Snow underwater? It's corals spawning

Waters off Republic's southern islands have recently been drawing scientists to the event
Audrey Tan Straits Times 1 May 16;

The beaches of Singapore's idyllic southern islands have been touted as a great place to unwind, but over the past week, the area has had a different draw for scientists and marine volunteers.

It has been the season for "underwater snow".

When the corals surrounding the southern islands spawn, they release millions of eggs and sperm bundles into the water at the same time. The pink or yellow bundles are buoyant, causing them to float upwards. For a diver witnessing the spectacle, it looks like it is snowing in reverse.

In Singapore, such mass synchronised coral spawning takes place once a year, and usually on three or four nights after the full moon in late March or April.

This year, the start of the local spawning period was last Monday, the third night after the full moon. The National Parks Board (NParks) has been monitoring the yearly affair for the past 10 years, as part of its management strategy for marine and coral biodiversity conservation.

Coral expert Chou Loke Ming said corals spawn at the same time to ensure successful fertilisation. Eggs and sperm released into the water join to form free-floating larvae, which float until they find a suitable home.

NParks' researchers, volunteers and scientists from institutions such as the National University of Singapore headed out to sea at dusk for four nights starting on Monday to observe the event in the reefs off Pulau Satumu, where monitoring was conducted in previous years. It is out of bounds to recreational divers.

Dr Karenne Tun, director of the coastal and marine branch of NParks' National Biodiversity Centre, said that over the past decade an average of 25 to 35 coral species have been recorded spawning over the entire spawning period.

When The Sunday Times went on a dive with the researchers on Monday, a total of seven species of hard coral were recorded spawning between 7pm and 9.30pm. But Dr Tun noted that more species could be recorded spawning if larger and more reef areas are surveyed.

Coral expert Chou Loke Ming, an adjunct research professor at the Tropical Marine Science Institute, said corals spawn at the same time to ensure successful fertilisation.

Eggs and sperm released into the water join to form free-floating larvae, which float until they find a suitable home - usually a hard surface they can latch on to.

"Many of the eggs, fertilised eggs, or larvae are sought after by fish because of the rich nutrition they provide. That's why spawning releases very large numbers, so that some will survive the perilous period until they settle on suitable substrates," said Prof Chou.

For Mr Stephen Beng, chairman of the marine conservation group of the Nature Society (Singapore), witnessing the event here was a special moment that surpassed his experiences watching coral spawn in places like Tioman, Dayang and Christmas Island.

He joined researchers from NParks on a dive to monitor the event on Wednesday.

"Even though this year's spawning was less intense compared to previous years', watching our corals reproduce sent feelings of joy.

"The circle of life always brings hope for the future, but we mustn't be complacent with doing our part to address the many threats our reefs face daily, such as climate change and pollution."