Australia's Great Barrier Reef is in peril from climate change and widespread bleaching, but scientists said a small portion may be resilient enough to keep much of the rest alive.
About three percent of the World Heritage site -- home to the planet's largest collection of coral reefs with 3,800 in all -- has so far emerged relatively unscathed from a host of threats, from warming waters to pollution to bleaching and disease, said the report in the journal PLOS Biology.
If properly protected, these cool-water reefs could supply larvae to nearly half (45 per cent) of the entire ecosystem in a single year, it said.
"Finding these 100 reefs is a little like revealing the cardiovascular system of the Great Barrier Reef," said the study's lead author Peter Mumby, professor at the University of Queensland.
Unlike many other parts of the reef, these 100 are not being eaten up by crown-of-thorns starfish predators.
They are also located in areas that enable them to send coral larvae along ocean currents, reaching a large number of reefs.
"The presence of these well-connected reefs on the Great Barrier Reef means that the whole system of coral reefs possesses a level of resilience that may help it bounce back from disturbances," said lead author Karlo Hock of the University of Queensland.
"Unfortunately, these findings by no means suggest that the Great Barrier Reef corals are safe and in great condition, and that there are no reasons for concern," he added.
"Indeed, the fact that the study only identified around a hundred of these reefs across the entire 1,400 mile (2,300 kilometer) length of the massive Great Barrier Reef emphasises the need for both effective local protection of critical locations and reduction of carbon emissions in order to support this majestic ecosystem."
The Great Barrier Reef has undergone unprecedented bleaching for the past two years, devastating more than two-thirds of the reef, experts say.
Many efforts are under way to save the iconic reefs, including one project to transplant larvae into damaged areas of the reef where the natural supply of coral larvae has been reduced or erased.
Scientists announced Monday this approach has shown some success in growing new juvenile coral, eight months after it began.
Corals may look like plants or rocks but they are actually animals. They feed on algae, and "bleach" -- turning bone-white -- when they are stressed by environmental changes, such as ocean warming or pollution.
Coral reefs make up less than one percent of Earth's marine environment, but are home to an estimated 25 percent of ocean life, acting as nurseries for many species of fish.