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Half of the Earth's coral reefs have died out in the last 70 years, according to a study published in the One Earth journal, cnet reported.

Researchers note that fishes caught per capita (or rather, per "unit of effort") have declined 60% since 1950, and that coral reefs are half as able to provide ecological services as they were in the 1950s. The result is less biodiversity in the world's reefs.

"Coral reefs worldwide are facing impacts from climate change, overfishing, habitat destruction, and pollution," the authors write in the study.  "With projected continued degradation of coral reefs and associated loss of biodiversity and fisheries catches, the well-being and sustainable coastal development of human communities that depend on coral reef ecosystem services are threatened."

Like redwood forests, coral reefs are ecosystems particularly sensitive to heat. Warming waters threaten coral reefs by prompting bleaching events. Algae provide coral with nutrients through photosynthesis, but if the algae become heat stressed or overexposed to sunlight, they instead produce a toxin. The coral then expel the algae, causing the coral to bleach. Bleaching, depending on severity, can be fatal. 

Temperatures don't need to rise much to cause major problems. A rise in ocean temperatures of 0.068 degrees Celsius has proved catastrophic for Australia's Great Barrier Reef, with three bleaching events over the past five years. The Belize Barrier Reef and the Great Florida Reef, the second and third biggest coral reef ecosystems in the world, have been similarly assailed by bleaching events in the past 5 years.

The team behind the study, led by Memorial University of Newfoundland researcher Tyler Eddy, reviewed data from 14,705 surveys of over 3,500 reefs from 87 countries. Among other results, the team found that biodiversity is falling, with temperature-resilient fish becoming more predominant, and a decline in fish catching per unit of effort.

"Our study indicates that the capacity of coral reefs to provide ecosystem services that are relied on by millions of people worldwide has declined by half since the 1950s," they write. "Achieving climate-change-emissions targets and reducing local impacts can reduce stress on coral reefs, allowing them and the ecosystem services that they provide to persist."

Scientists have attempted several methods of protecting reefs against the threat of rising ocean temperatures. These include cloud brightening, which involves thickening clouds with salt water so as to make them reflect more heat back into the atmosphere, autonomous killer drones and using advanced robotics to manufacture corals.

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