Photos from the field: why losing these tiny, loyal fish to climate change spells disaster for coral

Catheline Froehlich, Author provided

Catheline Y.M. Froehlich, University of Wollongong; Marian Wong, University of Wollongong, and O. Selma Klanten, University of Technology SydneyEnvironmental scientists see flora, fauna and phenomena the rest of us rarely do. In this series, we’ve invited them to share their unique photos from the field.

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If you’ve ever dived on a coral reef, you may have peeked into a staghorn coral and seen small fish whizzing through its branches. But few realise that these small fish, such as tiny goby fish, play a crucial role in helping corals weather the storm of climate change.

But alarmingly, our new research found gobies decline far more than corals do after multiple cyclones and heatwaves. This is concerning because such small fish — less than 5 centimetres in length — are critical to coral and reef health.

Unfortunately, the number of cyclones and heatwaves is on the rise. These disasters have begun to occur back-to-back, leaving no time for marine life to recover.

With the recent push by UNESCO to list the Great Barrier Reef as “in danger”, the world is currently on edge about the status of coral reefs. We’re at a critical stage to take all the necessary measures to save coral reefs worldwide, and we must broaden our focus to understand how the important relationships between corals and fish are affected.

This five-lined coral goby (Gobiodon quinquestrigatus) is taking a break on a coral branch.
Catheline Froehlich, Author provided

Goby fish: the snack-sized friends of coral

In all environments, organisms can form relationships where they work together to improve each other’s health. This is called a mutual symbiosis, like a you-scratch-my-back principle.

In coral reefs, other examples of mutual symbioses include invisible zooxanthellae algae living within coral tissue, small cleaner fish removing parasites from big fish, and eels and groupers hunting together.

While this shark is taking a nap, small yellow fish are hiding under its fin, and it is also getting cleaned by a cleaner wrasse (slender black fish with neon blue outline).
Catheline Froehlich, Author provided

Living on the edge: some fish live inside branched corals, while others live around the perimeter of coral bommies like this.
Catheline Froehlich, Author provided

Gobies that live in corals are small, snack-sized fish that rarely venture beyond the prickly borders of their protective coral homes. The Great Barrier Reef is home to more than 20 species of coral gobies, which live in more than 30 species of staghorn corals.

In return for the coral’s protection, the gobies pluck off harmful algae growing on coral branches, produce a toxin to deter potential coral-eating fish, and reduce heat stress by swimming around the coral and stopping stagnant water build up.

The blue-spotted coral goby (Gobiodon erythrospilus) is holding its position by pushing its front pectoral fins against coral branches.
Catheline Froehlich, Author provided

Paired romance: these lemon coral gobies (Gobiodon citrinus) live in monogamous pairs while also sharing their coral with a humbug damselfish (Dascyllus aruanus).
Catheline Froehlich, Author provided

Even if their corals become stressed and bleached, they remain steadfast within the coral, helping it to survive. Without their full-time cleaning staff, corals would be more susceptible when threatened with climate change.

Unfortunately, just like Nemos (clownfish) living inside anemones, climate change threatens the mutual symbioses between gobies and corals.

Coral gobies in decline

While SCUBA diving, we surveyed corals and their goby friends over a four-year period (2014-17) of near-continuous devastation at Lizard Island, on the Great Barrier Reef. Over this time, two category 4 cyclones and two prolonged heatwaves wreaked havoc on this world-renowned reef.

Coral gobies are often hard to spot, so we use underwater flashlights to identify them correctly.
Catheline Froehlich, Author provided

What we saw was alarming. After the two cyclones, the 13 goby species (genus Gobiodon) and 28 coral species (genus Acropora) we surveyed declined substantially.

But after the two heatwaves, gobies suddenly fared even worse than corals. While some coral species persisted better than others, 78% no longer housed gobies.

Importantly, every single goby species either declined, or worse, completely disappeared. The few gobies we found were living alone, which is especially concerning because gobies breed in monogamous pairs, much like most humans do.

After cyclones and heatwaves, we found a lot of dead corals surrounding pockets of living corals and reef life at Lizard Island.
Catheline Froehlich, Author provided

We surveyed coral and goby survival and often found a lot of coral debris after heatwaves.
Catheline Froehlich, Author provided

Without urgent action, the outlook is bleak

More and more studies are showing reef fish behave differently in warmer and more acidic water.

Warmer water is even changing reef fish on a genetic level. Fish are struggling to reproduce, to recognise what is essential habitat, and to detect predators. Research has shown clownfish, for example, could not tell predatory fish (rockcods and dottybacks) from non-predators (surgeonfishes and rabbitfishes) when exposed to more acidic seawater.

Finding Nemo swimming in anemone in Lizard Island. The bright pink surrounding it is the column of the anemone. Picture the column as your neck and the tentacles as your hair.
Abigail Shaughnessy, Author provided

The bigger picture looks bleak. Corals are likely to become increasingly vulnerable if their symbiotic gobies and other inhabitants continue to decline. This could lead to further disruptions in the reef ecosystem because mutual symbioses are important for ecosystem stability.

We need to broaden our focus to understand how animal interactions like these are being affected in these trying times. This is an emerging field of study that needs more research in the face of climate change.

Here, one of my assistants, Al Alder, is measuring the coral so that we can tell what happens to the size of corals after each climatic disaster.
Catheline Froehlich, Author provided

Several fish that are not coral gobies are still found swimming about even after four years of climatic disasters at Lizard Island.
Catheline Froehlich, Author provided

On a global scale, multiple disturbances from cyclones and heatwaves are becoming the norm. We need to tackle the problem from multiple angles. For example, we must meet net zero carbon emissions by 2050 and stop soil erosion and agricultural runoff from flowing into the sea.

If we do not act now, gobies and their coral hosts may become a distant memory in this warming climate.

Catheline Y.M. Froehlich, PhD Fellow, University of Wollongong; Marian Wong, Senior Lecturer, University of Wollongong, and O. Selma Klanten, Research Scientist, University of Technology Sydney

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Snorkellers discover rare, giant 400-year-old coral – one of the oldest on the Great Barrier Reef

Richard Woodgett

Adam Smith, James Cook University; Nathan Cook, James Cook University, and Vicki Saylor, Indigenous KnowledgeSnorkellers on the Great Barrier Reef have discovered a huge coral more than 400 years old which is thought to have survived 80 major cyclones, numerous coral bleaching events and centuries of exposure to other threats. We describe the discovery in research published today.

Our team surveyed the hemispherical structure, which comprises small marine animals and calcium carbonate, and found it’s the Great Barrier Reef’s widest coral, and one of the oldest.

It was discovered off the coast of Goolboodi (Orpheus Island), part of Queensland’s Palm Island Group. Traditional custodians of the region, the Manbarra people, have called the structure Muga dhambi, meaning “big coral”.

For now, Muga dhambi is in relatively good health. But climate change, declining water quality and other threats are taking a toll on the Great Barrier Reef. Scientists, Traditional Owners and others must keep a close eye on this remarkable, resilient structure to ensure it is preserved for future generations.

Muga dhambi is the widest coral structure recorded on the Great Barrier Reef.
Richard Woodgett

Far older than European settlement

Muga dhambi is located in a relatively remote, rarely visited and highly protected marine area. It was found during citizen science research in March this year, on a reef slope not far from shore.

We conducted a literature review and consulted other scientists to compare the size, age and health of the structure with others in the Great Barrier Reef and internationally.

We measured the structure at 5.3 metres tall and 10.4 metres wide. This makes it 2.4 metres wider than the widest Great Barrier Reef coral previously measured by scientists.

Muga dhambi is of the coral genus Porites and is one of a large group of corals known as “massive Porites”. It’s brown to cream in colour and made of small, stony polyps.

These polyps secrete layers of calcium carbonate beneath their bodies as they grow, forming the foundations upon which reefs are built.

Muga dhambi’s height suggests it is aged between 421 and 438 years old – far pre-dating European exploration and settlement of Australia. We made this calculation based on rock coral growth rates and annual sea surface temperatures.

The Australian Institute of Marine Science has investigated more than 328 colonies of massive Porites corals along the Great Barrier Reef and has aged the oldest at 436 years. The institute has not investigated the age of Muga dhambi, however the structure is probably one of the oldest on the Great Barrier Reef.

Other comparatively large massive Porites have previously been found throughout the Pacific. One exceptionally large colony in American Samoa measured 17m × 12m. Large Porites have also been found near Taiwan and Japan.

Muga dhambi was discovered in waters off Goolboodi (Orpheus Island).
Shutterstock

Resilient, but under threat

We reviewed environmental events over the past 450 years and found Muga dhambi is unusually resilient. It has survived up to 80 major cyclones, numerous coral bleaching events and centuries of exposure to invasive species, low tides and human activity.

About 70% of Muga dhambi consisted of live coral, but the remaining 30% was dead. This section, at the top of the structure, was covered with green boring sponge, turf algae and green algae.

Coral tissue can die from exposure to sun at low tides or warm water. Dead coral can be quickly colonised by opportunistic, fast growing organisms, as is the case with Muga dhambi.

Green boring sponge invades and excavates corals. The sponge’s advances will likely continue to compromise the structure’s size and health.

We found marine debris at the base of Muga dhambi, comprising rope and three concrete blocks. Such debris is a threat to the marine environment and species such as corals.

We found no evidence of disease or coral bleaching.

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The structure may be compromised by the advance of a sponge species across Muga dhambi (sponge is the darker half in this image).
Richard Woodgett

‘Old man’ of the sea

A Traditional Owner from outside the region took part in our citizen science training which included surveys of corals, invertebrates and fish. We also consulted the Manbarra Traditional Owners about and an appropriate cultural name for the structure.

Before recommending Muga dhambi, the names the Traditional Owners considered included:

• Muga (big)
• Wanga (home)
• Muugar (coral reef)
• Dhambi (coral)
• Anki/Gurgu (old)
• Gulula (old man)
• Gurgurbu (old person).

Indigenous languages are an integral part of Indigenous culture, spirituality, and connection to country. Traditional Owners suggested calling the structure Muga dhambi would communicate traditional knowledge, language and culture to other Indigenous people, tourists, scientists and students.

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It’s hoped the name Muga dhambi will encourage recognition of the connection Indigenous people have to the coral structure.
Richard Woodgett

A wonder for all generations

No database exists for significant corals in Australia or globally. Cataloguing the location of massive and long-lived corals can be benefits.

For example from a scientific perspective, it can allow analyses which can help understand century-scale changes in ocean events and can be used to verify climate models. Social and economic benefits can include diving tourism and citizen science, as well as engaging with Indigenous culture and stewardship.

However, cataloguing the location of massive corals could lead to them being damaged by anchoring, research and pollution from visiting boats.

Looking to the future, there is real concern for all corals in the Great Barrier Reef due to threats such as climate change, declining water quality, overfishing and coastal development. We recommend monitoring of Muga dhambi in case restoration is needed in future.

We hope our research will mean current and future generations care for this wonder of nature, and respect the connections of Manbarra Traditional Owners to their Sea Country.

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Read more:
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Adam Smith, Adjunct Associate Professor, James Cook University; Nathan Cook, Marine Scientist , James Cook University, and Vicki Saylor, Manbarra Traditional Owner, Indigenous Knowledge

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Coral, meet coral: how selective breeding may help the world’s reefs survive ocean heating

Anna Scott, Author provided

Emily Howells, Southern Cross University and David Abrego, Southern Cross UniversityA single generation of selective breeding can make corals better able to withstand extreme temperatures, according to our new research. The discovery could offer a lifeline to reefs threatened by the warming of the world’s oceans.

Our research, published in Science Advances, shows corals from some of the world’s hottest seas can transfer beneficial genes associated with heat tolerance to their offspring, even when crossbred with corals that have never experienced such temperatures.

Across the world, corals vary widely, both in the temperatures they experience and their ability to withstand high temperatures without becoming stressed or dying. In the Persian Gulf, corals have genetically adapted to extreme water temperatures, tolerating summer conditions above 34℃ for weeks at a time, and withstanding daily averages up to 36℃.

These water temperatures are 2-4℃ higher than any other region where corals grow, and are on a par with end-of-century projections for reefs outside the Persian Gulf.

This led us to ask whether beneficial gene variants could be transferred to coral populations that are naïve to these temperature extremes. To find out, we collected fragments of Platygyra daedalea corals from the Persian Gulf, and cross-bred them with corals of the same species from the Indian Ocean, where summer temperatures are much cooler.

Platygyra, a brain-shaped coral found in many parts of the world.
Emily Howells, Author provided

We then heat-stressed the resulting offspring (more than 12,000 individual coral larvae) to see whether they could withstand temperatures of 33°C and 36°C — the summer maximums of their parents’ respective locations.

Immediate gains

We found an immediate transfer of heat tolerance when Indian Ocean mothers were crossed with Persian Gulf fathers. These corals showed an 84% increase in survival at high temperatures relative to purebred Indian Ocean corals, making them similarly resilient to purebred Persian Gulf corals.

Genome sequencing confirmed that gains in heat tolerance were due to the inheritance of beneficial gene variants from the Persian Gulf corals. Most Persian Gulf fathers produced offspring that were better able to withstand heat stress, and these fathers and their offspring had crucial variants associated with better heat tolerance.

Conversely, most Indian Ocean fathers produced offspring that were less able to survive heat stress, and were less likely to have gene variants associated with heat tolerance.

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Survival of the fittest

Encouragingly, gene variants associated with heat tolerance were not exclusive to Persian Gulf corals. Two fathers from the Indian Ocean produced offspring with unexpectedly high survival under heat stress, and had some of the same tolerance-associated gene variants that are prevalent in Persian Gulf corals.

This suggests that some populations have genetic variation upon which natural selection can act as the world’s oceans grow hotter. Selective breeding might be able to accelerate this process.

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Heat-tolerant corals can create nurseries that are resistant to bleaching

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We are now assessing the genetic basis for heat tolerance in the same species of coral on the Great Barrier Reef and in Western Australia. We want to find out what gene variants are associated with heat tolerance, how these variants are distributed within and among reefs, and whether they are the same as those that allow corals in the Persian Gulf to survive such extreme temperatures.

This knowledge will help us understand the potential for Australian corals to adapt to rapid warming.

Although our study shows selective breeding can significantly improve the resilience of corals to ocean warming, we don’t yet know whether there are any trade-offs between thermal tolerance and other important traits, and whether there are significant genetic risks involved in such breeding.

Platygyra larvae. It remains to be seen whether the genetic benefits of heat-tolerance genes persist throughout life.
Emily Howells, Author provided

Our study was done on coral larvae without the algae that live in close harmony with corals after they settle on reefs. So it will also be important to examine whether the genetic improvements to heat tolerance continue into the corals’ later life stages, when they team up with these algae.

Of course, saving corals from the perils of ocean warming will require action on multiple fronts — there is no silver bullet. Selective breeding might provide some respite to particular coral populations, but it won’t be enough to protect entire ecosystems, and nor is it a substitute for the urgent reduction of greenhouse emissions needed to limit the oceans’ warming.

Emily Howells, Senior Research Fellow in Marine Biology, Southern Cross University and David Abrego, Lecturer, National Marine Science Centre, Southern Cross University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Oil Rigs Near Reefs?

When coral dies, tiny invertebrates boom. This could dramatically change the food web on the Great Barrier Reef

Shutterstock

Kate Fraser, University of TasmaniaThis week, international ambassadors will take a snorkelling trip to the Great Barrier Reef as part of the Australian government’s efforts to stop the reef getting on the world heritage “in danger” list.

The World Heritage Centre of UNESCO is set to make its final decision on whether to officially brand the reef as “in danger” later this month.

To many coral reef researchers like myself, who have witnessed firsthand the increasing coral bleaching and cyclone-driven destruction of this global icon, an in-danger listing comes as no surprise.

But the implications of mass coral death are complex — just because coral is dying doesn’t mean marine life there will end. Instead, it will change.

In recent research, my colleagues and I discovered dead coral hosted 100 times more microscopic invertebrates than healthy coral. This means up to 100 times more fish food is available on reefs dominated by dead coral compared with live, healthy coral.

This is a near-invisible consequence of coral death, with dramatic implications for reef food webs.

When coral dies

Tiny, mobile invertebrates — between 0.125 and 4 millimetres in size — are ubiquitous inhabitants of the surfaces of all reef structures and are the main food source for approximately 70% of fish species on the Great Barrier Reef.

These invertebrates, most visible only under a microscope, are commonly known as “epifauna” and include species of crustaceans, molluscs, and polychaete worms.

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When corals die, their skeletons are quickly overgrown by fine, thread-like “turfing algae”. Turf-covered coral skeletons then break down into beds of rubble.

We wanted to find out how the tiny epifaunal invertebrates — upon which many fish depend – might respond to the widespread replacement of live healthy coral with dead, turf-covered coral.

A sample of epifauna under the microscope.
Kate Fraser

I took my SCUBA gear and a box of lab equipment, and dived into a series of reefs across eastern Australia, from the Solitary Islands in New South Wales to Lizard Island on the northern Great Barrier Reef.

Underwater, I carefully gathered into sandwich bags the tiny invertebrates living on various species of live coral and those living on dead, turf-covered coral.

But things really got interesting back in the laboratory under the microscope. I sorted each sandwich bag sample of epifauna into sizes, identified them as best I could (many, if not most, species remain unknown to science), and counted them.

I quickly noticed samples taken from live coral took just minutes to count, whereas samples from dead coral could take hours. There were exponentially more animals in the dead coral samples.

The Great Barrier Reef may soon be listed as ‘in danger’
Rick Stuart-Smith

Why do they prefer dead coral?

Counting individual invertebrates is only so useful when considering their contribution to the food web. So we instead used the much more useful metric of “productivity”, which looks at how much weight (biomass) of organisms is produced daily for a given area of reef.

We found epifaunal productivity was far greater on dead, turf-covered coral. The main contributors were the tiniest epifauna — thousands of harpacticoid copepods (a type of crustacean) an eighth of a millimetre in size.

In contrast, coral crabs and glass shrimp contributed the most productivity to epifaunal communities on live coral. At one millimetre and larger, these animals are relative giants in the epifaunal world, with fewer than ten individuals in most live coral samples.

Dead coral rubble overgrown with turfing algae.
Rick Stuart-Smith

These striking differences may be explained by two things.

First: shelter. Live coral may look complex to the naked eye, but if you zoom in you’ll find turfing algae has more structural complexity that tiny epifauna can hide in, protecting them from predators.

A coral head is actually a community of individual coral polyps, each with a tiny mouth and fine tentacles to trap prey. To smaller epifauna, such as harpacticoid copepods, the surface of live coral is a wall of mouths and a very undesirable habitat.

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Second: food. Many epifauna, regardless of size, are herbivores (plant-eaters) or detritivores (organic waste-eaters). Turfing algae is a brilliant trap for fine detritus and an excellent substrate for growing films of even smaller microscopic algae.

This means dead coral overgrown by turfing algae represents a smorgasbord of food options for the tiniest epifauna through to the largest.

Meanwhile, many larger epifauna like coral crabs have evolved to live exclusively on live coral, eating the mucus that covers the polyps or particles trapped by the polyps themselves.

Harpacticoid copepod are just an eighth of a millimetre in size.
Naukhan/Wikimedia, CC BY

What this means for life on the reef?

As corals reefs continue to decline, we can expect increased productivity at the base level of reef food webs, with a shift from larger crabs and shrimp to small harpacticoid copepods.

This will affect the flow of food and energy throughout reef food webs, markedly changing the structure of fish and other animal communities. The abundance of animals that eat invertebrates will likely boom with increased coral death.

We might expect higher numbers of fish such as wrasses, cardinalfish, triggerfish, and dragonets, with species preferring the smallest epifauna most likely to flourish.

The dragonet species, mandarinfish, feeds on the smallest harpacticoid copepod prey.
Rick Stuart-Smith

Invertebrate-eating animals are food for a diversity of carnivores on a coral reef, and most fish Australians want to eat are carnivores, such as coral trout, snapper, and Spanish mackerel.

While we didn’t investigate exactly which species are likely to increase following widespread coral death, it’s safe to say populations of fish targeted by recreational and commercial fisheries on Australia’s coral reefs are likely to change as live coral is lost, some for better and some for worse.

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The Great Barrier Reef is undoubtedly in danger, and it’s important that we make every effort to protect and conserve the remaining live, healthy coral. However, if corals continue to die, there will remain an abundance of life in their absence, albeit very different life from that to which we are accustomed.

As long as there is hard structure for algae to grow on, there will be epifauna. And where there is epifauna, there is food for fish, although perhaps not for all the fish we want to eat.

Kate Fraser, Marine Ecologist, University of Tasmania

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Almost 60 coral species around Lizard Island are ‘missing’ – and a Great Barrier Reef extinction crisis could be next

Michael Emslie

Zoe Richards, Curtin UniversityThe federal government has opposed a recommendation by a United Nations body that the Great Barrier Reef be listed as “in danger”. But there’s no doubt the natural wonder is in dire trouble. In new research, my colleagues and I provide fresh insight into the plight of many coral species.

Worsening climate change, and subsequent marine heatwaves, have led to mass coral deaths on tropical reefs. However, there are few estimates of how reduced overall coral cover is linked to declines in particular coral species.

Our research examined 44 years of coral distribution records around Lizard Island, at the northern end of the Great Barrier Reef. We found 16% of coral species have not been seen for many years and are at risk of either local extinction, or disappearing from parts of their local range.

This is alarming, because local extinctions often signal wider regional – and ultimately global – species extinction events.

Healthy coral near Lizard Island in 2011, top, then six years later after two bleaching events, bottom.
Zoe Richards

Sobering findings

The Lizard Island reef system is 270 kilometres north of Cairns. It has suffered major disturbances over the past four decades: repeated outbreaks of crown-of-thorns seastars, category 4 cyclones in 2014 and 2015, and coral bleaching events in 2016, 2017 and 2020.

Our research focused on “hermatypic” corals around Lizard Island. These corals deposit calcium carbonate and form the hard framework of the reef.

We undertook hard coral biodiversity surveys four times between 2011 and 2020, across 14 sites. We combined the results with published and photographic species records from 1976 to 2020.

Micromussa lordhowensis is popular in the aquarium trade.
Zoe Richards

Of 368 hard coral species recorded around Lizard Island, 28 (7.6%) have not been reliably recorded since before 2011 and may be at risk of local extinction. A further 31 species (8.4%) have not been recorded since 2015 and may be at risk of range reduction (disappearance from parts of its local range).

The “missing” coral species include:

• Acropora abrotanoides, a robust branching shallow water coral that lives on the reef crest and reef flat has not been since since 2009
• Micromussa lordhowensis, a low-growing coral with colourful fleshy polyps. Popular in the aquarium trade, it often grows on reef slopes but has not been seen since 2005
• Acropora aspera, a branching coral which prefers very shallow water and has been recorded just once, at a single site, since 2011.

The finding that 59 coral species are at risk of local extinction or range reduction is significant. Local range reductions are often precursors to local species extinctions. And local species extinctions are often precursors to regional, and ultimately global, extinction events.

Each coral species on the reef has numerous vital functions. It might provide habitat or food to other reef species, or biochemicals which may benefit human health. One thing is clear: every coral species matters.

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Acropa abrotanoides, one of the corals ‘missing’ from around Lizard Island.
Zoe Richards

A broader extinction crisis?

As human impacts and climate threats mount, there is growing concern about the resilience of coral biodiversity. Our research suggests such concerns are well-founded at Lizard Island.

Coral reef communities are dynamic, and so detecting species loss can be difficult. Our research found around Lizard Island, the diversity of coral species fluctuated over the past decade. Significant declines were recorded from 2011 to 2017, but diversity recovered somewhat in the three following years.

Local extinctions often happen incrementally and can therefore be “invisible”. To detect them, and to account for natural variability in coral communities, long-term biodiversity monitoring across multiple locations and time frames is needed.

Acropora aspera has been recorded just once, at a single location, since 2011.
Anne Hoggett

In most locations however, data on the distribution and abundance of all coral species in a community is lacking. This means it can be hard to assess changes, and to understand the damage that climate change and other human-caused stressors are having on each species.

Only with this extra information can scientists conclusively say if the level of local extinction risk at Lizard Island indicates a risk that coral species may become extinct elsewhere – across the Great Barrier Reef and beyond.

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Zoe Richards, Senior Research Fellow, Curtin University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Beautiful, rare ‘purple cauliflower’ coral off NSW coast may be extinct within 10 years

Author supplied

Meryl Larkin, Southern Cross University; David Harasti, Southern Cross University; Steve Smith, Southern Cross University, and Tom R DavisWhen we think of Australia’s threatened corals, the Great Barrier Reef probably springs to mind. But elsewhere, coral species are also struggling – including a rare type known as “cauliflower soft coral” which is, sadly, on the brink of extinction.

This species, Dendronephthya australis, looks like a purple cauliflower due to its pink-lilac stems and branches, crowned with white polyps.

The coral primarily occurs at only a few sites in Port Stephens, New South Wales, and is a magnet for divers and underwater photographers. But sand movements, boating and fishing have reduced the species’ population dramatically.

Recent flooding in NSW compounded the problem – in fact, it may have reduced the remaining coral population by 90%. Our recent research found cauliflower soft coral may become extinct in the next decade unless we urgently protect and restore it.

An ovulid on a cauliflower coral colony. Such coral may be extinct within a decade.
Author supplied

Lilac underwater gardens

Cauliflower soft corals are predominantly found in estuarine environments on sandy seabeds with high current flow. They rely on tidal currents to transport plankton on which they feed.

The species is most commonly found in the Port Stephens estuary, about 200 kilometres north of Sydney. It’s also found in the Brisbane Water estuary in NSW, and has been found sporadically in other locations south to Jervis Bay.

The coral colonies form aggregations or “gardens”. At Port Stephens, these gardens are the preferred habitat for the endangered White’s seahorse and protected species of pipefish. They also support juvenile Australasian snapper, an important species for commercial and recreational fishers.

In recent months, the cauliflower soft coral has been listed as endangered in NSW and nationally.

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An alarming decline

Scientists first mapped the distribution of the cauliflower soft coral in 2011. They found none of the biggest colonies in the Port Stephens estuary were protected by “no take” zones – areas where fishing and other extractive activities are banned.

In research in 2016, we found a sharp decline in the extent and distribution of cauliflower soft coral.

Our recent study examined the problem in more detail. It involved mapping the southern shoreline of Port Stephens, using an underwater camera towed by a vessel.

We found the cauliflower soft coral in the Port Stephens estuary has declined by almost 70% over just eight years. It now occurs over 9,300 square metres – down from 28,600 square metres in 2011.

Our subsequent modelling sought to identify what was driving the corals’ decline. We found a correlation between coral loss and sand movements over the last decade.

Human changes to shorelines, such as marina developments, have changed the dynamic of currents across the estuary. For example, previous research found a large influx of sand from the western end of Shoal Bay smothered cauliflower soft coral colonies at two nearby locations. As of 2018, those colonies had disappeared completely.

While diving as part of the project, we identified other causes of damage to the coral. Dropped boat anchors and the installation of moorings had damaged some colonies. Others were injured after becoming entangled in fishing line.

It is possible that disease, and pollution or other water quality issues, may also be contributing to the species’ decline.

Fishing line damaging a colony of cauliflower soft coral in Port Stephens.
Author supplied

Then the floods hit

Some 18 months after our most recent mapping, cauliflower soft corals suffered yet another blow. Major flooding in NSW in March this year caused a massive amount of fresh water to discharge from the Karuah River into the Port Stephens estuary, where sea water is dominant. Fresh water can kill cauliflower soft corals.

Following the floods, we conducted exploratory dives at locations where the cauliflower soft corals had been thriving at Port Stephens. We found much of the coral had disintegrated and disappeared. In fact, we estimated as much as 90% of the remaining cauliflower soft coral population was gone.

We plan to remap the estuary in the coming weeks, and feel confident our initial estimates will be close to the mark. If so, this means less than 5% of the species area mapped in 2011 now remains.

The floods also devastated kelp forests and other canopy-forming habitats in the estuary. Further work by scientists at the NSW Department of Primary Industries is underway to quantify these losses and monitor the recovery.

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Read more:
Sydney’s disastrous flood wasn’t unprecedented: we’re about to enter a 50-year period of frequent, major floods

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Monitoring of existing cauliflower coral aggregations is ongoing.
Author supplied

Urgent work required

The cauliflower soft coral urgently needs protecting. This will require ongoing, coordinated research and management.

Clearly, action must be taken to reduce threats such as anchoring, fishing, and development that may magnify sand movement.

Best-practice rehabilitation is also needed. This may involve rearing the coral off-site and transplanting it into suitable habitat. Such trials at Port Stephens have shown promising signs.

Human activities are causing species loss at an alarming rate. We must do everything in our power to prevent the extinction of the cauliflower soft coral, and other threatened species, to preserve the balance of nature and its ecosystems.

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Australia’s threatened species plan sends in the ambulances but ignores glaring dangers

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Meryl Larkin, PhD Candidate, Southern Cross University; David Harasti, Adjunct assistant professor, Southern Cross University; Steve Smith, Professor of Marine Science, National Marine Science Centre, Southern Cross University, and Tom R Davis, Research Scientist – Marine Climate Change

This article is republished from The Conversation under a Creative Commons license. Read the original article.

The outlook for coral reefs remains grim unless we cut emissions fast — new research

Morgan Pratchett, ARC Centre of Excellence for Coral Reef Studies, CC BY-ND

Christopher Cornwall, Te Herenga Waka — Victoria University of Wellington and Verena Schoepf, University of AmsterdamThe twin stress factors of ocean warming and acidification increasingly threaten coral reefs worldwide, but relatively little is known about how various climate scenarios will affect coral reef growth rates.

Our research, published today, paints a grim picture. We estimate that even under the most optimistic emissions scenarios, we’ll see dramatic reductions in coral reef growth globally.
The good news is that 63% of all reefs in this emissions scenario will still be able to grow by 2100.

But if emissions continue to rise unabated, we predict 94% of coral reefs globally will be eroding by 2050. Even under an intermediate emissions scenario, we project a worst-case outcome in which coral reefs on average will no longer be able to grow vertically by 2100.

The latter scenarios would have dramatic consequences for marine biodiversity and the millions of people who depend on healthy, actively growing coral reefs for livelihoods and shoreline protection. This highlights the urgency and importance of acting now to drastically reduce carbon dioxide emissions.

Coral reefs are home to more than 830,000 species and provide coastal communities with food and income through fisheries and tourism.

The Great Barrier Reef alone contributes A$6.4 billion to the Australian economy. Critically, coral reefs also protect coastlines from storm surges and create land for many low-lying Indo-Pacific island nations.

Marine heatwaves, caused by ongoing ocean warming, have already had a severe impact on coral reef ecosystems by triggering mass bleaching events. These events are becoming more frequent and intense, and cause mass die-offs across large areas.

Marine heatwaves trigger mass bleaching and coral die-offs.
Morgan Pratchett, ARC Centre of Excellence for Coral Reef Studies, CC BY-ND

Ocean acidification also reduces the growth of corals by limiting their ability to build their skeletons from calcium carbonate. Together, these stressors threaten the ability of coral reefs to grow and keep up with sea level rise.

Complex impacts from ocean warming and acidification

Our understanding of how ocean warming and acidification threaten reef-forming species has improved considerably over the past decade. However, understanding how coral reef growth will be altered by climate change is more complex than simply measuring rates of change from individual taxonomic groups of corals.

Our study of 183 reefs worldwide provides the first quantitative estimate of how most of the processes that control reef growth respond to climate change and affect carbonate accumulation and growth rates.

Coral on the Great Barrier Reef during the 2020 bleaching event.
Morgan Pratchett, ARC Centre of Excellence for Coral Reef Studies, CC BY-ND

Reefs grow by layering calcium carbonate, produced either by corals and coralline algae. The amount of calcium carbonate built by these reefs depends on many factors.

Cyclones, waves and currents can flush parts of the reef away. Acidifying ocean water means more dissolves chemically. And there is a biological carbonate exchange, known as bio-erosion. Sponges, parrotfish, sea urchins and algae can all eat it, but then return some as defecated sand.

Depending on which of these processes dominates, coral reefs either grow and accrete vertically, or they start to erode. Most of these processes vary for each reef, and almost all are affected by climate change.

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Read more:
The Great Barrier Reef outlook is ‘very poor’. We have one last chance to save it

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To complicate matters, the frequency and intensity of marine heatwaves will vary geographically, making it difficult to estimate to what degree coral mass bleaching events will reduce coral cover.

In our research, we applied these local and global processes to 233 locations on 183 distinct coral reefs that vary in their species compositions and physical complexity. We found significant variability in responses to ocean acidification and warming.

Geographical and species variability

We predict coral mass bleaching events will have the largest impact on carbonate production across all sites. The world’s coral reefs have already been transformed dramatically by these events over the past few decades.

Coral reef in the Maldives, before coral mass bleachign event.
Chris Perry, CC BY-ND

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We just spent two weeks surveying the Great Barrier Reef. What we saw was an utter tragedy

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Experimental setup used to measure calcification coralline algae on the Great Barrier Reef.
Guillermo Diaz-Pulido, CC BY-ND

We used the documented impacts of the 2016 mass bleaching on the Great Barrier Reef, which affected a large range of reefs with different species compositions, depths and latitudes. During this event, each reef experienced varying heat stress, which manifested in different levels of coral cover loss.

This information helped us to calibrate models to predict heat-stress events globally between now and 2100 and to gauge the future magnitudes of heat stress and their impact on our study sites.

We found currently degraded reefs fared poorly in our model, even under lower emissions scenarios. Reefs whose carbonate production was more robust against the effects of climate change tended to be those with high present-day carbonate production rates, higher contributions from coralline algae (which are also vulnerbable, but comparatively more resistant to warming than corals) and low rates of bio-erosion.

Hope for coral reefs

In higher emissions scenarios, even reefs dominated by coralline algae began to suffer as ocean acidification and warming intensified. It is also important to note that such reefs will provide different, and perhaps reduced, services compared to coral-dominated reefs because they are structurally less complex.

Team members assess coral health during the 2016 bleaching event in the Kimberley, Western Australia.
Christopher Cornwall, CC BY-ND

We did not explore in depth whether remaining coral reef communities could gain tolerance to rising temperatures over time. This could manifest as an increase in the proportional abundance of heat-tolerant species as more heat-sensitive corals die during mass bleaching events.

Surviving corals could acclimatise or even adapt. But whether these mechanisms could provide hope for the continued growth of coral reefs in the future — and if so, to what extent — is largely unknown. Nor can we say if more heat-tolerant corals could sustain similar rates of reef growth and structural complexity.

A coral reef in Chagos before a bleaching event in April 2016.
Chris Perry, CC BY-ND

The best hope to save coral reefs and their ecological, societal and economic benefits is to reduce our carbon emissions dramatically, and quickly. Even under our projected intermediate scenarios we expect mean global erosion of coral reefs.

Under the lowest emissions scenario we examined, we expect profound changes in coral reef growth rates and their ability to provide ecosystem services. In this scenario, only some reefs will be able to keep pace with rising sea levels.

We owe it to our children and grandchildren to reduce emissions now, if we have any hope of them witnessing the majestic nature of coral reef ecosystems.

Christopher Cornwall, Rutherford Discovery Fellow, Te Herenga Waka — Victoria University of Wellington and Verena Schoepf, Assistant Professor, University of Amsterdam

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Watching a coral reef die as climate change devastates one of the most pristine tropical island areas on Earth

Sam Purkis, University of MiamiThe Chagos Archipelago is one of the most remote, seemingly idyllic places on Earth. Coconut-covered sandy beaches with incredible bird life rim tropical islands in the Indian Ocean, hundreds of miles from any continent. Just below the waves, coral reefs stretch for miles along an underwater mountain chain.

It’s a paradise. At least it was before the heat wave.

When I first explored the Chagos Archipelago 15 years ago, the underwater view was incredible. Schools of brilliantly colored fish in blues, yellows and oranges darted among the corals of a vast, healthy reef system. Sharks and other large predators swam overhead. Because the archipelago is so remote and sits in one of the largest marine protected areas on the planet, it has been sheltered from industrial fishing fleets and other activities that can harm the coastal environment.

But it can’t be protected from climate change.

A diver documents the coral reefs in the Chagos Archipelago.
Khaled bin Sultan Living Oceans Foundation

In 2015, a marine heat wave struck, harming coral reefs worldwide. I’m a marine biologist at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science, and I was with a team of researchers on a 10-year global expedition to map the world’s reefs, led by the Khaled bin Sultan Living Oceans Foundation. We were wrapping up our work in the Chagos Archipelago at the time. Our report on the state of the reefs there was just published in spring 2021.

As the water temperature rose, the corals began to bleach. To the untrained eye, the scene would have looked fantastic. When the water heats up, corals become stressed and they expel the tiny algae called dinoflagellates that live in their tissue. Bleaching isn’t as simple as going from a living coral to a bleached white one, though. After they expel the algae, the corals turn fluorescent pinks and blues and yellows as they produce chemicals to protect themselves from the Sun’s harmful rays. The entire reef was turning psychedelic colors.

Just before they turned white, the corals turned abnormally bright shades.
Phil Renaud/Khaled bin Sultan Living Oceans Foundation

That explosion of color is rare, and it doesn’t last long. Over the following week, we watched the corals turn white and start to die. It wasn’t just small pieces of the reef that were bleaching – it was happening across hundreds of square miles.

What most people think of as a coral is actually many tiny colonial polyps that build calcium carbonate skeletons. With their algae gone, the coral polyps could still feed by plucking morsels out of the water, but their metabolism slows without the algae, which provide more nutrients through photosynthesis. They were left desperately weakened and more vulnerable to diseases. We could see diseases taking hold, and that’s what finished them off.

We were witnessing the death of a reef.

Rising temperatures increase the heat wave risk

The devastation of the Chagos Reef wasn’t happening in isolation.

Over the past century, sea surface temperatures have risen by an average of about 0.13 degrees Celsius (0.23 F) per decade as the oceans absorb the vast majority of greenhouse gas emissions from human activities, largely from the burning of fossil fuels. The temperature increase and changing ocean chemistry affects sea life of all kinds, from deteriorating the shells of oysters and tiny pteropods, an essential part of the food chain, to causing fish populations to migrate to cooler water.

Corals can become stressed when temperatures around them rise just 1 C (1.8 F) above their tolerance level. With water temperature elevated from global warming, even a minor heat wave can become devastating.

In 2015, the ocean heat from a strong El Niño event triggered the mass bleaching in the Chagos reefs and around the world. It was the third global bleaching on record, following events in 1998 and 2010.

Bleaching doesn’t just affect the corals – entire reef systems and the fish that feed, spawn and live among the coral branches suffer. One study of reefs around Papua New Guinea in the southwest Pacific found that about 75% of the reef fish species declined after the 1998 bleaching, and many of those species declined by more than half.

Research shows marine heat waves are now about 20 times more likely than they were just four decades ago, and they tend to be hotter and last longer. We’re at the point now that some places in the world are anticipating coral bleaching every couple of years.

That increasing frequency of heat waves is a death knell for reefs. They don’t have time to recover before they get hit again.

Where we saw signs of hope

During the Global Reef Expedition, we visited over 1,000 reefs around the world. Our mission was to conduct standardized surveys to assess the state of the reefs and map the reefs in detail so scientists could document and hopefully respond to changes in the future. With that knowledge, countries can plan more effectively to protect the reefs, important national resources, providing hundreds of billions of dollars a year in economic value while also protecting coastlines from waves and storms.

We saw damage almost everywhere, from the Bahamas to the Great Barrier Reef.

Some reefs are able to survive heat waves better than others. Cooler, stronger currents, and even storms and cloudier areas can help prevent heat building up. But the global trend is not promising. The world has already lost 30% to 50% of its reefs in the last 40 years, and scientists have warned that most of the remaining reefs could be gone within decades.

The author, Sam Purkis, dives near a hawksbill turtle in the Chagos Archipelago.
Derek Manzello/Khaled bin Sultan Living Oceans Foundation

While we see some evidence that certain marine species are moving to cooler waters as the planet warms, a reef takes thousands of years to establish and grow, and it is limited by geography.

In the areas where we saw glimmers of hope, it was mostly due to good management. When a region can control other harmful human factors – such as overfishing, extensive coastal development, pollution and runoff – the reefs are healthier and better able to handle the global pressures from climate change.

Establishing large marine protected areas is one of the most effective ways I’ve seen to protect coral reefs because it limits those other harms.

The Chagos marine protected area covers 640,000 square kilometers (250,000 square miles) with only one island currently inhabited – Diego Garcia, which houses a U.S. military base. The British government, which created the marine protected area in 2010, has been under pressure to turn over control of the region to the country of Mauritius, where former Chagos residents now live and which won a challenge over it in the International Court of Justice in 2020. Whatever happens with jurisdiction, the region would benefit from maintaining a high level of marine protection.

A warning for other ecosystems

The Chagos reefs could potentially recover – if they are spared from more heat waves. Even a 10% recovery would make the reefs stronger for when the next bleaching occurs. But recovery of a reef is measured in decades, not years.

So far, research missions that have returned to the Chagos reefs have found only meager recovery, if any at all.

We knew the reefs weren’t doing well under the insidious march of climate change in 2011, when the global reef expedition started. But it’s nothing like the intensity of worry we have now in 2021.

Coral reefs are the canary in the coal mine. Humans have collapsed other ecosystems before through overfishing, overhunting and development, but this is the first unequivocally tied to climate change. It’s a harbinger of what can happen to other ecosystems as they reach their survival thresholds.

This story is part of Oceans 21

Our series on the global ocean opened with five in-depth profiles. Look for new articles on the state of our oceans in the lead-up to the U.N.‘s next climate conference, COP26. The series is brought to you by The Conversation’s international network.

Sam Purkis, Professor and Chair of the Department of Marine Sciences, University of Miami

This article is republished from The Conversation under a Creative Commons license. Read the original article.

These underwater photos show Norfolk Island reef life still thrives, from vibrant blue flatworms to soft pink corals

A big coral bommie in the lagoon at Norfolk Island.
John Turbull , Author provided

John Turnbull, UNSW

Environmental scientists see flora, fauna and phenomena the rest of us rarely do. In this new series, we’ve invited them to share their unique photos from the field.

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Two weeks ago, I found myself hitting the water on Norfolk Island, complete with a survey reel, slate and camera.

Norfolk Island is a small volcanic outcrop located between New Caledonia and New Zealand, 1,400 kilometres east of Australia’s Gold Coast. It’s surrounded by coral reefs, with a shallow lagoon on the south side that looks out on two smaller islands: Nepean and Phillip.

The island is picturesque, but like marine environments the world over, Norfolk Marine Park is subject to pressures from climate change, fishing pressure, habitat change and pollution.

I was diving in the marine park as a volunteer for Reef Life Survey, a citizen science program where trained SCUBA divers survey marine biodiversity in rocky and coral reefs around the world. We first surveyed Norfolk Island in 2009, then again in 2013, with an eight year hiatus before our return this month.

While the scientific analysis of our data is yet to be done, we can make anecdotal observations to compare this year’s findings with prior records and photographs. This time, our surveys turned up several new sightings and observations.

A red-ringed nudibranch (Ardeadoris rubroannulata). This beautiful little mollusc was a couple of centimetres long, nestled on the side of a wall covered in colourful algae. I had to look twice to notice it, but recognised it as a species I had seen before in Sydney. It had previously only been recorded in the Coral Sea, the east coast of Australia and Lord Howe island, so it was nice to get a record of it even further east in the Pacific.
John Turnbull, Author provided

What we saw

Diving under the waves in Norfolk Marine Park takes you into a world of crackling, popping reef sounds through clear blue water, with darting tropical fish, a tapestry of algae and hard and soft corals in pink, green, brown and red.

In these surveys we record fish species including their size and abundance, invertebrates such as urchins and sea stars, and habitat such as coral cover. This allows us to track changes in marine life using standardised scientific methods.

Emily Bay is a sheltered swimming beach at the eastern end of the lagoon, great for snorkelling too thanks to the diverse corals just below the surface.
John Turbull, Author provided

Banded parma are quite territorial — they charge you as you approach their turf. This one is guarding what it regards as its own personal coral clump.
John Turbull, Author provided

Given recent major marine heatwaves and bleaching events in Australia, we were pleased to see healthy corals on many of our survey sites on Norfolk. We even felt there had been increases in coral cover at some sites.

This may be due to Norfolk’s location. The island is further south than most Australian coral reefs, which means it has cooler seas, and it’s surrounded by deeper water. I’m a marine ecologist involved in soft coral monitoring at the University of NSW, so I particularly noticed the wonderful diversity and size of soft corals.

This photo shows the structure corals provide for fish and other animals to shelter in. They are the foundation for the whole tropical marine community. The corals here are a healthy brown — which comes from the symbiotic algae in their tissues – with no signs of bleaching.
John Turbull, Author provided

The soft corals on Norfolk Island are some of the largest I’ve seen. Their structure is made up of soft tissue, often inflated by water pressure, rather than hard skeleton.
John Turbull, Author provided

Hard corals come in a diversity of shapes and sizes, including this massive form growing on the side of rock wall.
John Turbull, Author provided

I noticed generally low numbers of large fish such as morwong and sharks on our survey sites. Some classes of invertebrate were also rare on this year’s surveys, particularly sea shell animals like tritons and whelks.

Urchins, on the other hand, were common, particularly the red urchin. Some sites also had numerous black long-spined urchins and large sea lamingtons.

These invertebrate observations follow patterns we see in eastern and southern Australia, where there are declines in the numbers of many invertebrate species, and increases in urchin barrens — regions where urchin populations grow unchecked.

The expansion of urchin barrens can threaten biodiversity in a region, as large numbers of a single species of urchin can out-compete multiple species of other invertebrates, over-graze algae and reduce habitat suitable for fish.

The abundant red urchin competes for space with other invertebrates, such as this one encrusting hard coral.
John Turbull, Author provided

Lamingtons are an Australian cake (although there are claims they were invented in NZ!) and I love this descriptive common name for the Tripneustes gratilla urchin. The sea lamingtons on Norfolk appear particularly fat and happy, as they cluster in sheltered grooves during the day to avoid predators. They can also be different colours — I’ve seen them on the east coast of Australia in orange and cream, even with stripes.
John Turbull, Author provided

A pair of banded cleaner shrimp, which grow to 9cm long. They advertise their fish cleaning services with their distinct banding and white antennae.
John Turbull, Author provided

A highlight of any survey dive is when you find an animal you suspect may not have been recorded at a location before, and I had several of those on this trip.

I recorded first sightings for Reef Life Survey of blue mao mao, convict surgeonfish, the blue band glidergoby, sergeant major (a damselfish), chestnut blenny, Susan’s flatworm, red-ringed nudibranch, fine-net peristernia and an undescribed weedfish.

While some of these sightings are yet to be confirmed by specialists, they gave a buzz of excitement each night as we searched the records to confirm our suspicions of a new find.

This big school of drummer circled us for several minutes on our first survey dive at Nepean Island. If you look closely you can see one of the fish is different, in the top right. This is one of a few blue mao mao circulating in the school – and a first sighting for Reef Life Survey at Norfolk. You might also notice another species in the school, the darker spotted sawtail down the bottom of the photo.
John Turbull, Author provided

Susan’s flatworm is a colourful invertebrate listed as living only in the Indian Ocean and Indonesia. This sighting from Norfolk Island is a new record in the Pacific Ocean. When I first saw this little worm at the end of a survey, I wondered if it was anything special. Just as well I took the photo anyway!
John Turbull, Author provided

Recruiting the locals

Other highlights for me included the warm welcome we received from the local community on Norfolk and the great turnout we had at our community seminar. Everyone I spoke to was supportive and encouraging when they heard we were on the island as volunteers doing surveys, and several people expressed interest in getting involved.

This is great news, as the best outcome is for local people to be trained to conduct their own local surveys.

Tyson, Sal, Jamie, Toni and me taking an underwater selfie on the west side of Phillip Island, 10 metres below the surface. It’s harder than on land, with your fins off the ground, everyone moving and bubbles to deal with.
John Turbull, Author provided

Ideally we will return for comprehensive surveys of our 17 sites every two years or so, allowing us to plot trends over time. Only then can we hope to understand what is really happening in our marine environment, and make evidence-based conservation decisions. Having a skilled local team would make this easier and more likely to happen.

In any case, our 2021 surveys in Norfolk Marine Park, conducted by our team of five dedicated volunteers and supported by many others, give us one more essential point in time in the Norfolk series, and gave me some great memories to boot.

You can view my full photo album from the Norfolk Island survey here.

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Photos from the field: zooming in on Australia’s hidden world of exquisite mites, snails and beetles

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John Turnbull, Postdoctoral research associate, UNSW

This article is republished from The Conversation under a Creative Commons license. Read the original article.