13 September 2010

Surprises in the seagrass at Kusu Island

Besides reefs, Kusu Island also has seagrasses and rocky shores.
Yesterday, there was a lush bloom of Sea lettuce in the lagoon! What creatures can we find here?

The Spoon seagrass (Halophila ovalis) at Kusu Island have very tiny leaf blades. But they are enough to shelter all kinds of creatures. Not just among their puny little blades, but also underground, where the mats of seagrass roots stabilise the sediments. Among the buried treasures are sea cucumbers. I'm quite thrilled to see the Remarkable sea cucumber (Holothuria notabilis) on Kusu Island! So far, we have only seen this sea cucumber on Chek Jawa, Changi and Cyrene Reef. In fact, I saw two of them! This is all that one might see of the usually buried sea cucumber. Another surprising find was the 'satay stick' or Slender sea pen (Virgularia sp.), our first sighting of this animal on our Southern shores. This colonial animal has a buried 'root' and can retract completely into the ground.
Chay Hoon also spotted a buried Ball sea cucumber (Phyllophorus sp.) which is also more commonly seen in the Northern shores. She also saw a strange sea cucumber.

Above ground, the green carpet of blooming Sea lettuce (Ulva sp.) provides even more hiding places. Such as for this tiny shrimp that I've not seen before.I also saw several tiny Eeltail catfishes (Plotosus sp.) wriggling among the tangle of seaweeds, lots of creeper snails (Family Cerithiidae) and tiny hermit crabs in creeper snail shells.
There are lots of little shrimps and crabs too. The sand-coloured Sentinel crabs (Macrophthalmus sp.) that usually forage on the silty shore are rather conspicuous on the green seaweed mat. The relatively larger young swimming crab (Family Portunidae) probably preys on the other smaller animals.
On the sandier parts of the lagoon, there are lots of Common sea stars (Archaster typicus). Many of them were in mating position with the male on top, locking arms with the female below. I notice that the males on Kusu Island seem rather small, some barely able to lock arms with the female.
There are also Cake sand dollars (Arachnoides placenta). The Striped hermit crabs (Clibanarius sp.) here seem rather small.
It was nice to see a Black lipped conch (Strombus urceus) and Gong-gong (Strombus canarium) as I have in the past.
When I see nudibranchs on the shore, it must mean that they are abundant. Indeed, everyone else also saw these nudis: the tiny 'Strawberry slugs' (Costasiella sp.) that infest the green Sea fan seaweed (Avrainvillea sp.).
And the lovely blue-spotted Dendrodoris denisoni nudibranch. The rest of the team of course saw lots of more that I didn't.
On Kusu Island's man-made seawalls live the very speedy Sally lightfoot crabs (Grapsus albolineatus). These usually come out in numbers only at night and can move very quickly. When cornered, they simply flatten and freeze, blending perfectly into the surroundings. Can you spot the crab?
Here's a closer look at the crab!
On the seawall, I also came across these anemones that I've not seen before.
Elsewhere were lots of other kinds of crabs. Including moon crabs (Matuta lunaris), flower crabs (Portunus pelagicus), Spoon pincer crabs (Leptodius sp.) and Ghost crabs (Ocypode cerathophthalmus).We also checked out the coral bleaching situation at Kusu Island.

Kusu Island is tiny, but has lots of interesting marine life!
Ringed by artificial walls, this island lies just off the main business district.
The Blue Water Volunteers conduct guided walks at Kusu Island. More information for visitors.

Other posts about this trip
  • James from tiny shrimp to sea moth
  • Russel beautiful landscape shots and lots of colourful animals including strange seahare
  • Marcus more corals and assessment of their health
  • Kok Sheng anemones and more, plus a peek at another side of Kusu

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