16 May 2010

Frog Island annual check up

Another 4am departure, this time to Pulau Sekudu or Frog Island!
Pulau Sekudu looks tiny at high tide but has a huge intertidal area that is exposed at low tide.

As seen from this GIS map done and shared by Dr Raju. Today, I wanted to check out the 'arm' on the eastern side and see if the corals and sponges have returned to this lower shore.
The tide wasn't very low so I eventually switched to Sneaky Swimming camera as I was mostly walking in knee deep water.

Some exciting finds

Special echinoderm finds of the day were a baby Knobbly sea star (Protoreaster nodusus) found by Jane! This is a good sign that the Knobblies may be returning. Alas, only one adult was spotted on Pulau Sekudu, and their numbers have also fallen at Chek Jawa. So a baby is good news! And Kok Sheng got to see the Pink sand dollar (Peronella lesueuri) that he wished for. So far, it has only been seen on Pulau Sekudu, with one also found by Chay Hoon on Changi.
A first time sighting for me on Sekudu are several ball flowery soft corals (Family Nephtheidae)! I saw them on Ubin recently, so it was not really a surprise to see them here as well.
Ball flowery soft corals are made up of 'branches'. And the crevices are snug hiding places for all kinds of animals. Today I saw lots of tiny commensal porcelain crabs in this single soft coral.
Another special sighting were many of these Little Ruby flatworms (Phrikoceros baibaiye). I haven't seen them since 2005. They seem to be seasonal. We see lots of them for a while, then none for a long time. I saw several tightly clasping some white ascidians. Do they eat these ascidians? Awesome!
How nice to see a shy Estuarine seahorse (Hippocampus kuda)! Could it be a pregnant papa? Wow.
I almost missed this superbly camouflaged octopus peeking out of its burrow. It has long 'horns' above its eyes! It wasn't very big, see the tiny spoon seagrass blades around it for a size comparison.

Sekudu check up

But how is Sekudu doing in general? The outer edge of the lagoon seemed less lively, compared to what I had seen many years ago. I only saw a few clumps of sponges, the long branching purple sponges (Callyspongia sp.) being the most numerous. Also only one small clump of Candy hydroids, and no sea fans (Order Gorgonacea).
I saw one colony of Pore corals (Porites sp.). It wasn't very large (about 15cm) but seems to be doing well. In 2003-2006, hard corals like Anemone corals (Goniopora sp.) and Favid corals (Family Faviidae) were seen here.
But there were lots of fishes! Little ones included: an unidentified stripey fish, a Crescent perch (Terapon jarbua), a twig-like halfbeak, many small rabbitfishes (Siganus canaliculatus), Three-spined toadfish (Batrachomoeus trispinosus), a large flathead (Family Platycephalidae).
The lagoon in the middle of the island is full of stingrays (Family Dasyatidae) and I saw one. I also saw a very large catfish, many large rabbitfishes (Family Siganidae), filefishes (Family Monacanthidae) as well as other large fishes that zoomed away before I could take a photo. There were also some Tropical silversides (Atherinomorus duodecimalis). The rest of the team also released a huge grouper (Family Serranidae) from a fish trap. And I saw two dead Spotted scat (Scatophagus argus) on the shore.

It was nice to see several large specimens of these beautiful flowery sea pens (Family Veretillidae) in maroon and white.
While I only saw a few Common peacock anemones (Order Ceriantharia), I did come across two of these special looking peacock anemones. I'm not too sure whether they are different from the usual ones we see.
Large areas of the laterite shores on the western shore remain covered thickly with Button zoanthids (Zoanthus sp.).
There were plenty of large Haddon's carpet anemones (Stichodactyla haddoni), several Tiny carpet anemones (Stichodactyla tapetum) and several Swimming anemones (Boloceroides mcmurrichi). Posy anemones encrusted large areas of coral rubble in deeper waters.

On the molluscan front, I didn't see any slugs. But the rest of the team saw lots of different kinds of slugs and snails including some we have not seen before. I saw a Pink moon snail and there were plenty of Fan shell clams (Family Pinnidae) all over the shore. A special sighting by Kok Sheng is of the presumed extinct Watering pot-shell clam (Brechites penis)!

There were also lots of Stone crabs (Myomenippe hardwicki) wandering happily all over the seagrass meadows. Usually, I only see these crabs hiding in crevices. So they must feel pretty safe on Sekudu. There was also a lovely pastel-coloured swimming crabs (Family Portunidae). Other crabs seen included the Spoon pincer crab (Leptodius sp.). There were also lots of Striped hermit crabs (Clibanarius sp.).
Pulau Sekudu usually has lovely echinoderm surprises. The rest of the team indeed saw lots of other kinds of sea stars. But the only sea stars I saw were the Biscuit star (Goniodiscaster scaber) and a tiny Painted sand star (Astropecten sp.).
In deeper water there were many White sea urchins (Salmacis sp.), often in clusters of several animals near one another. I also saw one large Thorny sea urchin (Prionocidaris sp.). Chay Hoon also found a heart urchin (Maretia ovata)!
There were several (but not many) Thorny sea cucumbers (Colochirus quadrangularis), and several very large Garlic bread sea cucumbers (Holothuria scabra) as well as a few long Big synaptid sea cucumbers (Family Synaptidae).
And I saw this sea cucumber floating about in the water. It looks like the Smooth sea cucumber that is usually buried in the ground.
The seagrasses are doing very well on Pulau Sekudu. Besides large areas of Spoon seagrasses (Halophila ovalis), there were also large clumps of Tape seagrass (Enhalus acoroides) and some patches of Fern seagrass (Halophila spinulosa).
There are a few mangrove trees on Pulau Sekudu too! Alas, some of the Perepat (Sonneratia alba) trees don't look too good, with bare leafless branches for most of the tree.
Near the 'highest' point of this tiny island are some other plants including a young Sea almond tree (Terminalia catappa) and a coconut palm (Cocos nucifera).
The large thicket of Bedara laut (Ximenia americana) is fruiting, while the Api-api bulu (Avicennia rumphiana) trees are flowering. I also saw one baby mangrove plant!
I checked up on the Pouched tomb bats (Saccolaimus saccolaimus) that have been seen roosting here. Alas, they were not there this morning.

Pulau Sekudu lies just off Chek Jawa. See the tiny white Chek Jawa beacon? Among the huge boulders found on Pulau Sekudu.
One these boulders does indeed look like a frog! Someone has helpfully added eyes and a smiley on the boulder. I have often wondered how that was done as the rock is rather tall.
We seldom visit this pretty island nowadays as it is off limits since 2007 and requires special permission from NParks. We were visiting with NParks and volunteers from Ubin to do a quick survey and to clean up the island.
Like many of our other shores, litter continuously washes up on Pulau Sekudu. There was a patch of blacked stuff with drink cans embedded in it. Lots of styrofoam including drink cups embedded among the boulders.
And plenty of plastic bottles.
Even where the shore is clean, the beautiful boulder are still scarred by the graffiti left by thoughtless people.
We took this opportunity to gather up the litter and to remove some fish traps that we found on the shore. It seems that restricting access to the shore has helped to reduce the trash load. We did not find as much trash as we did during our clean up in Dec 07. It was a great relief not to see any new driftnets here. In the past there was extensive driftnetting in the lagoon. So now the seahorses and other fishes are safe here.
On the way home, I saw three sand barges on they out away from Singapore. Usually, I see them coming in in the late morning. I wonder if they are doing the transfers earlier in the morning these days?
Pulau Sekudu is still alive, though it seemed a little quiet today. We should keep checking up on this shore to keep up with what is happening there.

Thanks to Alan for arranging the permit, Chay Hoon for the transport and other arrangements and it was lovely to have Jacky and Jane and Terry and Alyce with us on today's trip.

More adventures in another early trip tomorrow!

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