14 December 2008

Return to Pulau Semakau and the Big Moon

Back on Semakau again, this time with TeamSeagrass! The weather was glorious and we had a much better time on the shore than during our trip earlier in the week.
After helping to set up the Site 1 monitoring, I sneaked off to have a quick look at the northern end of Semakau.

This side of Semakau is just across from Pulau Bukom. The shores are thick with mangroves of all kinds and some parts are full of soft mud. So it was a bit slow going. Soon I had to turn back if I was to get back to the start point at sunset.The oil rig parked off Pulau Semakau is huge even at this distance.

With all that walking around I hardly had time to go to the low water mark, but still saw a few of the typical marine life found on Pulau Semakau. Some of them look very similar.Semakau has some hard corals such as this nice large brain coral (Family Mussidae). These are colonial animals which form a hard skeleton with meandering valleys that resembles a brain.Here's something that looks similar but is actually a group of corallimorphs (Order Corallimorphoria). They are also cnidarians like hard corals, but do not form hard skeletons. Each animal has a flat disk so they resemble mushrooms. Although the animals are often found very close to one another, they are not a colonial animal like hard corals.And here's another animal that looks similar. This is what a Giant carpet anemone (Stichodactyla gigantea) often looks like when exposed at low tide. The disk shrinks and tentacles are retracted. This particular situation may be a Giant carpet anemone in the process of splitting up into two, because there appears to be two mouths (the two white blobby things on either side of the constriction). But it could just be one very large anemone that got squished between the two rocks as it retracted. Sea anemones are solitary cnidarians.

Cnidarians can indeed look very similar.Here's the commonly seen Anemone hard coral (Goniopora sp.). It is a colonial animal and each colony member has a long body column topped with a ring of tentacles. When these polyps are expanded, the hard skeleton is hidden so the colony does indeed resemble an anemone. And here's a sea anemone with 'hairy' or branched tentacles. These Frilly sea anemones (Phymanthus sp.) are quite common on the coral rubble. Besides this dark coloured one with purple tips, these anemones come in a wide variety of patterns and colours.Here's one with banded tentacles. Here's more on how to tell apart large 'hairy' cnidarians commonly seen on our shores.

Squishy blob things are also often seen on our shores. This large flat green 'slabs' were particularly common where I was, something I've not seen before.
They are probably ascidians (Class Ascidiacea). Ascidians are actually closely related to vertebrates like us. We belong to same Phylum Chordata as they do! Although they look like blobs, an ascidian is a complex animal. It usually has a circulatory system, a digestive system, a heart and other organs, all encased in a little bag. They often form colonies embedded in a common tissue and look like these blobby slabs.These smaller bright blue and green blobs are the more commonly seen ascidians on our shores.There was also a whole bunch of pink blobs that I haven't seen before. These were on the high shore.

Large flatworms were also roaming the shores in numbers during the trip.
This one can be bigger than the palm of your hand! It is the Spotted black flatworm (Acanthozoon sp.). Flatworms are flat and most have no bits sticking out of the centre of their bodies. Their tentacles are pseudotentacles made out of folds of the front edge of the body. Flatworms are unsegmented worms belonging to the Phylum Platyhelminthes, which is a different group from the more commonly seen segmented marine worms of Phylum Annelida. And here's another flat animal that is sometimes mistaken for a flatworm. This is the Bohol nudibranch (Discodoris boholeinsis) which is sometimes commonly seen on our shores. This animal is a nudibranch or slug belonging to Phylum Mollusca (like snails and clams, and octopus and squid). Nudibranchs usually have a pair of tentacles called rhinophores at the top of the front end of the body (many also have a pair of tentacles under the body near the mouth). Many (but not all) nudibranchs also have feathery gills on the top of the back end of the body. Here's another nudibranch, the Polka-dot nudibranch (Jorunna funebris) that was widely sighted by everyone on this trip. Here's more on how to tell apart flatworms and nudibranchs.

It takes a while and many trips before we can quickly distinguish among the many similar but very different animals on our shores.

The team saw all kinds of stuff including a sea cucumber as long as Robin's forearm. Yvonne has a photo of it! We believe it is Stichopus herrmanni.
Here's the photo of this enormous sea cucumber, kindly shared by Eric. Thanks Eric!

We were anxiously awaiting moon rise today, after learning that the moon is the biggest in 15 years over the next few days. But it didn't rise until we got back to the mainland.It didn't seem much larger to me.

Here's a more scientific photo that was on the National Geographic News website.This is a composite picture, based on an image of the moon taken by the Galileo spacecraft, shows the apparent size differences between a full moon at perigee (the closest point in lunar orbit) and one at apogee (the farthest point), as seen from Earth. On December 12, 2008, the full moon will be at an unusually close perigee, offering sky-watchers a view of the biggest and brightest full moon seen since 1993. (Image courtesy NASA).

According to the article:
"While high tides happen each month when the sun, Earth, and the moon are aligned, there is going to be an enhanced effect, with the moon being the closest it's been in more than a decade. This would result in extra-large tides in regions that are susceptible to them, like Nova Scotia's Bay of Fundy. But even in such places, the effects of perigee are often modest, in most cases measurable in inches. But perigee tides can be higher if there happens to be a storm surge at the same time.
Well, we are getting a particularly low tide for this time of the year, but not very much lower than those we experience in the middle of the year. There sure is a lot more to learn about our tides and our shores.

Other blog posts about this trip

2 comments:

  1. re: the big moon, i don't know about low tide but when we were at ubin, the tide was unusually high. but i guess it's not flooding so it can't be much higher than normal?

    this was taken at ubin on saturday.
    http://www.flickr.com/photos/micamonkey/3107436490/

    it was sunny so i guess the waterlevel was well-behaved. but if it had rained it'd have definitely flooded all over ubin.

    Prof Teh was telling me the other day that the whole ubin jetty area is actually very low-lying... wonder if i understood him wrongly but it's.. "below sea level"? hmm interesting... he says "it's 3.2" so it's probably just low lying? hehe will clarify with him another time :)

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  2. Thanks for sharing this interesting observation November! Yes it does seem the tide is particularly high. Though we always wish it would be particularly low :-)

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