Optimism is rising among scientists that parts of the great barrier reef.

Scientists from the Australian Institute of Marine Science this month surveyed 14 coral reefs between Cairns and Townsville to see how they fared after being bleached.

They said they were surprised to find the coral had already started to reproduce.

Nearly two thirds of the great barrier reef was affected by bleaching in 2016 and 2017, killing up to 50 per cent of coral in those parts.

Tags: coral, Great barrier reef, Scientists