Sunday, March 15, 2009

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... 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).

Wild Fact Sheets of marine life on Singapore shores -

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

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