Upside Down Swimming

Perhaps it might not to others, but for noobish people like me it seems incredulous that horseshoe crabs actually swim upsidedown! And some of us were lucky enough to witness it during one of the coral spawning. Most of us thought that it was probably an injured or dead horseshoe crab floating face up on the water surface. Mr Lee scooped it up and the crab turned up to be a perfectly healthy one, because it was struggling so feriously on the boat.

Horseshoe Crabs are actually not crabs but more towards spiders. They are also commonly known as "living fossils" because they have changed little for hundreds of millions years. The Coastal Horseshoe Crab, Tachypleus gigas, is one of the two species of horseshoe crabs found locally, identifiable by its triangular and serrated tail.

Did some online surfing regarding this peculiar sighting. Apparently, it was just because of a mere physics and hydrodynamic thing. From Vosatka. Ohio Journal of Science. 70 (1970): 276–283, it was stated that this inverted swimming was due to its body design with the sloping cephalothroax helping to lift itself upwards when it swims. If it swims rightside up, the animal will just keep sinking. The legs of the horseshoe crab as well as the book gills provide propelling force while its tail serves as to nagivate (beside flipping itself up when overturned).

Above shows the swimming process of a horseshoe crab extracted from the journal. Below is a youtube video of a baby horseshoe attempting in vain (from 20s onwards) to swim.

Coral Spawning

In continuation from Peiya's posting (do visit her blog for more information), here are some more pimpled corals from the 23rd to 25th April night diving at Raffles Lighthouse! Really privileged to bear witness to this spectacular event.

Once again, this shows how amazing Singapore waters are!

The "eggies" almost bursting from the coral polyps

Acropora

Platygyra

Montipora

Favites?

And finally out they go!

Favites

Favites

The end result? Mass Orgy :)

Acropora

Photos courtesy of Karenne Tun and Yujie

Shark Sighting

Definitely a worthly enough topic for posting even though theres no pictures! Wow, me and E1 saw a shark at Raffles Lighthouse while helping YJ to collect eggs from the corals' mass spawning. It definitely does seemed to be a nurse shark (Family: Ginglymostomatidae) as YJ said when she saw it this Monday, since it looks like a benthic dweller (flattened body) with "moustache". Those moustache are actually chemosensory barbels to aid prey detection from the bottom. It was about 1.5m long, rather cute and harmless looking. But it swam off quickly despite our attempts to follow... alas. Still, a wonderful memory :)

It looked very similar to this.
Source: wikipedia

Last Dive before Exams!

This is possibly one of my last dive in the lab, at least before the exams. This is the first time I actually had an UW camera where I can snap all I want! O... how regretful I am for missing all those chances.

Took abit of tweaking in Photoshop, but obviously I'm still not good at it. The colors underwater are mostly green and blue, since they are the shortest wavelengths in the visible light spectrum and thus can travel further into the water column. Yes, this picture is taken in Singapore!

For those who think our waters are devoid of life, they are soo wrong. True, its rather turbid due to high sedimentation because of our country's endless pursue in increasing land area, but still life goes on underwater.

Picture perfect clownfishes. There are three on this sea anemone.

Sea Urchin. Divers beware! It can even penetrate through our wetsuits!

Copperband butterflyfish sucking on coral polyps?

A featherstar, resting on a boulder coral. They come in all sorts of beautiful colors, purple, yellow, green, red etc etc... I wonder if they represent different species or just a color variation.

This Giant Clam, Tridacna squamosa about half a metre, opened its mantle to photosynthsize.

I will even miss Lionel's resident filefish, which nibbled on my finger twice and the territorial damselfishes that pulled my hair. :)

Pictures by me and lionel