Open ocean sharks are elusive and mysterious. They undertake vast journeys that span hundreds to thousands of kilometres across immense ocean basins. We know very little about the secret lives of ocean sharks, where they live and why they are there.

What we do know is sharks are immensely important to the natural systems in which they live. Over 450 million years of evolution have perfected their role as apex predators and they play vital roles in fish community regulation and nutrient cycling. Healthy ecosystems rely on healthy shark populations.

Sharks, numbering more than 500 species, are also among the most threatened groups of vertebrates (animals with backbones). After surviving five mass extinctions through geological time, sharks are now facing the greatest threat to their survival from industrial fishing.

Their elusive nature and the immensity of our oceans means sharks are difficult to study. Our limited knowledge is particularly problematic given their threatened status. A solid understanding of the distribution of oceanic sharks is fundamental to their protection and our new research provides valuable insights into the secret lives of these wide-ranging predators.

Silky by name, silky by nature

Silky sharks (Carcharhinus falciformis), named for the silky-smooth feel of their skin, are emblematic of open ocean sharks. They are highly mobile, have long life-spans, and are slow to reproduce. They are found throughout tropical and sub-tropical waters.

Silky shark numbers have declined globally due to industrial-scale fishing. Targeted for their fins and meat, they are also frequently incidentally caught in tuna fisheries. In 2017 the International Union for the Conservation of Nature classified this species as vulnerable to extinction. Their trade is controlled under the Convention on International Trade in Endangered Species.

What we did

Baited remote underwater video systems, or BRUVS for short, are used to document the wildlife of the open oceans. Armed with a pair of small action cameras and baited to attract predators, BRUVS are suspended at 10m depth and drift with ocean currents. Video analysts review the footage to identify, count and measure all observed animals.

BRUVS have previously revealed the impact of human activity on marine predator populations, the ecological value of offshore oil and gas platforms as novel ecosystems, and even that tunas use sharks to scratch their itches.

We deployed more than 1,000 BRUVS across the Atlantic, Pacific and Indian oceans between 2012-20 to record where silky sharks hang out and predict how many there are and how big they are.

A love affair between silky sharks and seamounts

Silky sharks love seamounts. The closer we sampled to seamounts, the more frequently we observed silky sharks, and in higher numbers.

Seamounts are huge underwater mountains that rise from depths of thousands of metres to pinnacles that summit from hundreds to just tens of metres below the surface. The best estimate predicts the occurrence of more than 37,000 seamounts worldwide.

Seamounts are often hotspots of marine biodiversity. They act as landmarks in the otherwise relatively featureless open ocean seascape. Seamounts provide feeding, breeding, and resting spots for ocean roamers such as sharks, tuna, and whales. Migratory wildlife also use seamounts as navigational beacons and as stepping stones along their trans-ocean journeys.

Our results also reveal the smallest silky sharks hang out closest to seamounts. Seamounts may provide a rich smorgasbord for these rapidly growing youngsters.

A human footprint on silky sharks

Humans are leaving their heavy footprints on much of the ocean and silky sharks are no exception. Silky shark numbers declined the closer we sampled to coastal ports. Only the most remote areas had high numbers of silky sharks.

Silky sharks close to ports and human populations were also smaller than those observed further away. Such patterns are consistent with fishing impacts as exploitation typically first removes the largest individuals from the population. Our results reflect those for other open ocean sharks: hammerhead, sandbar, tiger and whale sharks have all declined globally in numbers and size .

The distribution of silky sharks exemplifies the pervasive and negative impacts of human activity on oceanic sharks more generally. It highlights the critical need for refuges in which these animals are protected from exploitation.

A path to protection

The need for improved protection for oceanic wildlife is well-recognised and marine protected areas are a key tool to deliver this protection. In 2022, under the Convention on Biological Diversity, nearly every country in the world committed to protect 30% of their oceans by 2030.

In 2023, the High Seas Treaty was ratified by the 193 member states of the United Nations, paving the path towards strong and effective protection of the vast swaths of ocean beyond national jurisdiction. Given that less than 2.9% of our oceans are currently highly protected, such opportunities are essential.

Our research provides clues on how best to harness these agreements to protect silky sharks and their open-ocean companions. If marine protected areas are going to work, they need to include areas that threatened wildlife inhabit. As seamounts are hotspots for silky sharks, they are a fitting focus for marine protected areas.

It has never been more important to protect sharks. We have never had as much knowledge to do so. We hope recent commitments to ocean protection will spur research to further unveil the secret lives of oceanic sharks and ensure their survival in the face of their greatest threat yet.

Shona Murray, PhD candidate, The University of Western Australia and Jessica Meeuwig, Wen Family Chair in Conservation, The University of Western Australia

31 July 2023

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

The Great Barrier Reef is not dead. Nor is it in good health. The truth is complex. To understand what’s going on takes more than a headline.

For the last 37 years, our organisation has monitored the health of the world’s largest reef. Each year, we add our findings to our dataset, the Reef’s longest running and largest coverage. This lets us produce annual updates for the northern, central and southern regions of the Reef. That makes us perhaps the team best qualified to answer the question many people have – how is the Reef going?

Released today, this year’s update paints a complex picture. It wasn’t long ago the Great Barrier Reef was reeling from successive disturbances, ranging from marine heatwaves and coral bleaching to crown-of-thorns starfish outbreaks and cyclone damage, with widespread death of many corals especially during the heatwaves of 2016 and 2017.

Since then, the Reef has rebounded. Generally cooler La Niña conditions mean hard corals have recovered significant ground, regrowing from very low levels after a decade of cumulative disturbances to record high levels in 2022 across two-thirds of the reef.

The Reef has shown an impressive ability to recover from widespread disturbances, when it gets a chance – it’s not all just bleaching and death. But it’s also true we’re heading towards a future where hotter water temperatures will likely cause bleaching every year, along with ongoing threats of cyclones and coral-eating starfish. Recovery requires reprieve – and those opportunities will diminish as climate change progresses.

Last year, for instance, parts of the Reef experienced bleaching in the middle of La Niña – the first time that’s happened on record.

What’s happening on the Reef?

To take the pulse of the Great Barrier Reef, one indicator we use is hard coral cover. It’s a widely used, robust indicator of reef health, but it doesn’t tell the whole story. We also collect detailed data on coral and fish populations, diversity, structural complexity, and abundance of juvenile corals. And we take digital photographs and convert them into 3D photogrammetry models so we can analyse what’s happening in more depth than ever before.

Here’s what our analysis shows.

Over the last few years, the Reef was mostly in La Niña conditions. That gave the hard-hit northern and central parts of the reef a chance to begin recovery. Many reefs had a high proportion of Acropora corals, of which the best known are the staghorn and plate corals. These species have been a vital part of the reef over 37 years of monitoring – and probably for millennia.

These corals are the most common on many reefs, and grow fast. Because of that, they tend to dominate trends in hard coral cover.

Does this mean the Great Barrier Reef’s recovery in 2022 relied on “weedy” corals which are taking over? Yes and no. The natural ecological niche of Acropora corals has always been to rapidly fill empty space, which means it tends to dominate trends in coral recovery.

Again, the story is more complicated than the headlines. Some reefs have recovered strongly, some very little. Some reefs are recovering with less Acropora than before, some with more. Each reef is charting its own course on the journey from impact to recovery and back again.

Overall, the record high hard coral cover seen last year was welcome news, representing recovery across much of the Reef in the absence of common coral killers.

But what about recent heating?

This year, the rapid coral rebound paused. Some reefs continued to recover, but these were offset by others which lost coral. Coral loss came from effects of the 2022 bleaching event in northern and central regions, crown-of-thorns starfish predation in the northern and southern regions, damage from Tropical Cyclone Tiffany in the north and coral disease in some areas of the south.

The picture is complex. Recovery here, fresh losses there.

While the recovery we reported last year was welcome news, there are challenges ahead. The spectre of global annual coral bleaching will soon become a reality.

Right now, marine heatwaves are sweeping through ocean basins in the northern hemisphere. Sea surface temperatures are far above long term averages.

At least eight countries are reporting coral bleaching, including the United States and Belize. This summer, it looks likely we’ll see our first El Niño on the Great Barrier Reef since 2016, bringing higher sea surface temperatures. That last El Niño – coupled with global heating – was the direct cause of the 2016–17 mass bleaching and mass death of corals.

The prognosis is, in short, extremely concerning. Yes, the Reef has rebounded beyond our expectations. But now the heat is back on. If we get mass bleaching like 2016 – or even worse – it could undo all the recent recovery.

Mike Emslie, Senior Research Scientist, Australian Institute of Marine Science; Daniela Ceccarelli, Research fellow, Australian Institute of Marine Science, and David Wachenfeld, Research Program Director- Reef Ecology and Monitoring, Australian Institute of Marine Science

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

August 9 2023

The Australian Labor government has introduced a bill to regulate “marine geoengineering” – methods to combat climate change by intervening in the ocean environment.

The bill would prohibit listed marine geoengineering activities without a permit.

Scientists are already experimenting with ways to store more carbon in the ocean or shield vulnerable ecosystems. They include ocean fertilisation and marine cloud brightening. But these proposals are yet to be deployed beyond small-scale outdoor tests, Further research is needed.

These technologies offer huge potential to combat climate change. But large-scale marine geoengineering could also cause harm, Targeted laws are needed to both enable crucial research and protect the marine environment. So does the bill to amend the Sea Dumping Act strike the right balance?

Getting to grips with marine geoengineering

Interest in marine geoengineering has grown over several decades as the climate crisis has worsened. Removing CO₂ from the atmosphere is now necessary to achieve “net-zero” emissions and limit global warming to 1.5℃. But marine geoengineering proposals also present risks to the marine environment.

The Southern Ocean – which extends from Australia’s southern coast to Antarctica – has been identified as a suitable location for ocean fertilisation. This involves feeding iron dust to marine algae. Through the process of photosynthesis, the algae pull CO₂ from the atmosphere, which is potentially stored in the deep ocean.

Another proposal is modifying acidity in oceans. Oceans naturally absorb large amounts of CO₂, which is making the water more acidic. Ocean acidification harms marine life, especially animals with shells. It also limits the amount of CO₂ that can be stored. A technology that essentially adds “antacids” to the ocean“ could help counteract this and enable the oceans to store more.

Other proposals seek to reduce the damage from marine heatwaves. "Marine cloud brightening” seeks to limit coral bleaching on the Great Barrier Reef, by spraying sea-salt particles into clouds. The idea is to make the clouds whiter, to better reflect sunlight away from the ocean and limit further warming of the water.

With help, the oceans could play an even bigger role in stabilising the climate. But there are concerns about unintended consequences of deliberately intervening. For example, ocean fertilisation could decrease water oxygen levels and “rob” neighbouring waters of nutrients, reducing marine productivity.

Marine geoengineering could also distract from efforts to cut emissions at source.

Strong rules to protect the marine environment

With this new bill, the Australian government has taken an important first step towards regulating marine geoengineering.

The bill involves proposed amendments to the Environment Protection (Sea Dumping) Act. It would introduce a permit system for legitimate scientific research activities.

Environment Minister Tanya Plibersek has said of the bill:

Regulating this type of activity, though a robust application, assessment and approval permitting process, would ensure that only legitimate scientific research activities exploring options to reduce atmospheric CO₂ can proceed. This amendment also provides for regulating other potentially harmful marine geoengineering research activities should they emerge in the future.

The bill implements Australia’s international obligations under the London Protocol, a marine pollution treaty that prohibits the dumping of waste at sea without a permit.

It follows a parliamentary inquiry that recommended Australia ratify these international rules. Australia’s support may encourage other countries to adopt these rules and make them legally binding.

Countries negotiated these rules in response to plans by private companies in the 2000s to conduct ocean fertilisation for profit. They decided new international rules were needed to protect the ocean. Currently, only ocean fertilisation is listed, and hence regulated, under these rules. But other activities may be listed in future.

The bill makes it an offence to place matter into the ocean for marine geoengineering without a permit. Permits may only be granted for scientific research activities. At present, these rules apply just to ocean fertilisation, as it is the only activity listed under the London Protocol.

If the bill is passed as it currently stands, commercial deployment of marine geoengineering cannot be conducted either in Australian waters or from Australian vessels.

Harsh criminal penalties will apply to people who conduct marine geoengineering without a permit. Offenders face 12 months imprisonment and/or a fine of up to $68,750.

The bill also establishes offences for loading and exporting material to be used for marine geoengineering without a permit.

Rules limit financial incentives for research

Prohibiting marine geoengineering deployment may be appropriate now. But without future prospects for deployment there may be little incentive to invest in research.

The treaty rules ban ocean-based research directly leading to financial and/or economic gain. This protection is important for building public trust and advancing the public interest. But broad prohibition could hamper marine geoengineering research for economic purposes such as eventual carbon crediting and trading. It could also call into question government subsidies and tax incentives encouraging private research investment.

The parliamentary inquiry did not consider the implications of the new rules for Australia’s carbon markets, or on research to save the Great Barrier Reef.

Changes could affect research to save the reef

Since 2019, the Australian government has invested in marine cloud brightening and other interventions to protect the reef from heat stress and coral bleaching. The first outdoor experiments were conducted in 2020.

The effectiveness of marine cloud brightening is yet to be demonstrated at scale. But modelling suggests a combination of marine cloud brightening and crown-of-thorns starfish control could help protect the reef until 2040.

The treaty rules do not currently apply to marine cloud brightening. However, countries are currently considering adding marine cloud brightening to the list of regulated activities. This could allow research but prohibit deployment. The government should evaluate how this could affect its investment in marine cloud brightening research and associated programs.

Australia’s marine environment is already suffering from warming and acidification. Appropriately-managed marine geoengineering activities may help reduce the damage and/or mitigate climate change.

The treaty’s environmental safeguards are important to ensure the risks from ocean fertilisation activities are rigorously evaluated.

The current bill favours risk management, which is appropriate at the early stages of research and development. But by ruling out future deployment, Australia may undermine incentives to advance research.

Kerryn Brent, Senior Lecturer, Adelaide Law School, University of Adelaide; Jan McDonald, Professor of Environmental Law, University of Tasmania, and Manon Simon, Research Fellow, University of Tasmania

11 July 2023

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

Australians have watched in horror this week as two separate humpback whales were tangled up in Queensland shark nets on the same day. These put the number of whales caught in Queensland shark nets to four this season – that we know about.

Worryingly, most humpback whales migrating north from Antarctica haven’t even passed Sydney yet. With more whales travelling to the warm Queensland breeding waters, this probably won’t be the last shark net entanglement we’ll hear about this year.

I’ve seen the reality of whale entanglement in shark nets firsthand, when I studied a humpback whale calf who died in a shark net a few years back. The animal autopsy (necropsy) conducted later confirmed the animal drowned. It was terrible.

So what are shark nets exactly, and how do they harm animals?

Shark nets don’t just harm sharks

Whale entanglement in fishing gear is a global problem. In some cases nets – combined with other human-made threats such as ship collisions – limit the recovery of some whale populations since whale hunting ceased, including the North Atlantic right whale.

Fortunately, the number of Australian humpback whales has been growing post-whaling. In fact, Australia’s east coast humpback whale population has an estimated 40,000 individuals.

The bad news is, more whales means more potential interactions with humans and our fishing gear, such as shark nets.

Shark nets are dotted around Queensland to try to minimise shark interactions with swimmers. These nets are anchored by chain to the seafloor and are designed to capture sharks before they swim too close to the beach.

But the nets offer little protection. For one, they’re typically between 124 and 186 metres long, 6 metres deep and don’t cover the entire beach, which means sharks can easily swim around and under them.

Indeed, despite the use of shark nets and other shark control equipment (such as drumlines), new data released today shows the number of shark bites in Australia have actually increased since 1791. Scientists caution that we are yet to understand why.

Sadly, shark nets usually kill the sharks that swim into them as they’re unable to move. And as we’ve seen this week, these nets do not discriminate. Other marine life – turtles, dolphins as well as whales – get caught up in this problem, too.

What happens when a whale is entangled?

We don’t exactly know why whales become entangled. Whales are extremely curious mammals and may investigate these dangers as they migrate, but get too close. Another reason may be that whales and other animals might simply not see the danger, and swim into it.

It’s not just shark nets, though. Whales in Australian waters get tangled up in a range of fishing gear – lobster and crab pots, longlines, gillnets and ghost nets (discarded or previously-used gear).

Whale entanglement can be an extremely stressful experience. Often, we see whales thrashing at the surface trying to free themselves. This can make the situation worse and limit their movement even further.

Depending on the entanglement and gear type, some whales may be unable to surface for air, and drown.

Alternatively, some whales might manage to get partially free, but suffer long-term consequences from dragging the nets and ropes, which can cut into their blubber.

Over time, these wounds can become infected, restrict the movement of the whale, or both. This leaves them vulnerable to predators such as killer whales and sharks, or unable to dive and dodge vessels.

Can we use technology to stop entanglements?

The reality is no one wants entanglements. Humans don’t want it to happen and I’m sure an entangled whale doesn’t enjoy the experience. It’s an unintended consequence of our attempts to protect swimmers.

So, what can we do about it? Stop swimming in the ocean? Remove the nets? Or is new technology our only answer?

Some suggest removing Queensland’s shark nets during winter when whales make their annual migration. This has yet to take place. What’s more, people often swim year-round in Queensland’s warm ocean waters.

In contrast, shark nets in New South Wales are removed during the winter to avoid the main part of whale migration. They’re deployed again later in the year, from September 1, which overlaps only with the southward migration back to Antarctica.

In the meantime, we can continue to trial other options. One is using SMART drumlines for a more targeted approach to capture and relocate sharks.

This is where a baited hook is placed on an anchor with two buoys and an attached satellite (GPS) technology unit. Once a shark takes the bait and is captured, authorities are alerted and can respond quickly to tag and relocate the animal offshore, away from the area of concern.

Scientists can then use shark movement data from the tag to learn more about shark habitat use.

While this isn’t a solution to whale entanglement, it does reduce the amount of netting in the water compared to shark nets. It’s also a much better option for sharks.

The Queensland government has invested in shark-control technology called “catch alert drumlines”, which are a type of SMART drumline. Trials of their use began in 2021.

Drone surveillance has also been a complimentary shark monitoring tool on Queensland beaches.

What should you do if you see an entangled whale?

Whale disentanglement should never be attempted by the general public.

Disentangling a whale requires trained personnel, specialised gear and trained vessel operators. Even experts with years of disentangling experience have been killed helping free whales from nets.

Whales are big. When they’re stressed and exhausted, they pose a serious threat to humans. Instead, if you see a whale caught in gear at the beach, tell the appropriate people about it immediately.

Authorities, such as the Queensland Government (The Department of Environment and Science) or The Sea World Foundation are key contacts in Queensland.

Other options include ORRCA (NSW based, with coverage in Queensland), which can relay important information to the people best placed to help. Social media can also be a powerful tool to alert authorities.

Queensland whale rescue crews also remain on standby during whale migration season and can deploy trained personnel to respond to entanglements swiftly, weather permitting.

As the whale migration continues north, lets hope these recent entanglements continue to prompt timely discussion about shark nets in Queensland waters.

Vanessa Pirotta, Postdoctoral Researcher and Wildlife Scientist, Macquarie University

7 July 2022

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

About the megalodon

As a scientist who studies sharks and other ocean species, I am fascinated by the awesome marine predators that have appeared and disappeared through the eons.

That includes huge swimming reptiles like ichthyosaurs, plesiosaurs and the mosasaurs. These incredible predators lived during the time of the dinosaurs; megalodon would not appear for another 50 million years.

But when it did arrive on the scene, about 15 million to 20 million years ago, the megalodon must have been an incredible sight.

A fully grown individual weighed about 50 metric tons – that’s more than 110,000 pounds (50,000 kilograms) – and was 50 to 60 feet long (15 to 18 meters). This animal was longer than a school bus and as heavy as a railroad car!

Its jaws were up to 10 feet (3 meters) wide, the teeth up to 7 inches (17.8 centimeters) long and the bite force was 40,000 pounds per square inch (2,800 kilograms per square centimeter).

Not surprisingly, megalodons ate big prey. Scientists know this because they’ve found chips of megalodon teeth embedded in the bones of large marine animals. On the menu, along with whales: large fish, seals, sea lions, dolphins and other sharks.

Are scientists sure megalodon is extinct?

Internet rumors persist that modern-day megalodons exist – that they still swim around in today’s oceans.

But that’s not true. Megalodons are extinct. They died out about 3.5 million years ago.

And scientists know this because, once again, they looked at the teeth. All sharks – including megalodons – produce and ultimately lose tens of thousands of teeth throughout their lives.

That means lots of those lost megalodon teeth are around as fossils. Some are found at the bottom of the ocean; others washed up on shore.

But nobody has ever found a megalodon tooth that’s less than 3.5 million years old. That’s one of the reasons scientists believe megalodon went extinct then.

What’s more, megalodons spent much of their time relatively close to shore, a place where they easily found prey.

So if megalodons still existed, people would certainly have seen them. They were way too big to miss; we would have lots of photographs and videos.

Why megalodon disappeared

It probably wasn’t one single thing that led to the extinction of this amazing megapredator, but a complex mix of challenges.

First, the climate dramatically changed. Global water temperature dropped; that reduced the area where megalodon, a warm-water shark, could thrive.

Second, because of the changing climate, entire species that megalodon preyed upon vanished forever.

At the same time, competitors helped push megalodon to extinction – that includes the great white shark. Even though they were only one-third the size of megalodons, the great whites probably ate some of the same prey.

Then there were killer sperm whales, a now-extinct type of sperm whale. They grew as large as megalodon and had even bigger teeth. They were also warmblooded; that meant they enjoyed an expanded habitat, because living in cold waters wasn’t a problem.

Killer sperm whales probably traveled in groups, so they had an advantage when encountering a megalodon, which probably hunted alone.

The cooling seas, the disappearance of prey and the competition – it was all too much for the megalodon.

And that’s why you’ll never find a modern-day megalodon tooth.

Michael Heithaus, Executive Dean of the College of Arts, Sciences & Education and Professor of Biological Sciences, Florida International University

20 June 2022

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

Sharks used to figure prominently in my nightmares: coming after me in the ocean, rivers, swimming pools. But after spending some time with these elusive creatures in 2015, a more compelling question started to keep me up at night — do the very creatures that invade my dreams engage in sleep themselves?

As the world’s leading — and only — authority in sleep in elasmobranchs (sharks and rays), my research team and I have begun to unravel this enigma, and our latest findings of physiological evidence of sleep in sharks are the most conclusive on the topic yet.

Circadian rhythms

Quiescence, or inactivity, is often the most basic behavioural characteristic that we associate with sleep. It was indeed this behaviour that my team set out to identify when we began our investigations into the presence of sleep in sharks. Specifically, we studied the presence of circadian-organized activity patterns, as sleep is controlled by the circadian clock (an internal, biochemical oscillator) in many animals.

Sharks are a unique group of vertebrates, however, as many species swim continuously to passively push oxygen-rich seawater over their gills — these are known as ram ventilators. Other species manually pump seawater over their gills while remaining motionless (buccal pumpers).

A study we conducted in 2020 found the presence of daily activity patterns in all the species investigated, buccal pumpers and ram ventilators alike. Importantly, these patterns were found to be internally regulated (circadian in nature) in buccal pumping species. This was a major discovery and a great step in the right direction, but were periods of inactivity indicative of sleep?

Sleep or quiet restfulness?

An animal’s responsiveness and awareness of external stimulation is reduced when asleep due to a sensory shutdown, or attenuation. As sleep researchers, we can exploit this ubiquitous sleep characteristic to behaviourally distinguish sleep from quiet restfulness.

Our 2021 study found that buccal pumping sharks were less responsive to mild electrical pulses following five minutes of inactivity. This became the criteria for our working definition of sleep in these animals.

Sleep is also internally regulated, so that animals can recover lost sleep by sleeping more. This characteristic was absent in the sharks in our study — they did not make up sleep following periods of sleep deprivation. This phenomenon is also >absent during sleep in other marine fishes.

These somewhat conflicting results highlight an important point: behaviour can be deceptive and misleading. Animals can appear to be asleep while being awake and >vice versa. Sadly, behaviour alone is often not enough to reliably identify sleep in animals.

The physiology of shark sleep

To conclusively verify our working definition of sleep in buccal pumping sharks (more than five minutes of inactivity is sleep), my team set out to find physiological evidence of sleep that aligned with what we had seen behaviourally.

To do this, we recorded changes in metabolic rates in New Zealand’s draughtsboard shark via recordings of oxygen consumption over a 24-hour period. A drop in metabolic rate during sleep has been reported in many animals and is considered a reliable physiological indicator of sleep.

We also recorded subtle behaviours associated with sleep in other animals, such as eye state (open/closed) and body posture (upright/flat). We found there to be no significant difference in metabolic rates between swimming sharks and sharks engaging in periods of inactivity that lasted less than five minutes.

When sharks were inactive for five minutes or longer, however, metabolic rates dropped dramatically. This physiological change was also accompanied by a conspicuous shift in posture, with sharks transitioning from an upright position (sitting up on their pectoral fins) to a completely recumbent position. Eye state, however, was found to be unrelated to the sharks’ state of consciousness, as the animals were often observed sleeping with eyes open.

Taken together, these data are the most conclusive evidence for sleep in sharks and verify our previous behavioural findings.

Moving forward

Sleep has been found in all animals studied to date, stretching as far back on the evolutionary scale as and jellyfish. As the earliest living, jawed vertebrates, sharks play an important role in helping us understanding the evolutionary history of sleep in vertebrates.

Our research has come a long way in uncovering the previously unanswered question of sleep in sharks, but we have only touched the tip of the iceberg. Now that we know that (at least some) sharks do indeed sleep, the next question to answer is how they sleep.

Nothing is known about sleep in ram ventilating sharks. Their need for constant swimming to facilitate gas exchange suggests they have likely evolved interesting adaptations to permit sleep under this unusual lifestyle. Our group is now conducting electrophysiological studies of brain activity that will provide comprehensive insight into the form that sleep takes in these animals.

Michael Liam Kelly, Postdoctoral research fellow, Neuroscience, Simon Fraser University

April 7 2022

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

On Jan. 15, 2022, the Hunga Tonga-Hunga Ha’apai volcano in Tonga erupted, sending a tsunami racing across the Pacific Ocean in all directions.

As word of the eruption spread, government agencies on surrounding islands and in places as far away as New Zealand, Japan and even the U.S. West Coast issued tsunami warnings. Only about 12 hours after the initial eruption, tsunami waves a few feet tall hit California shorelines – more than 5,000 miles away from the eruption.

I’m a physical oceanographer who studies waves and turbulent mixing in the ocean. Tsunamis are one of my favorite topics to teach my students because the physics of how they move through oceans is so simple and elegant.

Waves that are a few feet tall hitting a beach in California might not sound like the destructive waves the term calls to mind, nor what you see in footage of tragic tsunamis from the past. But tsunamis are not normal waves, no matter the size. So how are tsunamis different from other ocean waves? What generates them? How do they travel so fast? And why are they so destructive?

Deep displacement

Most waves are generated by wind as it blows over the ocean’s surface, transferring energy to and displacing the water. This process creates the waves you see at the beach every day.

Tsunamis are created by an entirely different mechanism. When an underwater earthquake, volcanic eruption or landslide displaces a large amount of water, that energy has to go somewhere – so it generates a series of waves. Unlike wind-driven waves where the energy is confined to the upper layer of the ocean, the energy in a series of tsunami waves extends throughout the entire depth of the ocean. Additionally, a lot more water is displaced than in a wind-driven wave.

Imagine the difference in the waves that are created if you were to blow on the surface of a swimming pool compared to the waves that are created when someone jumps in with a big cannonball dive. The cannonball dive displaces a lot more water than blowing on the surface, so it creates a much bigger set of waves.

Earthquakes can easily move huge amounts of water and cause dangerous tsunamis. Same with large undersea landslides. In the case of the Tonga tsunami, the massive explosion of the volcano displaced the water. Some scientists are speculating that the eruption also caused an undersea landslide that contributed to the large amount of displaced water. Future research will help confirm whether this is true or not.

Tsunami waves travel fast

No matter the cause of a tsunami, after the water is displaced, waves propagate outward in all directions – similarly to when a stone is thrown into a serene pond.

Because the energy in tsunami waves reaches all the way to the bottom of the ocean, the depth of the sea floor is the primary factor that determines how fast they move. Calculating the speed of a tsunami is actually quite simple. You just multiply the depth of the ocean – 13,000 feet (4,000 meters) on average – by gravity and take the square root. Doing this, you get an average speed of about 440 miles per hour (700 kilometers per hour). This is much faster than the speed of typical waves, which can range from about 10 to 30 mph (15 to 50 kph).

This equation is what oceanographers use to estimate when a tsunami will reach faraway shores. The tsunami on Jan. 15 hit Santa Cruz, California, 12 hours and 12 minutes after the initial eruption in Tonga. Santa Cruz is 5,280 miles (8,528 kilometers) from Tonga, which means that the tsunami traveled at 433 mph (697 kph) – nearly identical to the speed estimate calculated using the ocean’s average depth.

Destruction on land

Tsunamis are rare compared to ubiquitous wind-driven waves, but they are often much more destructive. The 2004 Indian Ocean tsunami killed 225,000 people. More than 20,000 lost their lives in the 2011 Japan tsunami.

What makes tsunamis so much more destructive than normal waves?

In the open ocean, tsunami waves can be small and may even be undetectable by a boat at the surface. But as the tsunami approaches land, the ocean gets progressively shallower and all the wave energy that extended thousands of feet to the bottom of the deep ocean gets compressed. The displaced water needs to go somewhere. The only place to go is up, so the waves get taller and taller as they approach shore.

When tsunamis get to shore, they often do not crest and break like a typical ocean wave. Instead, they are more like a large wall of water that can inundate land near the coast. It is as if sea level were to suddenly rise by a few feet or more. This can cause flooding and very strong currents that can easily sweep people, cars and buildings away.

Luckily, tsunamis are rare and not nearly as much of a surprise as they once were. There is now an extensive array of bottom pressure sensors, called DART buoys, that can sense a tsunami wave and allow government agencies to send warnings prior to the arrival of the tsunami.

If you live near a coast – especially on the Pacific Ocean where the vast majority of tsunamis occur – be sure to know your tsunami escape route for getting to higher ground, and listen to tsunami warnings if you receive one.

The eruption of the Hunga Tonga-Hunga Ha’apai volcano severed the main communication cable that connects the people of Tonga to the rest of the world. While the science of tsunamis can be fascinating, these are serious natural disasters. Only a few deaths have been reported so far from Tonga, but many people are missing and the true extent of the damage from the tsunami is still unknown.

Sally Warner, Assistant Professor of Climate Science, Brandeis University

January 19 2022

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

Valerio Micaroni

Sponges are ancient marine animals, very common throughout the world’s oceans and seem less affected by ocean warming and acidification.

Our latest research shows they can also survive low levels of oxygen.

This is a surprising finding because most sponges are rarely exposed naturally to low oxygen in modern seas.

We propose their tolerance is the result of their long evolutionary history and exposure to variable oxygen concentrations through geological time.

As our oceans continue to warm due to climate change, they are expected to hold less oxygen.

The ability of sponges to survive low-oxygen conditions means they are likely to tolerate these possible future environments better than other organisms living on the seafloor.

There are an estimated 8000-plus sponge species in the oceans. They are multicellular organisms with a body architecture built around a system of water canals, pores and channels allowing water to be pumped and circulated through them.

Their specialised pumping and feeding cells, called choanocytes, are highly efficient. Sponges can pump the equivalent of their own body volume in a matter of seconds.

In modern oceans, sponges are often the most abundant organisms in rocky reef environments. They fulfil important ecological functions as part of bottom-dwelling (benthic) communities worldwide.

Sponges have many roles in marine ecosystems, but their water-processing ability and efficiency at capturing small particles is the most important because it links the water column with the seafloor. Sponges also support diverse seafloor communities by transforming carbon.

Some sponge species have been shown to be very tolerant to climate change stressors, particularly changing temperature and acidity (measured as pH). This means sponges could be future winners in changing oceans.

Sponges in past oceans

We know that sponges are ancient organisms, but recently described 890-million-year-old fossils have turned our understanding of evolution on its head.

Most major animal groups, including arthropods and worms, first appear in the fossil record during a period known as the Cambrian explosion, 540 million years ago. But if the newly-described fossils are indeed sponges, they would have existed nearly 300 million years earlier, significantly pushing back the date of Earth’s earliest known animals.

If the ancestors of modern sponges are about 900 million years old, they would have evolved and survived during the Marinoan glaciation, 657-645 million years ago, when the oceans were extremely low in oxygen.

They would have also likely experienced wide fluctuations in other environmental conditions such as pH, temperature and salinity through evolutionary time.

Sponge tolerance to low oxygen

Our recent environmental tolerance experiments support this scenario, showing they are surprisingly tolerant to low levels of oxygen.

We assessed the response of sponges to moderate and severe low-oxygen events in a series of laboratory experiments on four species from the northeast Atlantic and southwest Pacific. Sponges were exposed to a total of five low-oxygen treatments, with increasing severity (40%, 20%, 6%, 5% and 1.5% air saturation) over seven to 12 days.

We found the sponges generally very tolerant of hypoxia. All but one of the species survived in the extreme experimental conditions, and that species only began to die off at the lowest oxygen concentration. In most experiments, hypoxic conditions did not significantly affect the sponges’ respiration rates, which suggests they can take up oxygen at very low concentrations in the surrounding environment.

As a response to the low oxygen, sponges displayed a number of shape and structural changes, likely maximising their ability to take up oxygen at these low levels.

Sponges in future oceans

Warmer ocean water holds less oxygen, and ocean deoxygenation is one of the major consequences of climate change.

Warmer water also becomes more buoyant than cooler water, which reduces the mixing of surface oxygenated water with deeper layers that naturally contain less oxygen. At the same time, warmer temperatures increase the demand of organisms for oxygen as metabolic rates increase and stress responses are initiated.

While oxygen levels in the ocean are only expected to fall on average by 4% across all oceans, these effects are likely to be much more extreme locally and regionally. In coastal waters, climate-driven ocean deoxygenation can be exacerbated by a process called eutrophication, essentially an increase in nutrients. This fuels plankton blooms, and when bacteria breakdown the dead phytoplankton, they use up all the oxygen.

Since the land is generally the source of these excess nutrients, shallow coastal areas are most at risk. These are areas where rocky reefs are typically dominated by sponges, particularly just below the depth of light penetration (typically 20-30m).

Our finding lends further support to the idea that sponges will be the survivors if our oceans continue to warm.

James Bell, Professor of Marine Biology, Te Herenga Waka — Victoria University of Wellington; Rob McAllen, Professor of Marine Conservation, University College Cork, and Valerio Micaroni, PhD Candidate in Coastal and Marine Biology and Ecology, Te Herenga Waka — Victoria University of Wellington

January 17 2022

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

Before COVID-19, global surf tourism spending was estimated at up to A$91 billion per year. And since the start of the pandemic, demand for surfing has boomed as people increasingly turn to outdoor activities. But surfing’s benefits to human well-being aren’t often studied in economics terms. This is a major knowledge gap we are now trying to fill. Such research is important. Changes to the coastline such as from sea walls and groynes can dramatically reduce the quality of surfing waves. But the consequences of coastal developments on surfing are often poorly understood and rarely quantified before projects start. It’s crucial we understand the real value of surfing, before we lose the myriad of benefits they bring – not only to Australia’s 1.2 million active surfers, but to hundreds of coastal towns where surfing underpins the local economy and lifestyle.

Surfing economics

There are many studies on the economic value of Australian beach pastimes such as fishing, swimming and diving. But not for surfing. Internationally, we know surfing is a major direct contributor to the economy of wave-rich places. However, until recently, the value of surfing to human well-being has been largely unaccounted for.

This is despite recent evidence pointing to surfing’s positive social and health outcomes, including among war veterans and children with chronic illnesses.

Surfing Economics is an emerging field of research that documents and quantifies the total economic value of surfing. This can include, for example, increased house prices near good quality breaks, or social welfare benefits people derive from visiting surf beaches.

Building on the few previous surfing economics studies in Australia, our research aims to calculate the total economic value of surfing.

Our forthcoming study on the Noosa World Surf reserve, so far, demonstrates that the local economic contribution of surfing is in the order of hundreds of millions of dollars. This in terms of surfers’ welfare, as well as direct spending on surf gear and travel.

Overseas, the economic contribution is a little clearer. A 2017 study used satellite imagery to demonstrate that economic activity grows faster near good-quality surf breaks, particularly in developing countries such as Indonesia and Brazil.

In the UK alone, the overall annual impact of surfing on the national economy is calculated at up to £5 billion (over A$9 billion).

How coastal projects make or break waves

Swell waves are typically formed by winds blowing many kilometres offshore. It’s perhaps easy to think that this natural,distant origin means there’s nothing we can do about the formation of waves.

But the truth is surfing waves are the product of complex interactions between waves, tides, currents, wind and the shape of the seabed. Shallow coral reefs, headlands and sand banks are responsible for making highly sought-after waves.

By directly or indirectly impacting any of these factors, wave quality has been changed for better – or for worse.

The world-renowned Mundaka wave, in northern Spain, temporally disappeared because dredging of the nearby rivermouth changed ocean dynamics. This resulted in a decline in economic activity and the cancellation of the Billabong Pro World Championship in 2005 and 2006.

In the Portuguese island of Madeira, the construction of a rock-wall severely disrupted the formation of the Jardim do Mar wave in 2005, and a fall in local economic growth rates followed. In Peru, the extension of a fishing pier negatively impacted Cabo Blanco, one of Peru’s best barrelling waves, by shortening its length.

Closer to home, the Ocean Reef Marina, currently under construction in Perth’s north, will significantly impact three local surf breaks. About 1.5 kilometres of mostly unmodified beaches are being redeveloped into a brand new marina.

Studies have shown that well planned coastal management interventions can dramatically increase benefits to surfers and non-surfers alike.

One of the most iconic examples is the “Superbank” at Snapper Rocks in the Gold Coast. There, a world class wave forms thanks to river sediment being relocated through the Tweed Sand Bypassing Project.

The project is costly to operate and has impacted nearby beaches. But its expenses are outweighed by improvements to surf quality and beach amenity, which underpin the local economy and the nature-based, active lifestyle the Gold Coast is famous for.

Giving waves legal protection

Building on efforts nearly 40 years ago to protect Victoria’s iconic Bells Beach wave, Peru and New Zealand have granted statutory protection to their surf breaks under environmental protection laws.

In practice, this means threats to surf breaks by coastal activities, such as sewage discharges or building offshore structures, must be avoided or mitigated.

Similar recognition and valuation of surfing resources is necessary and would be highly beneficial for Australia.

A rigorous, science-based evaluation of surfing’s total economic value could serve to inform cost-benefit analysis of coastal management programs. These may include fighting erosion to protect the coastline, or building artificial surf reefs.

In these uncertain times of COVID-19, many of us cannot yet travel far away. But with 85% of Australians living by the coast, many of us can still catch a wave at our doorstep – and that is priceless.

Ana Manero, Research Fellow, Australian National University; Alaya Spencer-Cotton, Research assistant, The University of Western Australia; Javier Leon, Senior lecturer, University of the Sunshine Coast, and Neil Lazarow, Senior Research Consultant, CSIRO

January 10 2022

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

From enormous tides to millions of shells, here are 6 unique beaches for your summer road trip

As lockdowns ease and we head into summer, many Australians have started thinking about their beach holiday. For most people, a beach involves sun, sand, salt, and waves. A beach is a beach – right?

For coastal scientists and engineers, it’s a little different. We wonder how these beaches are made and why they are so different.

Australia has over 35,000 kilometres of coastline to explore, and our beaches can differ radically. In Australia’s south, where tides are smaller and waves bigger, we get high energy beaches with lots of surf and sand. The north’s larger tides and smaller waves mean the beaches look quite different – they’re flatter, with big intertidal zones. Some even have mud instead of sand.

To pique your interest, here are six beaches from around the country with special characteristics, all well worth exploring on your summer road trip or beach holiday.

1. Sandy Cape – end of the line for the sand islands

K’gari (Fraser Island), Queensland.

Waves and storms along the east coast, from the New South Wales/Victoria border to K'Gari in Queensland, usually come from the south and southeast. This drives longshore sediment transport, a process where sand is moved up the coast by waves and wave-driven currents.

As the sand moves along the NSW coast and into Queensland, it beach-hops its way north, encountering natural barriers like headlands as well as human barriers such as breakwaters. Sand will often skirt these barriers in pulses, as tends to happen at Byron Bay.

As the coast turns to the west in southeast Queensland, the sand keeps getting pushed north. That’s how Australia got the largest sand islands in the world: Minjerribah (South and North Stradbroke), Mulgumpin (Moreton), Yarun (Bribie), and finally K’gari.

The northernmost point of K’gari, Sandy Point, marks where the sand heads underwater, moving along the continental shelf before dropping off the edge and sliding down the slope into the deep abyssal plains.

If you make it to this beach, you can see sand being swirled away into deeper water – the very end of the above-water part of the cycle.

2. The Funnel – the biggest tides in Australia

Collier Bay, Western Australia

The Kimberley region of Australia is home to the biggest tides in the country. Unfortunately, there aren’t many tide gauges in this area, with over 1,000km between instruments in places. So, to find the beach with the biggest tides, we either have to collect more data or use a computer model.

When we model the tides for every Australian beach, The Funnel in Collier Bay comes out as the beach with the biggest tides. Its range is a whopping 13.5 metres!

Getting to this beach might be tricky as you’ll need to arrive by boat. But it would be worth the trip, as the beach at high tide is composed of cobbles and likely sand and mud at low tide. Watching the tide roar in would be something to see – just watch out for crocs!

3. Goolwa Beach – the high energy beach

South Australia

When rivers as big as the Murray – whose basin covers one-seventh of mainland Australia – meet the ocean, they normally form huge deltas like the Mississippi or the Nile.

But because of Australia’s age, low rainfall and water extraction for agriculture, the Murray-Darling Basin only delivers a relatively small amount of water and sediment to the coast. So instead of a classic river delta at the end of the Murray, unusually, we have a beach system.

Goolwa Beach is part of this system, its fine sands representing the last barrier to the mighty Murray River on its journey to the ocean. The beach is also exposed to the huge waves rolling in from the Southern Ocean. That makes it one of our highest energy beaches – so much so it’s the archetype of the high energy beach type called “dissipative” in our Australian beach classification system.

4. Amity Beach – the beach with sinkholes

Minjerribah, Queensland

The islands of Minjerribah (North Stradbroke) and Mulgumpin (Moreton) form the barrier separating Moreton Bay near Brisbane from the Coral Sea. Between them lies Rainbow Channel through which the tide flows in and out of Moreton Bay.

These fast tidal currents cause large amounts of sand to form shifting sand shoals on both the ocean and bay sides of the channel.

Amity Beach sits on the edge of this channel and the constantly changing dynamics of this system cause “sinkholes” to occur regularly on this beach. Rainbow Beach near K'Gari is better known due to its habit of swallowing cars, but Amity Beach is unique. Why? Because the sinkholes always occur in the same place.

That makes it the only place in the world where scientists and engineers can reliably observe this amazing phenomenon to work out why sinkholes occur and how they work.

5. Shell Beach – walk on millions of shells

Shark Bay, Western Australia

Most of us tend to think of beaches as being made up by sand, but they don’t have to be. Beaches can be made of mud or cobbles or even just shells.

Shell Beach in Shark Bay is a rarity as it’s almost entirely made up of trillions of shells, with the piles up to 10m deep.

These shells all come from one mollusc, the Fragum cockle. The reason there are so many of these shells is because the waters of Shark Bay are saltier than the ocean.

This hypersaline environment makes it hard for most species to survive. That means the Fragum cockle has very few competitors or predators and can proliferate. Just remember to bring some footwear!

6. Bengello Beach – a time capsule made of sand

New South Wales

Coastal scientists and engineers love data about beaches, and especially long-term records of how much sand is on a beach.

Bengello Beach in southern NSW represents the longest record of beach surveys in Australia with measurements every 2-6 weeks since January 1972.

These measurements have captured beach erosion during storms and its subsequent recovery. Data like this underpins models forecasting how our beaches will respond to climate change.

Bengello is also a living snapshot of beach evolution, capturing the way many of Australia’s beaches have changed since sea level stabilised at about today’s level after the last ice age.

If you walk from the road to the beach, you pass over ridges of ancient sand dunes. These formed as the beach slowly built out towards the sea over the last 6,000 years, as waves and currents piled up more and more sand on the beach.

When road-tripping to Australia’s beaches, remember to check local weather and marine forecasts to make sure it’s safe to swim and leave only your footprints behind. And if you make it to any of these beaches, why not share your knowledge about their significance with your travel buddies?

Hannah Power, Associate Professor in Coastal and Marine Science, University of Newcastle

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

23 December 2021

Severe coastal flooding inundated islands and atolls across the western equatorial Pacific last week, with widespread damage to buildings and food crops in the Federated States of Micronesia, Marshall Islands, Papua New Guinea and Solomon Islands.

On one level, very high tides are normal at this time of year in the western Pacific, and are known as “spring tides”. But why is the damage so bad this time? The primary reason is these nations are enduring a flooding trifecta: a combination of spring tides, climate change and La Niña. La Niña is a natural climate phenomenon over the Pacific Ocean known for bringing wet weather, including in eastern Australia. A less-known impact is that La Niña also raises sea levels in the western tropical Pacific. In a terrifying glimpse of things to come, this current La Niña is raising sea levels by 15-20 centimetres in some western Pacific regions – the same sea level rise projected to occur globally by 2050, regardless of how much we cut global emissions between now and then. So let’s look at this phenomena in more detail, and why we can expect more flooding over the summer.

These spring tides aren’t unusual

Low-lying islands in the Pacific are considered the frontline of climate change, where sea level rise poses an existential threat that could force millions of people to find new homes in the coming decades.

Last week’s tidal floods show what will be the new normal by 2050. In the Marshall Islands, for example, waves were washing over boulder barriers, causing flooding on roads half a metre deep.

This flooding has coincided with the recent spring tides. But while there is year to year variability in the magnitude of these tides that vary from location to location, this year’s spring tides aren’t actually unusually higher than those seen in previous years.

For instance, tidal analysis shows annual maximum sea levels at stations in Lombrom (Manus, Papua New Guinea) and Dekehtik (Pohnpei, Federated States of Micronesia) are roughly 1-3cm higher than last year. Meanwhile, those at Betio (Tarawa, Kiribati) and Uliga (Majuro, Marshall Islands) are roughly 3-6cm lower.

This means the combined impacts of sea level rise from climate change and the ongoing La Niña event are largely responsible for this year’s increased flooding.

A double whammy

The latest assessment report from the Intergovernmental Panel on Climate Change finds global average sea levels rose by about 20cm between 1901 and 2018.

This sea level rise would, of course, lead to more coastal inundation in low-lying regions during spring tides, like those in the western tropical Pacific. However, sea level rise increases at a relatively small rate – around 3 millimetres per year. So while this can create large differences over decades and longer, year to year differences are small.

This means while global mean sea level rise has likely contributed to last week’s floods, there is relatively small differences between this year and the previous few years.

This is where La Niña makes a crucial difference. We know La Nina events impact the climate of nations across the Pacific, bringing an increased chance of high rainfall and tropical cyclone landfall in some locations.

But the easterly trade winds, which blow across the Pacific Ocean from east to west, are stronger in La Niña years. This leads to a larger build up of warm water in the western Pacific.

Warm water is generally thicker than cool water (due to thermal expansion), meaning the high heat in the western equatorial Pacific and Indonesian Seas during La Niña events is often accompanied by higher sea levels.

This year is certainly no different, as can be seen in sea surface height anomaly maps here and here.

From these maps, along with past studies, it’s clear Pacific islands west of the date line (180⁰E) and between Fiji and the Marshall Islands (15⁰N-15⁰S) are those most at risk of high sea levels during La Niña events.

What could the future hold?

We can expect to see more coastal flooding for these western Pacific islands and atolls over the coming summer months. This is because the La Niña-induced sea level rise is normally maintained throughout this period, along with more periods with high spring tides.

Interestingly, the high sea levels related to La Niña events in the northern hemisphere tend to peak in November-December, while they do not peak in the southern hemisphere until the following February-March.

This means many western Pacific locations on both sides of the equator will experience further coastal inundation in the short term. But the severity of these impacts is likely to increase in the southern hemisphere (such as the Solomon islands, Tuvalu and Samoa) and decrease in the northern hemisphere (such as the Marshall Islands and the Federated States of Micronesia).

Looking forward towards 2050, a further 15-25cm of global average sea level rise is expected. La Niña events typically cause sea levels in these regions to rise 10-15cm above average, though some regions can bring sea levels up to 20cm.

Given the projected sea level rise in 2050 is similar to the La Niña-induced rise in the western Pacific, this current event provides an important insight into what will become “normal” inundation during spring tides.

Unfortunately, climate projections show this level of sea level rise by 2050 is all but locked in, largely due to the greenhouse gas emissions we’ve already released.

Beyond 2050, we know sea levels will continue to rise for the next several centuries, and this will largely depend on our future emissions. To give low-lying island nations a fighting chance at surviving the coming floods, all nations (including Australia) must drastically and urgently cut emissions.

Shayne McGregor, Associate Professor, and Associate Investigator for the ARC Centre of Excellence for Climate Extremes, Monash University

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

Dec 16 2021

The presumed death of 57-year-old Paul Millachip in an apparently fatal shark bite incident near Perth on November 6 is a traumatising reminder that while shark bites are rare, they can have tragic consequences.

Despite the understandably huge media attention these incidents generate, there has been little scientific insight into how and why they happen.

Sharks in general, and white sharks in particular, have long been described as “mindless killers” and “man-eaters”.

But our recent research confirms that some bites on humans may be the result of mistaken identity, whereby the sharks mistake humans for their natural prey based on visual similarities.

Sharks have an impressive array of senses, but vision is thought to be particularly important for prey detection in white sharks. For example, they can attack seal-shaped decoys at the surface of the water even though these decoys lack other sensory cues such as scent.

The visual world of a white shark varies substantially from that of our own. White sharks are likely colourblind and rely on brightness, essentially experiencing their world in shades of grey. Their eyesight is also much less acute than ours – in fact, it’s probably more akin to the blurry images a human would see underwater without a mask or goggles.

The mistaken identity theory

Bites on surfers have often been explained by the fact that, seen from underneath, a paddling surfer looks a lot like a seal. But this presumed similarity has only previously been assessed based on human vision, using underwater photographs to compare their silhouettes.

Recent developments in our understanding of sharks’ vision have now made it possible to examine the mistaken identity theory from the shark’s perspective, using a virtual system that generates “shark’s-eye” images.

In our study, published last month, we and our colleagues in Australia, South Africa and the United Kingdom compared video footage of seals and of humans swimming and paddling surfboards, to predict what a young white shark sees when looking up from below.

We specifically studied juvenile white sharks – between of 2m and 2.5m in length – because data from New South Wales suggests they are more common in the surf zone and are disproportionately involved in bites on humans. This might be because juvenile sharks are more likely to make mistakes as they switch to hunting larger prey such as seals.

Our results showed it was impossible for the virtual visual system to distinguish swimming or paddling humans from seals. This suggests both activities pose a risk, and that the greater occurrence of bites on surfers might be linked to the times and locations of when and where people surf.

Our analysis suggests the “mistaken identity” theory is indeed plausible, from a visual perspective at least. But sharks can also detect prey using other sensory systems, such as smell, sound, touch and detection of electrical fields.

While it seems unlikely every bite on a human by a white shark is a case of mistaken identity, it is certainly a possibility in cases where the human is on the surface and the shark approaches from below.

However, the mistaken identity theory cannot explain all shark bites and other factors, such as curiosity, hunger or aggression are likely to also explains some shark bites.

Can this knowledge help protect us?

As summer arrives and COVID restrictions lift, more Australians will head to the beach over the coming months, increasing the chances they might come into close proximity with a shark. Often, people may not even realise a shark is close by. But the past weekend gave us a reminder that shark encounters can also tragically result in serious injury or death.

Understanding why shark bites happen is a good first step towards helping reduce the risk. Our research has inspired the design of non-invasive, vision-based shark mitigation devices that are currently being tested, and which change the shape of the silhouette.

We still have a lot to learn about how sharks experience their world, and therefore what measures will most effectively reduce the risks of a shark bite. There is a plethora of devices being developed or commercially available, but only a few of them have been scientifically tested, and even fewer – such as the devices made by Ocean Guardian that create an electrical field to ward off sharks – have been found to genuinely reduce the risk of being bitten.

Laura Ryan, Postdoctoral Researcher, Department of Biological Sciences, Macquarie University and Charlie Huveneers, Associate professor, Flinders University

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

Nov 10 2021

Am I not pretty enough? This article is part of The Conversation’s series introducing you to unloved Australian animals that need our help.

Australia’s oceans are home to a startling array of biodiversity — whales, dolphins, dugongs and more. But not all components of Aussie marine life are the charismatic sort of animal that can feature in a tourism promotion, documentary, or conservation campaign.

The echiuran, or spoon worm, is one such animal. It is also called the penis worm.

There is no “Save the Echiuran Foundation” and no influencers selling merchandise to help save them. But these phallic invertebrates are certainly worth your time as integral and fascinating members — of Australia’s marine ecosystems.

What makes them so interesting?

Taxonomists have classified echiurans in various different ways over the years, including as their own group of unique animals. Today, they’re considered a group of annelid worms that lost their segmentation. There is uncertainty about the exact number of species, but an estimate is 236.

The largest echiuran species reach over two metres in length! They have a sausage-shaped muscular trunk and an extensible proboscis (or tongue) at their front end. The trunk moves by wave like contractions.

Most echiurans live in marine sand and mud in long, U-shaped burrows, but some species also live between rocks. And they’re widespread, living up to 6,000 metres deep in the ocean all the way to the seashore, worldwide.

For example, one species, Ochetostoma australiense, is a common sight along sandy or muddy shorelines of Queensland and New South Wales, where it sweeps out of its burrow to collect and consume organic matter.

In fact, their feeding activities are something to behold, as they form a star-like pattern on the surface that extends from their burrow opening.

In another species, Bonella viridis, there is a striking difference> between the males and females — the females are large (about 15 centimetres long) and the males are tiny (1-3 millimetres). Most larvae are sexually undifferentiated, and the sex they end up as depends on who’s around. The larvae metamorphose into dwarf males when they’re exposed to females, and into females when there are no other females present.

Males function as little more than a gonad and are reliant on females for all their needs.

Why they’re so important

Echiurans perform a range of important ecological functions in the marine environment. They’re known as “ecosystem engineers” - organisms that directly or indirectly control the availability of resources, such as food and shelter, to other species. They do this mainly by changing the physical characteristics of habitats, for example, by creating and maintaining burrows, which can benefit other species.

Echiurans also have a variety of symbiotic animals, including crustaceans and bivalve molluscs, residing in their burrows. This means both animals have a mutually beneficial relationship. In fact, animals from at least eight different animal groups associate with echiuran burrows or rock-inhabiting echiurans — and this is probably an underestimate.

They’re beneficial for humans, too. Their burrowing and feeding habits aerate and rework sediments. Off the Californian coastline, for example, scientists noted how these activities reduced the impacts of wastewater on the seabed.

And they’re an important part of the such as the houndsharks, and species of commercial significance such as Alaskan plaice. Some mammals feast on them, too, such as the in the Bering Sea, and the southern sea otter. In Queensland they also contribute to the diet of the critically endangered eastern curlew.

And many people eat them in East and Southeast Asia, where they’re chopped up and eaten raw, or used as a fermented product called gaebul-jeot. They (allegedly) taste slightly salty with sweet undertones.

The unloved billions

In Australia there is very little known about the biology and ecological roles of our echiuran fauna. This can also be said of many of Australia’s soft sediment marine invertebrates — the unloved billions.

We simply do not understand the population dynamics of even the large and relatively common echiuran species, and the human processes that threaten them. Given their role as ecosystem engineers, impacts to echiuran populations can flow on to other components of the seabed fauna, imperilling entire ecosystems.

We can, in general terms, predict that populations have suffered from the cumulative effects of urbanisation and coastal development. This includes loss and modification of habitats, and changes to water quality.

Populations may also be harmed by undersea seismic activities used in oil and gas exploration, but this is still poorly understood. Until recently, scientists knew only of the threats seismic activity posed to the hearing of whales and dolphins. It’s becoming clearer they can also affect the planet’s vital invertebrate species.

It is a dilemma for marine conservation when so little is known about a species that impacts cannot be reliably predicted, and where there is little or no impetus to improve this knowledge base.

We cannot simply presume an animal does not play an important role in an ecosystem because it lacks charisma.

In George Orwell’s novel Animal Farm, it was said “All animals are equal but some animals are more equal than others”. This remains abundantly true in terms of how humans view animals. But we must move away from this philosophy if we are to conserve and restore the planet’s fragile ecosystems.

Daryl McPhee, Associate Professor of Environmental Science, Bond University

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

August 18 2021

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

Snorkellers 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.

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.

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.

‘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.

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.

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

August 20 2021

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