass (Enhalus acoroides). But the most abundant species are Spoon seagrasses (Halophila ovalis) . There are also lots of healthy looking Fern seagrass (Halophila spinulosa). I didn't manage to see the Serrated ribbon seagrass (Cymodocea serrulata) that I saw on in 2011. There were many Fan shell clams (Family Pinnidae) in the seagrass areas, with many dead ones in the now very sandy lagoon.
As seen from this GIS map done and shared by Dr Raju, Kok Sheng and I checked out the 'arm' on the eastern side. I noticed what seems to be a boat strike in one part of the island, while the entire lagoon and the outer 'arm' seems a lot sandier than on our previous trips. With large areas of bare sand and signs of immobile animals being buried. Where is the sand coming from?
Another disturbing sight, the Mangrove cannon-ball tree (Xylocarpus grantum) that grows in the middle of the island was almost completely leafless.
The two Perepat (Sonneratia alba) were also in the process of being denuded by the caterpillars.
Here's a closer look at the cocoon and caterpillar. I hope the trees can eventually recover from this.
Pulau Sekudu seems to be the last stronghold of the amazing marine life that I used to see on Chek Jawa in the past! Hopefully, should the situation at Chek Jawa return to the way it was before the 2007 mass deaths, the marine life from Pulau Sekudu will help to 're-seed' Chek Jawa. Pulau Sekudu is indeed an important part of the ecosystems not only at Chek Jawa, but also other northern shores like Changi.

Pulau Sekudu (and Chek Jawa) may be affected by the 2030 landuse plan by the Ministry of National Development. The plan includes plans for a road link (black line) from the mainland jumping off at Punggol, crossing to Pulau Ubin through Chek Jawa to jump off to Pulau Tekong before circling back to the mainland on Changi East. Proposed reclamation (in yellow) will bury Pasir Ris shores, Pulau Sekudu and Chek Jawa as well as a large amount of shore at Changi Beach.
Click on images for larger view.
I feel it is thus important to update our understanding of what is going on in the field at these sites including Chek Jawa and Pulau Sekudu. We hope to survey these more regularly.

Pulau Sekudu is off limits since 2007 and requires special permission from NParks. Thanks to NParks for permission and support to do these predawn low spring tide surveys of Pulau Sekudu. Our last survey was in May 2012. Thanks to Alan at NParks for permission to visit and to Chay Hoon for organising the trip! And for the rest of the volunteers for helping to thoroughly survey this small but very rich island.

Posts by others on this trip

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