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Report Details Climate Crisis Impacts on Coral Reefs, Warns of 'Human Tragedy'

Oceans
Report Details Climate Crisis Impacts on Coral Reefs, Warns of 'Human Tragedy'
A new report spotlights a U.N. estimate that at least 275 million people rely on healthy coral reefs. A sea turtle near the Heron Island in the Great Barrier Reef is seen above. THE OCEAN AGENCY / XL CATLIN SEAVIEW SURVEY

By Jessica Corbett

In a new report about how the world's coral reefs face "the combined threats of climate change, pollution, and overfishing" — endangering the future of marine biodiversity — a London-based nonprofit calls for greater global efforts to end the climate crisis and ensure the survival of these vital underwater ecosystems.


The report, entitled Marine Havens Under Threat: The impacts of the climate crisis on tropical coral reefs and the communities that rely on them, was published Wednesday by the Environmental Justice Foundation (EJF).

EJF warns that because of human activities that heat and pollute the planet, coral reefs "are under imminent risk of destruction," pointing to a recent estimate from the United Nations' Intergovernmental Panel on Climate Change (IPCC) that global warming of 2°C could kill 99 percent of all corals.

The ocean, which covers more than 70 percent of the planet, "has taken up between 20–30% of total anthropogenic CO2 emissions since the 1980s causing further ocean acidification," according to an IPCC special report from last year. The lead author of a study published last week said that "the amount of heat we have put in the world's oceans in the past 25 years equals to 3.6 billion Hiroshima atom-bomb explosions."

Some scientists refer to three key climate-related pressures on the marine environment — warming, acidification, and oxygen loss — as the "deadly trio." Experts also warn that human-caused global heating leads to sea level rise and certain extreme weather events becoming more frequent and intense.

"As the global temperature rises, reefs will be put at risk from warming oceans, higher frequency cyclones, increased precipitation, sea level rise, rising acidification, and changing ocean circulation," the EJF report says. "These factors alter the delicate balance of conditions necessary for tropical coral reefs to function, causing bleaching and destruction of reefs. In many cases, this damage is irreversible."

Marine heatwaves, which experts warn will become more common as humans continue to heat the planet, have led to major coral bleaching events around the world in recent years. A study from 2018 concluded that the Great Barrier Reef off the coast of Australia, the world's largest coral system, was "forever damaged" following back-to-back bleaching events that collectively killed half of the corals.

Bleaching refers to when stressors such as warm water and pollution lead coral to expel algae, its main food source, and turn white. Bleached coral faces a greater risk of disease and death but can recover if surrounding conditions improve. Last year, a study about severe marine heatwaves heightened alarm about the future; researchers found cases where "the water temperatures are so warm that the coral animal doesn't bleach—in terms of a loss of its symbiosis—the animal dies and its underlying skeleton is all that remains."

EJF, in its new report and an accompanying video, highlighted the consequences of coral bleaching and death events for both marine wildlife and humans.

Coral Reefs in Crisis

"Tropical coral reefs support an estimated quarter of all marine species: hundreds of thousands of animal and plant species, who rely on the reef for food, shelter, and a safe place to live and reproduce," the report says. "These complex ecosystems include hard and soft corals, sponges, crustaceans, molluscs, fish, sea turtles, sharks, dolphins, and much more—including 'foundation' and 'keystone' species such as corals and sea turtles."

The report also spotlights a U.N. estimate that at least 275 million people rely on healthy coral reefs as an "essential source of food, employment, income, and storm protection for coastal communities."

In terms of the economic value of coral reefs, EJF puts tourism and recreation at $9.6 billion, coastal protection at $9 billion, fisheries at $5.7 billion, and wildlife at $5.5 billion. Directly below the economic figures, the report features "a note of caution: Valuing biodiversity in this way is of course subjective, how do we put a value on a species' intrinsic right to exist?"

To combat the triple threat that coral reefs are facing, EJF puts forth recommendations to end the climate crisis: implement the Paris agreement and fully transition all industrial economies to zero carbon by 2030, create a European Union inter-agency taskforce "to drive a more effective, integrated" global response, and establish a U.N. special rapporteur on human rights, economic well-being, and climate change.

EJF presents another set of specific recommendations to ensure that remaining corals "survive the climate change that is irreversible," calling for an end to illegal and unsustainable fishing as well as pollution that harms coral, including agricultural runoff, sewage, and plastic. The group also calls for expanding marine protected areas to cover at least 30% of the ocean, and assuring that such zones have "clear restrictions and effective conservation aims."

"In all deliberations and future negotiations," the report adds, "all stakeholders must be included, with special reference to local communities."

Acknowledging that coral reefs "are not only a vital source of food and income for millions of people" but also "home to a vast diversity of irreplaceable wildlife," EJF executive director Steve Trent warned Wednesday that "failure to act now to protect them will cause environmental ruin and with it a human tragedy."

A net-casting ogre-faced spider. CBG Photography Group, Centre for Biodiversity Genomics / CC BY-SA 3.0

Just in time for Halloween, scientists at Cornell University have published some frightening research, especially if you're an insect!

The ghoulishly named ogre-faced spider can "hear" with its legs and use that ability to catch insects flying behind it, the study published in Current Biology Thursday concluded.

"Spiders are sensitive to airborne sound," Cornell professor emeritus Dr. Charles Walcott, who was not involved with the study, told the Cornell Chronicle. "That's the big message really."

The net-casting, ogre-faced spider (Deinopis spinosa) has a unique hunting strategy, as study coauthor Cornell University postdoctoral researcher Jay Stafstrom explained in a video.

They hunt only at night using a special kind of web: an A-shaped frame made from non-sticky silk that supports a fuzzy rectangle that they hold with their front forelegs and use to trap prey.

They do this in two ways. In a maneuver called a "forward strike," they pounce down on prey moving beneath them on the ground. This is enabled by their large eyes — the biggest of any spider. These eyes give them 2,000 times the night vision that we have, Science explained.

But the spiders can also perform a move called the "backward strike," Stafstrom explained, in which they reach their legs behind them and catch insects flying through the air.

"So here comes a flying bug and somehow the spider gets information on the sound direction and its distance. The spiders time the 200-millisecond leap if the fly is within its capture zone – much like an over-the-shoulder catch. The spider gets its prey. They're accurate," coauthor Ronald Hoy, the D & D Joslovitz Merksamer Professor in the Department of Neurobiology and Behavior in the College of Arts and Sciences, told the Cornell Chronicle.

What the researchers wanted to understand was how the spiders could tell what was moving behind them when they have no ears.

It isn't a question of peripheral vision. In a 2016 study, the same team blindfolded the spiders and sent them out to hunt, Science explained. This prevented the spiders from making their forward strikes, but they were still able to catch prey using the backwards strike. The researchers thought the spiders were "hearing" their prey with the sensors on the tips of their legs. All spiders have these sensors, but scientists had previously thought they were only able to detect vibrations through surfaces, not sounds in the air.

To test how well the ogre-faced spiders could actually hear, the researchers conducted a two-part experiment.

First, they inserted electrodes into removed spider legs and into the brains of intact spiders. They put the spiders and the legs into a vibration-proof booth and played sounds from two meters (approximately 6.5 feet) away. The spiders and the legs responded to sounds from 100 hertz to 10,000 hertz.

Next, they played the five sounds that had triggered the biggest response to 25 spiders in the wild and 51 spiders in the lab. More than half the spiders did the "backward strike" move when they heard sounds that have a lower frequency similar to insect wing beats. When the higher frequency sounds were played, the spiders did not move. This suggests the higher frequencies may mimic the sounds of predators like birds.

University of Cincinnati spider behavioral ecologist George Uetz told Science that the results were a "surprise" that indicated science has much to learn about spiders as a whole. Because all spiders have these receptors on their legs, it is possible that all spiders can hear. This theory was first put forward by Walcott 60 years ago, but was dismissed at the time, according to the Cornell Chronicle. But studies of other spiders have turned up further evidence since. A 2016 study found that a kind of jumping spider can pick up sonic vibrations in the air.

"We don't know diddly about spiders," Uetz told Science. "They are much more complex than people ever thought they were."

Learning more provides scientists with an opportunity to study their sensory abilities in order to improve technology like bio-sensors, directional microphones and visual processing algorithms, Stafstrom told CNN.

Hoy agreed.

"The point is any understudied, underappreciated group has fascinating lives, even a yucky spider, and we can learn something from it," he told CNN.

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