Palau Coral Experement

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Catching corals' spectacular moment
By Andrew Luck-Baker
BBC Radio 4, Palau




Luke's reef: Reared larvae will come here once they are ready to settle



The coral reefs in the tropical western Pacific are at the brink of one of the most spectacular and significant nights in their annual life cycle.

By the light of April's full moon on Sunday or, quite likely a night or two after, corals will be mating en masse.

Along the length of the island archipelago that makes up the Republic of Palau, millions of coral colonies will simultaneously release billion upon billion of eggs and sperm into the dark waters.

An hour or so after sunset, each spawning coral will discharge showers of sex cells, packaged in orange and pink blobs.

They will rise to the surface in such huge numbers that they may form oily slicks metres long.

If the sea conditions are right, spawn slicks can coalesce to be large enough to be visible from space.

Depressing need

Once on the surface, the packages burst open, liberating eggs and sperm for fertilisation.

Countless free-swimming coral larvae then develop and three or four days later, a few will have survived long enough to make it to the sea bed.




There they attach to a suitable hard surface and develop into single baby coral polyps. The next generation of corals on the reefs will be launched.

A team of marine biologists from Australia, Britain and the Philippines has come to Palau to take advantage of this wonder of nature in the cause of coral reef restoration.

The scientists are here to investigate the potential of an experimental technique known as coral seeding - in other words, collecting some of the spawn from mass mating events and using it to promote the growth of new corals on reefs in need of rescue.

The reefs around Palau are in good shape but elsewhere throughout the tropical world, many coral ecosystems are in a parlous state.

Plenty spare

Pollution, over-fishing and coral bleaching events, which are caused by marine heat waves, have reduced the amount of coral to the point where these naturally bio-diverse habitats are at varying degrees of degradation.

Many are nearing ecological collapse - some have gone forever, already.


Acropora is an important reef-builder and is common here

However, many reefs might be salvageable if they are first protected from pollution and overexploitation, and then are seeded with some surplus spawn from more vibrant reefs.

Most of the eggs and larvae from a mass spawning event are eaten or die before they get an anchor hold on the sea bed, so there is plenty of spawn to share around.

In the coming experiment on Palau, the scientists will not be using coral spawn produced on the open reefs.

Partly for practical reasons, they will harvest their spawn under more controllable conditions at the laboratory of the Palau International Coral Reef Center.

In the lab

On Saturday, I joined them on a trip to collect 10 dinner-plate-sized coral colonies from Luke's reef about 20 minutes speed-boat-ride from the Reef Center.

James Guest, from the University of Newcastle, UK, and Maria Vanessa Baria from the University of the Philippines dived to the sea bed, armed with hammers and chisels.

They were after a particular species of branching coral which forms large tables or shelves as it grows. It is this type which is one of the most abundant and most important reef builders.

It takes a few taps at the stony stalk base of each colony to break them free. Waiting on the boat to receive the corals was Andrew Heyward of the Australian Institute for Marine Science - one of the first biologists to describe the phenomenon of coral mass spawning in the 1980s.

The colonies were put straight into tubs of sea water, and once the tenth was on board, we headed back at a high rate of knots to the Reef Center.

Back at the Center, the coral were transferred with speed to larger tanks, filled with constantly refreshed seawater.

Setting up home

Now there's a lull before the spawn. The main event could happen Sunday or Monday or Tuesday night (Palau time). And some species will synchronously spawn the day after others.

When the captive corals in the lab release their eggs and sperm, the contained spawn will be transferred to children's paddling pools floating in the sea next to the lab.


The spawning for these corals will occur in laboratory tanks

Over the following few days, the researchers will check the developing larvae to see how many are mature enough to settle down and become fixed baby coral polyps.

When sufficient numbers are good to go, the team will take the batch of larvae back to the reef and pump them over areas of potential colonisation.

The new homes for the larvae are artificial reef balls placed there specially for the purpose. They are domes of limestone concrete about a one metre wide and high.

Before the larva can be introduced, the reef balls will have to be covered so the larvae don't just float away.

Big question

So the team will dive the five metres to the sea bed and erect two-man camping tents made of fine mesh over each artificial reef structure.

The baby corals will travel from the boat through the zipped door of the tent via a hose pipe. Andrew Heyward says the aim of this experiment is to be "low tech or no tech".

He feels this approach is vital if the technique of coral seeding is ever to be used on any scale in developing countries.


The approach has to be low-tech to succeed, the scientists believe

Twenty-four-hours later, the team will check to see how many of their "seeds" have settled by removing small tiles they've placed on the reef balls. They will do that again in a few months and after a year.

Each time they will compare the number of young corals with those on tiles from control balls which would have been settled by larvae born in the mass spawning on the reef.

Andrew Heyward points out that loading the dice in the larvae's favour before they settle is only part of the issue over whether coral seeding will work to restore reefs.

"If you boost the number of larval corals settling on a coral reef, so what? Does it make any difference to the longer term compared to an area where you did nothing?"

The answer will emerge in the next 12 months following this week's frenzy of mass reproduction on the reefs of Palau.

 

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Coral spawn turns Palau seas pink
By Andrew Luck-Baker
BBC Radio 4, Palau

Dense rafts and slicks of pink coalesced all around the boat

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.

I was snorkelling in what looked like a reverse snow storm of orange and pink particles

Andrew Luck Baker

Catching a spectacular moment

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.

Back on the boat, Peter Mumby, also from Exeter, estimated it was about half hour from the time the first colony unleashed its spawn to the time the last one spewed forth to multiply.

The time it all started was almost exactly the same as the moment the mass spawning began the previous year he'd visited Luke's reef to video the event.

Somehow all the colonies are running with synchronised biological clocks.

In some way not really understood by scientists, they are entrained by factors such as light levels and durations from the Sun and the Moon over a year and over individual months. The result is they spawn within minutes of each other.

That synchrony is vital if you reproduce as most corals do. The majority are hermaphrodites which release their eggs and sperm into the open water for fertilisation.

The chances they will have any offspring would be terrible if they did not have tight coordination so that eggs of one colony meet sperm from another.

By now, at the surface, the number of egg and sperm bundles was staggering. Dense rafts and slicks of pink were coalescing all around the boat for as far as we could see. The ripe smell of taramosalata hung in the air.

And we could see the water below the floating spawn begin to cloud up. Seawater was penetrating every spawn particle - breaking apart separate compartments of eggs and sperm. The visibility was falling as billions of coral sperm were liberated for fertilisation.