Coral reefs, clouds and rainforest

This article has been prompted by my recent holiday in Far North Queensland. Port Douglas is often promoted as the place where the ‘rain forest meets the reef’. The World Heritage listed wet tropics of the Daintree abuts the Great Barrier Reef. While there, I discovered that the relationship between the rain forest and the reef is complex and that healthy coral reefs make rain for the rain forest.

Dr Graham Jones from Southern Cross University in Lismore has been, for many years, researching the production of dimethyl sulphide (DMS) by the algae that live symbiotically in corals. When released into the atmosphere, DMS helps to ‘seed’ clouds by enhancing the formation of cloud condensation nuclei. Once formed, the clouds protect the coral reef from solar radiation and help to maintain the water temperature. The release of DMS and the consequent cloud seeding increases in the monsoonal summer months, when the coral needs more protection from the hot Sun.

However, Dr Jones’ studies have also shown that DMS production shuts down if the sea temperature rises by as little as 2 degrees C. This leads to a negative feedback situation where there are fewer clouds, so the sea temperature rises even further and the corals can suffer bleaching episodes.

The forests of Far North Queensland are in the path of winds such as the Southeast Trade Winds and the Northeast monsoon which blow the clouds produced by the reef to the forest. So any change to the cloud seeding capacity of reefs may greatly affect the precipitation in the nearby rain forest.


 Cape Tribulation, where the rainforest and reef meet. Image Credit: Pennie Stoyles

Cape Tribulation, where the rainforest and reef meet. Image Credit: Pennie Stoyles