It was relief to know that they spawned because our corals suffered from mass coral bleaching in 2016. [Update 21 Apr: "greatly reduced spawning intensity" was recorded this year compared to past years.] Thanks to the dedicated team who have been keeping an eye on this event every year, we get a glimpse of what happened in 2017.
What is Mass Coral spawning?
Once a year, on the fourth month, around four days after the full moon, our corals seed the seas with new life!
Some corals release their eggs and sperm all the same time. Called broadcast spawners, these mass spawning events usually occur once a year, a few nights after full moon. Tiny packets of eggs and sperm pop out of the coral polyps.
These packets drift to the water surface where they open up, releasing the eggs and sperm for fertilization.
After a few days, the embryos will have developed into coral larvae that drift about and eventually settle down on a hard surface to form new corals.
While bazillions of eggs and sperms are released during a mass spawn, most don't make it. Hordes of marine creatures gorge on the spawn, from fishes and crabs to jellyfishes.
As the tiny coral larvae develop, they have to survive the countless predators that constantly sieve the water for plankton and edible bits.
The coral larvae also have to overcome many other challenges that we are still learning about. Excessive sedimentation, for example, can interfere with fertilisation and other aspects of coral larvae survival and successful settlement.
Why is coral mass spawning in Singapore a big deal?
From Sex in the Tropics 2008 on the blooooooooooo blog
Coral mass spawning in Singapore was first recorded by Dr James Guest in 2002. It was the first record of coral spawning in the tropics. At least 18 different coral species from ten genera and five families (Acroporidae, Faviidae, Merulinidae, Oculinidae and Pectiniidae) have been observed to spawn in our waters! Mass spawning occurs on the third to fifth nights after the full moon between 8 and 10 p.m.
In interviews with the media, Dr James Guest emphasised that corals are part of Singapore's biodiversity and natural heritage. "There are 255 species of corals recorded here, and there may be some corals here that were around before Stamford Raffles arrived."
The fact that our corals mass spawn shows that our reefs are functioning well! According to Dr James, the number of coral species in Singapore that mass spawn is "as high as on other Indo-Pacific reefs, like the Great Barrier Reef... " This shows how rich Singapore's natural heritage is. We can find right at our doorstep: "diverse, functional and fascinating coral reefs, that people would normally associate only with countries like Australia."
Some observations on Mass Coral Spawning in 2017
Update 21 Apr: From Singapore mass coral spawning less intense this year by Audrey Tan Straits Times 21 Apr 17;
Dr Karenne Tun, director of the coastal and marine division at the National Parks Board's (NParks) National Biodiversity Centre, said: "The impact of the longer coral bleaching last year on this year's coral spawning is a major concern."
A "greatly reduced spawning intensity" was recorded this year compared to past years, Dr Tun said. "However, the species that did not bleach last year were not affected and displayed healthy spawning."
Healthy coral reefs are important as they draw in marine life and function as a nursery for baby fish. Corals depend on symbiotic algae, called zooxanthellae, for energy. Bleaching occurs when abnormally high sea temperatures cause corals to expel the algae, turning the corals white and depriving them of a key source of nutrition.
Last year, Singapore's corals endured the longest bleaching incident on record. It started in June and corals started recovering only at the end of the year. It was not just corals in Singapore that were affected. Last month, a study by Australian scientists found that two-thirds of the 2,300km stretch of the Great Barrier Reef had also suffered serious bleaching.
Scientists here think that the limited spawning this year could be because corals had more critical resource concerns.
Said Dr Toh Tai Chong, a marine biologist from National University of Singapore's Tropical Marine Science Institute (TMSI): "After bleaching, corals devote a lot of energy to recovering. This depletes the amount of energy they store in their tissues and reduces the amount of energy available to initiate or complete the sexual reproduction."
NParks scientists are planning another dive after the full moon next month, just in case there is any delayed spawning.
The last bleaching incident in Singapore occurred in 2010 between June and September. But corals affected then started recovering around the time the reproductive cycle in corals was expected to start. The spawning event in 2011 was observed to be less intense compared to the pre-bleaching 2010 spawning event. However, this year's spawning intensity was observed to be even weaker than that in 2011, said Dr Tun.
MORE photos of Mass Coral Spawning in 2017
Chay Hoon's facebook album of corals spawning on 15 Apr at Pulau Satumu.
Chay Hoon's facebook album of corals spawning on 16 Apr at Pulau Satumu.
Lisa Lim's facebook album of corals spawning at Pulau Satumu.
Heng Pei Yan's facebook photos of corals spawning at Pulau Satumu on 16 Apr.
Jeffrey Low's facebook album of corals spawning 5-17 Apr 2017 at Pulau Satumu.
Karenne Tun's facebook photos of corals spawning in 2017.
Minister Tan Chuan Jin's facebook photos of corals spawning in 2017.
Other posts about mass coral spawning 2017
- Minister Tan Chuan Jin's facebook post of corals spawning in 2017.
- Gina Tan's One of nature's most spectacular events on the Hantu Blog.
Updated 11 Aug 2017
Bleaching incident led to late coral spawning
Season was later than usual, likely because corals were recovering
Audrey Tan Straits Times 11 Aug 17;
"Warming seas caused Singapore's corals to suffer from the longest-ever bleaching incident on record last year, and observations show that the incident has far-reaching effects.
The reproductive capacity of Singapore's corals was reduced earlier this year, even though they have started to recover from bleaching since late October 2016.
Scientists have observed that some species of hard coral spawned outside of the usual reproductive season."
Previous posts about previous coral spawning