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Australia

Medical Q&A

Every year in November, one of nature’s greatest spectacles takes place - the annual mass coral spawning event on the Great Barrier Reef. It is an incredible sight to experience, and now, more than ever, its significance is profound, as Deborah Dickson-Smith explains

PHOTOGRAPHY: INDIVIDUALLY CREDITED

Having said that, here on the Agincourt Reef, in the last four years, since the last major bleaching events in 2016 and 2017, the corals have been growing beautifully, the reef is regenerating very well, but we are worried about the long-term health of the Reef

Right now, the world’s eyes are on the Great Barrier Reef – the best known and best-loved coral reef in the world. While we worry about the impact of climate change on the reef’s extraordinary diversity, scientists and tour operators look to this annual event as an indication of the Reef’s resilience.

Recently, UNESCO fired a warning shot to the Australian

Government, declaring the Reef endangered, which makes this year’s event all the more significant. I interviewed a few Great

Barrier Reef custodians about the annual coral spawning event and what it means to them. Master Reef Guides Glen

Burns (Quicksilver), Sam Gray (Reef Magic), Eric Fisher (Reef

Magic) and Pablo Cogollos (Sunlover) provide some inspiring insights into this event.

What is it like to witness the spawning for the first time? Sam: The first time you witness coral spawning you really have no idea what to expect. You may have heard about these underwater snowstorms and watched a documentary, but nothing will prepare you for sitting at depth, in the darkness and silence waiting with anticipation. You patiently watch the coral and see the build of the buds, getting ready to release. Then slowly the world around you is in a flurry as spawning begins. Bundles of red, orange and yellow slowly floating their way up to the surface, some of the corals look like they are smoking as they release their gametes, and you notice that the same species are spawning at the same time while others wait patiently for their turn as they reproduce on different days to prevent the creation of hybrids. It is a magical and otherworldly experience!

Glen: To witness it for the first time is really very exciting. I still get excited, and I’ve seen it many, many times, but the first time I saw it was back in the early 1980s, and it was here off the coast of Port Douglas. I was in the water at about 9pm and I remember coming around the corner, and here were some tiny pink balls, floating up from the coral. Look at that. It’s just like I’d seen in an earlier documentary, and I thought ‘I’m actually getting to witness the coral spawning’, it was really very exciting. After about 20 minutes, I came around the next corner and the ocean was just full of coral spawn. No matter where you shone your torch, you lit up millions of these tiny pink spheres, all slowly floating to the surface. It was really quite enchanting and very, very exciting.

Pablo: Witnessing the coral spawning event for the first time is a humbling experience. Seeing the corals that you care about in the most-important night of their year, a night that is important for their survival, is an incredible experience. And it’s not just the coral spawning that makes this night exciting. It’s all the marine life that aggregates for a feeding frenzy. The whole experience makes you feel really small and at the same time a part of it. When you start to see this cloud of pink and yellow eggs and sperm all around you - it looks like upside down snow as they rise to the surface! It is the highlight of the year for me.

Coral polyp Corals ready to be transplanted

In the years that you have witnessed this annual event, have you noticed any changes? Glen: It’s never quite the same twice. There are variables in the system. It happens over several nights, usually three or four nights after the full moon, and it depends which night you are there. if you’re lucky enough to be there on all nights, you might find that some of the corals are spawning on that first night. The branching corals might go first, or the plates. The next night you might witness the boulder corals spawning, which look quite different, as the gametes come off like smoke, so it looks like these massive boulder calls are steaming, underneath the water, a spectacular sight.

We are now able to measure the success of each year’s spawning event with greater accuracy. We have divers out here. We have researchers from James Cook University, University of Technology in Sydney and the Institute of Marine Science (AIMS). We have the Master Reef Guide network. It’s very exciting for biologists. We all love to get out there and watch the coral spawning.

Pablo: After the coral bleaching events of 2016 and 2017, we saw that the stressed corals did not spawn and that year the event was not as good, but since then, the event has been building and in 2019, we witnessed one of the best events I’ve ever seen on the Reef.

Ready for the coral spawning

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Eric: The annual mass synchronised coral spawning on the Great Barrier Reef is a good example of a significant biological event co-ordinated by several environmental rhythms operating over several temporal cycles.

This event happens every year on coral reefs and although there are environmental cues, they most likely entrain an internal biological clock within the coral polyp. This could explain the temporal differences between species on spawning nights. Even if corals have been stressed through mass bleaching, they still have the capability to spawn. For example, last year in the lagoon near Reef Magic Cruises Marine World, 67 per cent of the corals bleached. However, over 70 per cent of corals, both hard and soft, spawned on the fourth and the fifth night following the full moon.

At present there is no real measure of how many egg bundles are produced on a spawning night but measuring the settlement rate of new coral recruits is an indication of how good the event has been.

How significant is this event as a measurement of the Great Barrier Reef’s health? Eric: The mass broadcast spawning event is a significant measure of a reef’s health for two broad reasons. Firstly, for the event to happen you need healthy coral and the more

Corals ready to spawn healthy corals you have, the greater number of offspring are produced. Like all reproductive events this is the creation of new life and inherently super important, but this ability of a healthy reef to deliver new coral recruits to another healthy reef through natural hydrodynamic processes is what makes this spectacular event an awesome piece of arsenal in coral reef resilience. Glen: This is how the reefs are constantly regenerating themselves. We are all very worried about the future of the Great Barrier Reef. Having said that, here on the Agincourt Reef, in the last four years, since the last major bleaching events in 2016 and 2017, the corals have been growing beautifully, the reef is regenerating very well, but we are worried about the long-term health of the Reef. One of the ways that the Reef is going to be able to maintain itself is with this annual coral spawning event. It’s crucial.

One of the things that I’m particularly interested to see is what happens on the coral restoration project we’ve been managing at Agincourt Reef, where we’ve been nurturing heat tolerant corals. We know they are heat tolerant corals because the parent colonies had survived the bleaching events back in 2016 and 2017. During last year’s coral spawning, one of the most significant things for me was the fact that these corals that we had nurtured spawned at the same time as the rest of the reef. This is fantastic. This bodes so well.

The big question is, will this year’s new larvae show the same heat tolerance, the same resilience that the parent colonies show? This is what we’re hoping for. This will make a huge difference in how the reef is able to regenerate after these bleaching events, which we expect to see more of in the future.

Happy divers out on the Reef

What citizen science projects can divers participate in to help monitor the Reef’s health? Sam: There are a variety of projects which you can involve yourself in, including the Eye on the Reef Monitoring through the Great Barrier Reef Marine Park Authority (GBRMPA) identifying Key Indicator Species. That is species on the reef that play a role in indicating the health of the environment and conditions on the reef, as well as iconic species.

Glen: With the Eye on the Reef App you can take a photograph, write a comment and send it straight to GBRMPA. The more information we can gather, from as many sources as possible, over the length of the Great Barrier Reef, the better the overall picture we have of the event, and the Reef’s health.

Pablo: Eye on The Reef is the most important citizen science project out there, as it enables an enormous network of contributors to provide data to GBRMPA from the entire length and breadth of the Reef.

Various projects are taking place on the Reef

WITNESSING THE CORAL SPAWNING EVENT A number of Great Barrier Reef tour operators operate night dives and liveaboard trips for divers that are keen to witness this incredible event. Single night trips for the coral spawning depart Cairns over the predicted period, leaving late afternoon and returning after midnight.

Dive liveaboards including Pro Dive Cairns, Mike Ball Dive Expeditions and Divers Den operate over the predicted dates, however these are not dedicated coral spawning trips. Plans can vary depending on weather and time, so if you are interested in a liveaboard experience enquire directly with the company for their plans around the annual event. n • Pro Dive Cairns | Prodivecairns.com • Mike Ball Dive Expeditions | Mikeball.com • Divers Den | Diversden.com.au

Even if corals have been stressed through mass bleaching, they still have the capability to spawn

CORAL LARVAL RESTORATION PROJECT Led by Southern Cross University (SCU), with scientists from James Cook University (JCU) and the University of Technology Sydney (UTS) in 2019, the Coral Larval Restoration Project aims to restore coral populations and re-establish breeding corals on degraded reefs.

Project leader Professor Peter Harrison of SCU aims to increase the scale of coral restoration using innovative techniques. This includes the co-culturing of coral larvae with microscopic zooxanthellae, their algal partners (known as symbionts) and main energy source, in the wild to boost their one-in-a-million chance of survival before being settled on affected reef areas. Corals normally acquire zooxanthellae after they settle.

A collaboration with local tourism operators including Aroona Boat Charters and Reef Magic Cruises has been instrumental in enabling this logistical feat.

Reef Magic’s Eric Fisher heads up Reef Magic’s GBR Biology team, which has been involved in the project.

He said: “The Coral Larval Restoration concept was to capture millions of coral eggs and sperm produced by mass coral spawning event, rear coral larvae for five to seven days and then perform a targeted release of larvae onto heavily degraded sections of the Reef.

“In 2019, an exciting large field experiment was conducted on the sundeck at the Marine World Pontoon to provide coral larvae with a boost to help them survive these early parts of their life cycle. Marine World became the largest Reef Lab in a tourism operation where large tanks containing 3.2 million larvae were given 1 billion microalgae, which acted like battery packs of extra energy to ensure their survival. Some of the algae were thermally-tolerant species with the aim to help the coral larvae be resilient to warming ocean temperatures.

“After a week the mature larvae were released onto areas of reef at the precise time they are ready to settle on a hard stable substrate and develop into a baby coral. In 2018 this was carried out under large mesh settlement sheets at Vlasoff Cay. In 2019, a variety of delivery methods were trialled on impacted sections of Moore Reef which included settlement sheets, divers and specialised robots. This project led to a very impressive mass release of 28 million coral larvae at once! All these sites will be regularly monitored in the future to evaluate the success of these trials.” www.gbrbiology.com

Throughout the year, around the coast of Australia, several significant marine life events take place. The events, which attract thousands of participants, are usually centred around one thing: survival. Whether that’s aggregating to breed, feed or get it on. From the world’s largest aggregation of giant cuttlefish in Whyalla to the world’s biggest orgy on the Great Barrier Reef, here are our top four marine events in Australia.

1. RED CRAB MIGRATION (PLUS BONUS WHALESHARKS) Where: Christmas Island, Australia’s Indian Ocean Territories When: November to December Every year on Christmas Island, at the onset of the wet season, approximately 60 million red crabs leave their forest homes and migrate to the shoreline to mate and spawn. This huge migration all but shuts the entire island down, with many roads closed, and an elaborate system of crab tunnels (and even a bridge) diverting crabs away from the main roads.

In the morning and late afternoon around the last quarter of the moon, the egg-laden females descend from the terraces to the shoreline. They pack into shaded areas above the waterline at densities of up to 100 per square metre in places. The females usually release their eggs into the sea toward dawn, around the turn of the high tide. BONUS: The release of several billion crablings attracts migrating whalesharks, who visit here each year between November and April for a feast. 2. GIANT CUTTLEFISH AGGREGATION Where: Whyalla, Eyre Peninsula, South Australia When: May to August These ‘chameleons of the sea’ are one of the largest species of cuttlefish found, reaching up to 60cm in length and weighing up to 5kg. The migration by these creatures to these waters is for the sole purpose of spawning. Every year they come in their tens of thousands to mate and reproduce, in the process creating an amazing spectacle of cunning games, predation, underwater light shows and colourful kaleidoscopic displays.

It is believed they congregate here in such large numbers as it is the only area in the vicinity with rocky ledges suitable to lay eggs.

3. SPIDER CRAB AGGREGATION Where: Port Phillip Bay, Victoria When: May or June Unsurprisingly, crabs without fully formed shells are vulnerable to predators. So instead of facing that danger alone, they tend to moult together in a sheltered area. In the case of the crabs of Victoria’s Port Phillip Bay, the moulting animals don’t just huddle up - they pile up sometimes tendeep. In this vulnerable state, the crabs attract a feeding frenzy. According to Parks Victoria’s chief conservation scientist Dr Mark Norman: “Usually within a couple of hours of shedding they’re just firm enough to be able to start walking. But while they’re at their most vulnerable, it is a feeding frenzy for predators like cormorants, Pacific gulls, octopus and stingrays.” Only when the full moon approaches, does it become clear whether to head to Rye, Blairgowrie, St Leonards or Queenscliff to witness this natural phenomenon.

4. CORAL SPAWNING ON THE GBR Where: The Great Barrier Reef When: Mid to late-November One of the most-spectacular events to occur on the Great Barrier Reef is the annual synchronised spawning of corals. In simple terms, coral spawning is the reef having sex. Coral polyps simultaneously release egg and sperm bundles that they’ve spent months growing into the ocean for external fertilisation.This happens in a mass event annually often affectionately named the world’s largest orgasm on the world’s largest organism. During this time the Great Barrier Reef is transformed into an underwater spectacle resembling the inside of a snow globe. n

To witness any of these incredible Big Days Out, contact the team at Diveplanit Travel for more information. Diveplanit.com Email: enquire@diveplanit.com Phone: 1800 607 913