Explainer: mass coral spawning, a wonder of the natural world

During mass spawning events coral young rise from their parents to ocean surface.
Australian Institute of Marine Science, Author provided

Line K Bay, Australian Institute of Marine Science; Andrew Heyward, Australian Institute of Marine Science, and Andrew Negri, Australian Institute of Marine Science

During the late spring, corals on the Great Barrier Reef release little balls that float to the ocean surface in a slow motion upside-down snowstorm.

These beautiful events are studied avidly by scientists: the tiny bundles will become young corals, and unlocking their secrets is vital to the continuing life of our coral reefs.

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Read more: Newly discovered hermit crab species lives in ‘walking corals’

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The first major mass spawning of 2017 unfolded last week following the early November full moon, with another spawning event predicted for December.

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Mass spawning after the full moon

Coral species have a varied sex life. The majority of species are simultaneously male and female (hermaphrodites) and typically pack both eggs and sperm (gametes) into tight, buoyant bundles that are released after dark with remarkable synchronisation. The bundles float to the surface and open, allowing the eggs meet compatible sperm.

Less commonly, some coral species have separate sexes, and a few species even release asexually produced clones of themselves. For all species with sexual reproduction fertilised eggs develop into mobile larvae that settle on the sea floor and become polyps: the beginning of a new coral colony on the reef.

Mass spawnings are spectacular events, in which dozens of coral species release their gametes at specific times. Sometimes more than 100 species spawn on a single night, or over a few successive nights.

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Read more: Feeling helpless about the Great Barrier Reef? Here’s one way you can help

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This iconic celebration of sex on the reef was first described in the central Great Barrier Reef in 1984 by a group of early-career scientists. The discovery earned them a prestigious Australian Museum Eureka Award for Environmental Research in 1992.

The precise timing of this seasonal phenomenon is linked to seawater temperature, lunar phases, and other factors such as the daily cycle of light and dark. Mass coral spawning is the dominant reproductive mode for corals on the Great Barrier Reef, and has also been recorded on reefs around the world.

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The release of egg and sperm bundles is the culmination of many months of development. In years when the full moon falls early in October and November, many colonies are not quite ready and delay spawning for another lunar cycle. That’s why this year will see some action in November and another mass spawning event after the December full moon.

An important date in the scientific calendar

Spawning can be replicated in aquarium settings, which provide unique opportunities to researchers. All three of us work in the Australian Institute of Marine Science’s (AIMS) unique Sea Simulator, where large numbers of coral larvae are produced for scientific experiments.

Scientists from the Institute and around the world work through the spawning nights to collect gamete bundles, separate sperm and fertilise the eggs, then rear millimeter-long larvae and juveniles. Many experiments continue for days, weeks and even years to address critical knowledge gaps in how corals respond to and recover from stress.

New tools for coral reef management

The extensive coral death in the northern Great Barrier Reef following back-to-back bleaching events in 2016 and 2017 highlights the impacts of rapidly changing ocean conditions. AIMS scientists focus on developing ways to help coral adapt and restore damaged reefs.

Corals reefs are at a crossroads, but there is still hope. Experiments during this year’s spawning season will test whether surviving corals from recent bleaching events are naturally adapted to warmer reef temperatures, and if they produce more heat-tolerant young.

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Read more: The Great Barrier Reef can repair itself, with a little help from science

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This knowledge underpins the development of active reef management tools such as assisted gene flow.

The huge Sea Simulator lets researchers carefully test how corals respond to stress.
Australian Institute of Marine Science, Author provided

Assisted gene flow involves moving heat-tolerant corals (or their young) to reefs that are warming. This technique proposes to improve the overall heat tolerance of local coral populations, to help the buffer the reef against future bleaching events caused by warmer than normal water temperatures.

More local threats to corals include poor water quality and pollution from coastal development. The early stages of a coral’s life are very sensitive to exposure to pesticides, oil spills and sediments from dredging.

Carefully controlled experiments with aquarium-reared coral larvae provide insights into the role of these local pressures on the rate of recovery and replenishment following large-scale disturbances.

The present reality for coral reefs is one of increasing strain from climate change, cyclones, crown-of-thorns starfish predation, and declining water quality. The ability of coral reef ecosystems to recover from these challenges relies on the success of mass coral spawning both on the reef and advances in the laboratory to generate new options to enhance reef resilience.

Exploring reef restoration and adaptation needs to go hand-in-hand with ongoing (and increasing) efforts in conventional management, such as climate change mitigation, regional management of water quality and control of crown-of-thorns starfish.

Line K Bay, Senior Research Scientist and Team Leader, Australian Institute of Marine Science; Andrew Heyward, Principal Research Scientist, Exploring Marine Biodiversity, Australian Institute of Marine Science, and Andrew Negri, Principal Research Scientist, Australian Institute of Marine Science

This article was originally published on The Conversation. Read the original article.

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Don’t give up on Pacific Island nations yet

Jon Barnett, University of Melbourne

Fiji’s presidency of this year’s United Nations climate summit has put a renewed focus on the future of low-lying Pacific Islands. And while we should not ignore the plight of these nations, it is just as damaging to assume that their fate is already sealed.

Many people in Australia consider island nations such as Kiribati, Tuvalu and the Marshall Islands to be almost synonymous with impending climate catastrophe. After returning from Papua New Guinea in 2015, federal immigration minister Peter Dutton infamously joked that “time doesn’t mean anything when you’re about to have water lapping at your door”.

If influential and everyday Australians, and the rest of the world, hold the view that Pacific Island nations are doomed to succumb to climate change, the danger is that this will become a self-fulfilling prophecy.

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Read more: Australia doesn’t ‘get’ the environmental challenges faced by Pacific Islanders

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When we deny the possibility of a future for low-lying small islands, we are
admitting defeat. This in turn undermines the impetus to reduce greenhouse gas emissions and find ways to help communities carry on living in their island homes. It leaves us unable to discuss any options besides palliative responses for climate refugees.

There are other consequences of this pessimistic framing of islands. It may
undermine efforts to sustainably manage environments, because a finite future is
anathema to the sustaining resources in perpetuity. It can also manifest itself in harmful local narratives of denial or self-blame. And it can lead to climate change being blamed for environmental impacts that arise from local practices, which then remain unchanged.

We would do well to listen instead to what the leaders of low-lying island nations are saying, such as Tuvalu’s Prime Minister Enele Sopoaga, who told the 2013 Warsaw climate summit:

… some have suggested that the people of Tuvalu can move elsewhere. Let
me say in direct terms. We do not want to move. Such suggestions are
offensive to the people of Tuvalu. Our lives and culture are based on our
continued existence on the islands of Tuvalu. We will survive.

Those sentiments were echoed by the late Tony de Brum, former foreign minister of the Marshall Islands and described as the “voice of the Pacific Islands on climate change”, who said in 2015:

Displacement is not an option we relish or cherish and we will not operate on that basis. We will operate on the basis that we can in fact help to prevent this from happening.

Determined to survive

These leaders are determined for good reasons. Small islands are likely to respond in a host of different ways to climate change, depending on their geology, local wave patterns, regional differences in sea-level rise, and how their corals, mangroves and other wildlife respond to changing temperatures and weather patterns.

Evidence suggests that even seemingly very similar island types may respond very differently to one another. In many cases it is too early to say for sure that climate change will make a particular island uninhabitable.

But perhaps even more important in the future of low-lying small islands is the
way people adapt to climate change. There are all sorts of ways in which people can adapt their environments to changing conditions. Indeed, when the first migrants arrived in the low-lying atolls of Micronesia more than 3,000 years ago they found sand islands with no surface water and little soil, and settled them with only what they had in their small boats. Modern technologies and engineering systems can transform islands even more substantially, so that people can still live meaningful lives on them under changed climate conditions.

Adapting islands to climate change will not be easy. It will involve changes in where and how things are built, what people eat, how they get their water and energy, and what their islands look like.

It will also involve changes in institutions that are fundamental to island
societies, such as those concerned with land and marine tenure. But it can be done, with ingenuity, careful and long-term planning, technology transfer, and
meaningful partnerships between governments and international agencies.

Failure so far

Frustratingly, however, the international community is so far failing island states when it comes to this crucial adaptation. Despite their acute vulnerability having been recognised for at least 30 years, low-lying atoll countries such as Kiribati, the Marshall Islands and Tuvalu are attracting only low or moderate amounts of international adaptation funding. This is mostly as part of larger regional projects, and often focused on building capacity rather than implementing actual changes.

It is we who have failed to reduce greenhouse gas emissions and to help low-lying islands adapt, and it is we who cannot imagine any long-term future for them. It seems all we can do is talk about loss, migration, and waves of climate refugees. Having let them down twice, this defeatist thinking risks denying them an independent future for a third time. This is environmental neo-colonialism.

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Read more: Islands lost to the waves: how rising seas washed away part of Micronesia’s 19th-century history

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The international community has a moral responsibility to deliver a
comprehensive strategy to minimise the risks climate change poses to remote
low-lying islands. People living on these islands have a legal and moral right to lead dignified lives in their homelands, free from the interference of climate impacts. People who live in affluent countries high above sea level have several responsibilities here.

First, as most of us agree, we should reduce our greenhouse gas emissions. We have some control over that through how we consume, invest, vote and travel. Second, we should insist that our governments do more to help low-lying states to adapt to climate change. It is our pollution, after all. And we should argue for a reversal in our declining aid budgets.

And finally, and perhaps most importantly, we should all stop talking down the future of low-lying small islands, because all this does is hasten their demise.

Jon Barnett, Professor, School of Geography, University of Melbourne

This article was originally published on The Conversation. Read the original article.

We’ve found an exo-planet with an extraordinarily eccentric orbit

An artist’s impression of the exoplanet in close orbit to a star.
ESA, NASA, G. Tinetti (University College London, UK & ESA) and M. Kornmesser (ESA/Hubble)

Jonti Horner, University of Southern Queensland; Jake Clark, University of Southern Queensland; Rob Wittenmyer, University of Southern Queensland, and Stephen Kane, University of California, Riverside

The discovery of a planet with a highly elliptical orbit around an ancient star could help us understand more about how planetary systems form and evolve over time.

The new planet, HD76920b, is four times the mass of Jupiter, and can be found some 587 light years away in the southern constellation Volans, the Flying Fish. At its closest it skims the surface of its host star, HD76920. At its furthest, it orbits almost twice as far from its star as Earth does from the Sun.

Superimposing HD76920b’s orbit on the Solar system shows how peculiar it is. Its orbit is more like that of the asteroid Phaethon than any of the Solar system’s planets.
Jake Clark

Details of the planet and its discovery are published today. So how does this fit into the planet formation narrative, and are planets like it common in the cosmos?

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Read more: A fleeting visit: an asteroid from another planetary system just shot past Earth

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The Solar system

Before the first exoplanet discovery, our understanding of how planetary systems formed came from the only example we had at the time: our Solar system.

Close to the Sun orbit four rocky planets – Mercury, Venus, Earth and Mars. Further out are four giants – Jupiter, Saturn, Uranus and Neptune.

Scattered in their midst we have debris – comets, asteroids and the dwarf planets.

The eight planets move in almost circular orbits, close to the same plane. The bulk of the debris also lies close to that plane, although on orbits that are somewhat more eccentric and inclined.

How did this system form? The idea was that it coalesced from a disk of material surrounding the embyronic Sun. The colder outer reaches were rich in ices, while the hotter inner regions contained just dust and gas.

The Solar system formed from a protoplanetary disk, surrounding the young Sun.
NASA/JPL-Caltech

Over millions of years, the tiny particles of dust and ice collided with one another, slowly building ever larger objects. In the icy depths of space, the giant planets grew rapidly. In the hot, rocky interior, growth was slower.

Eventually, the Sun blew away the gas and dust leaving a (relatively) orderly system – roughly co-planar planets, moving on near-circular orbits.

The exoplanet era

The first exoplanets, discovered in the 1990s, shattered this simple model of planet formation. We quickly learned that they are far more diverse than we could have possibly imagined.

Some systems feature giant planets, larger than Jupiter, orbiting incredibly close to their star. Others host eccentric, solitary worlds, with no companions to call their own.

Artist’s impression of the Hot Jupiter HD209458b – a planet so close to its star that its atmosphere is evaporating to space.
European Space Agency, A.Vidal-Madjar (Institut d’Astrophysique de Paris, CNRS, France) and NASA

This wealth of data reveals one thing – planet formation and evolution is more complicated and diverse than we ever imagined.

Core accretion vs dynamical instability

As a result of these discoveries, astronomers developed two competing models for planet formation.

The first is core accretion, where planets form gradually, through collisions between grains of dust and ice. The theory has grown out of our old models of Solar system formation.

The competing theory is dynamical instability. Once again, the story begins with a disk of material around a youthful star. But that disk is more massive, and becomes unstable under its own self-gravity, causing clumps to grow. These clumps rapidly form planets, in thousands of years.

Massive protoplanetary disks can become unstable, rapidly giving birth to giant planets.

Both models can explain some, but not all, of the newly discovered planets. Depending on the initial conditions around the star, it seems that both processes can occur.

Each theory offers potential to explain eccentric worlds in somewhat different ways.

How do you get an eccentric planet?

In the dynamical instability model you can easily get several clumps forming and interacting, slinging one another around until their orbits are both tilted and eccentric.

Under the core accretion model things are a bit harder, as this method naturally creates co-planar, ordered planetary systems. But over time those systems can become unstable.

One possible outcome is for one planet to eject the others through a series of chaotic encounters. That would naturally leave it as a solitary body, following a highly elongated orbit.

Chaotic planetary systems can eject planets entirely, leading to lonely rouge planets.
NASA/JPL-Caltech

But there is another option. Many stars in our galaxy are binary – they have stellar companions. The interactions between a planet and its host star’s sibling could readily stir it up and eventually eject it, or place it on an extreme orbit.

An eccentric planet

This brings us to our newly discovered world, HD76920b. A handful of similarly eccentric worlds have been found before, but HD76920b is unique. It orbits an ancient star, more than two billion years older than the Sun.

The orbit HD76920b is following is not tenable in the long-term. As it swings close to its host star, it will experience dramatic tides.

A gaseous planet, HD76920b will change shape as it swings past its star, stretched by its enormous gravity. Those tides will be far greater than any we experience on Earth.

That tidal interaction will act over time to circularise the planet’s orbit. The point of closest approach to the star will remain unchanged, but the most distant point will gradually be dragged closer in, driving the orbit towards circularity.

All of this suggests that HD76920b cannot have occupied its current orbit since its birth. If that were the case, the orbit would have circularised aeons ago.

Extremely eccentric planets have been discovered before, but this is the first around such an ancient star.
Goddard Space Flight Center/NASA

Perhaps what we’re seeing is evidence of a planetary system gone rogue. A system that once contained several planets on circular (or near circular) orbits.

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Read more: Exoplanet discovery by an amateur astronomer shows the power of citizen science

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Over time, those planets nudged one another around, eventually hitting a chaotic architecture as their star evolved. The result – chaos – with most planets scattered and flung to the depths of space leaving just one – HD76920b.

The truth is, we just don’t know – yet. As is always the case in astronomy, more observations are needed to truly understand the life story of this peculiar planet.

One thing we do know is the story is coming to a fiery end. In the next few million years, the star will swell, devouring its final planet. Then, HD76920b will be no more.

Jonti Horner, Vice Chancellor’s Senior Research Fellow, University of Southern Queensland; Jake Clark, PhD Student, University of Southern Queensland; Rob Wittenmyer, Associate Professor (Astrophysics), University of Southern Queensland, and Stephen Kane, Associate Professor, University of California, Riverside

This article was originally published on The Conversation. Read the original article.

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