Coral Reefs: Breakdown in Iconic Spawning Puts Species at Risk of Extinction – New Research

Corals release millions of sperm and eggs in synchrony to reproduce.  Rich Carey/Shutterstock

Corals release millions of sperm and eggs in synchrony to reproduce. Rich Carey/Shutterstock

It’s rather tricky to reproduce if you’re stuck to the floor – unless you’re a coral. Their spectacular spawning events are a beautiful sight to behold. Once a year, they spill billions of sperm and eggs into the sea, peppering the deep blue with a palette of vivid reds, yellows, oranges, and whites.

But according to new research, some corals are no longer reproducing with the same clockwork timing, adding yet another survival threat to the long list already befalling reefs.

Corals are unlike any other animal on the planet. Thousands of polyps, each resembling an upside down jellyfish, live with each other in beds of limestone attached to the seabed. As they grow, they create the unified limestone skeleton we see as coral from the outside. Many of these coral colonies together create a complex three-dimensional reef structure that in turn creates a home for thousands of other plants and animals.

Corals release so many sperm and eggs that the slicks can often be seen from the air. LBM1948/Wikimedia Commons, CC BY-SA

To get around their firm attachment to the seabed, most coral species reproduce by the mass release of sperm and eggs directly into the water at the same time. This annual mass spawning is one of nature’s most iconic events – rising underwater snowstorms so thick that they create brightly coloured slicks on the sea surface, visible from high above.

Astonishingly, corals synchronise their reproduction despite not having a brain, nor any direct way of communicating between colonies. Sperm and eggs can only survive in the water for a few hours, so in the vast ocean space this synchrony is essential for a good chance of fertilisation.

Until recently, little more than this was known about the intricacies of coral reproduction. But in the context of rapid coral decline, researchers have started applying genetic and reproductive research techniques to understand how environmental conditions are impacting coral fertilisation.

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

The new research monitored mass spawnings on corals reefs in the northern Red Sea. The researchers compared spawning timings of five coral species between 2015 and 2018 to results from two other studies conducted on the same species in the 1980s. In the species Acropora eurystoma, they also measured various reproductive traits, such as the number of sperm and eggs within a colony, the number of colonies reproducing in a given area and the size of coral colonies in the area – an index of their age.

In the 1980s, all the coral species monitored had one or two well-defined periods of spawning, where eggs and sperm were released within a few days of each other. But by the 2010s, some species released them over as many as a couple of months. With a lower concentration of eggs and sperm in the water at any one time, fertilisation becomes much rarer.

Although visually the coral reefs appeared in overall good health, the researchers found that the corals that weren’t spawning at the same time had no baby corals. This means that affected species can appear to be abundant, but in reality be nearing extinction through reproductive failure.

Threat and opportunity

This is the first study to compare current spawning behaviour with historical data, providing evidence of increased desynchrony over time. Of course, there are many, many more coral species than the five measured in the current study, so we must be cautious of drawing general conclusions at this stage. However, evidence (without historical data for comparison) suggests that the same may be happening in other parts of the world too.

Unfortunately, it’s not yet known exactly what is causing the apparent decline in spawning synchrony, making it difficult to put forward a solution to the problem. Increases in light pollution from coastal development and hormone pollution from contraceptive pills have recently been shown to disrupt the natural triggers for coral spawning. The same is true of water temperature, which has increased by 1.2℃ at the test site since the 1980s. However, further research is needed to establish whether these factors are causing corals to reproduce out of sync with each other.

While these new advances in the understanding of coral reproductive biology are worrying, they also present opportunities. If we can identify why some corals are reproducing well and others not, we may be able to innovate new conservation methods that protect corals before they show signs of dying off. Using selective breeding techniques, for example, we may be able to imbue corals with greater resilience to the factors causing spawning desynchrony.

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

In the meantime though, all we can do to keep the glimmer of hope alive for reefs is redouble international efforts to tackle climate breakdown, and manage coastal areas responsibly. Without such intervention, these ecosystems rich in economic, ecological and cultural value will soon succumb to the multiple threats it faces.

HEIDI BURDETT is a Research Fellow, Lyell Centre for Earth and Marine Science and Technology, Heriot-Watt University.


Fighting Human Extinction in London and Beyond

Over the past week, governmental officials and police say, protesters have wreaked havoc in London—but it’s all part of an effort to address the sociopolitical factors wreaking havoc on our planet.

Parliament Square on April 19. DAVID HOLT. CC BY 2.0

Parliament Square on April 19. DAVID HOLT. CC BY 2.0

In the early afternoon of Monday, April 22, about 100 people entered London’s Natural History Museum and made their way to Hintze Hall. As sunlight streamed in from the skylights and illuminated the Romanesque arches that punctuate the stone walls, the protestors positioned themselves underneath Hope—the enormous blue whale skeleton suspended from the ceiling—and lay down on the ground. After about half an hour, most concluded their “die-in,” but a few remained; wearing face paint and crimson robes, they gave a classical music performance on the steps beneath the skeleton.

This unusual demonstration was part of a massive mobilization by Extinction Rebellion (abbreviated as XR), a non-partisan movement aiming to revise environmental policy with the goals of slowing climate change and minimizing the possibility of imminent human extinction. The group launched in the United Kingdom in October of 2018—in response to the Intergovernmental Panel on Climate Change report announcing that we have just 12 years to halt catastrophic change—and quickly proliferated worldwide.

Today, the movement boasts about 130 groups across the UK, and is active in countries from the U.S. to South Africa to Australia. Its core demands are threefold: Honesty and transparency from governments regarding the ecological crisis; reduction of carbon emissions to zero by 2025; and the implementation of a participatory democracy to monitor progress towards these goals.

The current actions in London, advertised on XR’s website as “UK Rebellion—Shut Down London!,” are the focal point of a constellation of protests planned in 80 cities across 33 countries. Beginning on April 15, thousands of protestors poured into the heart of London, blocking five major landmarks: Waterloo Bridge, Marble Arch, Parliament Square, Oxford Circus, and Piccadilly Circus. From the beginning, group members made it clear that they weren’t going anywhere, filling the bridge with trees and flowers and even setting up a skate park and stage. Live music emanated from Oxford Circus, and a life-sized model of a boat with “Tell the Truth” painted on the side blocked the center of the bustling junction.

Nearby at Piccadilly Circus, younger protestors chalked messages on the pavement, while inside an open-sided truck at Marble Arch, bands entertained hundreds of onlookers. In Parliament Square on April 15, Jamie Kelsey Fry—contributing editor for the Oxford-based New Internationalist magazine—encouraged demonstrators from an octagonal stage.

Chalk message on April 17. Felton Davis. CC BY 2.0

Chalk message on April 17. Felton Davis. CC BY 2.0

The audience waved flags and banners emblazoned with the symbol of the movement, dubbed by Steve Rose of The Guardian as the ubiquitous logo of 2019. According to Rose, the “X” signifies extinction, and the horizontal lines suggest an hourglass—reminding us once again that time is running out.

A high point for protestors was a visit from 16-year-old climate activist Greta Thunberg on Sunday, April 21. The Swedish teenager, who staged a “School Strike for Climate” at Sweden’s Parliament last year and initiated the weekly #FridaysforFuture school walkouts, received chants of “We love you” as she took the stage at Marble Arch.

Demonstrating on London’s Blackfriars Bridge last November. Julia Hawkins. CC BY 2.0

Demonstrating on London’s Blackfriars Bridge last November. Julia Hawkins. CC BY 2.0

While the protests have in some ways resembled a modern-day Woodstock, full of music and goodwill, London authorities—who have deployed some 9,000 police officers in response—see a different side of the story. As of April 22, more than 1,000 people had been arrested since the demonstrations began; the youngest to be charged was 19, and the oldest 74.

London mayor Sadiq Khan said that the protest was taking a toll on London’s police forces and businesses, commenting, “I'm extremely concerned about the impact the protests are having on our ability to tackle issues like violent crime.” Protestors, for their part, view the stress on police as unavoidable: “We wish we didn’t have to distract police resources,” their website states. “80 year old grandfathers would rather not be putting themselves in the physically uncomfortable position of being in a police cell and children don’t want to be skipping school  – but 30 years of government inaction have left us with no choice.”

Tent set up in Parliament Square. DAVID HOLT. CC BY 2.0

Tent set up in Parliament Square. DAVID HOLT. CC BY 2.0

As protesters continue to be removed from the scene one by one by the police, with more rushing in to take their place, the question is whether or not the government will be responsive to XR’s message. On the first day of the mobilization, XR wrote to Prime Minister Theresa May outlining its demands, requesting talks, and issuing a stern warning: Failing government action, the group’s disruptive demonstrations would only escalate over the coming weeks. On April 22—the day of the Natural History Museum die-in, and also Earth Day—the group said that they would soon hold a “people’s assembly” to determine next steps. The next day, protesters marched on Parliament in a renewed push to open dialogue with government officials.

London’s Energy & Climate Intelligence Unit has said that XR’s demand for carbon neutrality by 2025 “technically, economically and politically has absolutely no chance of being fulfilled,” but nevertheless supports the message behind the movement and the actions it has engendered. For XR, surmounting the impossible is the only way forward to ensure that human beings can continue to inhabit the earth: Their website reads, “Only a peaceful planet-wide mobilisation of the scale of World War II will give us a chance to avoid the worst case scenarios and restore a safe climate.” Only time will tell whether those in power agree.

TALYA PHELPS hails from the wilds of upstate New York, but dreams of exploring the globe. As former editor-in-chief at the student newspaper of her alma mater, Vassar College, and the daughter of a journalist, she hopes to follow her passion for writing and editing for many years to come. Contact her if you're looking for a spirited debate on the merits of the em dash vs. the hyphen.

Extreme Evolution: Widespread Poaching Spawns Generation of Tuskless Elephants

An elephant's tusks are used as foraging tools and weapons in combat. David Clode. Public Use.

An elephant's tusks are used as foraging tools and weapons in combat. David Clode. Public Use.

When scientists and journalists examine poaching in Africa, they tend to focus on actions taken by human beings to protect a hunted species. What hasn't been examined is how nature itself may intervene on behalf of endangered animals and prevent their extinction. For example, scientists in Mozambique are investigating a peculiar phenomenon in which more and more elephants are being born without tusks. This is believed to be an evolutionary response to the widespread poaching that threatens elephant populations.

An elephant’s tusks are basically overgrown teeth and about a third of those teeth lie embedded in the animal’s skull—removing the tusks is generally fatal to the elephants themselves. Conservationists who would readily saw off the horns of a rhinoceros to make it unattractive to poachers are unable to take similar measures with elephants and must instead rely on militarized anti-poaching units to keep the animals safe.  Despite the efforts of these units and an international ban on the ivory trade, poachers have managed to leave a permanent mark on elephant population numbers. A civil war that ravaged Mozambique for 15 years saw the deaths of many elephants, as their ivory funded military operations and their meat fed soldiers. During that time, only about two to four percent of female elephants in Mozambique were born without tusks. But the widespread slaughter of tusked females made the tuskless gene more common: about thirty percent of female elephants born after the war had no tusks, while male elephants, who are always born with tusks, had tusks much smaller than those of their predecessors.

Elephants can survive without tusks, and the elephants born in Mozambique seem healthy. Still, scientists are curious to see what long-term effects this phenomenon will have on the elephant population. Elephants are among the most intelligent creatures on the planet, with a sophisticated, highly social culture. Tusks are a vital part of that culture, serving as tools for foraging and weapons for sparring.  Some experts think that a lack of tusks may force elephants to travel greater distances in search of food. Elephants also act as nature’s bulldozers, clearing away trees and making areas of the forest more accessible to other animals. A tuskless elephant would have greater difficulty performing such a task and this may cause ripples in Mozambique’s environment. Scientists will have to wait and see how nature adapts, and what steps it will take moving forward.

JONATHAN ROBINSON is an intern at CATALYST. He is a travel enthusiast always adding new people, places, experiences to his story. He hopes to use writing as a means to connect with others like himself. 

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