An ancient light-sensitive gene has been isolated by researchers from the ARC Centre of Excellence for Coral Reef Studies (CoECRS) that appears to act as a trigger for the annual mass spawning of corals across a third of a million square kilometres of Australia’s Great Barrier Reef, shortly after a full moon.
The genes, known as a cryptochromes, occur in corals, insects, fish and mammals – including humans – and are primitive light-sensing pigment mechanisms which predate the evolution of eyes.
In a new paper published in the international journal Science on October 19, 2007, the team, headed by Marie Curie Scholar Dr Oren Levy of CoECRS and the University of Queensland, reports its discovery that the Cry2 gene, stimulated by the faint blue light of the full moon, appears to play a central role in triggering the mass coral spawning event, one of nature’s wonders.
Professor Ove Hoegh-Guldberg, who leads the University of Queensland laboratory in which the genes were discovered, said “This is the key to one of the central mysteries of coral reefs. We have always wondered how corals without eyes can detect moonlight and get the precise hour of the right couple of days each year to spawn.”
What allows corals to spawn simultaneously along the immense length of the Great Barrier Reef – and also in other parts of the world – has been a scientific mystery till now, though researchers knew that tide, water temperature and weather conditions played a part, says Dr Levy. However the remarkable synchronisation of spawning occurring all along the Reef immediately following a full moon suggested that moonlight was a key factor.
Exposing corals to different colours and intensities of light and sampling live corals on reefs around the time of the full moon, Dr Levy found the Cry2 gene at its most active in Acropora corals during full moon nights. “We think these genes developed in primitive life forms in the Precambrian, more than 500 million years ago, as a way of sensing light,” he explains. “The fact they are linked with the system that repairs damage from ultraviolet (UV) radiation suggests they may evolved in eyeless creatures which needed to avoid high daytime UV by living deep in the water, but still needed to sense the blue light shed by the moon to synchronise their body clocks and breeding cycles.”
“They are, in a sense, the functional forerunners of eyes,” Professor Hoegh-Guldberg said. In humans, cryptochromes still operate as part of the circadian system that tunes us to the rhythms of our planet, though their light-sensing function appears lost to us, he went on to explain.
“They play important roles in regulating the body-clocks of many species, from corals to fruit flies, to zebra fish and mice. The proteins they produce are similar to those in humans and other mammals, though they appear to function more like those in the fruit fly,” says Professor David Miller of CoECRS and JCU.
The coral cryptochrome genes were initially identified by Dr Levy and Dr Bill Leggat working with Professor Hoegh-Guldberg (UQ) on Heron Island. Prof. Miller and Dr David Hayward, of the Australian National University, were able to add information on the coral cryptochromes from a large library of coral genes that they have been compiling (so far they have catalogued about 10,000 out of an estimated 20-25,000 genes in coral), and leading circadian clock biologists from Bar-Ilan and Tel-Aviv Universities in Israel played important roles in interpreting the data.
Whether they have anything at all to do with human associations between the full moon and romance is not known, but cryptochromes probably still play a part in our body clock.
and this from the Cayman Island News :)
and a divers journal :)
Mass coral spawning at the East End of Grand Cayman
A 2003 Divers Report on our first ever dive witnessing Coral Spawning in the Cayman Islands
By Dr Alexander Mustard
It is always exciting news to tell about our experiences successfully predicting and observing mass coral spawning for the first time on Grand Cayman. Since the early studies of coral reefs, scientists thought that most corals reproduced by brooding their larvae and releasing them slowly through the year. The world already knew Spielberg’s ET before we learned the truth about corals. Most corals reproduce by releasing eggs and sperm into the water, the reason everyone had missed it is that corals only spawn on a couple of days during the year. It only lasts about half and hour and it happens at night! No wonder it took so long to be discovered.
Ever since coral spawning became well known people have been trying to see it in Grand Cayman. But everyone I have asked has told me they have looked and looked and never seen it. Cayman, apparently, has its own rules. To figure this out I went through all the Caribbean spawning reports I could find, I looked at the currents in the Caribbean and came up with my own predictions!
I was hardly brimming with confidence on the first evening, so Steve and I took the boat out alone. Best not to make everyone else suffer on my hunch! The moon hadn’t risen, the wind had dropped right down, and the ocean was glassy smooth and inky black. “It’s as if Mother Nature knows that tonight’s the night” Steve commented. After about 30 minutes in the water I spotted the first signs that our luck was in. About 30 minutes later we were rewarded by a decent display of spawning from staghorn coral! And my prediction was just 45 minutes out. After many years, we had seen coral spawning in Cayman.
Now filled with confidence we took a full boat out on the second night and were rewarded with an astonishing display. Early in the dive two species of gorgonian were spawning, my predictions said nothing about that! Then the staghorn went again, and one of the divers even saw an elkhorn coral spawn. But the best was still to come, Star coral is the dominant species on the site and it spawned within 3 minutes of my prediction. In a little over 10 minutes about 80% of it had spawned. Each tiny polyp releases a bundle of eggs and sperm and these filled the water floating slowly to the surface. It was like diving in the bubbles of Champagne and the water was so thick with the bundles that I couldn’t even find my way back to Nauti-Cat! We all went out again the next night and again the gorgonians, brain coral and two species of star coral spawned, although at slightly less spectacular levels than the night before.
All in all it was a fantastic experience. I am still feeling very chuffed that my predictions were spot on. Seven species in three nights… I can’t wait to head back again every year.
The big day
A 2004 Divers Report on Coral Spawning in the Cayman Islands
By Dr Alexander Mustard
As a child Christmas Day was always my favourite day of the year. But waiting for it… that was agony. Huge anticipation was always tempered with concern that maybe this year I hadn’t been well behaved enough to get on Santa’s “Good Children” list! But I guess that just made the actual day even better. As an adult, I thought that this excruciating mix of excitement and apprehension over a particular day were gone from my life. That was until I started studying coral spawning.
Regular divers of this Ocean Frontiers will know that in 2003 Steve Broadbelt and I were the first people to correctly predict, observe and photograph mass coral spawning in the Cayman Islands. Since then I have been counting down the days until September 2004 to see it again. But the opportunity also meant I would find out whether last year we were lucky or whether I could actually forecast the big day reliably. Just to raise the stakes, and to get my nerves really jangling, a group of British divers had come to Cayman specifically for the event. I wasn’t looking forward to climbing back on the boat after the dive if it was a dud! Thankfully the corals spawned right on cue, everyone in the group saw the action and a round of reserved British applause greeted me when I surfaced! Far more exciting was that we saw much more spawning this year, again spread over three nights, and we added first time observations of two species of hard coral and at least two species of gorgonians, expanding our dataset to cover 10 species.
My personal favourites from 2004 were seeing Elkhorn and Giant Star corals spawning for the first time. In the 1980s Elkhorn coral was nearly wiped out by white band disease and seeing it spawn successful gave me a real buzz. The big branching colonies are pretty spectacular when they go off too. Giant Start coral differs from most other hard corals because it is not a hermaphrodite and instead has separate sexes – some colonies are males the others females. This means that instead of all colonies releasing bundles of eggs and sperm, male colonies squirt out streams of sperm, while females explode with a dense cloud of eggs! Seeing such a different type of spawning behaviour was definitely a highlight.
One of the other big differences this year was that we witnessed a massive gorgonian spawning event. Last year two species of gorgonians were spawning sporadically, while this year at least 4 species were very active filling the water column with their white eggs for over an hour. The result is an incredible sight, like a thick underwater blizzard.
So many underwater experiences are there ready and waiting for us when we choose to dive. Coral spawning is so different – for once we must dive to nature’s rhythm to have a chance of seeing the show and our uncertainty of whether this really is the big day is a key part of the experience. Every year Ocean Frontiers run special trips to coincide with the spawning, and if you want an experience that will make you look at Cayman’s reefs in a completely new way, I hope you will join us at the East End. Despite our 100% record I cannot 100% guarantee that the corals will spawn, but then I would not want it any other way.
Its that time again
A 2006 Divers Report on Coral Spawning in the Cayman Islands
By Dr Alexander Mustard
They are certainly my favourite few days in Ocean Frontiers’ calendar – a handful of very specific nights during September when for once we time our dives to nature’s rhythm and see the corals of the reef burst into effervescent life and spawn. Over the last few years our predictions have been so accurate that we often joke that the corals must spawn every night of the year, because every time we go out and look they are spawning! But in reality it is more like searching for a needle in a haystack.
The adventure started back in 2003 when Steve Broadbelt and I were the first people to correctly predict, observe and photograph mass coral spawning in the Cayman Islands. Back then it really was a voyage into the unknown, but now we are much more confident often correctly predicting the spawning to the nearest minute! That said it is never 100%, and the uncertainty of will they or won’t they always adds a lot of excitement to every coral spawning dive. 2006 will be our forth year of butterflies in the stomach diving.
To the untrained eye last year’s event was as massive as usual, with coral after coral releasing a blizzard of egg/sperm bundles into the water. The most abundant coral species, Star Coral, spawned vigorously in 2005, but a couple of the species we had seen spawn in previous years did not spawn last year. These notable absentees were Elkhorn and Staghorn corals, and the most likely reason is that they were putting all their energies into growth.
Both Elkhorn and Staghorn corals are fast growing species that live exposed on top of the reef. They have a live fast, die young philosophy as their precarious position and branching structure make them susceptible to damage from storms and hurricanes. And that is exactly what happened in late 2004 after that year’s spawning event. From a scientific perspective it will be fascinating to see if they have recovered enough from Hurricane Ivan (2004) to spawn again this year.
An article published in Sport Diver UK Magazine
By Dr. Alexander Mustard
Mass coral spawning is one of the ocean’s most illusive sights; the majority of corals only spawn once a year, at night, and the whole show is done and dusted in less than 15 minutes. Even marine biologists only learned how it happened during the 1980s. It may be rare, but the spectacle is astonishing. A coral spends most of the year doing a good impersonation of a rock but on this one night the whole reef explodes into effervescent life. Seeing it remains a gamble, but Alexander Mustard fancied the odds
It was a night dive just like the many others I have enjoyed on the East End reefs on Grand Cayman. That was the problem, this wasn’t supposed to be just another night dive. I glanced down at my watch, it flashed back 20:20, indicating we had been in the water for fifteen minutes. In truth, this dive had started long before my giant stride from the boat, when I made a leap of faith that led to me buying plane tickets and flying across an ocean to be right here, right now. My eye was caught by a bright blue hunting octopus, I ignored it and I stared again at the coral in front of me. “Come on! Come ON!” Nothing. 20:26. The sun had set more than two hours ago.
20:31. I was expecting to see the first signs of spawning ten minutes ago and as each minute passed it became more likely that tonight was not the night. Coral spawning predictions are best guesses based on experience, and nobody had ever reported mass spawning in Grand Cayman before. In the hustle of the last hour of loading the boat, kitting up and jumping in, I had forgotten how much the odds were stacked against us, but now those thoughts returned and my stomach felt hollow. I had staked time, effort and money on being here. Maybe we were to late? Maybe the corals had spawned earlier in the evening? Maybe they had spawned yesterday? Maybe they had spawned a month earlier, along with corals from Florida to Puerto Rico? Maybe they just don’t spawn in Cayman? I looked at my watch again. Still 20:31!
Our target species on this night was staghorn coral, a species that was once widespread in the Caribbean, but along with the closely related elkhorn coral, was decimated during the 1980s by white band disease. In many areas both species are now extinct, but on the East End of Grand Cayman you have the chance to dive back in time and see them in dense thickets. If tonight went to plan we were going to see the underwater equivalent of giant pandas mating!
20:33. I was now feeling guilty for dragging my buddy into the water. Steve Broadbelt is the co-owner of Ocean Frontiers dive centre and like me has a keen interest in marine life, something that is clearly reflected in how his dive centre operates. Steve had been trying to see coral spawning for many years, and I had been bullish about our chances to persuade him to try again. We were optimistic when we left the dock, Steve noting of the conditions “only rarely does it get so glassy calm out here, it’s as if Mother Nature knows that tonight’s the night”. Now I was less confident. Steve was on the other side of the reef spur, which was silhouetted by his light. The moon was yet to rise and we had chosen weak torches so as not to put the corals off. The water was inky black and blood hot. It was claustrophobic and uncomfortable, like wearing a suit that is too thick at a summer wedding. I wasn’t relaxed and I tried to concentrate on the coral.
Suddenly the staghorn coral looked different. Perhaps I had been staring at it for so long that my eyes were inventing new patterns. I screwed up my eyes, blinked, and stared again. As I inched closer I could see the shape of the polyps was subtly, but definitely changing, as beige bundles a few millimetres across were beginning to dome up from within the polyps. I raced to over to Steve, flapping frantically to get his attention and dragged him back to the coral. I could now see the change from several metres away, even the colour of the colony was different. Staghorn, like many corals, is a hermaphrodite, being both male a female at the same time and these bundles were made up of eggs laced together with sperm. I checked the next colony and the next, everywhere I looked staghorn coral was preparing to spawn.
Steve and I exchanged perhaps the most cheerful OK signs ever made and a few less traditional underwater communication gestures that clearly indicated spawning was definitely on! About 30 minutes later the bundles started to burst free. The buoyant fat filled eggs slowly pulling themselves away from the spiky branches of the staghorn. Within a couple of minutes there was a steady stream of bundles rising from colonies across the reef. It was like diving in a glass of Champagne, the bundles looking just like tiny bubbles. They made an intoxicating sight.
I’m sure that you know what happens if you smile while you are diving? As the corners of your mouth go up, your cheeks rise, your mask no longer fits and water gushes in and rushes straight up your nose. Well, just at this moment I really did not care. Although I was now coughing water out of my regulator, nothing could dampen my spirits. Steve and I finned around with the joy and disbelief of children running in snow for the first time. All around us coral bundles were heading to the surface, where they would break open so eggs could be fertilized and start the next generation of staghorn coral, and with a bit of luck help drag this species back from the brink.
Back on the boat I sat contented in the warm evening air, knowing that success with the staghorn meant we now had even odds for the main event. The most abundant coral on the East End of Cayman is star coral, with large plate and boulder shaped colonies, and we were expecting these to spawn a day or two after the staghorn. Their large size promised an even more spectacular spawning and by the next evening we had a full boat of 12 divers eager to share the experience. As we splashed into the water we were greeted by two species of gorgonian corals spawning. This was not in the plan. Gorgonians have separate sexes, with some colonies being male and others female, and all around female colonies were busy releasing small white eggs. Male gorgonians were probably releasing sperm but this was too small to see. I took a few photographs of the lady gorgonians, but in general I was trying to move about as little as possible to save my air and give myself the longest observation window. The last thing I wanted was to be running low for the main attraction.
I shouldn’t have worried because bundles started to appear on the star corals right on cue, just three minutes before predicted. Half an hour later spawning began with a bang. Unlike the staghorn and the gorgonians that released a steady stream, the star coral true to its name is a much more spectacular performer and releases all its bundles within a few seconds. Large plates of star coral, about the size of a garage door, were releasing their bundles in waves that spread across the surface of the colony like a blush. Initially the bundles did not float away, instead hanging an inch or so above the coral. After a few moments the bundles found their buoyancy and floated upwards in a dense plume and filled the water in every direction I shone my torch. The masses of bundles rising from star coral colonies reminded me of the ghosts that float up out of cartoon characters following a TNT encounter. But these were spirits of reincarnation, givers of new life to the reef.
The intensity of spawning was shocking, visibility dropped from about 25m to about 5m in about 2 minutes. It was like diving in a blizzard, with the tiny bundles drifting slowly to the surface like snowflakes. Suddenly diver silhouettes were only torch beams in the murk, and I could no longer see the strobes marking the position of the dive boat. I headed back down to the reef, relieved to have something solid to look at. Brain corals were also releasing bundles from their grooves, and deep red brittlestars climbed high on top of corals and spawned. The explosion of activity was astonishing, the true coral animals had been revealed, and I knew that on the other 364 days I would never look at them the same way again. I checked my contents gauge, which was buried in the red, and reluctantly left this tropical, underwater snowstorm behind.
Safety stopping for a couple of minutes at 5m, my mind turned to Grand Cayman’s famous attraction Stingray City, a shallow dive site inhabited by large rays. Stingray City, like so many of diving’s experiences is available “guaranteed” for us to enjoy everyday of the year. Coral spawning is a different experience; for once we had been forced to adopt some humility and dive to nature’s rhythm. Strange as it sounds, it was a pleasing thought that we would have to wait 12 months to see this show again.