With over 100 people logging into the reefside chat on December 9, there were too many questions to answer in the time available. Not to be undone by the tyranny of time, LIRS Director Anne Hoggett has provided written answers to many of the questions that did not get airtime on the night. The answers are based on her experience at LIRS over the past 30 years and they are her personal views. Some questions involved duplication and these have been rationalised a little. Many thanks to everyone that participated. It is great to see such strong interest in the great science being done at this wonderful place on the Great Barrier Reef.
Beyond general awareness of the GBR do you think the public knows enough about the reef to help protect it? What more can be done to raise that awareness?
Most Australians have a soft spot for the GBR but it’s not something that’s front and centre in their minds. They all have lives to live and lots of other things to worry about that affect them personally in the short term. I think that the best thing that we can do as individuals is to talk about it whenever we get the chance – to friends, at school, at work, to extended family. The more that people spread the word and show their own concern (especially young people), the more others may start to care. There’s probably not much point trying to change the views of those who see no need for change at all and think it’s all a beat-up. But a large proportion of the population seems to be either curious but doesn’t know what to do, or dubious about the need for change but willing to accept it when provided with information. That’s where personal, genuine and knowledgeable interactions can help. That probably sounds a bit weak but it’s the best I have. Movements like Extinction Rebellion also have their place and they do reach some people but can turn off others.
Can you provide an update on the approach of the Queensland and Federal governments to marine reserves and heritage areas in Australia?
The GBR Marine Park Authority is a federal government agency that oversees protection of the GBR and the Qld government is involved in its day-to-day management. Both governments show appropriate levels of concern and respect for it, although resourcing is always an issue. There are fisheries-related issues in Qld that could be better managed by the state (e.g. sharks, trepang) but my feeling is that the marine protected areas in Qld are safe and relatively well-managed. A large number of offshore marine protected areas all around Australia were established by the federal govt some years ago, including the Coral Sea Marine Part that is seaward of the GBRMP. There has been some talk of protections being removed or reduced in some of these new reserves, but I’m not up on the details. Marine Parks do work! You only need to snorkel between North Steyne and Shelly Beach at Manly in Sydney to see the benefit of marine protected areas. Twenty years ago, that area was a wasteland due to overfishing. Now, it’s full of life.
Given the cyclones and bleaching events is it still going to be a great underwater experience visiting Lizard Island?
Yes, it’s definitely worth visiting Lizard Island and it’s getting better with every month that passes. Summer is always the scary time because of the risk of cyclones and bleaching but we have all our fingers crossed that we’ll get through this coming Summer unscathed.
Do high levels of diving by tourists place a major strain on the reef?
Tourist diving is well regulated on the GBR and most operators seem to look after the environment well, so I don’t think it’s a strain on the reef. Careless individual divers can have an impact but I think the damage is very slight in the scheme of things.
Thank you for showing the images of the reef over the 3 years. Could you tell us how close the area is to the island itself?
The images were taken near the mooring in Mermaid Cove, on the northwest side of Lizard Island. It’s a beautiful little cove where the coral has bounced back really well from all the disasters in 2014-2017.
Is the likelihood of bleaching low for 2021 because of La Nina?
Possibly, because that brings clouds and rain which cool the water and also reduces stress from sunlight. But even so, NOAA modelling predicts heat buildup by Feb/Mar 2021 that may cause bleaching. It seems that it will come down to the local weather pattern at the critical time.
Do visiting scientists have any estimates of the number of bleaching events that might be expected per decade over the next 20-30 years?
I’ve seen it stated quite often that bleaching could be an annual event by some time in the next few decades. I haven’t seen any paper that sets out the reasoning for that conclusion but I can believe it. Warming that’s already in the system means that corals are close to their upper tolerance limit quite often in Summer now. An unknown is whether corals can adapt naturally to warmer temperatures in such a short timeframe. The annual scenario must assume that they can’t.
Are the corals growing since the bleaching events more resilient to higher temperatures?
The short answer to this is ‘I don’t know’. It’s obviously a very important question and one that’s being addressed by at least one LIRS researcher and probably by a lot of scientists at the Australian Institute of Marine Science, which is very into coral genetics. However, and unfortunately, our observations suggest that new corals aren’t more resilient. Following bleaching in 2016 and 2017, most branching and plate corals were dead in this area. By early this year, new ones had grown to 20-50 cm diameter. The third major bleaching event in five years started in Feb this year and those new corals started to bleach, just as the others did earlier, and a small proportion of them died. The only reason that more didn’t die is that the weather changed in mid-March, just in time to drop the water temperature before irrevocable damage was done.
Are some coral species more susceptible to the warming waters? For example, are the hard corals more likely to bleach than the softer ones?
Both hard and soft corals are susceptible to bleaching but within both kinds, some species are more susceptible than others. Hard corals are the important ones because they’re the main reef-builders whose death affects many other organisms that live there. Within the hard corals, it’s the prettiest ones that are most susceptible – the branching and plate corals. These are the ones that provide great habitat for other reef creatures because they have lots of nooks and crannies for things to hide in. They’re also among the quickest-growing corals, so if they get a chance (including decent water quality and the right temperature range), they can bounce back quite quickly as we’ve seen here at Lizard.
Can zooxanthellae go back to a coral, after being expelled?
Yes indeed – zooxanthellae exist in the water column. If the stress that caused them to be expelled from he coral is removed in time, the coral can take them in from the water column. Recent research here has shown that zooxanthellae can even sort-of hibernate in the sediment, forming a calcareous coat and becoming a grain of sand.
Have you noticed any increase in coral diseases recently?
No, we haven’t noticed an increase, and I think that we would if there was one. There was regular monitoring for coral disease in this area until a few years ago but that research project has concluded. The Australian Institute of Marine Science’s long-term monitoring program records disease outbreaks and they have several sites in this area but no change has been noted in recent years.
What changes have you seen in fish populations over recent years?
When most of the branching and plate corals died in this area after cyclones and bleaching (2014-2017), there was a noticeable decrease in the number of small, coral-associated fishes and a lot of fat, happy predators such as coral trout. Research has corroborated those impressions. Coral-associated fishes vacate corals within five days of their home coral’s death and it’s likely that many of those fish die, even if another live coral is nearby. After the bleaching events, the average size of fishes actually went up in this area. Small fishes were hammered but the large predators weren’t affected and may even have gained benefit by easier access to food. Now that habitat-forming corals have reached a decent size again, it appears that the small fishes have also returned. This must be through recruitment of larvae rather than adults swimming in from other reefs because these little fishes just don’t swim (or survive swimming) those sorts of distances. It highlights the importance of scale and the need to have very large marine protected areas.
Do you have any recommendations for removing fragments or colonies from the reef for lab analysis, without stressing the corals.
Corals, particularly branching ones, are able to recover from fragmentation quite easily. Branches break during storms and can be bitten off by large parrotfish. When researchers do it, it must be under permit from the Great Barrier Reef Marine Park Authority and there are limits on the size and number of fragments to be taken. They usually snap off short pieces of branch tips using wire cutters and that doesn’t seem to be harmful to the remaining colony. The fragment may be retained for analysis (e.g. DNA) or it may be glued back onto the reef using marine cement.
Do corals spawn in a regular cycle so that you can time when you photograph that external fertilisation or do you have to have your camera on the ready for a period of time?
We have a very good idea of when the coral spawning will happen – it’s usually on the fifth night after the full moon in November or December. Whether it’s Nov or Dec depends on when in the month the full moon occurs – if the full moon is early in the month, spawning will probably be in Dec rather than Nov as it was this year. It’s not totally synchronous though, and there’s usually some spawning the night before and the night after, as well as even the month before and the month after. But one night is usually the biggest. Once you’ve got the night right, you just have to go out between 8:30 and 10:30 pm and it happens all around you. It’s truly amazing.
How many babies can a coral spawn?
Good question! A coral colony can be made up of many thousands of coral polyps. In most coral species, each polyp spawns one or more bundles containing multiple eggs and sperm. The number of eggs in a bundle would differ between species, but let’s say there’s 20. If there’s 10,000 polyps in the colony, that’s 200,000 potential babies from that colony if each polyp only spawns one bundle, and I think that many species can spawn several bundles. But eggs are only potential babies. Only a fraction of eggs are fertilised and only a fraction of those survive the larval phase to settle and start a new colony. Sounds like a research project is needed!
How was the recent coral spawning event around Lizard Island? How did it compare to past events?
The coral spawning happened last weekend, right on cue, and it was a good one. Corals have recovered really well in this area following the annual disasters between 2014 and 2017 so there are plenty of local corals big enough to spawn now, and they did. Very different to 2016 and 2017 when there was very little spawning. Researchers have been collecting settlement data and eventually that will be published. The recovery is not uniform – some areas are starting to look fabulous again while others are just beginning to recover. It shows that the reef is still naturally resilient, in this area anyway. The problem, obviously, is how long it can continue to bounce back. Every summer is a nail-biting time now.
What are the main factors that trigger an explosion in Crown-of-Thorns Starfish (COTS)?
This is a really broad and complex question! In brief, COTS have enormous reproductive potential – a single large female can spawn 100 million eggs in a season. With that huge number, a tiny increase in the proportion that survive to adulthood will have a big impact on the size of the adult population. Many things affect survivorship of COTS (e.g. food supply, salinity, temperature, predation) and they have varying levels of importance at different life history stages – larvae, juveniles (which hide in the reef and don’t eat coral) and adults (which do eat coral). COTS larvae are even able to split themselves apart to form two clones from one. We don’t yet know if that’s a big part of the puzzle, but it’s an unsettling thought that this ability might provide a virtually infinite supply of larvae.
From the four recorded outbreaks on the GBR, they occur at fairly regular intervals (14 to 17 years apart) and they start at the northern end of the GBR and move southwards over a decade or more. It seems that corals need to recover to a certain level after the last outbreak before an area can sustain a new outbreak. Reefs in the northern GBR are highly connected to each other due to their water circulation patterns. This means that larvae that are spawned in that area can easily reach nearby reefs, and they’re also retained in that area so juveniles can build up over time. It’s been shown in the lab that juveniles can remain small for up to 6.5 years if they don’t have coral to eat. It seems likely that the number of juveniles builds up over years in the northern GBR, not causing a problem because they’re hidden away and not eating corals. Then, when the coral cover is good, they emerge in big numbers and start to eat corals.
Are you working on any new solutions (or conducting research) to combat possible future impacts to the reef?
The Crown-of-Thorns Starfish research that I touched upon in the talk is directly related to management of future outbreaks. As well as developing methods for detecting the starfish and controlling their numbers, it also involves basic biological research to determine where and when interventions are likely to be most successful. Other research is mostly interest-driven but much of it has implications for management. For example, there’s a lot of climate change related work going on and research into the impacts of noise on reef organisms. All of this information is of interest to reef managers and it’s an incremental process to build up the body of knowledge.
ed. Geoff Shuetrim
LIRRF Trustee