Corals are animals in the phylum Cnidaria. An individual coral build by billions of tiny polyps which produce calcium carbonate skeletons also known as reef building corals or hermatypic corals. Whereas nearly all the soft corals lack of hard skeletons called non-reef building corals or ahermatypic corals.
Nearly all the hermatypic corals have Zooxanthellae - symbiotic algae live in the coral tissue, play important function to enable coral to deposit calcium carbonate much faster and also provide food to the coral polyps.
Corals growth and reproduce by sexually and asexually. The colony grows as the polyps repoduce and also polyps divide to form new polyps. Corals reproduce eggs and sperm just like other animals.
Usually the corals spawn at the night time. When the night falls, coral polyps start to expand and pink coloured bundles are held under the mouth of the polyps are visible through the transparent tissues and waiting for the time to release. When the biological clock stikes, the eggs and sperm released into water in bundles from the mouth of the coral polyps and float to the surface and get fertilize. Fertilized planktonic coral larvae called planula, drift with current for days and reach a suitable habitat to settle and growth to form a new reefs.
For mass coral spawning to take place, synchornized by the tidal change, moon and water temperature which is the specific cue to released all the eggs and sperm exactly the same time. However, the exact time of coral spawning still unpredictable. Mass spawning overwhelms the predator such as huge plankton feeder - whale sharks and other fishes. Besides, mass spawning also important to increase the opportunities of fertilization.
During this early of June, few days after the full moon, there are 4 Japanese divers who was lucky to experienced the unpredictable dive in our house reef here. We saw three species of table coral spawned.
Kiuchi Hirotaka san waiting for the coral to spawn.