London: Nutrient-rich slurry from farms in Australia had been contributing to the collapse of the corals in the Great Barrier Reef for 90 years, researchers at the University of Queensland have revealed.
The corals collapsed between the 1920s and 1950s as European settlers started to incorporate farming as their source of living, according to John Pandolfi at the University of Queensland in Brisbane and his colleagues.
The researchers took cores from three reefs and worked out when the corals died.
Two had little coral left after the 1950s, while the third had been colonised since then by different types.
This may be because, the researchers pointed out, by the 1920s, European settlers were farming intensively near rivers flowing onto the reef, boosting agricultural run-off by up to a factor of 20.
Though events like cyclones kill coral, the extra nutrients in the water help seaweed move in afterwards, preventing coral from regenerating, said Terry Done of the Australian Institute of Marine Science in Townsville, Queensland.
The reefs were already in decline again when monitoring began in the 1980s, said Joana Figueiredo of James Cook University, also in Townsville.
Pandolfi’s work, published in the Proceedings of the Royal Society, shows that it was pristine until the 1920s.