Semakau, in the Early Morning Light 140309

A couple of days back marked the last of afternoon and evening low tide windows. So, from now till several months along, trips are scheduled for the early morning.

In the wee hours of Saturday morning, dozens of Project Semakau volunteers left their homes in order to reach Marina South Pier by 5 am. We were going to the island to conduct the first transect survey.

It was still dark when we got to the pier and similarly when the ferry reached Semakau.

As transport is not provided at such an early hour, we had to walk to the intertidal zone from the visitor centre. The early morning air was cool and punctuated with bird calls, as our diurnal feathered friends slowly awoke from their slumber.

In no time, we had walked through the secondary forest and reached the intertidal area. At the beginning of the seagrass meadow, we had an encounter with...

...an unknown sea hare (Order Anaspidea).

Wen Qing, Samuel and myself were in seagrass transect team 2. While doing the survey, we saw plenty of seagrass in the 30 m stretch (but not as much as before like during the transect training) and also some interesting things like the mucus coating made possibly by a wrasse (Family Labridae) or some other kind of fish [edit]. One interesting fact about wrasses is that they can change their gender! O.O

Seagrass is indeed tricky as we soon realised for ourselves...

1) Thalassia hemprichii.

According to the ID sheet, the leaves have "short, black bars of tannin cells". But as you can see, these bars aren't obvious at all. This is a good example of how things in the field often differ from what is on paper... So how to ID Thalassia? Though their sickle-shaped leaves are a good giveaway, if unsure, it's best to feel for their rhizomes which are scarred and appear reddish-brown :)

2) Cymodocea serrulata.

Often confused with Enhalus acoroides and Thalassia hemprichii, this species does have one visible distinguishing feature - a serrated leaf edge! If that does not help, feel for the rhizomes, which are smooth and closer to the surface than Thalassia.

3) Halodule uninervis.

We didn't think we'd encounter this species, so we had to confirm its ID with Ron. The above is a young specimen. It has a white rhizome with black scars. In mature specimens, a distinctive centre vein is visible, and leaf tips have three distinct points.

Mostly, there was a lot of Tape Seagrass (Enhalus acoroides), noticeable numbers of Syringodium isoetifolium (Noodle Seagrass), some Cymodocea serrulata (Serrated Ribbon Seagrass), a little of Halophila ovalis/minor (Spoon Seagrass), even less of Thalassia hemprichii (Sickle Seagrass) and only one quadrat with Halodule uninervis (Needle Seagrass). For more info, visit the I.D. Seagrass page of the Seagrass-Watch website :)

After completing the transect survey, we were given some time to explore. One group followed Ron, while the other followed July. Saw this Sandfish Sea Cucumber (Holothuria scabra) soon after heading out.

There were numerous juvenile Knobbly Sea Stars (Protoreaster nodosus) out that day! Yay! They really come in a myriad of colours. As echinoderms have a water vascular system, they will get stressed and die if left out of water for too long. That's why we always replace them after a quick photo.

Knobbly no. 1.

Underside of Knobbly no. 1

Knobbly no. 2. One of its arms is slightly shorter than the rest which could be a result of an injury and subsequent regeneration.

Knobbly no. 3.

Underside of Knobbly no. 3, with focus on its mouth (centre) and the ambulacaral areas which house its tube feet.

Knobblies no. 4 and 5. The Knobbly on the left looks really 'juvenile' (but that's just my opinion).

Knobbly no. 6. With two of its arms closer than normal to each other, this sea star here looks like it's getting ready to dance.

Saw a few more Knobblies, but didn't upload all the pics here.

Growing in bunches were some green algae (Caulerpa sp.).

This is a first for me! In one of the tidal pools, this Heart Cockle (Corculum cardissa) was clearly visible in the shallow and clear water. When it dies, the heart breaks...

An Orange-edged Black Flatworm (probably Pseudobiceros uniarborensis). Another 'first' for me on Semakau.

Looking like a protrusion from the substrate was this Common Hairy Crab (Pilumnus vespertilio). The hairs on its body trap sediment which, over time, allows it to look like a piece of the substrate itself.

A view of the coral rubble area.

Growing in between this magnificent Staghorn Acropora Coral (Acropora sp.) was a fan shell (Family Pinnidae).

Hmm..egg cases of a mollusc? It's likely an egg ribbon of a nudibranch or some other species of slug.*

This sea cucumber (Actinopyga sp.) is thought to be a juvenile Stonefish Sea Cucumber due to similar physical traits, but that is based on speculation and not yet confirmed*.

This is by far the smallest Noble Volute (Cymbiola nobilis) that I have seen. Is it a juvenile? From its shell alone, I wouldn't have been able to ID it as the typically associated 'mountain ranges' pattern is absent. Lucky its black with orange spots muscular foot was showing.

Saw a lot of these Common Sea Stars aka Sand-sifting Sea Star (Archaster typicus). Here is a pair getting ready to mate with the male on top (such pairing behaviour is known as pseudocopulation) [edit]. Like other sea stars, external fertilisation takes place (meaning reproductive organs don't actually meet).

References:

Wild Fact Sheets of marine life on Singapore shores - http://www.wildsingapore.com/wildfacts/

Acknowledgements:

[edit], *Thanks to Ron for the corrections and IDs!

The Sun Blazes Down on Semakau 080309

Remember how in primary school there were a couple of 'standard' phrases used in writing compositions? I've never been a fan of them but if there ever was a time to use one, it would be to describe the weather on Sunday. So here goes:

The sun beat mercilessly down on us...(haha!). After doing battle with the mozzies (they love me but the feeling isn't mutual) in the forest trail, we finally arrived at the intertidal area. Split into 2 groups, Wen Qing, Nonis, Xiu Li and myself followed Luan Keng while Hui Yi, Ying Wei and Elvin had Ron as their leader. We were there to pile in the transect markers for the upcoming transect this Saturday. As we headed out...

...LK spotted this Mangrove Horseshoe Crab (Carcinoscorpius rotundicauda). Two species can be found in Singapore - the one above as well as the Coastal Horseshoe Crab (Tachypleus gigas). Two easy indicators to look out for are colour and tail structure. The mangrove species is brownish with a rounded tail while its coastal relative is greyish with spines on its tail. Read more about horseshoe crabs in general here, and the 2 species that can be found in Singapore here.

Kinda seemed apt that the first animal spotted was a horseshoe crab, for on that very day in the evening, a Horseshoe Crab Population & Distribution Survey was conducted around the mainland, organised by the Nature Society (Singapore). I sure hope that minimal damage was incurred for volunteers had to dig up (a lot of) mud in order to locate the horseshoe crabs...

After crossing the seagrass meadow, we entered the coral rubble/coral reef area where two huge pore corals (Porites sp.)* caught our attention with their different colouration.

Sadly, the top of both corals are dead and the scorching sun didn't help matters.

After piling in the transect markers, we had some time to explore. Hunter-seekers who arrived before everyone else found this synaptid sea cucumber (Family Synaptidae) and marked out its location.

Another find by the hunter-seekers was this Noble Volute (Cymbiola nobilis) and its eggs. Was amazed to see that the mass of eggs it laid was as big as it was. Its shell kind of looked faded to me, compared to the previous ones I'd seen at Changi before. Also, it was smaller. Size can't be used to judge its maturity, I realised.

A dead octopus (Class Cephalopoda, Order Octopoda).* Wen Qing's close examination of it revealed that some of its tentacles were shorter than the others. We learned from one of the visitors that tentacles can get bitten off by predators and are subsequently regenerated. Cool!

Bakaus (Rhizophora spp.) greet visitors to the Semakau intertidal area. Learned that 2 species can be found growing on the edges of the sandy shore - R. apiculata and R. stylosa.

Though both species look similar, they can be told apart even at a distance by their roots. Both mangroves have stilt or prop roots, but those of R. apiculata are not so spread out as compared to that of R. stylosa. In addition, the stipule^ of the former is red while that of the latter is yellow. The stipule wraps over the apical bud, protecting it. The red stipules will eventually drop off as the young leaves grow.* Can you tell which picture is of which species? One last thing to note, R. apiculata has a shorter flower stalk than R. stylosa.

Another Rhizophora species, R. mucronata has big leaves which distinguish it from the two above.

Taking one last look at a Rhizophora stylosa before we leave.

Some other things seen but not photographed:
i. Mosaic Crab (not too sure...it ducked for cover really quickly so I only caught a glimpse)

ii. Crab with yellowish-brown carapace (ditto the above)

iii. Black-lipped Conch

iv. Sand-sifting Sea Star aka Common Sea Star

v. Ovum Cowrie

vi. Eagle

Heard about the sightings of Knobbly Sea Stars and turtles from Ron but didn't get to see them D:

Acknowledgements:
Thanks to LK for the info! And to everyone for the company :)

*Ron, thanks for the corrections!

^Thanks to Anonymous for bringing my attention to the terms used (ie. stipule and apical bud)! [Refer to Anonymous' comment]

Notes:

Given the weather, a cap and a lot of water are essentials!

For other takes on the trip, check these entries out:

i. Ron's - http://tidechaser.blogspot.com/2009/03/scorching.html

ii. July's - http://wherediscoverybegins.blogspot.com/2009/03/discover-semakau-landfill-island-8.html

iii. Samson's - http://mantamola.blogspot.com/2009/03/semakau-tidal-walk-8-march-09.html

iv. Meiyi's - http://appreciateandlove.blogspot.com/2009/03/semakau-after-so-long.html

v. Eunice's - http://naturallyours.blogspot.com/2009/03/48-semakau-guiding-w-meiyi-giant-clams.html

Transect Training at Semakau 100109

The 10th of Jan marked my second trip with the Raffles Museum of Biodiversity Research (RMBR) and fellow volunteers to Pulau Semakau. It was my first time doing an actual transect survey.

Here are the tools of the 'trade' (clockwise from left): ruler, transect tape, clipboard with recording sheet, ID chart and quadrat. We grouped ourselves into team of threes. Gerald, Samuel and I worked together :)

At the perimeter of the seagrass meadow, Gerald sighted a Blue-spotted Fantail Ray (Taeniura lymma) hiding among the seagrass.

Some blades of seagrass had ascidians on them. Note that ascidians are not plants but animals! They are vertebrates and belong to the Phylum Chordata (like us!). These are affectionately known as Green Gum Drops Ascidians, and are colonial. The seagrass also has quite a lot of epiphyte (a kind of tiny algae) cover, giving it a dirty appearance.

This is the female flower of the Tape Seagrass (Enhalus acoroides).

Among the seagrass, there were many small bunches of this red algae (Gracilaria sp.). [Edit]

Drifting lazily on the surface of the water and blown about by gusts of wind were the tiny white male flowers of the Tape Seagrass (Enhalus acoroides).

Blue corals (Heliopora coerulea) in the seagrass meadow! Note that these may appear to be hard corals, but they are actually soft corals. Edit: These may actually be Green Gum Drops Ascidians too as suggested by Ria. Thanks!

Woohoo! My first time seeing a Knobbly Sea Star (Protoreaster Nodosus) on Semakau.

If quickly flipped over, one will be able to see its tube feet waving about as well as the protruding muscle-like mass which is its stomach.

This pic looks familiar, right? It was my first header!

Check out the intricate detail on the Knobbly's body. Simply amazing.

This tentacle-waving anemone (probably a Wiggly Star Anemone) is very shy indeed. It quickly retracted its tentacles and ducked away (methinks it is motile) when I approached it. Had to wait for a little while before it felt comfortable enough to venture out again.

Some more anemones nearby. These had bright greenish-yellow tentacles, and were about 1-2 cm in diameter. I've no clue as to what kind of species they might be. Edit: These are probably zoanthids (Order Zoanthidea) instead! They are commonly confused with sea anemones (Order Actiniaria) as they look similar. However, "while sea anemones are solitary polyps, most zoanthids live in colonies like corals do.". They also have a different make-up from corals. Thanks Ria!

The first time I saw a cowrie was on Sultan Shoal. This appears to be an Arabian Cowrie (Cypraea arabica) with its mantle covering its shell. When the mantle is retracted, the shell is glossy and smooth. Edit: This is NOT an Arabian Cowrie as I previously thought. The Arabian Cowrie has brown spots on the outer edges (the lighter part of the shell, in this photo) which the cowrie here clearly does not have. So it's probably either a Wandering Cowrie (Cypraea errones) or an Ovum Cowrie (Cypraea ovum). [Refer to Ron's comment]

A Spotted Black Flatworm (Acanthozoon sp.) swimming away.

Upon closer inspection, the flatworm is not really flat but actually has raised white bumps on its body.

This fish (a scorpionfish, maybe?) announced its presence by thrashing about wildly in the sargassum it was taking shelter in.

Ying Wei spotted this rare find: a Heart Urchin!

The cacophony coming from the direction of the sandy shore alerted me to the presence of these two birds, Great-billed Herons (Ardea sumatrana) probably . They were making barking/honking noises and one could have easily mistaken them for some other kind of animal!

And what better way to wrap up the day by having another sea star sighting? July chanced upon this Cryptic Star (Cryptasterina sp.) which was hiding under a rock.

Having been to Semakau twice already, I nevertheless look forward to the next trip. Each trip never fails to bring pleasant surprises (Knobbly Sea Stars, yay!). In due course, I hope that my photography skills will improve and more importantly, I'll be able to spot and identify more organisms. Glad to have met many new friends in Project Semakau as well :)