Great Barrier Reef: Coral spawning season begins on the world's largest reef

Off Australia's northeast coast, the season is starting in which the world's largest coral reef shows its most spectacular side. According to the Great Barrier Reef Marine Park Authority (GBRMPA), corals usually spawn on the nights following the October, November and December full moons – typically one to six nights afterward, depending on the reef's location. Many corals take their cue from the moon's light and gravitational pull, while warming water heading into summer helps eggs and sperm mature. The egg-sperm bundles start forming about six months beforehand.

Spawning almost always happens at night, which helps protect eggs and sperm from predators. The GBRMPA says the exact date and time cannot be predicted, but some operators run trips around the predicted dates. People who witness spawning can submit sightings and images through the authority's Eye on the Reef app.

UNESCO inscribed the Great Barrier Reef on the World Heritage List in 1981. The site spans about 348,000 square kilometers, stretches for some 2,000 kilometers along the Queensland coast and includes about 2,500 individual reefs and more than 900 islands. According to UNESCO, it is home to about 400 coral species, more than 1,500 fish species and more than 4,000 mollusc species. UNESCO names climate change as the biggest long-term threat, along with declining water quality, loss of coastal habitat and fishing pressure.