Sunday, March 04, 2007

First Semakau Public Walk of the Year

Was kind of excited today as it was the first Semakau walk for the year, and I had been really looking forward to it. We gathered at West Coast Pier and took a half-hour boat ride to get to the island. Reclaimed from two islands – Pulau Sakeng and Pulau Semakau, Semakau Landfill is the only landfill in Singapore. However, while all of old Sakeng and half of old Semakau were reclaimed, the other half of the original Semakau was left the way it was – with lots of corals and other marine life.

At the island, we started with a video presentation by NEA, followed by a land tour. However, Mother Nature seemed to be rather moody today, and she started crying.

table tennis

We were stuck in the activity room for quite a while, but thankfully, the rain eventually stopped and we managed to go ahead with the walk :)

It turned out to be a very fruitful trip, despite the rain, and we saw lots of interesting things. It’s just impossible to include everything we see here, and so I’ll just highlight some of them.

Common sea star, starfish, Archaster typicus

The common sea star, also known as the burrowing sea star (Archaster typicus). You are now looking at its underside, with its mouth in the middle. This sea star, like many others, can push its stomach out of its mouth to digest externally organic materials (aka detritus) on the sand surface! A sea star uses sea water instead of blood to support its body and to move its tube feet, so don’t remove them out of water for too long, as it is very stressful for them.

We had to cross a seagrass lagoon to get to the coral rubble, and the seagrass lagoon at Semakau is HUGE.

Seagrass lagoon

Seagrasses are flowering plants, and their roots and underground stems help stabilise the sediments. Many marine animals thus like to lay their eggs here, as it is sheltered from strong waves, and has lots of food. We have a group of volunteers in Singapore who monitors the seagrass in Singapore. Find out more about them at the Team Seagrass blog!

On reaching the coral rubble, we saw this cute sandfish sea cucumber (Holothuria scabra).

Sandfish sea cucumber, Holothuria scabra

This sea cucumber is edible, but must be properly treated before they can be consumed because they contain toxins. Sea cucumbers are related to sea stars, as they are all echinoderms, i.e. from the same phylum Echinodermata.

Towards the end of coral rubble, we saw an upside-down jellyfish (Cassiopea sp.).

Upside-down jellyfish, Cassiopea sp.

This jellyfish usually remains in an upside-down position as it has symbiotic algae, mostly in its tentacles, which photosynthesise better with it being upside-down.

We also saw two long-spine sea urchins (Diadema setosum). This sea urchin species has an orange rim on its anal cone. They are echinoderms too! This was the first time we saw sea urchins on our guided walks!

Long-spine sea urchin, Diadema setosum

But the Number One highlight of the walk was usually this – knobbly sea star (Protoreaster nodosus).

Knobbly sea star, Protoreaster nodosus

We found two of them today, each about 30cm wide!

We also saw many corals, including the sunflower mushroom coral (Heliofungia actiniformis) on below left and the lovely soft coral that I don’t know the name.

Sunflower mushroom coral, Heliofungia actiniformis

And near the soft coral, I had another surprise find – a seahorse (Hippocampus sp.) among some sargassum seaweed!

Seahorse, Hippocampus kuda

A seahorse is actually a fish. Interestingly, the male seahorse has a pouch, and the female seahorse will lay her eggs in it. Thus, if you see a seahorse that looks like it’s pregnant, it may be a male one! This is only the second time we found seahorse on a guided walk. They are usually very hard to find, since they are very well-camouflaged.

Today was also a day for nudibranchs, and we saw four different species! Nudibranchs are sea slugs, i.e. snails without shells.


Clockwise starting from top left, we found the orange-spotted gymnodoris nudibranch (Gymnodoris rubropapulosa, the black phyllid nudibranch (Phyllidiella nigra), the green ceratosoma nudibranch (Ceratosoma sinuata), and the polka dot nudibranch (Jorunna funerbris). Nudibranchs are hermaphrodites, meaning each slug has both male and female reproductive organs. Thus, they often fertilise each other when they mate. Sometimes, one may take on a male role, the other a female role. Read more sexy stories about the Gymnodoris on one of my earlier blog entry! And coincidentally, another fellow guide just asked me about the ceratosoma a few days ago, and today I actually saw it! I’ve only seen them once before at Sisters Island.

We also found two other species of sea cucumber.

Sea cucumbers, Actinopyga lecanora and Stichopus horrens

The one on the left looked like a stonefish sea cucumber (Actinopyga leconora), but while it had the five ‘teeth’ usually found on a stonefish sea cucumber's anus, it didn’t have the whitish zone surrounding the anal region. Thus, I’m not really sure if it is a related species, or is it a stonefish sea cucumber that happened to have a less whitish anal zone. Not sure about the name of the one on the right though. This is the second time I saw it on Semakau.

And on the way back, we found two moon crabs (Ashtoret lunaris) having a wrestling match!

Moon crabs, Matuta lunaris

What were they actually doing? Was the smaller one the prey of the bigger one? Anyway, moon crabs have four pairs of paddle-like legs that they use for swimming and burrowing. When I touched the big one with my steel chopsticks, it immediately swam off and disappeared into the sand in an eye-blink, still holding onto the smaller one with the right pincer.

And here’s a shot of my group – the clown fish!

Although we didn't managed to find any clownfish today (they were probably hiding some where from the low tide), it still had been a very fruitful walk with lots of good finds. And of course, not to forget that we had a lovely sunset to end the day!


Thanks to all the participants for making the walk such an interesting one!

And if anyone reading this would like to join one of the intertidal walks or other nature walks, do drop by the WildSingapore Website's Calender of Events for more information!

Read also:
Samson's experience at Semakau!


FullTimeDayDreamer said...

Hi there...I was doing a search on Google about arrow crabs (since I'm interested in seeing what are predators to jellyfish, since they're becoming an issue by overpopulating in the Black Sea due to ballast water from the US) when I came across your site. It was SO interesting and informative! Thank you SO much for putting those pictures and information out there. You all are so brave to go into that water and find such creepy looking creatures and not go screaming like I probably would! I loved reading it, however...much less stressful coming from my computer screen from you than hands'-on experience. I wish you luck and safety in your further endeavors! Keep us spineless observers informed via your site b/c I'll be back!! :)

Ron Yeo said...

Thanks Michelle! It was always so encouraging to know that other people enjoy reading about our various nature trips :)

Do venture out to the shores one of these days - it's definitely not as scary as you may think :P