Thursday, January 3, 2008

Discovery Corals @ Semakau

Forty third Discovery posting:

This is a follow up entry on the Christmas day trip to Semakau. But this entry will solely focus on corals as part of the assignment requirement. However, i will not do exactly what the assignment required us to do (to do a Coral IDs blog posting, as SY (fellow group member) has already done one. So i've decided to do what others have not covered, to give a brief introduction on what are corals.

What are Corals? An example from Genus Faviidae is shown (picture below).
Discovery Note:
1. Corals are animals.
2. They belong to a group of ancient and simple group of animals known as Cnidarians (pronounced as "nai-day-rians") Jellyfishes and sea anemones are also from this phylum Cnidaria.
3. Cnidarians are aquatic and they share a common and unique feature of having stinging cells used for protection and catching of prey.

Now as said, corals are animals, which means...

Discovery Note:
1. They are generally composed of more than one tiny animal, probably tens / hundreds / thousands of them in one coral structure, that's why you have heard of "Coral Colony".
2. These tiny animals are called polyps which feed on microscopic plankton or small organisms.
3. A polyp begins its life as a tiny, free-swimming larva; the larva is only the size of the head of a pin. Once it finds a hard support, it will settle there and will never move again. It reproduces by budding (in which an identical polyp sprouts out of the polyp's side) and by sexual reproduction (in which polyps release eggs and sperm, which mix in the water).
4. Budding usually occurs when the coral is "young" (meaning there is only a few polyps in the colony)
5. Look at the picture below, inside each "walled" section, you will find a polyp.
Now, some of you may have been always wondering about this, why are coral reefs so colourful? How do they do it?

Discovery Note:
1. From what i know, there are two possible reasons, one is due to fluorescence (which i will not go further into, as TC have already covered about it). The other reason is due to the colourful zooxanthellae algae they host.
2. These algae form a symbiotic relationship (one which they help one another) with the corals.
3. Through photosynthesis, these algae generate "food" for themselves and pass the extras to the coral which will help to the coral to grow into a larger colony. In return, the coral provides a "home" for these algae.
4. Thus, corals are usually found in clear and shallow waters, as sufficient sunlight is essential in photosynthesis.

Genus Oulastrea (picture below)
Have you ever been on a guided tour to an inter-tidal area and heard the guide telling you about hard and soft corals?

Discovery Note:
1. As we go down the list on how to classify corals, Corals belong to the class of Anthozoa.
2. And this can be divided further into two subclasses, Octocorallia and Zoantharia
3. Subclass Octocorallia. Polyps are characterized by having eight pinnate (side- branching) tentacles. Octocorallians include sea pens and soft corals.

4. Subclass Zoantharia. Polyps are characterized by having tentacles in multiples of six. Zoantharian tentacles are rarely pinnate. Black corals and reef-building corals are members of this subclass. Reef-building corals are also known as "hard corals" or "stony corals".
5. Hard corals are hard because of the calcium carbonate they produce to form the rock-like skeleton.

6. Soft corals also produce calcium carbonate, but in little amounts to help them keep their shape.
7. It is possibly because of this that the soft corals usually "grows" at a faster rate than hard corals.

Example of a hard coral. Genus Acropora (picture below) Example of a soft coral. Genus Sinularia (picture below)Close up view of soft coral. Notice the polyps... (picture below)Thanks again to Jani, our instructor for the Coral Workshop and Luan Keng for organising this .

Extra:
Read SY's blog for more coral IDs.
Read RY's blog for another entry of coral IDs.
Read TC's blog on Coral fluorescence.
Read more about Corals on wikipedia.

2 comments:

juanicths said...

oulastrea not outlastrea dude...

SY said...

The Acropora is might be porites instead, not sure but its not acropora cos no axial corallites =)