Coral spawn turns Palau pink

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The annual mass spawning of corals on the Palau archipelago in the western Pacific has occurred right on cue.

With Sunday night’s full moon, coral polyps let forth a huge swathe of sperm and egg, to seed the next generation.

The event was short-lived – only about 30 minutes – but so vast in its scale that it turned the sea water pink.

Scientists from Palau, Australia and the UK are studying the practicality of collecting coral larvae to help restore damaged reefs elsewhere.

As we got into the boat for our trip to Luke’s reef, I admit I was not really expecting to see the mass spawning on the exact night of the full Moon.

All the visiting scientists here thought it was more likely the reproductive extravaganza would happen the next evening or the following one – based on what had happened the last two years.

The only person who seemed sure it would happen on cue was Steven Victor, the Palauan director of the Palau International Coral Reef Center. Local knowledge was spot on, as it turned out.

Almost as soon as the boat engine switched off, we got a sense that something might be brewing.

There was a faint fishy whiff in the air, and then in the torchlight, one, then two orange particles – coral spawn – suspended in the water.

Scanning from the other side of the boat, the excitement went up another notch – a steady stream of orange spat was rising to the surface in one small isolated patch.

Main event

Scuba gear was flung on and the marine biologists were overboard. I paddled on the surface with snorkel, mask and diving torch, watching the scientists check the coral colonies on the reef bed five metres below.

The minutes ticked by – lots of them. If our first stream of spawn was the warm up act, was the main attraction having a mighty tantrum and refusing to come on tonight? Apparently not.

Sonia Bejarano, from the University of Exeter, UK, surfaced with an update. A great many of the branching table corals and stag horn corals – the chief reef builders – were close to spawning.

The little egg and sperm bundles were visible in the open mouths of most of the individual coral polyps of each colony.

Depending on the size of the colony, the number of tiny sea anemone-like polyps ranges from hundreds to thousands.

At 8.29pm the mass spawning began. Across the reef, polyps contracted into their stony skeletons. Spawn particles popped out of their mouths.

Because the egg and sperm bundles contain waxy yolk, they are buoyant and rise in the water column.

Within minutes, I was snorkelling in what looked like a reverse snow storm of orange and pink particles. It became thicker and thicker as more and more colonies across the reef fired their latest shots at founding a new generation.

The spawn just kept coming – the sea was becoming a pink soup. Pink was emerging as the dominant colour.

Akin to taramosalata

There was a rising pale rose particle for every cubic centimetre of seawater at least. Above water, the odour of spawn was also thick in the air – it smelt like taramosalata, the pink Greek dish made of fish roe.

I spent most of the time in a state of amazement at the surface but I managed to get down a couple of times to the reef bed to see a colony close-up as it released its spawn.

Profusions of pink blobs, each with a little tail of mucus, wafted from the antler branches of a stag horn colony.

The reef fish were also excited. Earlier most of them were hidden, lurking in dark crevices and overhangs for safety away from night-time predators. But with the spawn bonanza, many threw caution to the winds and came out to feast.