The story of a wave: from wind-blown ripples to breaking on the beach



By the time a wave reaches shore, it may have travelled tens of thousands of kilometres.
Ian Mitchinson / Shutterstock

Shane Keating, UNSW

It’s a cliché, but Aussies love the beach. And little wonder: with 36,000 kilometres of coastline, Australia is blessed with some of the best beaches in the world.

Around 20 million Australians live within 50 kilometres of the coast. As summer temperatures soar, we flock to the ocean to splash, swim, surf, paddle, and plunge in the waves.

But where do those waves come from? How do they form, and why do they break? As it turns out, what we see at the shore is just the last few moments of an epic journey.




Read more:
Hidden women of history: Isabel Letham, daring Australian surfing pioneer


Great waves from tiny ripples grow

The waves we see crashing on the beach can begin their lives tens of thousands of kilometres away. Surface waves, as they are known, are born when the wind blows over the ocean, amplifying small ripples and transferring momentum from the atmosphere to the water.

The height of the wave depends on how long the wind is blowing and the distance – or fetch – over which it blows. The largest waves are created by distant storms, which churn up the surface of the ocean and radiate waves outwards like ripples in a pond.

Surface waves don’t move the water itself very far – each water molecule travels forward and back in a circle a few meters across and ends up back at its starting point.

As the wave crest rises, water molecules gather gravitational potential energy that is released as kinetic energy when the water descends into the trough of the wave. This energy is then passed onto the next crest in a see-saw of kinetic and potential energy that can propagate across an entire ocean basin.

The mounting wave

Once a wave leaves the open ocean and approaches land, the sea floor begins to exert its influence. Surface waves transmit their energy more slowly in shallow water than in deep water. This causes energy to pile up near the shore. Waves start to shoal, becoming taller, steeper, and more closely spaced.

Once a wave grows too steep to hold together, it breaks. Breaking waves come in different varieties.

Spilling breakers, which crumble gently into white water, occur when the sea floor rises relatively slowly.

By contrast, plunging breakers – the classic rolling waves favoured by surfers – form when the sea floor rises sharply, particularly near reefs and rocky headlands.

Finally, surging waves occur when the shore is almost vertical. These waves don’t produce breakers but rather a rhythmic rise and fall of the sea surface.

Bend it like bathymetry

The shape or topography of the sea floor – called bathymetry – can have remarkable effects on breaking waves. If the depth of the sea floor changes parallel to the coast, incoming waves will refract or bend so their crests line up with the shoreline.

The effect can be clearly seen near headlands: waves close to the headland move slowly because the water is shallow, while waves further out move more quickly. This causes waves to curl around the headland like a marching band rounding a corner.

Bathymetry is also responsible for some of the biggest waves on Earth. Famous big wave surf spots like Mavericks in Northern California and Nazaré in Portugal benefit from undersea canyons that refract incoming waves and focus them into monsters. The Nazaré wave originates from an undersea canyon almost 5 kilometres deep to produce waves as tall as an eight-storey building.




Read more:
Don’t get sucked in by the rip this summer


Don’t risk the rip

The story of a wave doesn’t end when it breaks, however. Breaking waves push water towards the shore, raising the water level. This water will try to flow back offshore via the lowest point along the beach. The result is a rip current: a swift, narrow current that flows out to sea.

Rip currents are Australia’s number one coastal hazard, responsible for more fatalities per year than shark attacks, bush fires, floods, and cyclones combined. Inexperienced swimmers caught in a rip can panic and try to swim against the current, which is a dangerous recipe for exhaustion. Yet most Australians are unable to identify a rip current, and two-thirds of those who think they can get it wrong.

Purple dye traces the path of a rip current.
Rob Brander

To spot a rip, look for a gap in the waves, a dark channel, or ripples surrounded by smoother water. The safest thing to do is to stick to patrolled beaches and swim between the flags. If you do find yourself caught in a rip, Surf Lifesaving Australia advises you to stay calm and conserve your energy.

Rip currents are usually quite narrow, so swim at right angles to the current until you are outside the rip. If you are too tired to swim, tread water and let yourself go with the flow until the rip weakens and you can signal for help.

Above all, if you are unsure, don’t risk the rip. Sit back and enjoy the waves from a safe distance instead.The Conversation

Shane Keating, Senior Lecturer in Mathematics and Oceanography, UNSW

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

Acidic oceans are corroding the tooth-like scales of shark skin



CT scan of a catshark hatchling head. Note the ridged scales.
Rory Cooper, Kyle Martin & Amin Garbout/Natural History Museum London, Author provided

Rory Cooper, University of Sheffield

Shark skin might look perfectly smooth, but inspect it under a microscope and you’ll notice something strange. The entire outer surface of a shark’s body is actually covered in sharp, little scales known as denticles. More remarkable still, these denticles are incredibly similar to human teeth, as they’re also comprised of dentine and enamel-like materials.

Your dentist will no doubt have warned you that acidic drinks like fizzy cola damage your teeth. This is because acid can dissolve the calcium and phosphate in the enamel tooth covering. For the first time, scientists have discovered a similar process acting on the tooth-like scales of sharks in the ocean.




Read more:
How we uncovered the feeding habits of sharks, thanks to plankton ‘post codes’


The carbon dioxide (CO₂) that humans release into the atmosphere doesn’t just heat the planet. As more of it dissolves in the ocean, it’s gradually increasing the acidity of seawater. In the past 200 years, the ocean has absorbed 525 billion tonnes of CO₂ and become 30% more acidic as a result. Now scientists worry that the lower pH is affecting one of the ocean’s top predators.

Denticles have sharp ridges and are arranged in an overlapping pattern, similar to chainmail.
Rory Cooper, Author provided

An unwelcome sea change

Over hundreds of millions of years, the denticles that make up shark skin have evolved to allow sharks to thrive in different environments. Different species have distinct denticle shapes and patterns that enable a range of remarkable functions. I’ve spent the last four years attempting to understand how the development of these scales is genetically controlled in shark embryos, and how their intricate details give each species an edge.

Denticles have highly specialised ridges which help reduce drag by up to 10%, allowing sharks to swim further and faster while using less energy. This works in a similar fashion to the ridges in the hulls of speed boats, which help the vessel move more efficiently through the water. In fact, these scales are so effective at reducing drag that scientists and engineers have long tried to create shark skin-inspired materials for boats and aircraft that can help them travel further on less fuel.

A catshark embryo about 80 days after fertilisation.
Rory Cooper, Kyle Martin & Amin Garbout/Natural History Museum London, Author provided

The patterning of denticles also works as a defensive armour, which protects sharks from their environment and from other predators. Some female sharks – such as the small-spotted catshark – have even developed a region of enlarged denticles which provide protection from a male shark’s bites during mating.

The changing chemistry of the ocean has been linked to coral bleaching, but its effect on other marine animals is less clear. To address this, researchers exposed puffadder shysharks – a species found off the coast of South Africa – to different levels of acidity in aquariums, and used a high-resolution imaging technique to examine the effect of acid exposure on their skin. After just nine weeks, they found that increased water acidity had weakened the surfaces of their denticles.

The puffadder shyshark (Haploblepharus edwardsii) is a slow moving species that lives on the sea floor.
Derekkeats/Wikipedia, CC BY-SA

Corrosion and weakening of the denticle surface could degrade the highly specialised drag-reducing ridges, affecting the ability of these sharks to swim and hunt. Many shark species are top-level predators, so if they’re not able to hunt as effectively, this might have an unpredictable impact on the population size of their prey and other animals in the complex marine environment. Some species of shark need to swim constantly to keep oxygen-rich water flowing over their gills and to expel CO₂ – another process which might be hindered by increased drag.




Read more:
Sharks: one in four habitats in remote open ocean threatened by longline fishing


Sharks belong to an ancient group of vertebrates known as the cartilaginous fishes, which split from the bony fishes – a lineage that later gave rise to humans – roughly 450 million years ago. Sharks, and other cartilaginous fish like rays, arose long before the dinosaurs, and have outlived multiple mass extinction events. But the rate of change in the marine environment over the last few centuries is an unprecedented challenge. These ancient predators may struggle to adapt to the fastest known change in ocean chemistry in the last 50 million years.The Conversation

Rory Cooper, PhD Researcher in Evolutionary Developmental Biology, University of Sheffield

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

Fish larvae float across national borders, binding the world’s oceans in a single network


Larval black sea bass, an important commercial species along the US Atlantic coast.
NOAA Fisheries/Ehren Habeck

Nandini Ramesh, University of California, Berkeley; James Rising, London School of Economics and Political Science, and Kimberly Oremus, University of Delaware

Fish populations are declining around the world, and many countries are trying to conserve them by regulating their fishing industries. However, controlling fishing locally may not do enough to strengthen fish populations. Often one nation’s fish stocks depend on the spawning grounds of a neighboring country, where fish release eggs and sperm into the water and larvae hatch from fertilized eggs.

We do research on oceans, climate and fisheries. In a recent study, we showed that global fisheries are even more tightly connected than previously understood. The world’s coastal marine fisheries form a single network, thanks to the drift of larvae along ocean currents.

This suggests that country-by-country fishery management may be fundamentally insufficient. If a fish species that provides food to one country should decline, the amount of fish spawn, or eggs and larvae, riding the ocean currents from there to other countries would also decline dramatically, resulting in further loss of fish elsewhere.

Many countries live with this risk, although they may not realize it. To manage fisheries effectively, nations must understand where the fish in their territories originate.

Ocean currents affect the speed at which fish eggs and larvae drift and vary through the year. This map shows surface current speeds for January: yellow = fastest, dark blue = slowest. Each country’s territory is highlighted with red dots during the month of maximum spawning activity in that country. In each territory, a different number of species spawn in each month of the year. The red dots appear in the month during which the largest number of species spawn in that territory.

Crossing national borders

Fish don’t recognize political boundaries, and regularly travel internationally. Scientists have tracked adult fish movements using electronic tags, and have shown that a few species migrate over long distances.

Countries and territories have negotiated agreements to ensure sustainable sharing of migratory fish. One such agreement joins several nations in the Western and Central Pacific Fisheries Commission to ensure that the territories fish cross share them sustainably.

But fish eggs and larvae are much harder to follow. Many species lay eggs in large numbers that float near the ocean surface. When they hatch, larvae measure a few millimeters long and continue to drift as plankton until they grow large enough to swim. During these stages of the life cycle, ocean currents sweep fish spawn across international boundaries.

Simulating the journeys of eggs and larvae

Like weather on land, the pattern of ocean currents varies with the seasons and can be predicted. These currents are typically sluggish, traveling about an inch per second, or less than 0.1 miles per hour.

There are a few exceptions: Currents along the eastern coasts of continents, like the Gulf Stream in North America or the Kuroshio in Asia, and along the equator can be significantly faster, reaching speeds of 2 miles per hour. Even a gentle current of 0.1 miles per hour can carry spawn 40 miles over a month, and some species can float for several months.

Government and academic scientists use a vast network of satellites, moored instruments and floating buoys to monitor these surface flows. Using this information, we performed a computer simulation of where drifting particles would be carried over time. Scientists have used this type of simulation to study the spread of marine plastic pollution and predict where debris from plane crashes at sea could have washed ashore.

Different fish species spawn in different seasons, and a single species may spawn in several months at different locations. We matched the seasons and locations of spawning for over 700 species with ocean current data, and simulated where their spawn would drift. Then, using records of where those species have been fished, and information about how suitable conditions are for each species in different regions, we deduced what fraction of the fish caught in each country arrived from other countries because of ocean currents.

A small-world network

Scientists and policymakers can learn a lot by studying these international connections. Each species that floats across international boundaries during its plankton stage represents a linkage between countries. These linkages span the world in a dense, interconnected network.

Each color represents a region in the network of fish larvae connections. This map shows the strongest 467 connections among a total of 2,059 that the authors modeled.
Nandini Ramesh, James Rising and Kimberly Oremus, CC BY-ND

At a global level, this network of connections has an important property: It is a small-world network. Small-world networks connect regions that are far apart to each other by just a few steps along the network. The concept is rooted in social scientist Stanley Milgram’s 1960s experiments with social networks, which found that it was possible for a letter to reach almost any total stranger by passing through six or fewer hands. Milgram’s work was popularized in the 1990 play “Six Degrees of Separation.”

Among fisheries, the world seems even smaller: We found that the average number of degrees of separation among fisheries is five. This means that local problems can become global risks.

For example, imagine that a fishery collapses in the middle of the Mediterranean. If the population in one spawning region collapses, it could quickly put pressure on neighboring fisheries dependent upon it. If fishers in those neighboring countries overfish the remaining population or shift to other species, the disturbance can grow. Within just a few years, a fisheries disturbance could travel around the world.

We assessed how countries would be affected in terms of food security, employment and gross domestic product if they were to lose access to fish spawn from other territories. The most affected countries cluster in the Caribbean, the western Pacific, Northern Europe and West Africa. These hotspots correspond to the network’s most clustered areas, because the effects of these flows of fish spawn are most pronounced where many coastal countries lie in close proximity.

International flows of fish eggs and larvae affect countries’ total catch, food security, jobs and economies.
Nandini Ramesh, James Rising and Kimberly Oremus, CC BY-ND

Thinking globally about fisheries

Because the world’s fisheries are so interconnected, only international cooperation that takes flows of fish spawn into account can effectively manage them. Aside from egg and larvae connections, fisheries are linked by movements of adult fish and through agreements among countries allowing them to fish in each other’s waters.

All of this suggests that fishery management is best conducted at a large, international scale. Proposals for doing this include defining Large Marine Ecosystems to be jointly managed and creating networks of Marine Protected Areas that safeguard a variety of critical habitats. Ideas like these, and careful study of interdependence between national fisheries, are crucial to sustainable use of the oceans’ living resources.

[ Expertise in your inbox. Sign up for The Conversation’s newsletter and get a digest of academic takes on today’s news, every day. ]The Conversation

Nandini Ramesh, Postdoctoral Researcher in Earth and Planetary Science, University of California, Berkeley; James Rising, Assistant Professorial Research Fellow, London School of Economics and Political Science, and Kimberly Oremus, Assistant Professor of Marine Policy, University of Delaware

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

Whales and dolphins found in the Great Pacific Garbage Patch for the first time



Adult and infant sperm whales have been spotted in the Great Pacific Garbage Patch.
Inf-Lite Teacher/Flickr, CC BY-SA

Chandra Salgado Kent, Edith Cowan University

Scientific research doesn’t usually mean being strapped in a harness by the open paratroop doors of a Vietnam-war-era Hercules plane. But that’s the situation I found myself in several years ago, the result of which has just been published in the journal Marine Biodiversity.

As part of the Ocean Cleanup’s Aerial Expedition, I was coordinating a visual survey team assessing the largest accumulation of ocean plastic in the world: the Great Pacific Garbage Patch.




Read more:
The ocean’s plastic problem is closer to home than scientists first thought


When the aircraft’s doors opened in front of me over the Pacific Ocean for the first time, my heart jumped into my throat. Not because I was looking 400m straight down to the wild sea below as it passed at 260km per hour, but because of what I saw.

This was one of the most remote regions of the Pacific Ocean, and the amount of floating plastic nets, ropes, containers and who-knows-what below was mind-boggling.

However, it wasn’t just debris down there. For the first time, we found proof of whales and dolphins in the Great Pacific Garbage Patch, which means it’s highly likely they are eating or getting tangled in the huge amount of plastic in the area.

The Great Pacific Garbage Patch

The Great Pacific Garbage Patch is said to be the largest accumulation of ocean plastic in the world. It is located between Hawaii and California, where huge ocean currents meet to form the North Pacific subtropical gyre. An estimated 80,000 tonnes of plastic are floating in the Great Pacific Garbage Patch.




Read more:
The major source of ocean plastic pollution you’ve probably never heard of


Our overall project was overseen and led by The Ocean Cleanup’s founder Boyan Slat and then-chief scientist Julia Reisser. We conducted two visual survey flights, each taking an entire day to travel from San Francisco’s Moffett Airfield, survey for around two hours, and travel home. Along with our visual observations, the aircraft was fitted with a range of sensors, including a short-wave infrared imager, a Lidar system (which uses the pulse from lasers to map objects on land or at sea), and a high-resolution camera.

Both visual and technical surveys found whales and dolphins, including sperm and beaked whales and their young calves. This is the first direct evidence of whales and dolphins in the heart of the Great Pacific Garbage Patch.

Mating green turtles in a sea of plastics.
photo by Chandra P. Salgado Kent, Author provided

Plastics in the ocean are a growing problem for marine life. Many species can mistake plastics for food, consume them accidentally along with their prey or simply eat fish that have themselves eaten plastic.

Both beaked and sperm whales have been recently found with heavy plastic loads in their stomachs. In the Philippines, a dying beaked whale was found with 40kg of plastic in its stomach, and in Indonesia, a dead sperm whale washed ashore with 115 drinking cups, 25 plastic bags, plastic bottles, two flip-flops, and more than 1,000 pieces of string in its stomach.

The danger of ghost nets

The most common debris we were able to identify by eye was discarded or lost fishing nets, often called “ghost nets”. Ghost nets can drift in the ocean for years, trapping animals and causing injuries, starvation and death.

Crew sorts plastic debris collected from the Great Pacific Garbage Patch on a voyage in July 2019.
EPA/THE OCEAN CLEANUP

Whales and dolphins are often found snared in debris. Earlier this year, a young sperm whale almost died after spending three years tangled in a rope from a fishing net.

During our observation we saw young calves with their mothers. Calves are especially vulnerable to becoming trapped. With the wide range of ocean plastics in the garbage patch, it is highly likely animals in the area ingest and become tangled in it.

It’s believed the amount of plastics in the ocean could triple over the next decade. It is clear the problem of plastic pollution has no political or geographic boundaries.




Read more:
There are some single-use plastics we truly need. The rest we can live without


While plastics enter the sea from populated areas, global currents transport them across oceans. Plastics can kill animals, promote disease, and harm the environment, our food sources and people.

The most devastating effects fall on communities in poverty. New research shows the Great Pacific Garbage Patch is rapidly growing, posing a greater threat to wildlife. It reinforces the global movement to reduce, recycle and remove plastics from the environment.

But to really tackle this problem we need creative solutions at every level of society, from communities to industries to governments and international organisations.

To take one possibility, what if we invested in fast-growing, sustainably cultivated bamboo to replace millions of single-use plastics? It could be produced by the very countries most affected by this crisis: poorer and developing nations.




Read more:
Designing new ways to make use of ocean plastic


It is only one of many opportunities to dramatically reduce plastic waste, improve the health of our environments and people, and to help communities most susceptible to plastic pollution.The Conversation

Chandra Salgado Kent, Associate Professor, School of Science, Edith Cowan University

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

Tens of thousands of tuna-attracting devices are drifting around the Pacific



Fish are attracted to floating objects, especially with dangling ropes or nets.
WorldFish/Flickr, CC BY-NC-SA

Joe Scutt Phillips, Secretariat of the Pacific Community; Alex Sen Gupta, UNSW; Graham Pilling, Secretariat of the Pacific Community, and Lauriane Escalle, Secretariat of the Pacific Community

Tropical tuna are one of the few wild animals we still hunt in large numbers, but finding them in the vast Pacific ocean can be tremendously difficult. However, fishers have long known that tuna are attracted to, and will aggregate around, floating objects such as logs.

In the past, people used bamboo rafts to attract tuna, fishing them while they were gathered underneath. Today, the modern equivalent – called fish aggregating devices, or FADs – usually contain high-tech equipment that tell fishers where they are and how many fish have accumulated nearby.




Read more:
Sustainable shopping: how to buy tuna without biting a chunk out of the oceans


It’s estimated that between 30,000 and 65,000 man-made FADs are deployed annually and drift through the Western and Central Pacific Ocean to be fished on by industrial fishers. Pacific island countries are reporting a growing number of FADs washing up on their beaches, damaging coral reefs and potentially altering the distribution of tuna.

Our research in two papers, one of which was published today in Scientific Reports, looks for the first time at where ocean currents take these FADs and where they wash up on coastlines in the Pacific.

A yellowfin tuna caught by purse seine fishers. This individual is one of the largest that can be caught using FADs.
Lauriane Escalle

Attracting fish and funds

We do not fully understand why some fish and other marine creatures aggregate around floating objects, but they are a source of attraction for many species. FADs are commonly made of a raft with 30-80m of old ropes or nets hanging below. Modern FADs are attached to high-tech buoys with solar-powered electronics.

The buoys record a FAD’s position as it drifts slowly across the Pacific, scanning the water below to measure tuna numbers with echo-sounders and transmitting this valuable information to fishing vessels by satellite.

Tuna hauled aboard the fishing vessel Dolores. The tuna trade in the Pacific Ocean is worth more than US$6 billion a year.
Siosifa Fukofuka (SPC), Author provided

Throughout their lifetimes FADs may be exchanged between vessels, recovered and redeployed, or fished and simply left to drift with their buoy to further aggregate tuna. Fishers may then abandon them and remotely deactivate the buoys’ satellite transmission when the FAD leaves the fishing area.

The Western and Pacific Ocean provides around 55% of the worlds’ 5 million tonne catch of tropical tuna, and is the main source of skipjack, yellowfin and bigeye tuna worth some US$6 billion annually.

Pacific Islanders with a FAD buoy that washed up on their reef.
Joe Scutt Phillips, Author provided

Fishing licence fees can provide up to 98% of government revenue for some Pacific Island countries and territories. These countries balance the need to sustainably manage and harvest one of the only renewable resources they have, while often having a limited capacity to fish at an industrial scale themselves.

FADs help stabilise catch rates and make fishing fleets more profitable, which in turn generate revenue for these nations.

However, they are not without problems. Catches around FADs tend to include more bycatch species, such as sharks and turtles, as well as smaller immature tuna.

The abandonment or loss of FADs adds to the growing mass of marine debris floating in the ocean, and they increasingly damage coral as they are dragged and get caught on reefs.

Perhaps most importantly, we don’t know how the distribution of FADs affects fishing effort in the region. Given that each fleet and fishing company has their own strategy for using FADs, understanding how the total number of FADs drifting in one area increases the catch of tuna is crucial for sustainably managing these valuable species.

Where do FADs end up?

Our research, published in Environmental Research Communications and Scientific Reports, used a regional FAD tracking program and fishing data submitted by Pacific countries, in combination with numerical ocean models and simulations of virtual FADs, to work out how FADs travel on ocean currents during and after their use.

In general, FADs are first deployed by fishers in the eastern and central Pacific. They then drift west with the prevailing currents into the core industrial tropical tuna fishing zones along the equator.

We found equatorial countries such as Kiribati have a high number of FADs moving through their waters, with a significant amount washing up on their shores. Our research showed these high numbers are primarily due to the locations in which FADs are deployed by fishing companies.

In contrast, Tuvalu, which is situated on the edge of the equatorial current divergence zone, also sees a high density of FADs and beaching. But this appears to be an area that generally aggregates FADs regardless of where they are deployed.

Unsurprisingly, many FADs end up beaching in countries at the western edge of the core fishing grounds, having drifted from different areas of the Pacific as far away as Ecuador. This concentration in the west means reefs along the edge of the Solomon Islands and Papua New Guinea are particularly vulnerable, with currents apparently forcing FADs towards these coasts more than other countries in the region.

FAD found beached in Touho (New Caledonia) in 2019.
A. Durbano, Association Hô-üt’, Author provided

Overall, our studies estimate that between 1,500 and 2,200 FADs drifting through the Western and Central Pacific Ocean wash up on beaches each year. This is likely to be an underestimate, as the tracking devices on many FADs are remotely deactivated as they leave fishing zones.

Using computer simulations, we also found that a significant number of FADs are deployed in the eastern Pacific Ocean, left to drift so they have time to aggregate tuna, and subsequently fished on in the Western and Central Pacific Ocean. This complicates matters as the eastern Pacific is managed by an entirely different fishery Commission with its own set of fisheries management strategies and programmes.

Growing human populations and climate change are increasing pressure on small island nations. FAD fishing is very important to their economic and food security, allowing access to the wealth of the ocean’s abundance.




Read more:
How blockchain is strengthening tuna traceability to combat illegal fishing


We need to safeguard these resources, with effective management around the number and location of FAD deployments, more research on their impact on tuna and bycatch populations, the use of biodegradable FADs, or effective recovery programs to remove old FADs from the ocean at the end of their slow journeys across the Pacific.The Conversation

Joe Scutt Phillips, Senior Fisheries Scientists (Tuna Behavioural Ecology), Secretariat of the Pacific Community; Alex Sen Gupta, Senior Lecturer, School of Biological, Earth and Environmental Sciences, UNSW; Graham Pilling, Principal Fisheries Scientist, Secretariat of the Pacific Community, and Lauriane Escalle, Fisheries Scientist, Secretariat of the Pacific Community

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

Meet the super corals that can handle acid, heat and suffocation


Resilient corals are offering hope for bleached reefs.
Emma Camp

Emma F Camp, University of Technology Sydney and David Suggett, University of Technology Sydney

Climate change is rapidly changing the oceans, driving coral reefs around the world to breaking point. Widely publicised marine heatwaves aren’t the only threat corals are facing: the seas are increasingly acidic, have less oxygen in them, and are gradually warming as a whole.

Each of these problems reduces coral growth and fitness, making it harder for reefs to recover from sudden events such as massive heatwaves.




Read more:
Acid oceans are shrinking plankton, fuelling faster climate change


Our research, published today in Marine Ecology Progress Series, investigates corals on the Great Barrier Reef that are surprisingly good at surviving in increasingly hostile waters. Finding out how these “super corals” can live in extreme environments may help us unlock the secret of coral resilience helping to save our iconic reefs.

Bleached coral in the Seychelles.
Emma Camp, Author provided

Coral conservation under climate change

The central cause of these problems is climate change, so the central solution is reducing carbon emissions. Unfortunately, this is not happening rapidly enough to help coral reefs, so scientists also need to explore more immediate conservation options.

To that end, many researchers have been looking at coral that manages to grow in typically hostile conditions, such as around tide pools and intertidal reef zones, trying to unlock how they become so resilient.

These extreme coral habitats are not only natural laboratories, they house a stockpile of extremely tolerant “super corals”.

What exactly is a super coral?

“Super coral” generally refers to species that can survive both extreme conditions and rapid changes in their environment. But “super” is not a very precise term!

Our previous research quantified these traits so other ecologists can more easily use super coral in conservation. There are a few things that need to be established to determine whether a coral is “super”:

  1. What hazard can the coral survive? For example, can it deal with high temperature, or acidic water?

  2. How long did the hazard last? Was it a short heatwave, or a long-term stressor such as ocean warming?

  3. Did the coral survive because of a quality such as genetic adaption, or was it tucked away in a particularly safe spot?

  4. How much area does the coral cover? Is it a small pocket of resilience, or a whole reef?

  5. Is the coral trading off other important qualities to survive in hazardous conditions?

  6. Is the coral super enough to survive the changes coming down the line? Is it likely to cope with future climate change?

If a coral ticks multiple boxes in this list, it’s a very robust species. Not only will it cope well in our changing oceans, we can also potentially distribute these super corals along vulnerable reefs.

Some corals cope surprisingly well in different conditions.
Emma Camp, Author provided

Mangroves are surprise reservoirs

We discovered mangrove lagoons near coral reefs can often house corals living in very extreme conditions – specifically, warm, more acidic and low oxygen seawater.

Previously we have reported corals living in extreme mangroves of the Seychelles, Indonesia, New Caledonia – and in our current study living on the Great Barrier Reef. We report diverse coral populations surviving in conditions more hostile than is predicted over the next 100 years of climate change.

Importantly, while some of these sites only have isolated populations, other areas have actively building reef frameworks.

Particularly significant were the two mangrove lagoons on the Great Barrier Reef. They housed 34 coral species, living in more acidic water with very little oxygen. Temperatures varied widely, over 7℃ in the period we studied – and included periods of very high temperatures that are known to cause stress in other corals.

Mangrove lagoons can contain coral that survives in extremely hostile environments, while nearby coral reefs bleach in marine heatwaves.
Emma Camp, Author provided

While coral cover was often low and the rate at which they build their skeleton was reduced, there were established coral colonies capable of surviving in these conditions.

The success of these corals reflect their ability to adapt to daily or weekly conditions, and also their flexible relationship with various symbiotic micro-algae that provide the coral with essential resources.

While we are still in the early phases of understanding exactly how these corals can aid conservation, extreme mangrove coral populations hold a reservoir of stress-hardened corals. Notably the geographic size of these mangrove locations are small, but they have a disproportionately high conservation value for reef systems.




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


However, identification of these pockets of extremely tolerant corals also challenge our understanding of coral resilience, and of the rate and extent with which coral species can resist stress.The Conversation

Emma F Camp, DECRA & UTS Chancellor’s Research Fellow, Climate Change Cluster, Future Reefs Research Programe, University of Technology Sydney and David Suggett, Associate Professor in Marine Biology, University of Technology Sydney

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